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CORNELL
UNIVERSITY
LIBRARY
FROM
Miss Jean Mc Dermott
Cornell University Library
TR9 .J76
+
Cassell's cyclopedia of photograph'
3 1924 030 707 867
olin Overs
¥2
Cornell University
Library
The original of this book is in
the Cornell University Library.
There are no known copyright restrictions in
the United States on the use of the text.
http://www.archive.org/details/cu31924030707867
^m^Mf^r:^t--^^^^^^'^'^>'M^.
PROSPECT STREET, RYE
Bv I. K. Grant, E.R.P.S.
A photograph in natural colours, taken on ihe Autochrome piate, and reproduced by the
four- colour process.
GASSELL'S
cygloptEdia of
photography
EDITED BY
BERNARD E. JONES
EDITOR OF "WORK"
ILLUSTRATED BY TWENTY-FOUR FULL-PAGE
PLATES IN COLOUR AND HALF-TONE, AND BY
HUNDREDS OF LINE DRAWINGS IN THE TEXT
^OPTICIANS
vaPHOTOsyppuESi
26E.23"-°sy
CASSELL AND COMPANY, LTD.
London, New York, Toronto and Melbourne
1911
[all rights reserved]
LIST OF CHIEF CONTRIBUTORS
T. Thorne Baker, F.G.S,
'• •
Henry W. Bennett, F.R.P.S.
A. H. Blake, M.A.
George E. Brown, F.I.G.
Theodore Brown
J. G. Burrow, F.R.P.S. . .
Gharles p. Butler, A.R.G.Sc.
(Lond.), F.R.P.S., F.R.A.S.
Drinkwater Butt, F.R.P.S. .
Edgar Glifton, F.R.P.S. .
F. Martin Duncan, F.R.P.S.
William Gamble
Arthur D. Godbold .
Walter Kilbey, F.R.P.S..
Arthur LoGKETT, Honours Silver
Medallist in Photography, City and
Guilds.
Thomas Manly, F.R.P.S. • .
J. I. PiGG, F.R.M.S., F.R.P.S. .
Percy R. Salmon, F.R.P.S. •
E. J. Wall, F.R.P.S. . • •
W. L. F. Wastell, F.R.P.S. .
Isochromatic Photography, Photo-
telegraphy
Architectural Photography, Garbon
Process, Lantern Slides, etc.
Night Photography
Gopyright
Stereoscopic Photography, Kine-
matography
Mine Photography
Astronomical Photography
Studio Design and Gonstruction
Lenses
Natural History Photography
Photo-mechanical Processes
Studio Work
Focal-plane Shutter Work
Gameras, Apparatus, Special Pro-
cesses, etc.
Ozobrome, Ozotype
Photomicrography, X-ray Photo-
graphy
Historic and General Processes,
Developers and Miscellaneous
Ghemistry, Golour Photography,
Special Processes
Pictorial Photography and Special
Processes
PREFACE
MANY years ago, while assisting in the production of a small photographic
manual, the difficulty experienced in finding room for everything that ought
to have been included brought to my mind a suggestion for an encyclo-
paedic work covering all the phases of photography. It was not imtil this suggestion
had been discussed, seven years later, with Mr. Percy R. Salmon that it became crys-
tallised into something concrete and workable. To Mr. Salmon, more than anyone
else, is due the credit for the particular form which this work has assumed. Together
we planned it, and together decided the majority of the multitudinous questions of
detail that arose.
Of photographic dictionaries and cyclopaedias printed in the EngUsh language
there have been as many as could be counted on the fingers of one's hands ; but the
present volume is essentially different from any of them, and is undoubtedly the most
ambitious work of its kind yet projected. With possible exceptions, its predecessors
were written or compiled from cover to cover by one hand ; whereas this work is the
result of the co-operation of many men, each having special knowledge of his own
particular branch. Modem photography has so many ramifications, each calling for
the application of special knowledge, that I felt that the only proper course, in attempt-
ing to produce a photographic cyclopaedia at once authoritative and complete, was
to enlist the services of as many specialists as possible. About a score of the best-
known and most authoritative expert photographic writers extended their co-operation,
and their contributions constitute the bulk of this work.
While it must be confessed that complete accuracy is almost too much to hope
for in the first edition of a work of reference, I have taken care to do all that could
be done to check and verify the statements made. My especial thanks in this connec-
tion are due to Messrs. Percy R. Salmon, E. J. Wall, Arthur I^ockett and William
Gamble, for the trouble they have taken in reading the proofs. I shall appreciate
and acknowledge any minor corrections that readers may send me, and shall hope
to be able to incorporate them in later editions, in the happy event of such being
called for.
The scope of the work demands some words of explanation. The object has been
to include every accepted photographic term and to survey the whole field of photo-
graphic knowledge, whilst giving particular attention to the requirements of the
working photographer, both amateur and professional. This cyclopaedia is intended
essentially as a simple guide to photographic practice, whatever else it may be. In
all cases where the process described is commonly used, or is likely to be worked
nowadays, working directions and definite formtilse are given.
This work is intended not only for the practical photographer, but also for the
scientific student, who will find in all those articles that have been written especially
for liim valuable, because authoritative, summaries of what has already been attained
in the many branches of photographic science. The manufacturer, too, especially the
manufacturer of materials, will find in this volume a mass of information relating to
what others have done before him, and by profiting by it he will be prevented from
wasting time and money in useless trials in some directions and possibly be given
ideas as to commercially remimerative lines of experiment in others.
vl PREFACE
There are two matters, in particular, upon which I think it desirable to address
a word to the critical reader. It wiU be noticed that a few biographies are given,
and the question as to why such and such men are included and others omitted is
sure to arise. The biography of no living photographer will be found in these pages J
and with regard to the dead worthies, I have done my best to include only those
who, when viewed historically, have real claims to distinction. And in such a matter
much must be left to personal opinion. The other matter is the omission, with a
few exceptions, of trade names. Their inclusion, a highly debatable point, would
have meant the addition of more than thirteen hundred headings, the informa-
tion given under which might rapidly have gone out of date. The exceptions, as in
the case of a certain camera which it would be superfluous to mention, have now
become part of the language, and are associated in the public mind quite as much
with broad tj^es of apparatus or certain classes of materials as with any particular
brands of manufacture.
The illustrations call for a word of explanation. The monochrome plates have
been selected as representing separate phases of photographic art, and are o£fered as
being good examples of their kind. On the other hand, three of the coloured plates are
intended to represent merely the capabilities of the screen plates with which the
original pictures were made ; while, of the remaining two, one plate shows the steps
in the production of a four-colour print and the other the composition of six of the
best-known screen plates. The line drawings throughout the book (almost all of
which have been drawn by E. S. W. Cunnington from the contributors' sketches) have
the sole object of elucidating the text ; much thought was given to the advisabiUty
or otherwise of using photographic illustrations in the text, but it was decided that
drawings would be far more instructive. In many cases the drawings have been
based upon illustrations appearing in trade catalogues, and in this connection my
thanks are due to a large number of firms, including the following : Adams & Co. ;
A. H. Baird ; Bausch and I^omb Optical Co. ; R. and J. Beck, I^td. ; W. Butcher
and Sons, Ivtd. ; J. J. Grifiin and Sons, I^td. ; J. Fallowfield ; J. Halden and Co. ;
Houghtons, I/td. ; Infallible Exposure Meter Co. ; Kodak, Ltd. ; J. I^ancaster and Son,
Ltd. ; Marion and Co., Ltd. ; G. Mason and Son ; Newman and Guardia, Ltd. ; A. W.
Penrose and Co., Ltd. ; Ross Ltd. ; Sanger Shepherd and Co., Ltd. ; O. Sichel and
Co. ; Thomton-Pickard Mfg. Co., Ltd. ; W. Tyler ; A. G. Voigtlander and Sohn ;
Watkins Meter Co. ; W. Watson and Sons, Ltd. ; Westminster Engineering Co., Ltd. ;
Westminster Photographic Exchange, Ltd. ; and C. Zimmermann and Co.
For the principal information given in the article " Ceramic Process " I am indebted
to Mr. W. Ethelbert Henry's standard work, " Photo-Ceramics."
With regard to the formulae, in practically all cases the parts are given in both
British and Metric measures ; by whichever system a solution is made up, the relative
proportions of the ingredients will be almost exactly the same, although the actual
quantities nearly always differ.
B. E. J.
LIST OF COLOURED PLATES
"Prospect Street, Rye." A Photograph on the Autochrome Plate. By
T. K. Grant, F.R.P.S Frontispiece
FACING PAGE
Still Life A Photograph on the Dufay Dioptichrome Plate • • . . -97
A Four-colour Print and the Consecutive Steps in its Production . 193
Portrait. A Photograph on the Thames Plate. By H. ESSENHIGH GORKE,
F.R.P.S 337
Screen Plates for Photography in Natural Golours .... 433
LIST OF MONOCHROME PLATES
FACING PAGE
Studio Portraiture— " Portrait of A. Haddon." By Furley Lewis,
F.R.P.S. 16
Architectural Photography (Interior)— " In Westminster Abbey." By
Henry W. Bennett, F.R.P.S. 49
Zoological Photography— " Head of English Ram." By W. L. F.
Wastell, F.R.P.S 64
Various Renderings of Daffodils in Blue Vase ii3
Landscape Photography— " On Wisley Gommon." By J. B. B.
Wellington, F.R.P.S. ^45
Night Photography. By A. H. Blake, M.A. 160
Architectural Photography (Exterior)— " Ghurch of Notre Dame,
Gaudebec-en-Gaux." By H. W. Bennett, F.R.P.S. • • 208
Seascape and Skyscape Photography— "After a Storm" • • -241
Combination Printing— " Dawn and Sunset." By (the late) H. P.
Robinson ^^
Home Portraiture. By PERCY R. Salmon, F.R.P.S 289
viii LIST OF MONOCHROME PLATES
FACING t>AGB
Kinematograph Films 304
Celestial Photography— " The Moon." Photographed at the Paris
Observatory 352
Photomicrography— "Group of Insects' Eggs." By J. I. PiGG,
F.R.M.S., F.R.P.S. 385
Influence of the Lens on Perspective. By P. R. SALMON, F.R.P.S. 400
Radiography, or X-ray Photography.— " A Head." By J. I. PiGG,
F.R.M.S., F.R.P.S 448
Firelight Effect. By H. ESSENHIGH CORKE, F.R.P.S. . . -481
Focal Plane Shutter Work. By WALTER Kilbey, F.R.P.S. • • 496
Snow and Hoar Frost Photography. By (the late) Col. J. Gale 529
Telephotography — " North Doorway, Rheims Cathedral." By Ernest
Marriage, F.R.P.S 544
CASSELL'S
Cyclopaedia of Photography
ABAT-JOUR (Fr.) (Ger., Schrdge Fenster,
Oberlicht)
A skylight or aperture for admitting light to a
studio, or an arrangement for securing the same
end by reflection. In the days when studios for
portraiture were generally found at the tops of
buildings hot originally erected for that purpose,
and perhaps in narrow thoroughfares or with a
high obstruction adjacent, it became necessary
to obtain all the avmlable top light. This alone,
however, is not well suited for artistic lighting'
a side light being usually preferable. The abat-
jour, therefore, was so designed as to give what
was practically a side light, although coming
principally from above. A style much used
formerly, and still occasionally met with, is
Two Styles of Abat-jour
shown at A. Into a bevelled opening cut in the
waU, the roof, or both, is let a slanting glazed
frame. Another form (b) is an inclined box-
like structure open at the top and furnished with
a mirror, or painted white inside, to reflect light
downward through the window or glazing. The
reflector used in daylight enlarging is really an
application of the latter kind of abat-jour, by
which the Ught, falling vertically from the sky,
is reflected in a horizontal direction on the nega-
tive in the enlarging camera.
ABAXIAL
Away from the axis. A term applied to the
oblique or marginal rays passing through a lens.
ABBE CONDENSER
One of the most popular types of substage
condensers for the microscope and used in photo-
1
micrographic work. It is made in two forms.
The first consists of two lenses, and is of low
numerical aperture. The second, used for high-
power objectives, has three lenses, and is of
higher numerical aperture (N.A.).
ABBE, ERNST
Professor Abbe died at Jena on January 14,
1905, aged 65 years. He was associated with the
optical firm of Carl Zeiss, and paid particular
attention to microscope objectives, with which
his name is now generally connected. In 1881
he took an interest in the smelting of new optical
glasses which was being made by Dr. Schott,
and this was the beginning of the Jena glass
factory of Schott and Genossen, the products of
which have been used by lens makers as the raw
materials of the large-apertured lenses known as
anastigmats. Professor Abbe was the first to
apply these glasses in a practical way to photo-
graphic lenses. On the death of Carl Zeiss in
1888 Professor Abbe became sole proprietor,
and in 1896 he introduced an arrangement by
which the employees became practically the
owners of the business.
ABERRATION (Fr., Aberration; Ger., Abir-
rung)
A term used in photographic optics to express
a fault in a lens. {See " Cluromatic Aberration,"
" Spherical Aberration," " CurviUnear Distor-
tion," " Astigmatism," etc.)
ABRADING POWDER
Rubbed on the smooth siurface of dried nega-
tives and bromide enlargements in order to give
a " tooth " for subsequent pencilling. Such abra-
sives as pumice, cuttle-fish bone, etc., are gener-
ally used, and these must be very finely ground
and be free from grit. On negatives the powder
is rubbed on lightiy with the finger-tip, but on
bromide prints it is applied with a leather stump.
An excellent abrading powder for negatives con-
sists of I part of powdered resin and 2 parts of
cuttle-fish bone, the whole being sifted through
silk. Cigar or tobacco ash also serves the pur-
pose. Negatives may be reduced by means of a
moist abrading mixture as described imder the
heading " Baskett's Reducer." Various grades
of emery powder and carborundum axe used
in lens and screen grinding, etc.
Abrasion Marks
Absorption
In process work, pumice and emery powders are
used with water for cleaning or polishing zinc
or copper. Fine emery powder is employed for
graining the thick glass plates used for collotype
printing. Pumice powder is used for removing
gloss from prints that have to be retouched.
ABRASION MARKS
Black or pencil-like markings upon bromide
and gaslight papers, chiefly occurring on glossy
surfaces. They are seen only upon Qie finished
print, and are due to pressure upon the gelatine
film, and particularly to scratching against the
printing frame or edges or comers of tiie packet
when withdrawing the sheets. Handling the
paper carefully will prevent them, and the use
of a special developer, such as the following,
wiU generally be of assistance : —
Metol . . -34 grs.
Hydroquinone . . 60 „
Sodium sulphite . . 240 „
Sodium carbonate . 400 „
Potass, iodide . . 20 „
Potass, bromide (10 %) 36 drops
Water to . . .20 oz.
3-4 g.
6„
24..
40,,
2„
4 drops.
1,000 CCS.
Any other metol-hydroquinone developer may
be used if i grain of potassium iodide is added
to each ounce of developer used. The addition
of potassium cyanide is also resorted to, the
proportion being 3 or 4 drops of a lO per cent,
solution to I oz. of developer. But the use
of a special developer does not answer for all
papers. Abrasion marks may often be removed
from the finished print by rubbing lightly with
a pad of cotton wool soaked in water, weak
ammonia (5 drops per ounce of water), or methyl-
ated spirit. An effective — although rather
troublesome — plan is to immerse the finished
print for one minute in the following solution : —
Potass.
iodide .
. 20 grs.
2g.
Iodine
. ,
• 2 „
0-2 „
Water
. 20 oz.
1,000 CCS.
When the white parts of the print turn blue,
transfer to a fresh " hypo " fixing bath for five
minutes, and then wash thoroughly. If the
iodide bath is allowed to act too long, it acts
as a reducer.
ABSORPTION (Fr., Absorption: Ger., Absorp-
tion)
This term is used both in a chemical and an
optical sense. In the former sense it is used to
designate the taking up of one substance by
another, just as a. sponge absorbs or sucks up
water. As a rule, tihis is not accompanied by
any chemical, but merely a physical change.
Optically, absorption is applied to the sup-
pression of hght, and to it are due all colour
effects (see " Colour"). It is of great import-
ance from a photographic point of view, as on
Draper's law, according to which only those
rays which are absorbed by a substance act
chemically on it, is based the whole of the photo-
chemical action of light. Light, when absorbed,
is not lost but is converted into some other form
of energy, either heat or chemical action. The
absorption spectra of dyes are of great interest,
as by their aid it is possible to prepare colour
filters of any given tint. Many substances and
dyes have simple absorption spectra — that is to
say, more or less well defined continuous por-
tions of the spectrum are absorbed ; other sub-
stances, on the other hand, such as chlorophyll,
have complicated absorption spectra, which
change in character according to the concen-
tration of the solution, or the depth of the solu
tion, which is practically the same thing.
The position and shape of the absorption bands
of a substance are in many cases so characteristic
that they serve as a means of identification.
Obviously, the most opaque substances are the
metals, but even these are translucent in thin
films ; silver, for instance, appears blue, whilst
gold in thin films is green. Bven such trans-
parent and colourless substances as water,
alcohol, glycerine, etc., possess characteristic
absorption spectra, and therefore appear coloured
when in sufficiently thick films. In studying the
absorption spectra of coloured solutions, either
the visual or the photographic method may be
used, and the latter will be found not only more
reUable, but considerably quicker. The visual
method can obviously be applied only to the
visible portion of the spectrum, whilst by the
aid of photography the ultra-violet and infra-
red regions can also be mapped out.
Dr. Kenneth Mees and S. H. Wratten, who
have made a special study of dye absorption
spectra by photographic means, give the following
outline of the methods which may be adopted :
" (i) One may take a series of photographs with
increasing dilution of the dye ; (2) one may
take a series of photographs with a constant
concentration of the dye, but an increasing
thickness of the cell ; (3) one may take a
series of photographs with a constant con-
centration and constant cell thickness, but
with a varying exposure. These three methods
will all produce results differing slightly, though
(i) and (2) are nearly equivalent to one another,
(i) is a very slow method, and it would be
probably quicker to use a spectro-photometer.
(2) and (3), though quicker, are still slow if
carried out as described. But if in method (2)
instead of varying thicknesses of cell there is
used a cell of which the thickness varies through-
out the length — that is to say, a wedge-shaped
cell placed in front of the slit so that the thick-
ness of the layer of dye solution in front of the
slit varies from end to end of the sUt — the method
resolves itself into taking one or possibly two
photographs of each dye. Method (3) is inferior
to the two other methods, as it involves the inter-
pretation of the photograph of the plate curve.
It is, however, a convenient way of examining
the absorptions of coloured films and filters."
This method is most conveniently carried out by
placing directly in front of the slit a small wedge
of black glass so that the intensity of the light
varies from end to end of the slit. This black
wedge consists of a narrow prism of neutral tinted
glass cemented to a similar prism of white glass,
which of course destroys the prismatic effect by
forming a parallel plate. With this the intensity
of the light varies from i to 10,000.
For visual measurement of absorption spectra
a spectro-photometer is used. This consists of
a spectroscope and some means of comparing
the brightness of two spectra of one light source.
This can be effected in several ways, as, for
Accelerator
Acetic Acid
instance, by two slits, which can be independently
opened or closed, or by polarising prisms. The
disadvantage of the variable sUt system is that
the two spectra are of unequal purity, and
therefore accurate readings are impossible. In
the polarising spectro-photometers the sUt is
usually divided across the middle by a small bar
of metal, and the two light beams are polarised
and dispersed, or dispersed and polarised, equality
being obtained by rotation of a Nicol prism. The
two spectra are brought into juxtaposition at the
eyepiece, and equaUty of illumination obtained
throughout its length. As one spectrum is con-
tinuous and the other darkened ty the absorption
band, the former is reduced in brightness till the
two are equal and the necessary readings obtained
from the varied width of the slit or the angle
through which the Nicols are turned. The
transmitted light, divided by the incident light,
which is always taken as unity, equals the
extinction coefficient.
ACCELERATOR (Fr., AccSUrateur ; Ger.,
Beschleuniger)
A substance added to developing solutions to
shorten the duration of development and bring
out the image more quickly. Usually it is an
alkali which hastens the development owing to
its power of absorbing the bromine set free from
the silver salt during development, thus forming
an alkaline bromide which acts as a restrainer,
and as this increases with continued or repeated
use of a developer, due allowance should be made.
Common accelerators are sodium carbonate,
washing soda, ammonia, potassium carbonate,
sodium hydrate (caustic soda), and potassium
hydrate (caustic potash). " Hypo " (sodium hypo-
sulphite) has been recommended when develop-
ing with a mixture of ferrous-oxalate, but not
infrequently it causes a partial reversal of the
image ; merely adding a few drops of a weak
solution of " hypo " to the normal developer has a
wonderftd accelerating efiect in some cases.
Attempts have been made to introduce substi-
tutes for alkaline accelerators in the form of
acetone with sodium sulphite, tribasic sodium
phosphate, and other chemicals, but only the
two named have met with any success. Some
" one solution " developers — such as rodinal,
azol, etc. — include an accelerator ; but in " two
solution " developers, the developer proper is
generally induded in bottle " A " or " No. i,"
and the accelerator in bottle " B " or " No. 2."
It was long thought that an increase of the
accelerator in cases of under-exposure brought
out more detail, but photographers are now
growing out of the idea. It is never advisable
to add much alkali, because this invariably tends
to produce fog. Accelerators cannot be used
as the fancy dictates, some being more suitable
for certain developers than others. Ammonia
and sodium carbonate, for example, are found
to give their best results in conjunction with pyro.
Some of the newer developers — amidol, for
example — do not require an alkali accelerator,
and they will work with sodium sulphite, which
is a preservative rather than an accelerator. In
regard to the comparative strengths of the
numerous alkalis used for accelerating develop-
ment, a table will be found imder the heading
" Alkalis, Chemical Equivalence of."
ACCOMMODATION OF THE EYE {See
"Axial Accommodation.")
ACCUMULATOR (Fr. Accumulaleur ; Ger.,
Akkumulator)
Accumulators or storage batteries are used in
X-ray work when the electric current cannot be
obtained from mains. An accumulator consists
of a series of lead grids filled in with lead oxide
and immersed in dilute sulphuric acid. The
potential of an accumulator when fully charged
is 2 volts, and recharging is necessary when it
falls to I -8. Current is always leaking from
accumulators even when not in use, and they
should therefore be recharged at least once a
month, or the plates will be ruined. The posi-
tive terminal of a cell is painted red, the nega-
tive black. In coupling up two or more cells Qie
positive terminals are connected up with the
negative terminals, the free terminals being then
connected with the induction coil. A coil giving
a lo-in. spark requires from six to eight accumu-
lators, supplying a current of s to lo amperes.
ACETALDEHYDE {See "Aldehyde.")
ACETATES
Salts formed by acting upon metals or their
oxides with acetic acid. Examples are lead
acetate, sodium acetate, etc., etc., which are
described rmder their own headings.
ACETIC ACID (Fr., Acide acetique : Ger.,
Essigsaure)
Also known as purified pyroUgneous acid.
HC2H3O2. Molecular weight, 60. There are
three kinds of acetic add: — (i) gladal, con-
taining about 99 per cent, of add and i per cent,
of water (sp.g., 1-065) ; gladal acetic acid is the
most widdy used for photographic purposes, and
recdves its name from the fact that it soUdifies
and freezes into long ice-like crystals at com-
parativdy low temperatures ; (2) commercial
" strong," about one-third the strength of the
glacial variety, and containing about 33 per
cent, of acid, sometimes known as Beaufoy's
acetic add (sp.g., 1-044); (3) dilute acetic add,
made by mixing i part of the " strong " add
with 7 parts of water (4|- per cent.), and sold as
" distilled white vinegar " (sp.g., i-oo6). Acetic
is the oldest of acids, and is given in old diction-
aries as " acetous add." Its impurities may be
hydrochloric, sulphuric and sidphurous acids,
but most samples sold by chemists are quite
pure enough for photographic purposes. Acetic
add readily dissolves in water, alcohol, and
ether ; it is a strong escharotic, causing painful
blisters if allowed to remain on the skin, but
the application of a solution of soda or any other
alkali will at once neutralise it. It is extremely
volatile, and should be kept in a glass-stoppered
bottle and in a cool place. It has many uses in
photography, and in the early days, when it
cost as much as 8d. per ounce, was largely used
as a constituent of the developer for wet plates.
Nowadays, it is used for dearing the iron out of
bromide prints after development with ferrous
oxalate, to assist uranium toning, and, on rare
occasions, as a restrainer when developing with
hydroquinone. Acetic add is a solvent for
celluloid, gelatine, and pyroxyline.
Acetic Ether
Acetylene Generator
In process work, acetic acid is used in the iron
developer for wet plates. The amount required
increases as the working temperature increases ;
at 60° F. ^ oz. of glacial acetic acid to 20 oz. of
developer is a suitable proportion. The acid
retards the action of the ferrous sulphate. A
mixture of acetic acid and salt is used for clean-
ing up the copper plates during half-tone etching
to enable the etcher to see the image better when
proceeding to re-etch. It is also used for remov-
ing the magnesia that is rubbed into the etched
plate to make the image visible.
ACETIC ETHER (Pr., ither acitique, AUtate
d'Mhyle ; Ger., Essig aether)
Synonym, ethyl acetate. CHs CO 0(C2H5).
Molecular weight, 89. Solubilities, i in 17 water,
miscible in aJl proportions with alcohol and
ether. It should be kept in well-stoppered
bottles away from fire, as the vapour is very
inflammable. A light, volatile, colourless liquid,
with pleasant acetous smell, obtained by dis-
tillation from alcohol, acetic acid, or sodium
acetate with strong sialphuric acid. Sometimes
used in making collodion.
ACETOL (Fr., AcMol; Ger., Acetol)
A gelatine with an acetic acid substratum,
used for collodion emulsion. It is said by its
advocates to give a beautiful surface and spotless
negatives.
ACETOMETER (Fr., AcStomUre : Ger., Aceio-
meter)
A hydrometer specially graduated to show
the strength of acetic acid.
ACETONE (Fr., Acitone ; Ger., Aceton)
A colourless volatile liquid of peculiar and
characteristic odour, having the formula C3 Hj O
or CH3 CO CH3. It is met with commercially in
various qualities. It is miscible in all propor-
tions with water, alcohol, and ether. As the
vapour is highly inflammable, the hquid should
be kept in a bottle with a close-fitting cork or
glass stopper. Acetone has two separate and
distinct uses in photography, as an addition to
developers and in varnish making. It acts as
a solvent for resins, camphor, celluloid, etc., and
should therefore never be used for films or in
u celluloid dish.
As a constituent of a developer acetone works
best perhaps with pyro in the following one-
solution form : —
Pyro .... 180 grs. 18 g.
Sodium sulphite (crystals) 1,120 ,, 112,,
Acetone . . . .24 mins. 2'4 ccs.
Water to . . .20 oz. 1,000 „
It may, however, be used with other developers.
When mixed with sulphite it forms acetone
sulphite, and the soda of the stdphite combines
with the developing agent to form a pheno-
late, so that it may be used in place of an
alkali when sulphite is present. It gives a very
clean-working developer, moderately free from
stain, and hardens the gelatine, or at any rate
does not soften it as alkalies do. As a developer
for paper prints it is best when combined with
metol-hydroquinone in the following form : —
Metol . . .27 grs. 27 g.
Sodium sulphite . 5i oz. 275 „
Hydroquinone . . 88 gis. 8-8 ,,
Potass, bromide (10 %) 22 mins. 2-2 „
Acetone . . .40 drms. 25 ccs.
Water to . . . 20 oz. 1,000 „
This is a one-solution developer which, as above
compounded, is ready for use for both plates
and papers.
ACETONE SULPHITE (Fr., AcHone sulfite:
Ger., Acetonsulphit)
A compound of acetone with acid sodium sul-
phite, inbroduced as a substitute for sodium sul-
phite and the metabisulphites for development.
It has the form of a white powder, and its formula
is NaHSOj CO(CH3)2 H^O. It is soluble in
water (up to 50 per cent.), but less so in alcohol,
and it is used for making concentrated forms of
developers, also for fixing baths and to blacken
negatives after being bleached with mercury.
Unlike acetone itself, it does not make the
developer active, and consequently an alkali or
a carbonate must be used. Ten parts of acetone
sulphite are equivalent to 7 parts of potassium
metabisulphite or 20 parts of anhydrous sul-
phite of soda (40 of soda sulphite crystals) in
a developer. As a preservative for pyro, J oz.
of acetone sulphite should be added for each
ounce of dry pyro used.
ACETOUS ACID
The old, and now obsolete, name for acetic
acid (which see).
ACETYLENE (Fi., Acdtyline ; Gei., Acetylen)
A hydrocarbon gas (C^H^) having, when pure,
a sweet odour, the well known unpleasant smell
associated with this gas being due to the pre-
sence of impurities. It bums in air with a. very
bright flame, and is largely used by photographers
for studio lighting, copying, etc., and as an
ilium in ant in enlarging and projection lanterns.
It is produced by the action of water upon
calcium carbide (which see), 1 lb. of which will
yield about 5 ft. of gas. It was first described
and demonstrated in the year 1836 at a meeting
of the Royal Dublin Society under the auspices
of Edmund Davy, a professor of chemistry, and
was brought into commercial use about half a
century later by the discovery of the modem
method of manufacturing calcium carbide in the
electric furnace. Acetylene forms, hke other
combustible gases, an explosive mixture with
ordinary air, the presence of as little as 4 per
cent, of the gas being sufficient to constitute a
dangerous combination. It was in the early
part of 1895 that photographers began to turn
their attention to the photographic value of
acetylene, and photometric tests prove that
acetylene has eight times the actinic power of
the average incandescent gas mantle. As an
illuminant in optical lanterns, acetylene is bel^ter
than the incandescent gas mantle, but not so
good as limelight. (See " Optical Lantern Illu-
minants.")
ACETYLENE GENERATOR (Fr., GHirateur
d'acStyUne; Ger., Acetylengasentwickler)
An apparatus for generating acetylene by the
action of water on calcium carbide. Of the two
Acetylene Generator
Acetylene Generator
types of generators, that is probably the better
in •which the carbide is immersed in or dropped
into the water, as when water is permitted to
fall on the carbide great heat is created, tending
to the production of inferior gas, and the evolu-
tion of oily products which are Uable to accu-
mulate in the pipes. However, many generators
in which the water drips very slowly on the
%
p:
^
z
s
A. Bucket-type
Acetylene Generator
B. Hopper and Valve-
type Acetylene Generator
carbide, as in the majority of acetylene lamps
for cycle use, have a high reputation. Carbide
to water generators are filustrated herewith. In
the apparatus shown at A the water is contained
in the tank E, in which slides the gas bell or
reservoir F. The receptacle G, fiUed with lump
carbide, is suspended from the top of the reservoir,
which falls by its own weight, acetylene begiimjng
to generate directly the carbide comes in contact
with the water. The gas, filling the reservoir,
causes it to rise and lifts tiie carbide receptacle,,
thus stopping further generation until by the
consumption of the gas the reservoir again falls.
The carbide receptade is introduced or removed
by extracting the tightly-fitting plug h. In the
generator shown at B graniUated carbide is
contained in the hopper g, in which is a small
opening or valve closed by the conical plug j.
The plug is attached to a rod having a weight k
as its lower end. The reservoir falls when empty,
until the weight strikes the bottom of the water
tank, this causing the rod to push up the plug
J, allowing a small quantity of carbide to fall
through the opening. The ascent of the reservoir
as gas is generated raises the weight, which pulls
down the plug and again closes the aperture.
B is better in principle than A, as the carbide is
acted upon in smaller quantities at a time.
In all the earlier generators the carbide re-
ceptade was attached to the reservoir, causing
an unnecessary pressure, and one also that varied
as the carbide was consumed. Another dis-
advantage was the fact that the waterseal was
furnished from the same water as that used for
generation. In the devices shown at C and D
these objections are obviated. In the former of
these the plug j is weighted to keep it normally
dosed, and its rod is connected at its upper end
to a T-piece, this being in turn pivoted at each
side to angle irons, which carry wheels at their
outer ends. The reservoir F, in falling, depresses
the angle irons, and these raise the plug rod by
means of the T-piece, thus liberating a small
charge of carbide. The plug is re-closed by the
weight as the gas-laden reservoir rises. In
the device shown at D the hopper g containing
the carbide has an upward-closing plug j fixed
to a rod. The reservoir F in falling presses on
the top of the rod and opens the plug, while the
spring I, serves to return the rod and dose the
opening when the reservoir rises.
Except when the carbide is dropped in small
quantities into a suffident excess of water, a
washing apparatus of some kind is called for.
If any quantity of acetylene is made, it is better
also to remove the remaining impurities by
passing the gas through caldum chloride with
which is mixed a littie unslaked lime, the mixture
being contained in muslin bags arranged on
perforated shelves, one over the other, in the
purifier. A similar mixture is sold ready-pre-
pared, and with this no bags or shelves are
required, the lumps being merely packed in the
receptade.
The pressure should not rise above two or
three inches of water in the generator, and the
pipes should not be less than f in. diameter.
All taps must be well ground in, and should be
lubricated with vaseline to prevent the corrosive
action exerted by acetylene on brasswork.
Since the gas leaks more easily than ordinary
house gas, greater care must be taken with all
joints. Tar and paint are quickly affected.
C. "Ever Ready"
Acetylene Generator
D. "Dreadnought"
Acetylene Generator
and should not be used for this purpose ; red-
lead or white-lead, appUed sparingly, is best.
To detect a leak, a solution of soap and water
may be applied, noticing if bubbles appear.
In starting, the first gas coming ofE should be
allowed to escape, as it contains an admixture
of air. The generator should be kept at least
8 ft. or lo ft. distant from any light, and no
light should be at hand when emptying it after
use. Copper should not be employed in acetylene
Acetylide Emulsion
Acid Resist Varnish
geaerators, as under certain conditions a deton-
ating explosive compound is formed. The best
material for tiie body is tinned or galvanised
sheet-iron, brass being used only for taps.
Special burners are required for acetylene.
The best are of steatite, on the air-injector
principle. For photographic use, Bray's ooooo
(acetylene) burners are perhaps most suitable.
Fifteen of these, mounted in a white reflector,
can be employed for studio portraiture, but a
slightly larger number is better. Two-, three-,
and four-burner jets are made for optical lantern
and enlarging purposes. The soot that soon
collects on the burners may be removed with a
toothbrush or anything similar, while the holes
may be cleared with a fine needle or wire.
ACETYLIDE EMULSION
Wratten and Mees prepared a silver acetyHde
emulsion by passing acetylene into ammoniacal
solution of silver nitrate and emulsifying the
precipitate, which is very explosive, in gelatine.
They found that it blackened in daylight about
tea times faster than silver chloride paper, but
could obtain no evidence of the formation of a
latent image with short exposures.
ACHROMATIC (Fr., AchromaHque; Ger.,
A Chromatis ch)
A photographic lens is said to be achromatic
when the visual image as focused upon the
ground glass falls upon the same plane as the
actinic image which forms the impression upon
the sensitive surface. In telescopes and micro-
scopes, achromatism means that the visual
images are free from colour fringes, but it is
quite possible for a photographic lens to show
Uiese fringes upon the focusing screen and yet
to be capable of giving a sharply defined image
upon the plate. " Actinic " is a better term to
use in connection with photographic instruments
than achromatic. (See also " Chromatic Aberra-
tion.")
ACHROMATISM
The condition of being achromatic.
ACID BLAST
The name given to an etching machine for
process work, invented by Louis E. Levy, of
Philadelphia. The working principle is that the
acid is blown up to the plate, by means of air
under compression, from a series of atomisers
or sprays projecting upwards ; a partial vacuum
is maintained in the etching diamber above
them, and the plate is held face downwards, and
slowly moved to and fro horizontally to equalise
the etching.
ACID CHROMATE OF POTASH (See
"Potassium Chromate.")
ACID DEVELOPERS
A term usually appUed to ferrous sulphate and
other wet-plate developers in an acid condition.
ACID FIXING BATH
The " hypo '' (hyposulphite of soda) fixing
bath made acid. Ordinary " hypo " fixing baths
are neutral, not acid ; but acid fixing baths
may be used for negatives and bromide and gas-
light prints, although not for prints on print-
out papers. Their advantages are that they
immediately stop the action of the developer,
prevent stains, and keep quite clear in use. It
does not do simply to add any acid — say sul-
phuric or hydrochloric — to an ordinary "hypo"
bath, inasmuch as this causes a yellow pre-
cipitation with the accompanying evolution of
siiiphuretted hydrogen, which militates against
the permanency of Sie prints. Sulphurous acid,
however, may be added to an ordinary hypo
fixing bath in the proportion of 2 drms. to
I pint. The best acid fixer is made by adding a
little potassium metabisulphite to the ordinary
solution of " hypo " ; the exact proportions are of
no importance, -J oz. to i pint being, however,
a good average. The following is a precise
formula suitable for prints : —
Sodium hyposulphite .
Potass, metabisulphite .
Water
3 oz.
150 g.
25 „
1,000 CCS.
This is suitable for negatives if the "hypo" is
increased to 4 oz. A cheaper form of acid fixer
is the following : —
"Hypo" solution (I in 5) 25 oz. 1,000 ccs.
To which add a mixture of : —
Tartaric acid solution
(i in 2) . . . f oz. 30 ccs.
Sodium sulphite solu-
tion (I in 4) . . If „ 70 „
There is a danger of overworking acid baths
and consequently of not fixing properly, as the
clearness of the solution is apt to lead to the
belief that it is still in a good working condition,
although really it may be partly exhausted.
ACID OXALATE OF POTASH (See
" Potassium Oxalate.")
ACID RESIST
A term applied in process work to all sub-
stances used to form the image or protecting
coating which prevents portions of the metal
from being attacked. Practically all resinous
bodies — bitumen, pitch, waxes, lacs, indiarubber,
guttapercha — and fatty bodies form acid resists.
Talc, graphite, siUca, sulphur, carbon, and other
inert bodies also form acid resists when dusted
on to an image of a tacky nature. Non-corrosive
metals form another class of resists, as the
image may be formed by a metal that is not
attacked by the acid, which, however, attacks
the base plate. Colloid bodies — such as gelatine,
glue, gums, and albumen — also form add resists,
as in the so-called " enamel process " (which see).
Acid resists are applied as varnishes for protect-
ing the back and margins of the plate, as etching
grounds, for scratching or engraving through with
needle points and gravers, as etching inks, paints,
dusting powders, Ught-sensitive films, electro-
lytic deposits, fused metals. They are used for
relief and intagho etching, for hthography on
stone, zinc, and aluminium, for protecting vessels
and other articles used for etching, and for elec-
trolytic etching or deposition.
ACID RESIST VARNISH
Shellac is probably the best and most used
of the gum resins as a resist varnish. Cover
Acid Stain Removers
Actinic
the shellac with -wood alcohol, and leave for a
few hours to dissolve. For 4 oz. of shellac about
8 oz. of methylated spirit -will be required, and,
for colouring, about 2 drms. of methyl violet
dye. To prevent the varnish setting too hard,
add to every pint about ^ oz. of Unseed oil.
Shellac varnish is said to contain impurities
which, when exposed to light, become insoluble,
so that the varnish is difficult to remove ; the
remedy is to add 60 drops of oil of Invender to
each pint of varnish, and use the varriish a little
thinner.
ACID STAIN REMOVERS
Acid solutions used for clearing away stains
caused by developers. Their use is open to
objection, as fully explained under the heading
" Stain Removers."
ACID SULPHITE (See " Sodium Bisulphite.")
ACIDS (Ft., Acides : Ger., Sduren)
Hydrogen compounds, which have a sharp
taste and redden blue litmus paper. Acids may
be solid, liquid, or gaseous, and are divided into
strong and weak, organic and inorganic. Organic
acids are usually such as contain carbon, whilst
inorganic are those containing a metal. A
further subdivision is made as to hydrogen or
oxy-hydrogen acids ; of the former, hydrochloric
acid HCl is an example, and of the latter, sul-
phuric acid HgSO*, as this contains oxygen as
well as hydrogen. Acids are further differen-
tiated into mono-, di-, tri-, etc., basic acids, and
this refers to the number of molecules of hydrogen
which are replaceable by a metal. For instance,
nitric acid HNO3 is monobasic, and forms salts
of the typical formula XNO3 (X here being a
metal). Dibasic acids can be exemplified by
oxalic add, H2C2O4, which would form a salt
having the composition of X2C2O4 — e.g. K2C2O4,
oxalate of potash. An example of a tribasic acid
is boric acid HaBOg, which forms borates XsBOa.
In process work, acids play an important part.
Nitric acid is almost exclusively the mordant
used for etching zinc. Acetic, chromic, citric,
fluoric, formic, gallic, hydrochloric, nitrous,
phosphoric, picric, and tannic acids are all used
in photo-mechanical processes.
ACIDS, TESTS FOR
Whilst strictly belonging to the domain of
chemistry, it may be useful to give the usual
tests for the acidity or otherwise of a solution.
Blue htmus paper is reddened by acids. Phenol-
phthaleiu solution (30 grs. in 10 oz. alcohol), a
colourless solution, is reddened by alkalis, and
the colour discharged by acids. Methyl orange
(4 grs. in 10 oz. of water), an orange solution,
turns pink with acids.
ACLASTIC (Pr., Aclastique ; Ger., Aclas-
tisch)
Not capable of refracting, or bending, light.
ACRIDINE YELLOW AND ACRIDINE
ORANGE NO (Fr., Jaune d'acridine,
Orangi d'acridine NO; Ger., Akridingelb,
Akridinorange NO)
Two complex basic aniline dyes which have
been suggested as sensitisers for emulsion work.
They are two of the most powerfid sensitisers
for green, but have found no practical appUcation,
as they stain gelatine very deeply, alcohol alone
removing the stain.
ACROGRAPH (Fr., Acrographe; Ger., Ahro-
graph)
An engraving machine invented by N. S.
Amstutz, an American engineer. Its essential
features are a revolving cyUnder and an engrav-
ing tool — a V-shaped graver — carried along
parallel to its axis ; a phonograph, or a screw-
cutting lathe, gives the idea. A photographic
gelatine reUef , such as a carbon transfer on cellu-
loid with the image in perceptible reUef, is
wrapped round the cylinder, and over this relief
is stretched a sheet of thin celluloid. As the
cylinder revolves, a spiral thread is cut on the
celluloid, this having the effect of making cuts
in straight lines across the picture, but as the
tool passes over the relief it cuts more or less
deeply, according to the hght and shade of the
picture. Thus it reproduces the photograph as
a kind of half-tone. The celluloid cutting can be
printed from direct, or it can be made to serve
as a matrix for electrotyping and stereotyping.
By filling in the lines with transfer ink it can
be used as a lithographic transfer, or by filling
them with any opaque substance it can be used
as <x negative for printing an image on to metal.
The elaborations from the simple principle
outlined above are in the form of micrometer
adjustments for the tool, a microscope and
electric lamp for watching the progress of the
cutting and for setting lie tool, and dividing
wheels for varying the pitch of the lines.
ACROMETER (Fr., OUomitre ; Ger., Oelwage)
A kind of hydrometer speaally graduated
for testing the specific gravity of oils ; known
also as an oleometer or oil tester. An instru-
ment of this description is sometimes useful for
verifying the purity of the oils used in certain
photographic and photo-mechanical processes.
ACTINIC (Fr., Aciinique ; Ger., Aktinisch)
A term applied to light that is rich in actinism,
this being the property of Ught that causes
chemicals to combine and decompose. In the
early days of photography it was assimied that
only the ultra-violet, violet, and blue rays were
chemically active or actinic, hence these regions
of the spectrum were so termed. Later researches
have proved that it is practically merely a ques-
tion of length of exposure which determines the
photo-chemical action of light ; in other words,
that all the rays of the spectrum or all colours
will act on sensitive emulsions it sufficient expos-
ure be given. The expression most usual now
is the "more refrangible " or " less refrangible"
rays.
In process work, where the electric arc light is
almost entirely used, the actinic value of the
light is of great importance. It is found that
the enclosed arc is very rich in actinic rays,
and these are increased by operating the lamps
with a comparatively high voltage, resulting in
a long flowing arc emitting a violet light. This
is photographically very active, and exposures
are greatly reduced compared with those neces-
sary with the open arc.
Actinic Doublet ^
ACTINIC DOUBLET {See "Lens")
ACTINIC FOCUS
A term generally used to express the focus
for the blue end of the spectrum, to which the
sensitiveness of the earlier photographic plates
was almost entirely limited. The focus of the
yellow or strongly luminous region of the spec-
trum did not sJways coincide with that of the
blue and violet rays, so that an image sharply
focused, as far as visual observation went, gave
a blurred image on the sensitive plate. A lens
giving such a result was said to have the visual
and " chemical " or actinic foci non-coincident.
This is very rare in modem lenses, even of the
cheaper class. [See also " Lens.")
ACTINOGRAPH
An instrument for estimating the exposure
necessary for a photographic plate, invented by
Hurter and Driffield. It embraces no new
principle, but is simply a kind of slide-rule for
arriving at a result without calculation in a
manner precisely similar to that which was
adopted in the exposure tables that were pub-
lished by W. K. Burton and other pioneers
of modem photography. It consists of two
parts, a light scale and a scale of subjects, plate
speeds, and lens apertures. The light scale is
based on the fact published by Dr. Scott about
1880 that in clear weather the actinic value of
the light varies in direct proportion to the height
of the sun above the horizon. For example,
the altitude of the sun is nearly four times as
great in mid-summer as in mid-winter, and little
more than one-fourth of the exposure is neces-
sary in the middle of June when compared with
that of December. In practice its use is less
satisfactory to the ordinary worker than the
exposure meter.
ACTINOMETER
An instrument for gauging the depth of print-
ing ia those processes in which little or no visible
image is produced by exposure to light ; knowTi
Actinometer
and simpler pattern consists of a small box with
an opaque cap or lid, in which is a small opemng.
At one side of this opening is a small square
painted in a medium dark colour to resemble
as closely as possible the colour that silver paper
assumes and passes during printing. It is essen-
A. Actinometer with Paper Scale
also as a print meter. There are two types of
actinometers, differing both in character and in
method of using. The essential feature in each,
however, is that a piece of silver printing-out
paper is exposed to light until a certain effect
is produced, and by this the correct printing of
the invisible image can be estimated. The older
B. Johnson's Actinometer
tial that this tint should be a medium tint m
silver printing, and that the paper should pass
the colour by continuing the exposure ; other-
wise it would be difficult to determine when the
correct matching of the colour, or the correct
time of printing, had been reached. A square
or a strip of silver printing-out paper is placed
under the lid and kept in fair contact by a pad.
The actinometer is put out to print with the
frames containing the carbon prints, and the
small portion of the silver paper visible through
the opening gradually darkens until it matches
the printed tint at the side of the opening. The
time necessary for this is called " one tint." As
soon as one tint is printed the silver paper is
moved forward and a second tint printed, and
so on until the prints are completed. Experience
alone can determine how many tints will corre-
spond with the correct exposure for any print ;
as negatives and actinometers vary considerably.
With this form of actinometer each succeeding
tint need not always be exposed immediately
the preceding one is printed if the light is uniform.
The time of matching the tint may be noted, and
three or four succeeding tints timed from that.
The second form of actinometer is more simple
in use, and more suitable for the amateur worker.
It consists of a series of squares of varying density
— practically a test negative — and is used exactly
as an ordinary negative. These squares range
from one very thin up to a density equal to that
of the sky in a very strong negative, and they are
numbered consecutively to facilitate reference
in printing. If a piece of silver paper is exposed
to light under this test plate, a short exposure
will show a faint image of the first two or three
squares, and with a longer exposure more of the
squares will be visible on the silver paper. The
squares are surrounded by an opaque margin
to render the image more plainly visible. The
actinometer is put out to print at the same
time as the frames containing the carbon prints,
and each is brought in when the number con-
sidered correct for that negative is reached on
the actinometer. The actinometer is examined oc-
casionally, and the "number " that is considered
printed is the square bearing the highest number
that can be seen. Of course, a very faint image
of that square is all that will be visible, the lower
numbers, that have been fully printed for some
Actinometric
Adurol
time, being seen as darker squares. These darker
squares assist in determining the highest number
visible — the faintest square that can be seen.
One actinometer will serve for several frames,
provided that all are put out at the same
time.
In process work, various forms of actinometers
are used for timing the printing of the image on
the plate when exposed to daylight. The sim-
plest form is that shown at A, consisting of a
series of thicknesses of tracing paper bearing a
number corresponding to the layers underneath.
Another form has a glass scale bearing a
Woodbury film, the pigmented gelatine graduat-
ing in thickness from transparency to opacity.
Burton's actinometer consists of a series of six
tiny negatives made by the carbon process. The
negative to be printed can be compared with
these, and a corresponding exposure given.
This form of actinometer is very useful for collo-
type and photogravure work. Johnson's acti-
nometer B is chiefly used for carbon printing.
It only registers one tint, which is compared
with a siiitably coloured mask. If more than
one tint is required to complete an exposure,
the sensitive paper is shifted to a fresh position.
The Sanger-Shepherd fraction tint actinometer
consists of a scale of densities on a quarter-plate
glass which is put into a printing frame and a
piece of sensitised paper exposed behind it. It
is very useful for timing the bichromated films
in colour transparency work and for carbon
printing, but it can be applied to any other
process in which the exposure has to be accurately
timed.
ACTINOMETRIC (Fr., AciinomStrique ; Get.
A ktinometrisch )
Pertaining to actinometers, or to the measure-
ment of the chemical, or actinic, power of light.
Actinometry is the branch of science that deals
with the numerous methods of testing the
chemical activity of light, and which makes a
study of the variations in its intensity in differ-
ent quarters of the globe, or at different seasons
and hours.
ACTINO-POLYCHROME (Pr., Actino-Poly-
chrome ; Ger., Farbenphotograph)
An esirly name for a photograph in natural
colours.
ACTION
More often than not, action is rendered in an
unsatisfactory manner by photography, although
this does not apply to cinematograph renderings.
A person's mental impression of a man walking,
a horse running, and so on, is the result of a
blending of all the different positions assumed
during the action. A single photograph natur-
ally records but one position, and inadequately
suggests the idea of action {see " Chromo-photo-
graphy "}.
What IS known as an " instantaneous " picture
of a railway train or other object in rapid motion
will not convey the impression of speed if it
shews, for example, the spokes of the wheels
sharply defined ; rather would it suggest sus-
pended motion. O. G. Rejlander once well ex-
emplified this in a couple of photographs of a
lady at a spinning wheel. In one, the foot and
spokes were of microscopic sharpness; in the
other, the foot and wheel were slightly blurred
by intentional movement. Yet it was the
second that gave the better impression of an
" instantaneous " picture and the more complete
suggestion of action.
ADAMANTEAN
An old form of ferrotype plate, largely used
for the wet collodion process.
ADAMANTINE PROCESS
A secret process of half-tone etching on copper
invented by A. C. Austin in the United States.
It produced an extremely hard black enamel
resist image for etching. Probably it was a
modification of the fish-glue process, but no
details have been published.
ADAPTERS {See "Plate Adapters" and
" tens Adapters.")
ADHESIVE TISSUES
Thin sheets of paper prepared, generally by
the use of shellac, for use in the dry-mounting
process.
ADIACTINIC (Fr., Inactinique ; Ger., Un-
actinisch)
Non-actinic ; a term sometimes applied to the
red or orange glass and fabric used to screen the
light in a dark-room. No light, however, is
absolutely non-actinic, since any light, what-
ever its colour may be, will affect a photographic
plate if sufficient time is allowed. Photographs
have, in fact, been taken by the light obtained
from a ruby lamp, although the exposure was,
necessarily, very prolonged. For this reason,
the plate should not be unduly exposed to the
light of the lamp when developing, however
" safe " it is believed to be. The " safety " of
any so-called non-actinic glass or fabric is merely
relative, and much depends on the nature of
the plate or paper and its particular colour-
sensitiveness. Thus, a yellow fabric or material
that is quite safe for developing bromide papers
will instantly fog a rapid dry plate ; while even
a deep ruby light will have a marked effect on
a panchromatic plate.
ADIAPHOROUS (Fr., Adiaphore : Ger.,
Adiaphor)
Neutral ; a chemical term, sometimes applied
to substances that are neither acid nor alkaline.
ADON
A low-power telephoto lens, especially suit-
able for hand-camera use. The positive lens is
placed in front of the ordinary lens of a camera,
in this way producing an enlarged image without
abnormal extension of the camera or substantial
reduction of the working aperture of the lens.
ADUROL (Fr. and Ger., Adurol)
A developer intermediate in character between
the short factor developers, such as pyro and
hydroquinone, and the longer factor developers
such as metol, rodinal, amidol, etc. ; introduced
in 1899. It is a mono-chlor (or mono-brom)
hydroquinone. Adurol-Hauff has the formula
C8H,a(0H)j, and Adurol-Schering CeHj Br(OH) »
Adurol
lo
Aerial Image
— their actions being similar. The developer
as purchased is in the form of a white or greyish-
white crystalline powder, readily soluble in
water and alkalis. In its action and results it
resembles hydroquinone, but it is more soluble,
keeps better, and the negatives are slightly softer.
The addition of potassium bromide as a restrainer
has not much effect, and the developing action
is not much slower when the solution is cold.
Since its introduction many formulae have been
published for one-solution, two-solution, and
three-solution developers. The following are
those in most general use : —
Sodium sulphite
. 8oz.
400 g.
Potass, carbonate
• 6 „
300 „
Water
• 20 „
1,000 CCS,
Shake till dissolved, then add —
Adurol . . . I oz.
100 g.
For negatives and gaslight paper dilute with
3 to 5 parts of water ; and for bromide prints
with from 7 to 10 parts of water.
The above is a one-solution developer, and
may be used over and over again. The formula
for the two-solutiou developer is : —
No. I. Adurol . . 85 grs. 17 g.
Sodium sulphite . if oz. 175 „
Water to . .10 „ 500 ccs.
No. 2. Potass, carbonate. i|- „ 125 g.
Water to . .10 „ 500 ccs.
For use with plates and gaslight paper mix
3 parts of No. 1 with 2 parts of No. 2 ; for
bromide prints add an equal quantity of water.
A three-solution adurol developer is as
follows : —
No. I . Sodium sulphite . 650 grs. 1 30 g.
Adurol . . 80 ,, 16 ,,
Water to . .10 oz. 500 ccs.
No. 2. Sodium carbonate. 100 grs. 20 g.
Water to . .1 oz. 50 ccs.
No. 3. Potass, bromide . 48 grs. 10 g.
Water to . .1 oz. 50 ccs.
For soft negatives mix i oz. of No. i, 310 minims
of No. 2, and 20 minims of No. 3. For more
brilliant negatives use 10 drms. of No. i, ^ oz. of
No. 2, and i drm. of No. 3. The three-solution
formula is best for time-exposed plates, and when
over-exposure is suspected.
Adurol combines well with metol and gives
a developer which acts like metol-hydroquinone.
One formula is : —
Metol
Adurol
Water to
130 grs. 13 g.
I oz. 50 ,,
20 „ 1,000 ccs.
Dissolve and add gradually —
Sodium sulphite . 7 oz. 350 g.
Potass, carbonate . 4^ „ 225 „
For negatives and gaslight papers, dilute with
10 times the quantity of water ; for bromide
prints, with 15 times the quantity of water,
or take of the stock adurol-metol developer as
above i drm. and sufficient water to make
2 oz., and add a little bromide.
Adurol is the best developer for obtaining
warm tones on bromide paper by direct develop-
ment. The concentrated one-solution developer
as given above (let it be called A) is used with
three others — namely, 10 per cent, solutions of
potassium bromide, B ; ammonium bromide,
C ; and ammonium carbonate, D. The colours
are obtained by altering the exposures and vary-
ing the proportions of the four solutions.
ADVERTISING, PHOTOGRAPHY IN
Photographs are extensively resorted to in
the production of effective pictorial advertise-
ments reproduced by the half-tone process.
They are only occasionally used in the form of
straight prints, but are nearly always " worked
up " by skilled artists into what are actually
monochrome wash drawings. Frequently the
advertiser wants ideas rather than technically
good prints, and he has at his command the
services of men who can work up the poorest
print imtil the desired effect is arrived at. So
much work, in fact, is generally done by the
artist that the photographer may easily fail to
recognise the finished picture. A plan frequently
adopted by the artist is to cut away the back-
ground, paste as much of the print as required
on white cardboard, and then " work up " by
means of the air-brush, etc., introducing sidt-
able wording, etc. Often only the head is used
from a photograph of a model, there being always
a fairly brisk demand for studies of pretty ladies
and children ; but in submitting pictures to
advertisers care should be taken about copy-
right matters {see " Copyright "), as any error
on the part of the photographer may possibly
put the advertiser to much trouble and expense.
It is courteous, and often necessary, to obtain
the model's permission to use his or her photo-
graph in the proposed manner. Rough prints of
suitable subjects should be submitted to adver-
tisers with the intimation that, if desired,
enlargements will be supplied upon bromide
paper for working up. More often than not it
is a waste of time on the photographer's part to
work up a photograph according to his own
ideas, and it is better to submit an untouched
print and to leave the rest to the advertiser's
artist.
AERIAL FOG (See "Fog.")
AERIAL IMAGE (Fr., Image aerienne ; Get.,
Aetherisch Bild)
A properly corrected lens produces, as it were,
an aerial model at its focus of the scene at which
it is directed. Each portion of this model is at
the same relative distance from other portions
as are the corresponding parts in the scene
itself. Different parts of this aerial model are
brought into focus on the ground-glass screen
as the lens is racked in or out, so that the pic-
ture shown on the screen and recorded by the
plate may be regMded as a section, vertical to
the axis of the lens, through the many light rays
which constitute, or proceed from, the aerial
model. Owing to the coarse grain of the ground-
glass screens at first supplied with photographic
apparatus, it used to be thought that critical
focusing could only be accomplished when the
aerial image is directly inspected, which could
be done by means of a telescope attached to the
camera and arranged to focus simultaneously
with it, or by having a transparent spot on the
Aerial Perspective
Aerial Screen
focusing screen, made by cementing a micro-
scopic covei glass on the latter with Canada
balsam. This idea is theoretically correct for
obtaining the greatest possible sharpness ; but
general satisfaction is now given by the definition
obtainable by the ordinary method of focusing,
especially if finely-groimd glass is used. Ground
glass of quite superior fineness is now procurable
which, in conjunction with a really good lens,
should remove most of the difficulties met with
by earlier workers. An advantage of the tele-
scope attachment was that it enabled moving
objects to be followed, with the plate in position
ready for exposure, a result now achieved more
conveniently by the use of a reflex camera.
AERIAL PERSPECTIVE
A gradual softening down as objects recede
into the distance, whereby they lose strength
both in colour and in light and shade. Very
distant objects are often seen as a mass of light
grey without detail. A print which success-
fully renders this is said to possess " atmo-
sphere," and the suggestion of space and air is
of very great value in pictorial work. The use
of orthochromatic plates in conjunction with
deep colour screens frequently destroys aerial
perspective to a greater or less extent.
AERIAL PHOTOGRAPHY
The art of taking photographs from aeroplanes,
airships, balloons, kites, etc. Very quick expo-
sures are necessary because of the movement and
of the great flood of Ught. Photographs were
first taken from a balloon by Nadar, of Paris, in
1858, since when photography from balloons has
been practised in war time very considerably,
particularly during the American and South
African wars. In balloons, airships, etc., the
operator holds the camera, but in kite work the
shutter is released by means of a cord held by
the operator on the ground as explained under
the heading " Kite Photography," where details
of working will be foimd. The best photographs
from balloons are, according to the late Rev.
J. M. Bacon, those taken at an elevation of
between 250 ft. and 4,000 ft. At a greater
height than 4,000 ft. it ceases to be worth while
to use the camera, since the particles of water
and dust suspended in the atmosphere spoil the
definition and sharpness of the pictures. M.
Antonin Boulade, the eminent French authority
on the subject, has advocated orthochromatic
plates, and those sensitive to rays chiefly
between the G and P lines. The choice of a
screen is also of the utmost importance, and
the best results in his opinion were those obtained
with a two or three " times " screen. Prom
great altitudes, where the action of the blue of
the sky is very intense, yellow screens needing
about six times the normal exposure produce
the best negatives.
AERIAL SCREEN (Pr., Ecran d'air : Ger.,
Windschirm)
A form of screen for giving relief and other
effects for optical lantern pictures, its special
object being to arrest the light coming from a
lantern and to reflect it back to the point at
which the projected image is to be observed.
The " Bruce " aerial screen consists of a white
lath, tummg on a vertical axis in a plane parallel
with the lantern lens. The mechanism and the
rotating lath occupy a position in front of a
black velvet screen or background, which absorbs
all rays of Ught not falling on the lath and thus
prevents them from reaching the eye of the
observer. An ordinary optical lantern projects
the subjects, which are preferably pictures of
statuary in which fine photographic quality is
present, giving as much rotundity as possible,
and having a black background. The revolving
lath, which takes the place of the ordinary lan-
tern sheet, is caused to rotate at a moderate
speed, calculated to make one revolution within
the time needed to satisfy the laws of persist-
ence of vision. Viewing it in broad daylight as
it is rotated at the specified speed, it would
present the appearance of a transparent cylinder.
When the apartment is darkened and the pic-
ture is projected upon the rotating lath, the
subject presents a somewhat solid aspect, and
the audience will not be conscious of a revolving
device, the illusion being caused by light from
all parts of the image impiuging upon the lath
as it arrives at each and aii of its positions. In
virtue of the law of persistence of vision, there-
Producing Illusion with Invisible Screen
fore, a complete image will be made up. The
chief object of this form of aerial screen is to
bring about relief, but naturally a full stereo-
scopic effect is not obtained in this way. Another
form of aerial screen consists of a column of
vapour rising from the ground and acting as a.
reflector of the projected rays of light, just as
a cloud in the sky may reflect the rays of the
sun, but as the medium cannot be controlled
as regards its reflecting surface it is only useful
for producing weird effects in which absolute
definition is not a necessity.
Yet another and much more recent form of
aerial screen is that in which the laws of partial
reflection are made use of ; it is termed " the
invisible screen," because the medium upon
which the image is actually received is hidden
from the observer's view by the front of the
proscenium. A method of reflection somewhat
similar to that used in the old illusion known as
" Pepper's Ghost " is adopted, but there are
variations in the arrangement of the apparatus
which make the results far more perfect and
reaUstic. An observer situated in the auditorium
at A (see the illustration) looks towards the pro-
scenium B, and sees in a dear plate glass C the
aerial image d E, and at the same time observes
at P any actors (real persons) who may be
performing. The light rays constituting the
Aerograph
Aerograph
spectre d e are arrested before reaching the
glass c by a semi-transparent screen G. In the
basement under the stage an ordinary optical
lantern, or a kinematograph projector h, is set
up. A mirror j, placed at an angle of 45 deg.
in relation to the optical axis of the lantern
objective, diverts the light from its horizontal
course into a vertical direction, so that the
defined picture or image is received upon the
semi-transparent screen G. In virtue of the
angle of reflection being equal to the angle of
incidence, whatever may be projected on c will
be seen by the observer at A, and will appear to
be situated in mid-air in the vicinity of F.
Hence, the so-called " invisible screen " may be
regarded as the aerial screen, although the
aeriograph is seen in quite a different place. The
chief object of the invisible screen in this case
is to afiord means for producing aerial images
or spectra in combination with real actors ;
whilst by the use at H of a kinematographic
apparatus instead of an ordinary lantern many
startling effects, otherwise impossible, are pro-
duced.
AEROGRAPH. OR AIR BRUSH (Pr.,
Aerographs; Ger., Aerograph)
A mechanical sprayer working by means of
compressed air, and used for finishing and work-
ing up both prints and negatives ; invented by
Charles L. Burdick, of Chicago, in 1892, and
introduced into England a year later. It is
capable of great technical possibilities, and pro-
Aerograph Handpiece
duces effects varying from peculiarly soft and
beautiful graduations to strong and vigorous
work. At will, and in successive instants of time,
the operator can draw lines or wide bands of
colour, and shadows, either soft and delicate, or
hard and coarse. The complete outfit includes the
handpiece, or fountain air brush, an air pump
with compressed air reservoir, an air pressure-
gauge, rubber tubing, liquid colour, etc. ; inas-
much as a high and uniform air pressure is
essential to the best results, a motor-driven air
pump is superior to the foot-operated one, and
both kinds are manufactured. Cylinders of com-
pressed carbon dioxide (" carbonic acid gas ")
may be used in place of the pump with equal
convenience. When using the foot pump the
pressure obtained is about 1 5 lb. per square inch,
and when using the motor pump from 30 lb. to
40 lb. per square inch, this producing a much
finer grain.
The illustration shows the appearance of the
aerograph. Air is pumped into a chamber
connecting with the handpiece by means of a.
rubber tube at A. Finger pressure on a button B
opens a valve and admits the air, which sucks
the liquid colour from the reservoir c and throws
it from D in the form of a fine spray, over which
the operator has complete control. The spray
is regulated and stopped by a needle-like rod E
worked by B.
In the management of the aerograph, scrupu-
lous cleanliness is always necessary. Keep the
pencil in the case when not in use, and before
fitting it up for service, pump air into the
cylinder, squeeze the tube for a moment or so,
and then release so as to allow the dust inside
the tube to blow out. Use the colour thinly,
and go over the work several times to get a fijie,
even grain. Use fresh colour for every occa-
sion, and change the water frequently to avoid
dust, which otherwise will cause the colour to
splutter. Before and after using the instrument,
pass two or three lots of clean water through it,
and clear away any accumulation of paint with
a wet brush. To adjust the needle, just fit it
easily to the platinum point where the valve
lever is as far forward as it will go. Do not
jam it hard and push far in, otherwise too much
colour wiU be ejected on pressing down the
valve. Also see that the rubber tubes are free
from kinks or bands. Having mixed the colour
in a clean saucer, transfer to the reservoir by
means of a brush. Spray a little in the air
before treating the original, to make sure that
all the cleaning water is expelled and the brush
is working properly. Hold the aerograph about
6 in. distant from the original, press the lever
down and slightly backwards, move it horizon-
tally with a gUding sweep from left to right,
beginning at the top left-hand comer, and
releasing the valve at the end of each journey
until it has travelled in this way downwards
over the whole space to be covered. The air
brush unaided does not produce sharply defined
lines and edges ; paper masks must therefore
be used to obtain these, or if the background has
merely to be painted out, then the parts that are
to be protected can be covered over with a
special preparation, " Masklene," supplied by
the makers of the aerograph ; the colour is
sprayed on, and the protected parts are then
cleaned with a pledget of cotton wool soaked
in benzine.
In process work, the aerograph is extensively
employed for working up originals for repro-
duction, especially photographs of objects for
catalogue illustration. Backgrounds are in most
cases put in with the aerograph and vignetted
off. Sometimes the main object is cut out of
the photographic print with scissors or a sharp
knife, then mounted on cardboard, and a back-
ground and other detail put in. Another
method largely adopted is to stop out portions
on which the aerograph spray is not to be
applied, the stopping-out medium being of such
a nature that it can afterwards be removed with-
out injuring the rest of the drawing. The
medium used may be either of a greasy nature,
such as vaseline, which may be afterwards
cleared away with benzol, or it may be a cellu-
loid varnish, which may be removed with amyl
acetate or other solvent of celluloid. India-
rubber solution and yolk of egg are other sub-
stances used for the same purpose. The former
can be peeled off by rubbing with the ball of the
finger, whilst the latter will flake off. In either
case the colour applied by the aerograph comes
away with the medium, and leaves quite clean
the portions which have been covered. Larger
surfaces may be stopped out by cutting out
masks of tracing paper and attaching these
Aerometer
13
Albert's Colour Process
temporarily to the print with rubber solution.
The colours used should be mixed to match as
nearly as possible the tints of the original to be
worked up. Chinese white should be avoided,
as it photographs darker than the white papers
on which it is applied. Albanine, Ullmaniae, and
Blanc d' Argent are good whites to use for this
work. Lampblack and " process black " are
the blacks commonly employed. For large
lithographic work, such as posters, a larger hand-
piece is employed. Which will give a coarser spray
and wiU not dog with the transfer ink necessi-
tated by the lithographic process.
AEROMETER
A hydrometer for measuring the density of
acids.
.ffiSCULIN (Fr., Msculine ; Ger., Mshulin,
Schillerstoff)
Synonyms, esculine, esculin, escuUnic acid,
polychrome, bicolorin, enallachrom. An ex-
tract obtained from the bark of the horse-
chestnut {^sculus Hippocastanum). CisHuOj.
Molecular weight, 340. A white powder, a
solution of which, of a strength of about i part
in SCO parts of water, is used as a filter to
absorb tUtra violet rays.
In process work, where the white (particularly
Chinese white) reproduces as if it were yeUow,
an eescuUn filter should be used. This may be
a solution contained in a glass ceU having parallel
sides, or it may be in the form of a dry ^ter.
AGAR-AGAR, OR AGAL-AGAL (Malayan)
(Fr. and Ger., Agar-agar)
A gelatinous vegetable material obtained from
certain white seaweeds (Gracilaria lichenoides
and Eucheuma spinosum), foimd principally on
the shores of the Red Sea. It is used to a small
extent as a substitute for gelatine in plate and
paper making, but it is more difiScult to melt
than gelatine, and is not generally so satis-
factory for emulsion work. It has also been
recommended as a substitute for arrowroot in
the preparation of silver paper, the latter, if
very porous, being first sized with a i^ per cent.
solution of gelatine. Five parts of agar-agar
are allowed to soak for an hour or two in
500 parts of water, heated till dissolved, boiled
for five minutes, and then mixed with twenty
parts of common salt and strained through a
cloth. It is carefully brushed on the paper, and
this, when dry, is floated in tiie dark upon a
14 per cent, solution of silver nitrate containing
10 per cent, of citric acid. In the case of thick
and coarse paper, the silver solution is first
brushed on, and then, when dry, the paper is
floated on the agar-agar solution and again dried
in the dark. After being sensitised the paper
keeps well. It is printed and toned as other
plain silver papers, but if platinum is used as a
toner the picture must be deeply printed.
In process work, agar-agar has been suggested
as a substitute for fish glue in the enamel pro-
cess of preparing the resist for etching, but it
has not come into commercial use.
AGATE BURNISHER
A burnisher consisting of a polished piece of
agate fitted to a handle ; it was used in the
original method of burnishing albumen prints.
The unmounted print was laid on plate glass or
marble and polished with the burnisher. The
operation was thought to cure " measles " on
prints, and give depth to the shadows. The
process was rendered obsolete by the intrb-
duction of the burnishing machine.
AIR-BELLS {See "Bubbles.")
AIR BRUSH (See "Aerograph.")
AIROSTYLE
A form of air brush, introduced in 1907.
AKTINAL (Fr., Actinal)
A preparation sold in Germany as a desensi-
tiser for exposed plates, after treatment with
which they may safely be developed in daylight,
using a metol-hydroquinone developer, with
caustic potash as the accelerator, and fully
restrained with potassium bromide. It is said
to be a 4 per cent, solution of potassium iodide.
ALABASTER, OR ALABASTRINE, PRO-
CESS
A very old process for improving the quality
of positives made on glass by the wet collodion
process. The picture was bleached in a solution
of mercuric chloride in order to increase the
brilliancy of the white image, was then varnished,
and finally, when dry, was bound at the back.
The process is even now occasionally used in
obtaining a good result from a thin gelatine
negative, which must be free from fog. The
faulty negative is bleached in a solution of mer-
curic chloride, washed, dried, backed with black
material, and copied in the camera. Ready-
made mercury solutions for the process have
been sold under the name of " alabaster " solu-
tions. The original formula is : Water, 2 oz. ;
nitric acid, 60 minims ; hydrochloric acid, 60
minims ; to which must be added sufficient
mercuric chloride to saturate the solution,
the excess remaining in crystals ; finally, 60
minims of alcohol must be added. A more
modern mixture — and one equally suitable for
dry (gelatine) plates — is : Water, 2 oz. ; bichloride
of mercury, 40 grs. ; hydrochloric acid, 1 drm. ;
sodium chloride (common salt), 20 grs. ; and
sulphate of iron, 20 grs. Wet collodion pictures
bleached with this are permanent if varnished,
and so protected from tiie atmosphere, but dry
plate negatives thus bleached will not remain
white for long if kept in a strong light.
ALBANINE
A very pure white water-colour pigment used
by process retouchers for working up originals
either by brush or with the aerograph. It
photographs as white, and should be employed
pure for brilliant touches in the highest lights
of a drawing or print. It can be mixed with
"process black" for obtaining graduations of
shadow. No other white should be mixed with it.
ALBERINI'S PROCESS (See " Asphaltum." )
ALBERT PAPER (See " Photo-Lithography.")
ALBERT'S COLOUR PROCESS (See •' Cito-
chrome.")
Albert's Relief
14
Albumen
ALBERT'S RELIEF OR GALVANO PRO-
CESS (Fr., Mithode d rehausser d' Albert :
Oct., Albert's Unterlage)
A method of imparting a varying relief to the
surface of printing blocks, so as to avoid the
necessity for overlaying to bring up the darker
portions in typographic printing ; invented by
Dr. E. Albert, of Munich. A heavily inked
proof is taken from the plate, and transferred
to a thin zinc plate. The ink image is strength-
ened by dusting with resin or bitumen powder
and heated to fuse the powder and ink. Then
the plate is etched strongly until the highest
lights are etched away, and the half-tones
partially, the shadows remaining solid and, con-
sequently, in the highest relief. This plate is
covered with a sheet of thin gutta-percha, and
the back of the original plate placed on it in
exact register, the whole being then put into a
heated press, with a soft packing over the face
of the plate. On strong pressure being apphed
the underlay plate is attached to the original
plate, and the undulations of surface on the
former communicate relief to the latter plate.
The combined plate is mounted on wood or
metal to type height, and is then ready for
printing, no " making-ready " by the printer
being necessary.
ALBERTYPE, ALBERT-TYPE, OR ALBERT-
OTYPE (Fr. and Ger., Albertypie)
The first workable collotype process made
known ; invented by Josef Albert, of Munich.
It differs somewhat from the present-day collo-
type process. A piece of glass f in. thick is
coated, in a dark-room, with the following solu-
tion : —
Water
Albumen .
Gelatine .
Potassium bichromate
300 parts.
150 „
15 „
When the film is dry it is exposed to light for
two hours through the glass, backed by a piece of
dark cloth, so that the film may harden from
the bottom (next the glass) to the surface. The
exposed plate is now coated with the following : —
Gelatine .... 300 parts.
Potassium bichromate . 100 „
Water .... 1,800 „
When again sufficiently dry the plate is exposed
from the coated side under a negative, and is
then washed for fifteen minutes, and dried.
The film is next damped, and inked in the usual
way. Printing is done in a Uthographic press,
or in a proper collotype press. The process is
said to give prints with fine half-tones, but it
requires considerable care and experience in
manipulation, much depending on the printing.
ALBUM (Fr. and Ger., Album)
Blank-leaved books for storing and display-
ing photographic prints. They may be roughly
divided into two classes — sUp-in and paste-
down. As the names suggest, the former has a
double page with cut-out openings on the upper
leaf so that the prints (generally glazed) may be
slipped in between the two sheets ; the latter
has plain pages on to which the prints are pasted.
The colour of the leaves is important ; white is
generally unsuitable, and bright tints should be
avoided. It is also important when prints are
to be pasted down to make sure that both paper
and adhesive are free from acid or anything that
will be deleterious to the photographs. Prints
do not show to the best advantage when many
are crowded together on one page. A print
that is worth mounting at all deserves to be
presented alone on a separate page, of a tint
that is harmonious and unobtrusive. Special
albums are made for the storage of fihn nega-
tives, thus affording an easy means of indexing
and reference.
ALBUMEN (Fr., Albumine; Ger., Albumen)
A very complex organic compound containing
carbon, hydrogen, oxygen, and sulphur, which
occurs botii in the animal and vegetable kingdom.
Animal albumen exists as the serum or white
fluid of blood, but photographically the white
of eggs is the only animal albumen used. To
prepare it for photographic purposes the whites
of eggs should be separated from the yolks and
the germ, and thoroughly beaten to a froth,
allowed to settle for twelve or twenty-four hours,
and then filtered. Actually, the albumen is
contained in minute cells, and the beating has
the purpose of breaking the cell walls, which
subsequently form the flocks or scum.
Albumen is coagulated by heat (150° F. or
65-5° C), by alcohol, and most metallic and
inorganic salts, the resultant precipitate with
the latter being albumeuates. It is an almost
colourless, giumny liquid, which dries to a pale
yellow sohd. Seventy grains of the dried egg
albumen dissolved in one fluid ounce of distilled
water forms a solution equal to the fresh white
of egg. The solution is extremely liable to
decomposition, and should be either freshly pre-
pared or preserved with an antiseptic. It is
used for albumenised paper, the albumen nega-
tive, beer, and positive processes.
Invert albumen is obtained from ordinary
albumen by first treating with acid and then
with alkali, by which treatment it is so altered
in character that it becomes soluble in alcohol.
The following process has been suggested by
Sanger Shepherd : —
White of eggs . 20 oz. i,ooo ccs.
Glacial acetic acid . 148 mins. 16-5 „
Beat up thoroughly, and allow to stand for one
hour, then add a 20 per cent, solution of sodium
hydrate drop by drop with constant stirring till
the mixture thickens ; next allow to stand for
one hour, break up into small pieces, and wash
(see "Emulsion"), drain well, and dissolve in
boiling alcohol. Invert albumen gives an
extremely tough, structureless film, and was
suggested for m^ng colour filters.
In process work, albumen is used as a sub-
stratum, or for edging the glass plates in making
wet plate negatives. Also, it is almost univers-
ally employed with potassium bichromate for
sensitising the zinc plate for photo-etching.
Albumen is also often mixed with fish-glue in
making up the enamel solution for printing on
zinc or copper from half-tone negatives. Dried
albumen is frequently employed in preference
to the liquid white of eggs. Varying opinions
are expressed as to the quantity of dried albumen
Albumen Process
IS
Albumen Process
required to equal the albumen of one egg, but
70 grs. to I oz. of water may be taken as a safe
standard.
ALBUMEN PROCESS
Negatives. — An old process invented by
Niepce de St. Victor, in 1848. Glass was
coated with albumen containing potassium
iodide, and the film was sensitised by dipping
in a nitrate of silver bath. Many modifica-
tions followed, but probably the process most
widely used was the one published on May 21,
1855, by Mayall ; this comprised six distinct
operations, as follow : —
(i) The albumen (white) of a fresh egg is
beaten to a snow-like mass with a bunci of
quills, afterwards dropping into it 10 drops of
a saturated solution of potassium iodide and
allowing to stand six hours at a temperature of
60° F. (2) A piece of plate glass having smooth
edges is cleaned by rubbing over it nitric add
with cotton wool, and polished with Tripoli
powder moistened with a few drops of a concen-
trated solution of potassium carbonate. To the
centre of the ba(± of the glass is attached a
pneumatic holder to serve as a handle. (3) The
prepared albumen is strained through linen, and
is then used to coat the polished side of the glass,
this being placed on a level slab in a warm and
dustless place to dry. The glass is now known
as the iodo-albumenised " glass, and it will
keep in a good condition for any length of time.
It may be prepared in daylight. (4) The sensi-
tising mixture, or " exciting solution," is made
by dissolving 50 grs. of silver nitrate in a mix-
ture of I oz. of distilled water and 120 minims
of strong acetic add, which operation and the
following one must be done in a weak yellow
light. Four the sensitising mixture into a clean
porcelain dish a Uttie larger than the plate to
be coated ; place one end of the albumenised
glass in the solution ; with a quill, support the
upper end of the glass and let it fall suddenly
into the solution, Ufting it up and down for ten
seconds ; take it out, and place it face upwards
in another dish half filled with distilled water ;
allow the water to pass over the surface twice,
take out and set aside in the dark to drain and
dry. The plate at this stage is ready for expo-
sure in the camera, and will keep good for ten
days if kept from the light, in a moderately
warm place, and free from moisture. The sur-
plus sensitising solution may be filtered back
into a black bottie for use again and again,
adding occasionally a few drops of acetic add
and keeping in the dark. Exposure varies from
four to ten minutes, according to light and stop.
On a very bright day, and using the //16 stop,
Mayall recommended an exposure of five min-
utes, (s) For development, the glass is placed
film side upwards on a levelling stand, and a
concentrated solution of gallic add is poured
over it ; the image takes from thirty minutes to
two hours to develop. A temperature of 10°
higher than that of the room is advised, and
if the image is feeble the plate is rinsed and
covered with a solution of equal quantities of
aceto-nitrate of silver and gallic add diluted
with water to half strength. This causes the
image to appear more quickly and stronger. The
plate is next washed in three waters, and is
then ready for fixing. (6) The fixing solution
is made by dissolving 3 drms. of hyposulphite
of soda in i oz. of water. The plate is allowed
to remain until all the yellow iodide has dis-
appeared, and is next well washed and dried.
" Success," said Mayall, when publishing this
process in the Athenesum (No. 1,220), " is sure
to attend anyone practising this method, pro-
vided the eggs are fresh and the glass quite
dean ; if the glass is not dean and the eggs
stale, the albumen will split off the plate during
the fixing." Among the modifications which
followed for the purpose of quickening the plates
were the addition of grape sugar, honey, and
potassium fluoride, the latter proving to be the
best of all. Malone's and other processes in use
in the 'fifties of the nineteenth century differed
in detail from the above, but in essentials were
the same.
FosiTivES. — At one time the albumen pro-
cess was widely used for the production of posi-
tives or lantern slides, and even at the present
time, owing to the exquisite results obtainable
with it, the albumen process is used by some
of the largest lantern and stereoscopic trans-
parency firais in the world. It is hardly a pro-
cess for the beginner, because of the somewhat
complicated formtds and manipulations. The
famous " Perrier et Soulier " slides were pro-
duced by the albumen process, but the exact
formula used was kept secret. Other formulae
have, however, been published and worked
successfully, the best being that in which the
plate is coated first with collodion and then with
iodised albumen ; the details are as follow :
Pieces of good clear glass should be thoroughly
deaned by washing in a solution of 8 oz. of
soda in i gal. of hot water, and rubbing well
with rags tied to a wooden stick. Next, the
plates are rinsed in plain water and placed
in dilute hydrochloric add (i in 20). A sub-
stratum is next required, and this is made
by mixing the white of one egg with 50 oz.
of water ; the mixture being shaken up thiee or
four times during the day and allowed to stand
all one night, it is then filtered through fine
muslin. The plates are taken from the acid
bath, rinsed, drained slightiy, and coated on one
side with the albumen substratum mixture,'
next they are laid flat and dried. Great care
is necessary to avoid dust and to get an even
coating. When dry, collodionising and sensi-
tising may take place. Some ready-made
iodised collodion is obtained (the longer it ha'!
been iodised the better), and the following
solution is prepared : —
Distilled water . . 20 oz. 1,000 ccs.
Silver nitrate . • 2 „ 100 g.
Potass, iodide . . 2 grs. .2 „
Shake weU, stand in sunlight for a day, and
filter into a glass dipping bath, when it is ready
for use. The following albumen solution must
also be prepared and kept ready at hand for use
after collodionising : —
Albumen (fresh white of
egg) . . . 8 oz. 800 ccs.
I/iquor ammonise . 2 drms. 25 „
Potass, bromide . 10 grs. .4 g.
Potass, iodide . • SO „ 2-0 „
Distilled water . . 3 oz. 300 ccs.
Albumen Process
i6
Albumenised Paper
The albumen must be well beaten up with a
silver fork, the bromide and iodide mixed with
it, the water and the liquor ammoniae being then
added. The mixture should stand twenty-four
hours before use, and then be filtered through
muslin. Take one of the plates prepared with
the substratum, coat with the iodised collo-
dion, drain, and move to and fro in the air so
that the ether may evaporate, place at once
upon the dipper and immerse in the silver
nitrate bath. A deep ruby light is not neces-
sary, an orange or a deep yellow Ught being
quite safe enough. The plate must be moved
up and down in the silver bath a few times,
allowed to stand for two minutes, taken out, the
silver drained off, and then washed for a few
minutes and drained, but not dried. While the
surface is still damp the plate is covered with
the albumen solution, drained, and again coated
with the albumen. "When dry, the plate must
be treated in order to make the bromo-iodised
albumen more sensitive to light, for which pur-
pose the following bath is used : —
Silver nitrate (recrys-
tallised) . . . 600 grs. 60 g.
Distilled water to . 20 oz. 1,000 ccs.
Glacial acetic add . 1 10 drms. i cc.
The plates are allowed to remain in this bath
for two or three minutes, washed well, and
flowed over with a nearly saturated solution of
gaUic acid, and finally dried in a warm dark
place. The plates are then ready for exposing.
The time of exposure will be about fifteen times
as long as an ordinary modem gelatine lantern
plate. Over- is better than under-exposure.
The following pyro developer should be used : —
A. Pjrrogallic acid . 96 grs. 100 g.
Alcohol to . .1 oz. 500 CCS.
B. Potass, bromide . 12 grs. 125 g.
Water to . .1 oz. 500 ccs.
C. Ammonium carbon-
ate . . .80 grs. 84 g.
Water to . .1 oz. 500 ccs.
To prepare the developer for use, 12 drops of
A are mixed with .1 dram of B and 6 drams of C.
The image soon appears, but will be thin and
usually requires to be strengthened by redevelop-
ment, which is done by applying a small quantity
of the following developer, after washing ofE the
first developer ; —
Pyrogallic acid . . 6 grs. 4 g.
Distilled water to . 3 oz. 85 ccs.
Citric acid . . . li grs. 1 g.
Before using this, add a few drops of a solution
of 30 grs. of silver nitrate in i 02. of water. As
soon as dense enough, the plate is fixed in a
solution of sodium hyposulphite (4 oz. to 20 oz.
of water), washed for about five minutes, and
dried.
Mary other formulae have been advocated,
some much more simple than the above and
without the use of collodion, but the process
described probably gives the most satisfactory
results and ofiers fewer opportunities for failure.
ALBUMEN PROCESS (BEER)
A dry collodion process for solar photography,
introduced by Sir William Abney iu 1874, also
of use for landscape work. Abney's formula
is : —
Alcohol (-825) . 4J-3 drms. 270-180 ccs.
Ether . . 3J-S „ 210-300 „
Pyroxyline . 7 grs. 7 g.
Ammonium iodide 2 „ 2 „
Cadmium bromide 5 „ 5 »
The relative proportions of alcohol and ether
are adjusted according to temperature. The
plate is then sensitised in a silver bath of from
40 to 60 grs. per oz., and is next washed, and the
first preservative applied : —
Albumen . . . i oz. 100 ccs.
Water . . . i „ 100 „
Liquor ammoniae . i drm. 12-5 „
This is beaten to a froth and allowed to settle.
The clear part is mixed with an equal quantity
of flat beer or stout immediately before use,
and is then applied to the plate ; fresh bottled
beer or stout must not be used. The excess is
then drained off, the film washed for two min-
utes, and finally covered with a solution made
by adding to every ounce of plain beer 2 grs. of
pyrogallic acid. The plate is then dried in the
usual way. Great latitude in exposure is per-
missible, even up to twenty times the correct
amount, and, it desired, the plates need not be
developed for a month, but they need to be
washed just previous to development. For
developing, four solutions are necessary : — •
A.
Pyrogallic acid
12 grs.
12
g-
Water .
I oz.
500
ccs.
Liquor ammoniae
(•880)
I drm.
62
ccs.
Water .
i oz.
250
,,
Citric acid .
60 grs.
60
g-
Acetic acid .
30 mins.
2
ccs.
Water .
I oz.
500
,J
Silver nitrate
20 grs.
30
g.
Water, distilled .
I oz.
500
ccs.
D.
Three drops of B are mixed with each half-oimce
of A, and flowed over the plate. The image will
then gradually appear. Two more drops of B
per half-ounce are added, the solution again
flowed over the plate and returned to the meas-
ure. Six drops of C are placed in a measure, and
the partially used developer poured on to it,
afterwards adding a few drops of D. The appli-
cation of this solution intensifies the image.
Abney states that it is not advisable to bring
out too much detail with the pyro-ammouia
solution, but to allow some of it to be brought
up at the finish with the intensifier. When the
image is sufficiently dense, the plate is fixed
either by , a solution of potassium cyanide or
with " hypo," then washed and dried. The pro-
cess is not an easy one, and many failures are
likely to be met with, but the resultant negatives,
when all goes well, are of a remarkably high
quality.
ALBUMEN PROCESS (PHOTO-MECHANI-
CAL) (See " Zinc Etching.")
ALBUMENISED PAPER
A prepared paper for obtaining prints from
negatives. It is similar to plain salted paper,
except that albumen is used with the first or
salting solution in order to give the paper a gloss.
PORTRAIT OF A. HADDON
By Furley Lewis, F.R.P.S.
STUDIO PORTRAITURE
Alcohol
17
Aldehyde
and to keep the silver sensitising solution on
the suiface. The introduction of albumenised
paper has been credited to Talbot, but definite
instructions for making it emanated from other
experimenters — notably Le Gray, Hunt, and
Pollock — during the years 1851, 1852, and 1853.
For about forty years albumen paper remained
the most popular of all printing processes, and
reigned supreme imtil the introduction of gela-
tino-chloride (P.O. P.) and similar papers. It,
however, is still used by some professional
workers and for some special processes, as
crystoleum work, for example. Ordinary white
papers were used at first, but in 1863 methods of
slightly tinting the papers mauve, pink, etc.,
by means of dyes, were introduced.
ALCOHOL (Pr., Alcool ; Ger., Alkohol)
Chemically, alcohols are neutral compounds
formed by the replacement of hydroxyl OH
for one atom of hydrogen in a saturated carbon
compound ; for instance, C^Hj ethylene gives
CjHj OH ethyl hydrate, or ordinary alcohol.
They unite witi acids wiUi elimination of water
to form ethers. Alcohols are hydrates of organic
radicles and may be considered as equivalent
in organic chemistry to the metallic hydrates
in inorganic. For example, KOH potassium
hydrate ; CjHs OH ethyl hydrate. They are
divided into mouatomic, diatomic, triatomic,
etc., according to the number of OH groups
attached to the organic radicle.
Alcohol, Ethyl (Pr., Alcool ordinaire, Alcool
Sthyligue ; Ger., Aethylalkohol)
Synonyms, ethylic alcohol, ethyl hydrate.
CjHj HO. Molecular weight, 46. Solubilities,
miscible with water and ether in all proportions.
A colourless, volatile, inflammable Uquid of
pleasant odour ; it is obtained from grain,
starch, or sugar by fermentation and subsequent
distUlation. It is principally used for preparing
collodion (which see).
Absolute Alcohol contains from 98 to 99 per
cent, of pure alcohol, and is used for making
collodion.
Rectified spirit or spirits of wine contains
10 per cent, of water, and is known as 58 over-
proof. The term " proof spirit " refers to an
old test with gunpowder, which was moistened
with the spirit and then a Ught applied ; if the
gunpowder fired the spirit was termed proof.
Alcohol, Methyl or Methylic (Pr., Alcool
mSthyliqve ; Ger., Methylalkohol, Holz-
geist)
Synonyms, wood alcohol, wood spirit, wood
naphtha, methyl hydrate or hydroxide. CH, OH.
Molecular weight, 32. Solubilities, miscible with
water, alcohol, and ether in all proportions. A
colourless, mobile hquid, prepared by the de-
structive distillation of wood. It is an excel-
lent solvent for resins and pyroxyline, with
which it gives a very tenacious film.
Alcohol, Methylated (Pr., Alcool dSnaturi ;
Ger., Brennspiriius)
Sjmonjrms, methylated spirit, denatured
alcohol or spirit. Solubilities, miscible with
water and ether in all proportions. It usually
contains about 90 per cent, of aqueous ethyl
alcohol with about 10 per cent, of methjl alcohol
and i of I per cent, of mineral naphtha to render
2
it unpotable. Industrial methylated spirit does
not contain naphtha, and can only be obtained
by special permit of the Inland Revenue under
a heavy bond ; it may be used for nearly all
photographic purposes instead of pure alcohol,
except for printing-out collodion emulsions. The
admixture of methylated spirit with water turns
it milky in consequence of the separation of the
naphtha.
In process work, alcohol plays an important
part. For making up collodion for the wet
plate process, absolute alcohol of -805 sp. g.
is usually employed. Spirit of wine is used
in the wet plate developer to overcome the
repellent actions of the silver solution on
the plate when the bath has become charged
with alcohol through the frequent sensitising of
plates. As the bath gets older the proportion
of alcohol is increased. Methylated spirit is not
generally employed on account of the presence
in it of mineral naphtha, which is apt to give
fog, scum, and other troubles, but industrial
alcohol (wood spirit) may replace the pure
spirit on the score of economy. In making up
collodion emulsion only pure alcohol should be
employed. Alcoholic solutions of dyes are
largely used in colour sensitising, and in this
case only pure alcohol should be used. Methyl-
ated spirit is used for drying off the fish-glue
print after development. It is also employed for
developing resinous images, for making up acid
resist varnish, for diluting stopping-out varnish,
and for cleaning off varnish coatings. In the
aquatint process alcohol is used with resin to
give the granular ground which is formed on
the plate for etching. Similarly, alcohol is used
in certain bitumen processes, such as the Prey
process, where the alcohol with the asphalt
causes the film to reticulate — that is, to form a
network. An alcoholic solution of bichromate
is used for sensitising carbon tissue, the object
being to promote quicker drying.
ALCOHOLOMETER (Pr., AlcoolmHre ; Ger.,
Alkoholometer)
A hydrometer graduated so that the percentage
of alcohol can be read ofi directly on the scale.
ALDEHYDE (Pr., AldShyde ordinaire; Ger.,
Aldehyd)
Synonyms, acetaldehyde, ethaldehyde, acetic
aldehyde. CH, CHO. Molecular weight, 58.
Solubilities, miscible in all proportions with
water, alcohol, and ether. A colourless, light,
inflammable liquid, with pungent smdl, ob-
tained by oxidising ethyl alcohol with chromic
add. It was suggested by Ivumi^e and
Seyewetz as a substitute for the alkaline
caustics and carbonates in developers, but it
is rarely used. It forms, as does acetone (which
see), conpounds with the bisulphites, and its
action ir, developers may be represented by the
same equation.
In process work, aldehyde as an impurity in
alcohol is often the cause of foggy negatives in
wet collodion and collodion emulsion. The
aldehyde may be detected by adding a small
quantity of a strong solution of silver nitrate
to the alcohol and exposing the whole to Ught
for some hours, when the Uquid will gradually
blacken if aldehyde is present.
Alethoscope
i8
Alkalis
ALETHOSCOPE (Fr., AUthoscope : Ger.,
AUthoskop)
An optical device invented by Signer Ponti,
of Venice, and intended for the inspection of
transparencies or ordinary photographic prints.
It consisted of a large single lens, suitably
mounted, somewhat after the manner of the
modem lantemoscope or pautoscope used for
viewing lantern sUdes. It was claimed that the
alethoscope showed single photographs with
stereoscopic relief, but that is a theoretical
impossibiUty, although it is possible to obtain
a deceptive approximation to reUef when looking
with both eyes through a large convex lens at a
single photograph, provided the hghting, model-
ling, and perspective of the picture are good and
natural ; but this effect is more due to imagina-
tion and suggestion than anything else. If a
coloured picture is used the illusion is heightened.
According to Sir Howard Grubb, who investigated
this effect as seen in the graphoscope, this is
due to the lens being non-achromatic, so that
it fringes everything with red on one side and
with blue on the other. Thus the outline of,
say, a red flower is a httle extended on one side
to the right eye and on the other side to the
left eye, which causes the two pictures seen by
the respective eyes to be really dissimilar, in
such a manner as to give the appearance of reUef
when combined, although not properly stereo-
scopic.
ALGRAPHY
A process of lithographic printing from alu-
minium plates, as a substitute for lithographic
stone, patented by Joseph Scholz, of Mainz,
Germany. Aluminium had previously been used
for hthographic printing, but Scholz was the
first to make it a commercial process. His
method chiefly relates to the preparation of the
surface, phosphoric acid playing an important
part in the process.
ALIZARINE, ARTIFICIAL (Fr., Alizarine
artificielle ; Ger., Alizarin kiinstlich)
Synonym, dioxyanthraquinone a — ;8. A
group of organic dye-stuSs obtained from
anthracene. The only one of importance is
alizarin S, the sodium-bisulphite compound,
which has been occasionally used for sensitising
plates for red. Its action is somewhat uncer-
tain, and it has been entirely replaced by the
isocyanines (which see).
ALIZARINE, NATURAL (Fr., Alizarine
naturelle; Ger., Alizarin nattirlich)
Synonyms, madder, rubia. The root of rubia
tinctorum, obtained from South Europe and the
Orient, yields by extraction the colouring matter
alizarine, which is used for making carbon
tissue and in dyeing.
ALKALI (Fr., Alcali : Ger., Alkali)
The direct opposite to an acid. A term by
which the accelerator used in development is
often known. An alkaline solution is one that
will turn red litmus paper blue, or change the
yellow colour of turmeric paper to brown. Most
of the modern developers for dry plates are
known as alkaline developers because of an
alkah — ammonia, soda, etc. — being used as the
accelerator. In 1862 a Mr. Leahy, of Dublin,
found that liquor ammonia assisted the pyro
developer, but Major Russell, the inventor of
the tannin process, had for some time been
experimenting in the same direction, and in
1862 published the first complete account of a
workable system of alkaline development. Since
then alkalis other than ammonia — ^namely,
sodiimi and potassium carbonates — have come
into wide use. Previous to 1862 ammonia was
largely used in America, but not in the de-
veloper itself ; the plates were merely exposed
to the fumes of ammonia before the pyro was
applied.
ALKALIS, CAUSTIC
Potassium hydrate, sodiimi hydrate, and
lithium hydrate are examples of the caustic
alkalis, being often referred to, respectively,
as caustic potash, caustic soda, and caustic
Uthia. Their caustic nature is easily demon-
strated by the rapidity with which they will
disintegrate the human skin. The carbonates
are sometimes referred to as the "mild"
alkalis to distinguish them from the hydrates
or " caustic " alkalis. Caustic soda is, as a
rule, purer than caustic potash, but both have
an action upon glass, and render grease soluble
in water. (See also "Caustic")
ALKALIS, CHEMICAL EQUIVALENCE OF
All alkalis are not ahke in their action as
accelerators in developers, and one caimot be
used in the place of another indiscriminately.
The table below, compiled by George E.
Brown, is the most widely used for finding the
equivalent values of the alkaUs : —
s
^
.« a
■a "3
III
•a 3
1^
1"
•kS,
^11
^ll
■5?
80
112
97-14
106
286
138
174
I
1-400
-867
1-325
3-575
1-725
2-174
•714
I
I-2II
-946
2-553
1-232
1-554
•834
I-I53
I
I -091
2-944
I -42 1
1-791
•755
I '033
-916
I
2-698
1-302
I -641
■280
•392
•340
•371
I
-483
-608
•580
■812
•704
-768
2-072
I
I -260
■460
■644
■558
-609
1-644
-793
I
The ammonia solution (-880) should be weighed,
not measured. To find weights of other alkaUs
equivalent to any particular compormd, run the
finger down the proper column until the figure i
is reached. The figures in the same horizontal
line are the equivalent weights of the other alka-
Us as denoted at the head of each column.
Thus, I gr. of carbonate of soda (crystals) equals
•280 grs. caustic soda or -608 grs. potassium car-
bonate crystals. A rough and ready method,
said to work well in practice when changing from
one accelerator to another, is to consider that
one drop of liquor ammoniEB is equivalent in its
action to 8 gr. of sodium carbonate or 5 grs.
of potassium carbonate crystals. Dr. Mason
gives the following comparative table : —
Alkalimeter
19
Alpha Papers
Potassium hydrate. . .112 grs.
Sodimn hydrate . . .80
Potassium, carbonate . . 165
Sodium carbonate (anhydrous) 106
Sodium carbonate (crystals) . 286
Sodiimi bicarbonate . . 168
{See also "Accelerator.")
ALKALIMETER (Fr. AlcaUmitre : Gee.,
Alkalimeter)
An instrument for testing the amount of
alkali present in a commercial sample which
may have an admixture of impurities. It was
invented by P. A. H. Descroizilles, of Dieppe,
though some have claimed the discovery for
Dr. Andrew Ure, of Glasgow. It consists of a
graduated glass tube divided into 100 degrees
A. Faraday
Alkalimeter
B. Burette Pattern
Alkalimeter
and furnished at one end with a dropping
nozzle. The form recommended by Dr. Para-
day is shown at A, but many now prefer to use
the more convenient burette pattern B, hav-
ing a glass tap or pinchcock at its lower end.
The tube of the alkalimeter is filled with dilute
sulphuric acid, containing as much of the strong
acid as would suffice to neutraKse a given weight,
say 100 grs., of potassium carbonate or sodium
carbonate. One hundred grains of the alkali
to be tested is then dissolved in water, the
solution being placed in a glass beaker or flask,
and the add solution is allowed to drop gradu-
ally into it until the mixture is neutralised. The
purer the substance the more of the add will
be required. If the tube is emptied to, say,
80 deg., the alkaU is known to contain 20 per
cent, of impurities. The point at which neutral-
isation occurs used to be determined by means
of litmus or turmeric, but more sensitive and
easily recognisable indicators are now employed,
the prindpal of these being methyl-orange and
phenol-phthalein. A mixture of these two re-
agents in alcoholic solution gives a pale yellow
colour to a perfectly neutral liquid, which is
instantly changed to pink by the least trace of
add, or to a deep red by a trace of alkali. Com-
merdal potassium carbonates and sodium car-
bonates frequently contain a certain proportion
of the sulphate or chloride, silicates, etc., and
since the value of the sample depends on the
proportion of carbonate present it is obviously
requisite to ascertain this. Impure com-
merdal alkaUs are, of coiirse, scarcely suitable
for photographic purposes, but the above
method of testing is often usefrd. By using an
alkaline solution of known strength instead of
the add solution, the strength of adds may be
tested ; or the strength of a solution of silver
may be ascertained by charging the instrument
with a standard solution of sodium chloride.
ALKALINE FIXING BATH
A " hypo " (hyposulphite of soda) fixing
bath that is not in an add condition. Fixing
baths for printing-out papers should always be
distinctiy alkaline, and as ordinary mixtures of
hyposulphite of soda and water are sometimes
slightly acid, various methods of destroying the
acidity have been recommended. A normal
fixing bath may be rendered alkaline by adding
suffident liquor ammoniae until after stirring
it smells faintly, or by adding sodium carbonate
or bicarbonate. A standard formula for an
alkaline bath is : —
Hyposulphite of soda
2 oz.
124 g.
Washing soda .
i „
16 „
Common salt .
i „
16 „
Water
18 „
1,000 ccs
At least one authority considers this too weak,
and reduces the water to 12 oz. or 14 oz. Some
advocate the use of J oz. of sodium sulphite
in place of the J oz. of washing soda. It is
not advisable to use this bath with any paper
having a substratum tinted pink or mauve, as
these colours, which are aniline dyes, would in
almost every case be destroyed.
ALLONGi: PAPER
A rough-grained hand-made drawing paper,
used by artists in crayon drawing for process
reproduction. It has a very pleasing siirface
grain, and may be used on the right or wrong
side with different results, the right side being
the rougher and perhaps the better. This paper
may be sensitised for printing a photographic
image on to it as a guide to the artist. {See
" Sensitising.")
ALLYL-SULPHOUREA, ALLYL-THIO-
CARBAMIDE. AND ALLYL-THIO-
UREA (Sea "Thiosinamine.")
ALPHA PAPERS AND PLATES
A particular make of chloro-bromide printing
paper and transparency plate introduced in 1890
and 1891 respectively by IlEord, I<td. The plate
or paper is printed by artificial light, and after-
wards developed ; the image may fiien, if desired,
be toned in a toning bath, which gives a large
variety of colours.
Altogravure
20
Alum Baths
ALTOGRAVURE
A process for the production of half-tone
intagUo plates for power-press printing after the
style of Rembrandt photogravure.
ALTO-RELIEVO (Fr., Uaui relief; Ger.,
Hochrelief)
Derived from the Italian term alto rilievo,
meaning high relief ; applied to sculptured,
carved, or modelled ornaments and figures which
stand out from their backgroimd by more than
half their proportionate thickness. The term is
sometimes employed in processes in which relief
is obtained by methods depending on the action
of light, the results so produced being known as
photo-reHefs. As a rule, however, these pro-
cesses are not capable of jdelding a great amoimt
of relief. A low degree of relief is known as a
basso-relievo, or bas-relief (which see) ; while a
medium amount is known as a mezzo-relievo.
ALUM (Pt.yAlun; Ger., Alaun)
This term comprises a large class of salts
characterised by the formula M'^SOj M"\
(SO 4)3 24H2O, in which M' and M"' are moua-
tomic and triatomic metals. AH the alums
crystallise in octahedra, but all do not contain
alumina. The following are the principal alums
used in photography : —
Ammonia Alum (Fr., Alun d' ammoniaque ;
Ger., Ammoniakalaun)
(NHJ2SO4 Al,(S0i)3 24H3O. Molecular
weight, 906. Solubilities, i in 8-5 water, inso-
luble in alcohol and ether.
Potash Alum (Fr., Alun de potasse ; Ger.,
Kalialaun)
Synonym, aluminium and potassium sulphate.
K.SOi Al2(S04)3 24HjO. Molecular weight,
948. Solubilities, i in 7-5 water, insoluble in
alcohol and ether. This is the most generally
used " alum," and is met with in large octa-
hedral clear crystals or a white powder of pecu-
liar astringent taste. It is used for a hardening
and clearing bath and for making the " hypo ' '
and alum bromide toning bath.
In process work, potash alum is used with dilute
nitric acid for graining or matting the surface of
zinc plates previous to coating them with the
albumen-bichromate sensitising solution. The
graining makes the coating hold better, and after
the image has been inked and developed, the
grained surface holds the damping solution, which
prevents the ink from spreading and soiling the
whites when rolling up.
Soda Alum (Fr., Alun de soude ; Ger., Natri-
umalaun)
Synonyms, sodium alum, sodium and alu-
minium sulphate. Solubilities, i in 2-2 water ;
insoluble in alcohol and ether. This is occasion-
ally used in place of the ammonia or potash alum.
Chrome Alum (Fr., Alun de chrome ; Ger.,
Chromalaun)
Synonym, chromium and potassium sulphate,
KjSOj Crj(S04)j 24H2O. Molecular weight.
916. Solubilities, i in 6-25 water, insoluble in
alcohol and ether. This is in the form of rich
violet coloured crystals, giving a dichroic solution
that is reddish violet by transmitted, and green
by reflected light, obtained as by-products in
the manufacture of alizarine, aniline violet, etc.
Stolze suggested the addition of sufficient
ammonia to chrome alum solution to give a per-
manent precipitate after well stirring and tiien
filtering. Namias suggested the admixture of
equal quantities of a 10 per cent, solution of
ordinary and chrome alums, rendering the mix-
ture alkaline with ammonia, boiling and filtering.
I/umiire and Seyewetz have also confirmed the
statement that alkaline chrome alum exerts a
greater hardening effect. The maximum hard-
ening effect is produced by 2 per cent, of the
total dry gelatine employed.
Chrome alum is used as an addition to emul-
sions, and for this purpose it is general to render
the solution distinctly alkaline with ammonia,
filter, and then render neutral by the addition
of glacial acetic or hydrobromic acid. It is also
used in the fixing bath (which see) and combined
bath (which see).
Lumi^re and Seyewetz have pointed out that
100 parts of gelatine are most hardened by
0-64 parts of alumina, and the following table
gives the quantities of the aluminium compounds
which contain this quantity of alumina : —
Potash alum . . .6 parts
Ammonia alum . . . 5-6 „
Aluminium sulphate . . 4-2 ,,
Aluminium chloride, anhydrous i-6 „
Aluminium nitrate. . • 4"5 „
Below these quantities the full hardening efiect
is not produced, whilst increase produces no
greater hardness. They have also pointed out
that " alum " has the least hardening efiect,
and is extremely liable to fungoid growths,
so that it is far better to use chrome alum in
its place.
In process work, chrome alum is used as a
hardening agent for gelatine. It is added some-
times to fish-glue when the image has a tendency
to wash away too freely. Also it has been added
to the nitric acid bath when etching enamel
images on zinc, with the object of preventing
the images from being softened.
Iron Alum (Fr., Alun de fer ; Ger., Ammo-
niaheisenalaun)
Synonyms, ammonia - iron - alum, ammonio-
ferric-sulphate, ferric ammonium sulphate.
(NH^j^SO^ Fej(S04)3 24Hj,0. Molecular weight,
962. Solubilities, i in 2 water, insoluble in
alcohol and ether. This is in the form of large
pale violet or amethyst octahedral crystals, whidi
give a brown solution when dissolved in tap
water, due to the formation of basic iron salts.
Used for making ferric oxalate (which see).
ALUM BATHS
These are used in both negative and print
making. In negative work an alum bath was
originally used for the purpose of hardening the
film, but with most modem plates and modem
improvements in working such treatment is
rarely necessary. It serves another purpose,
however. If the bath is rendered acid, alum re-
moves all development stain and improves the
colour of the negative. A good formula is : —
Common alum . . i oz. 58 g.
Hydrochloric acid . i drra. 50 ccs.
Water . . .20 oz. 1,000 „
Alum Trough
Aluminium
After a short rinsing from the developer, the
plate should be immersed in this bath for two
or three minutes, then well washed for tea or
fifteen minutes, and fixed as usual. The use
of a good add fixing bath renders the employ-
ment of an acidified alum bath unnecessary, as
it clears and hardens the film while fixing is pro-
gressing.
In the carbon and allied processes, in which
a bichromate is used for sensitising, an alum bath
is employed after the print is developed. Its
object is twofold. It hardens those parts of the
film that may remain partially soluble, and also
removes any yellow bichromate stain that may
be left after development. The following is an
excellent formula : —
Alum
Water
I oz.
20 „
55 g-
I, coo CCS.
Hot water should be uged for dissolving the
alum, but the bath must not be used imtil it is
quite cold.
ALUM TROUGH
A glass-sided trough containing alum solution,
and sometimes used in the optical lantern
between the light and the condenser in order to
absorb the heat rays before they reach the slide
or other object to be projected. Alum troughs
are widely used for cinematograph films, and
slides by the screen-plate (colour) processes, as
these are easily damaged by heat. Glycerine and
other solutions have been advocated in place of
a saturated solution of alum, while even plain
water, circulating through pipes and a tank on
the thermo-syphon principle, is sometimes
employed.
ALUM-HYPO TONING
A method of toning black-and-white prints
on bromide and gasUght papers to a sepia colour,
sometimes referred to as the " boiHng process "
and as "sulphur toning" ; actually it is a sulphur
toning process, but not the only one. The
formula for the bath is : —
Sodium hypostdphite
Powdered alum
Granulated sugar
Boiling water to
2ioz. 125 g.
i „ 25 „
i „ 25 ..
20 „ I,OCXD CCS.
Dissolve the " hjrpo " in the water first, add the
alum slowly, and next the sugar, although this
may be omitted if desired. When all is dissolved
the solution should be milk white and a sediment
should form at the bottom of the bottle, but it
should not be filtered. The bath should be
heated two or three times to about 120° P.
(nearly 49° C), allowing to cool in between ;
this " ripening " is necessary because were it
omitted the newly-made batii would not work
well, and would bleach the prints. The older
and more used the bath is (it may be used over
and over again) the more evenly it works, and
the richer the tones. When possible, one part of
an old bath should be added to four parts of the
new bath. Another method of ripening the bath
is to tear up some old prints and place in the
solution previous to heating ; still another is to
add s grs. of silver nitrate to each ounce of the
bath, this tending to give a purplish-brown tone.
The fixed black-and-white prints to be toned
should be placed in the bath when this is cold,
and the whole then warmed, keeping the prints
on the move. The time of toning will vary
according to the kind of paper and developer,
age of print, and temperature of solution. The
quickest results are obtained by raising the
temperature as high as the picture will stand,
generally about 100° P. (nearly 38° C), but the
best tones are those obtained at about 85° P.
(between 29° and 30° C), the average time being
fifteen minutes. The bath may be used cold,
in which case toning may take as long as two
or three days. Prints developed with amidol
appear to tone the quickest, and those toned
with hydroquinone the slowest. When the
prints reach the desired tone they are allowed to
remain in the solution until it is tepid, or cold,
and then well washed.
Another method of toning with this bath is
to harden the prints first of all in a solution of
alum (alum i oz. ; water 30 oz.), or a portion of
the cold toning bath, and then place in the alum-
hypo bath made hot, and, after toning, in the
alum-aud-water solution again, finally washing.
The object of the alum baths is to prevent
bhsters, which would in all probabiHty occur if
the prints were put direct into the hot toning
bath, and thence into cold water for washing.
The use of the extra alum baths is obviated by
warming the toner containing the prints. Rich
and good tones depend upon the print having
been properly developed, and upon the ripeness
of the bath. If the toned prints are washed for
about one hour they may be considered quite
permanent, the image consisting of silver sul-
phide.
The alum-hypo bath may also be used for
toning P.O.P. prints. The prints must first be
washed, fixed in an ordinary " hypo" bath, next
placed in a cold alum-hypo bath, where they tone
to a good purple-brown colour, and then washed
well. P.O.P. prints to imdergo this treatment
should be over-printed, since they reduce con-
siderably in toning.
ALUMINIUM, OR ALUMINUM (Fr. and
Ger., Aluminium)
Al. Atomic weight, 27. A very light, sil-
very-white metal, obtained by electrolysis from
aluminium chloride. It is principally used for
the construction of Ught cameras and for lens
fittings, but difficulties in working it and its soft-
ness led to the introduction of a harder alloy
of aluminium and magnesium, called magnalium.
Aluminium is used in some flashlight powders,
and in algraphy (which see). " Aluminum " is
now the accepted American spelling.
Aluminium plates are now largely used for
lithography as a substitute for hthographic
stone. (See " Algraphy.")
In process work, aluminium has been used for
reUef etching, but is not commercially in vogue.
Nitric add has Uttie action on it, but hydro-
chloric add attacks it more readily. Phos-
phoric and fluo-siUdc adds are active mordants,
but not convenient to use. Perchloride of iron
has a strong action upon it ; a solution of common
salt will also attack it freely. Aluminium is
largely used for the screen and plate holders of
process cameras, as it is not readily acted on
by the silver nitrate solution.
Aluminium Chloride
Amber
ALUMINIUM CHLORIDE (Pr., Chlorure
d' alumina ; Ger., Chloraluminium)
AljCl, 12 HjO. Atomic weight, 483. Soluble
in water, alcohol, and ether. It is a yellowish-
white granular crystalline powder wlich (very
rarely) is used in the gold and platinum toning
baths. It is extremely deliquescent, and must
be kept in well-stoppered bottles.
ALUMINIUM FLASHLIGHT
Aluminium bronze powder, also known as
" silver bronze," may be used in place of, or in
conjunction with, magnesium for flashlight work.
It is cheaper than magnesium, bums under cer-
tain conditions with less smoke, but it is not
quite so actinic. The first experiments with
tills metal appear to have been carried out by
Dr. Pifiard, of New York, in 1888. Dr. Miethe
has found that fine aluminium bronze powder
(5 to 10 per cent, of aluminium and 90 to 95
per cent, of copper) bums almost completely in
the flame of a Bunsen burner. Aluminium, how-
ever, is better, even if more dangerous, when
mixed with potassium chlorate, in which form it
becomes an explosive mixtirre, and must be
treated as such ; that is to say, the mixture
must have a light applied to it, and not be blown
through a flame. The potassium chlorate
intended for mixing with the aluminium bronze
powder should be quite free from the deliques-
cent potassium chloride, because if this is present
the chlorate will tend to be moist. The chlorate
should be well dried, and powdered sufficiently
finely as to pass through a sieve of eighty meshes
to the inch. The aluminium and the chlorate
must not be mixed together in a mortar, but
with a feather or a flat blade on a sheet of paper.
A suitable formula is : —
Aluminium
Potassium chlorate
I part.
2j parts.
For more rapid flashes, antimony sulphide should
be added, ihe formula being : —
Antimony sulphide . . 3 parts.
Aluminium . . • 5 „
Potassium chlorate . .15 1,
Another formula is : — ■
Aluminium . . .20 parts.
Lycopodium . . .5 ,,
Ammonia nitrate . . 1 part.
All these mixtures are explosive and dangerous,
and proper precautions should be observed,
as directed imder the heading " Flashlight
Mixtures," where a formula for aluminimn
in conjvmction with magnesium wiU be
found.
A flashlight mixture, patented in 1904 by Dr.
G. Krebs, gives very littie smoke and consists
of aluminium 2 parts, magnesium- 2 parts, and
chrome alum 10 parts. A " time " powder, also
due to Dr. Krebs, contains aluminium 20 parts,
magnesium 80 parts, chrome alum or copper
sulphate 100 parts, lime oxide, carbonate, or
glass 20 parts. Aluminium cartridges, to con-
tain a flash mixture and bum with it, have
lately been made, the metal case being of from
•I to '3 mm. thickness.
Alumiuiun leaf burned in oxygen gives a very
powerful Hght. The method is to place a few
leaves of aluminium in a dry bottle containing
oxygen gas, and on applying a lighted taper to
the top leaf the contents of the bottle bum with
a flash which, for actinic power and general
brightness, is said to exceed anything obtainable
with an equal amount of magnesium.
ALUMINIUM POTASSIUM SULPHATE
(See "Alum.")
ALUMINIUM SULPHATE (Fr., SulfaU d'alu-
mine ; Ger., Aluminiumsulfat)
AlatSOj), iSHjO. Molecular weight, 166.
Solubility, i in 2 water. White crystals with
sweet, astringent taste, obtained by dissolving
aluminum hydrate in sulphuric acid. It has
been suggested as a hardening agent, but has
found very little use.
ALUMINIUM SULPHOCYANIDE (Fi.,Sulfo-
cyanure d'alumine ; Ger., Aluminium-
rhodanid)
Synonym, aluminium sulphocyanate or
rhodanide. Al2(CNS)e. Molecular weight, 402.
A yellowish powder occasionally used as a
preliminary bath for self -toning papers. It is
extremely deliquescent, and must be kept in well-
stoppered bottles.
ALUMINOGRAPHY (See " Algraphy.")
AMACRATIC
A term relating to photographic lenses and
implying that the chemical rays of light are
united into one focus. "Amasthenic" is a term
with the same meaning.
AMASTHENIC (See " Amacratic")
AMATEUR PHOTOGRAPHER
One who practises photography as a pastime,
and not as a profession. In photography the
question of who is and who is not an amateur is
a difficult one to decide. So-called amateurs do
not hesitate to accept a little payment for their
prints " just to cover the cost of materials,"
while others win prizes in cash competitions, or
seU prints to periodicals. It is maintained in
many quarters that the acceptance of money
by an amateur for his work places him in the
professional category. The consensus of opinion,
however, is that a photographer who does not
advertise, invite custom, or rely upon the art as
a livelihood, is an amateur. The old controversy
and jealousy between amateurs and professionals
has, at any rate in Great Britain, faded away
to extinction, and the two classes of photo-
graphers understand more dearly that their
interests are parallel and do not clash, and
that photographic progress has need of them
both.
AMBER (Pr., Ambre jaune ; Ger., Bernstein)
A fossil, yellow and translucent resin used
occasionally in varnishes, for which purposes it
must first be fused.
Fused amber
Chloroform to
3 oz-
20 „
150 g.
1,000 CCS.
When dissolved, filter and use cold.
Ambrotypes
23
Amidol
Another formula is that known as Braunt's,
namely : —
Fused amber . . 4 oz. 400 g.
Sandarac . . . 6 „ 600 „
Elemi . . . . i „ 100 „
Methylated spirit (90 X) . 12 ,, 1,000 ccs.
When dissolved add —
Camphor . . . ■} oz. 12|- g.
AMBROTYPES
The American name for wet collodion positives
upon glass or " tin " (thin plates of enamelled
iron or steel). Those upon glass are some-
times said to be by the alabastrine process "
{which see) ; those upon " tin " are called " tin-
types " or " ferrotypes." Ambrotjrpes are pro-
duced by the " finished while you wait " process
formerly so extensively practised by itinerant
photographers, but now practically superseded.
Pull particulars will be found under the heading
" Ferrotype Process."
AMIDINE (Pr., Amidon : Get., Amidin)
Synonyms, amadine, amylum. An amyl-
aceous substance identical in chemical composi-
tion with ceUulose, and found in many cereals
and vegetables. It is practically equivalent to
starch. It forms the lianslucent jelly or paste
obtained when boiling water is poured on ordinary
starch, so extensively used as a photographic
mountant.
AMIDO-ACETIC ACID (Pr., GlycocoU; Ger.,
Amidoessigsdure, Glykokoll)
Synonyms, glycocoll, amido-glycollic acid,
amino-acetic acid, glycocine, sugar of gelatine.
NHj CH, COOH. Molecular weight, 75. Solu-
ble in water. White crystals, formed by re-
placing one of the hydrogen atoms of ammonia
by the acetic acid. It possesses both acid and
basic properties, and the sodium salt NHj CHj
COONa was introduced (1902) under the name
of Pinakolsalz N by Meister, Lucius and Briin-
ing as a substitute for the alkaUs in developers,
but on account of its high price did not replace
them in practice.
Amido-acetic add is called sugar of gelatine
on account of its sweet taste, and from its being
a product of the decomposition of gelatine by
acids or alkalis. It is sometimes termed glycin,
but must not be confused with the developer of
that name {which see), this being a phenol de-
rivative of it, having the formula CjH^OH NH
(CHjCOOH).
AMIDO-BENZINE {See "Aniline.")
AMIDO-CARBOXYLIC ACIDS {See "Carb-
oxyUc Acids.")
AMIDO-GLYCOLLIC ACID {See "Amido-
acetic Acid.")
AMIDO-PHENOL (Sea "Amidol.")
AMIDOL, OR DIAMIDOPHENOL (Pr. and
Ger., Amidol)
A developer having the formula CjH,
OH(NHj)2 ,and introduced in the year 1892. It
is sold in the form of a white or greyish crystal-
line powder, which keeps weU in a dry state but
in solution rapidly loses its developing powers.
The dry amidol is therefore best added to the
solution immediately before use. It forms a
developer when mixed with a solution of sodium
sulphite, no alkali being needed, and it works
very rapidly, the detail appearing almost imme-
diately the developer is applied to the plate.
This sudden appearance is apt to deceive those
unacquainted with it, but the negative must not
be taken from the developer until it has attained
the required density. It has been stated that
amidol will develop when in an acid condition,
and appropriate formulae have been published,
but it is better to regard amidol as an alkaline
developer, because, even if it does work when
sUghtly acid, it works better when slightly
alkaline. The addition of acetone sulphite in
quantity equal to that of the amidol preserves
the developer for a considerable time, but acts
as a restrainer ; other preservatives have been
advocated, but it is better to add the dry amidol
when required for use. A normal developer
consists of : —
Sodium sulphite
Amidol
Water to .
600 grs. 60 g.
40-60 „ 4-6 „
20 oz. 1 ,000 CCS.
The mixed developer will keep well for four or
five days. It should be made up with a new
solution of fresh and pure sulphite. It is usual
to make up a stock solution of sodium sulphite
and to add 2 to 3 grs. of dry amidol to each
ounce of solution.
Potassium bromide has but Httle restraining
effect in an amidol developer, except when used
in large quantities, but when added in small
quantities it has a clearing effect. In cases of
over-exposure, about 15 drops of a 10 per cent,
solution of potassium bromide may be added
for every ounce of developing solution. Acetic,
citric, and tartaric acids have been recommended
as restraiaers and sodium hyposulphite (" hypo " )
as an accelerator, but with the latter the image
loses density beyond a certain point. Two- and
three - solution amidol developers are rarely
resorted to, as they have but little advantage
over the one-solution, which is in wide use, par-
ticularly for bromide paper, for which most
paper-makers give a special formula. The two-
solution form is not given here because it is of
doubtful value.
Amidol has the property of staining the
finger-nails. Sometimes it stains bromide prints
a rosy pink colour, which may be removed by
the use of eau-de-javelle followed by citric acid.
Another formula with bromide, and specially
recommended by Abney for the development of
" instantaneously " exposed plates, is : —
Amidol .
Sodium sulphite
Potass, bromide
Water to
S g«. 5 g-
40 „ 40 „
1 ., I .,
2 oz. 1,000 CCS.
This solution will keep for a few days, but is
most energetic when fresh.
Another form of a one-solution amidol de-
veloper is that known as Balagny's acid-amidol,
which has found great favour upon the
Continent, both for negatives and bromide
paper.
Ammonia
24
Ammonium Bichromate
loj oz.
30 grs.
300 CCS.
2 g.
8 „
One of its advEintages is its slowness. The
original formiila is : —
"Water .
Amidol
Sodium sulphite
crystals
Potassium bromide
solution (10 %) . 170 mins. 10 ccs.
Sodium bisulphite
solution . . 340 „ 20 „
The bisulphite solution is a commercial article.
A substitute can be made by preparing a satu-
rated solution of the commercial bisulphite and
then adding i drm. of strong sulphuric add to
each i pint. Many similar acid-amidol mixtures
have been advocated.
It has been frequently stated that amidol-
developed negatives and prints should not be
fixed in an acid fixing bath, because of its
causing fogging or further development during
fixation, but T. H. Greenhall says that there is
nothing to be feared in this respect when using
bromide paper. Au old acid fixing bath heavily
charged with amidol and sulphite gave stronger
prints than plain " hypo," due to the fact
that plain " hypo " had a slight reducing
action, and not to any defect in the acid
fixer, which was absolutely necessary for some
papers.
Some photographers find that amidol has an
efiect upon the skin resembling that of metol,
but not so intense.
AMMONIA (Fr., Ammoniaque ; Ger., Ammo
niak, Ammoniahwasser, Salmiakgeist)
A volatile, pungent gas, which for photographic
and many other purposes is used in the form of
a watery solution (NHaOH) ; formerly known
as " spirit of hartshorn." The strongest solu-
tion, and that mostly used, is of -880 sp. g.,
contains 35 per cent, of the gas NHj, and is
commonly known as " ammonia "880 " or " hq.
ammon. fort." " Liquid ammonia " is the
incorrect, popular form of the term " liquor
ammoniae." A weaker liquor, kept by most
chemists, one-third the strength of the -880
solution, is rarely used in photography. Ammo-
nia has many uses in photography, the principal
being as an accelerator in the pyro developer,
for blackening the mercury-bleached image in
intensification, in emulsion-making, and as an
addition to the bichromate bath for sensitising
carbon tissue. Liquor ammonise should be kept
in a glass-stoppered bottle, as it loses its
strength rapidly if exposed to the air, and cork
stoppers very soon deteriorate. The fumes of
ammonia are extremely irritating to the eyes,
throat, and nose, and particular care should be
taken when opening bottles of it in hot weather,
or when the bottles have been left on a warm shelf,
as the liquid may spurt out and cause serious
damage. Bottles containing liquor ammonise
should be kept in a cool place, as heat develops
great pressure, which may blow out the stopper
or burst the bottle.
A. Haddon states that experiments show
that ammonia expands on dilution with water
about 18 per cent., and points out how very un-
reliable and varying is a solution of ammonia
in hot weather, freshly bought samples of the
•880 solution varying in specific gravity from
that to -904, or from 35-8 to 26-9 NH, per cent,
volume. It is this variation that makes it
unreliable as an accelerator in development;
hence the necessity of using it fresh or keeping it
in a gas-tight bottle and in the cool.
In process work, ammonia is not largely used.
It is added to the albumen bichromate solution
and also to the fish-glue solution to neutralise
acidity, and increase the keeping qualities. A
few drops added to the developing water makes
the albumen bichromate image develop more
quickly. A dilute solution of ammonia with
whiting is used for cleaning copper, to free the
surface from grease. Perchloride of iron solution
for etching, especially for photogravure, is often
neutralised by the addition of ammonia. Added
to copper sulphate until a bright blue solution is
formed, ammonia makes a bath for coating zinc
with a film of copper without the use of an elec-
tric battery.
AMMONIA FUMING
Years ago, when most photographers, both
professional and amateur, prepared their own
plain salted and albumenised papers, it was
customary to expose these to the fumes of
ammonia in a box. The ammonia, uniting with
the free silver nitrate in the paper, gave greater
sensitiveness and richer prints. It has now
fallen into almost entire disuse, but it formerly
found favour owing to the briUiance imparted
to the prints so treated.
AMMONIA METER
A small glass bulb, devised by Haddon and
Grundy, which floated at exact balance in a 2'9
per cent, solution of ammonia of a certain
temperature, thus enabling the strength to be
determined without analysis. It has also been
known as a " specific gravity ball."
AMMONIA-IRON-ALUM {See " Alum.")
AMMONIA, ROCK (See " Ammonium Car-
bonate.")
AMMONIO-CITRATE OF IRON {See
" Ferric Ammonio-citrate.")
AMMONIO-NITRATE
" Bmulsion.")
PROCESS
{See
AMMONIO-OXALATE OF IRON {See
"Ferric Ammonio-oxalate." )
AMMONIUM {See "Ammonia.")
AMMONIUM ALUMINIUM
{See "Alum.")
SULPHATE
AMMONIUM BICHROMATE (Fr., Bichro-
mate d' ammoniaque ; Ger., Ammonium-
dichromat; Saures chromsaures ammon)
(NH4)jCr20,. Molecular weight, 252. Solu-
bilities, I in 4 water, soluble in alcohol ; known
also as ammonium dichromate. Orange crystals,
obtained by neutrahsing chromic acid with
ammonia. It is sometimes used for sensitising
carbon tissue, gum bichromate, and in some
photo-mechanical processes, as it has a stronger
Ammonium Bromide
25
Ammonium Molybdate
sensitising power, and is more soluble than the
potassium salt, and in carbon printing gives
richer pictures.
In process work, ammonium bichromate is
largely used as a sensitiser with fish-glue for
printing half-tone images on zinc and copper.
It is believed to be a better sensitiser than
potassium bichromate in this respect, the latter
being chiefly used with albrunen for the line
process. It gives a more sensitive solution with
fish-glue, the solution keeps better, and develops
more freely. Ammonium bichromate is said to
be more than twice as sensitive to light as
potassium bichromate.
AMMONIUM BROMIDE (Fr., Bromure
d' ammonium ; Ger., Bromammonium)
NH^Br. Molecular weight, 98. SolubiUties,
I in 1-4 water, i in 31 absolute alcohol. A white,
crystalline, sMghtiy hygroscopic powder, with
pungent saline taste, obtained by neutralising
hydrobromic add with ammonia, evaporating
the solution and crystaUising. It is sometimes
used as a restrainer in place of the potassium
salt, but must not be used with the caustic
alkalis or carbonates, as ammonia is set free,
which may give rise to fog. Its principal use
is in emulsion making. If the salt has become
damp by absorption of aqueous vapour, it may
be dried in an oven without injury.
AMMONIUM CARBONATE (Pr., Car-
bonate d' ammoniaque; Ger., Kohlensaures
ammon, Ammoniumkarbonat)
Synonyms, hartshorn, rock ammonia.
(NHi)HC03 (NHJNHj COj. Molecular weight,
157. Solubility, i in 4 water. Keep in well-
stoppered bottie, and before use scrape off any
adherent white powder. White, hard, translu-
cent, striated masses, obtained by heating
ammonia salts and chalk. It is used in place of
liquor ammoniae in some developers. Hot water
must not be used to dissolve it.
AMMONIUM CHLORIDE (Pr., Chlorure
d'ammoniaque ; Ger., Chlorammonium)
Synonyms, sal-ammoniac, muriate or hydro-
chlorate of ammonia. NHiCl. Molecular weight,
53-5. Solubilities, i in 3 water, i in 8 alcohol. A
white, crystalline powder, or tough, transparent,
fibrous masses, the latter usually known as sal-
ammoniac. The pure powdered salt is apt to
attract aqueous vapour from the air, whilst sal-
ammoniac remains dry. It is chiefly used for
salting albumenised paper and also in preparing
chloride emulsions.
AMMONIUM CITRATE (Pr., Citrate
d'ammoniaque: Ger., Ammoniumcitrat)
(NHi)jC,H,Or. Molecular weight, 243. Solu-
bility, 1 in 0-5 water, soluble in alcohol. This
salt is so deUquescent and so easy to make that
the user should prepare it himself : —
Citric acid . . i oz. 100 g.
Distilled water . 2 „ 200 ccs.
When dissolved add —
I/iq.ammonise -880, (about) 250 mins. 50 ccs.
The ammonia should be cautiously added, and
the solution tested for neutrality with Utmus
paper. When neutral, make the total bulk up
to 10 oz. or 1,000 ccs. with distilled water,
which practically gives a 10 per cent, solution.
It is used as a restrainer with the pyro developer
in the proportion 5 to 10 grs. per ounce.
AMMONIUM FLUORIDE (Pr., Fluorure
d' ammonium; Ger., Fluor ammon)
NH4P. Molecular weight, 36. Soluble in water
and alcohol. This is in the form of small, deliques-
cent, colourless, flat crystals, and it is used for
etching glass and stripping negatives. As it
attacks glass, it must be kept in indiarubber or
wax-lined botties.
AMMONIUM HYDRATE
A very seldom used synonym for liquor
ammonise, NH5HO.
AMMONIUM HYDROSULPHIDE (See
"Ammonium Sulphydrate.")
AMMONIUM HYPOSULPHITE (Pr., Hypo-
sulphite d'ammoniaque: Ger., Ammonthio-
sulfat)
Synonym, ammonium thiosulphate. (NH^),
SijOs. Molecular weight, 148. Very soluble in
water. It occurs in colourless crystals, or can
be readily made in solution, as follows : —
Sodiimi hyposulphite . 5 oz. 248 g.
Ammonium chloride . 2J „ 106 „
Distilled water to . 20 „ 1,000 ccs.
It was suggested first in 1888 by John SpiUer
as a substitute for the sodium S£dt, on account
of its greater solubihty, and therefore of the
greater ease with which it can be washed out of
prints and negatives. It has recenUy been
patented as a fixing salt. I,umi^e and Seyewetz
point out that fixation is only quicker when the
proportion of thiosulphate is less than 40 per
cent., and if the proportion of chloride is only
sufficient to convert one-fourth of the sodiimi
salt, and further that the use of this salt must be
regarded with suspicion on account of the rapid
decomposition of the silver salts formed if the
subsequent washing is not very rapid.
AMMONIUM IODIDE (Fr., lodure d'ammo-
nium ; Ger., lodammon)
NHjI. Molecular weight, 145. Solubilities,
I in 0-6 water, i in 9 alcohol, slightiy soluble in
ether. It is a white to yellowish-white hygro-
scopic crystalline powder, which is very unstable,
readily giving off iodine, which may be dissolved
out by ether. It is occasionally used in
making iodised collodion and negative gelatine
emulsions.
In process work, ammonium iodide is a con-
stituent in most iodising formulae.
AMMONIUM MOLYBDATE (Pr., Molybdate
d'ammoniaque ; Ger., Molybdansaures
ammonium)
(]SlH4)«Mo,02i4H20. Molecular weight, 1,236.
Soluble in water. It is in the form of large
colourless or slightiy greenish crystals, readily
decomposed by heat. It has been suggested as
an ingredient in printing out emulsions in order
to obtain greater contrast.
Ammonium Nitrate
26
Ammonium Sulphocyanide
AMMONIUM NITRATE (Pr., Azotate
d' ammonium : Ger., Salpetersaures ammon)
NH4NO3. Molecular weight, 80. Solubilities,
I in 0'5 water, i in 2-2S alcohol. These colour-
less, long, rhombic crystals are obtained by
neutralising ammonia or ammonium carbonate
with nitric acid. It has been suggested as a
substitute for the potassium salt in flashlight
mixtures {which see), though its hygroscopic
nature is somewhat against it. It is also formed
in emulsion making by double decomposition
between ammonium bromide and silver nitrate,
and is removed in washing. It is deliquescent,
and should be kept in well-stoppered bottles.
AMMONIUM OXALATE (Pr., Oxalate
d' ammoniague ; Ger., Ammonoxalat)
(NIl^)^C^0i3.^0. Molecular weight, 142.
Solubilities, i in 25 water. It is in the form of
colourless crystals, obtained by neutralising
oxalic acid with ammonia, and it is used to pre-
pare ferric ammonio-oxalate.
AMMONIUM PERSULPHATE (Fr., Per-
sulfate d' ammoniague ; Ger., Ueberschwe-
felsaures ammonium)
(NHi)^ S,0,. Molecular weight, 228. Solu-
bility, I in 2-5 water. It takes the form of
colourless crystals, which are obtained by electro-
lysis. It is principally used as a reducer, and is
especially valuable in that it reduces the high
lights more than the shadows. The following
formula may be used : —
Ammonium persulphate 480 grs. 50 g.
Distilled water to 20 oz. 1,000 ccs.
The negative should be immersed in this until the
reduction is nearly complete, and then rapidly
washed. A stop bath of sodium sulphite (5 per
cent, solution) is sometimes recommended, but it
occasionally gives rise to stains, and it is better
to use water only. The chemical action which
takes place is supposed to be —
Ag -t- (NH J, S.O, = (NH Ja SO^ -1- Ag.SO.
Silver Persulphate Ammonium Silver
sulphate sulphate
The silver sulphate dissolves in water. Namias
states that a solution of persulphate acidified
with nitric acid acts like the ordinary " hypo "
and ferricyanide reducer.
The addition of 0-5 to 1 per cent, to the normal
platinotype developer shortens the scale of
gradation, and is thus useful for over-exposed
prints.
H. W. Bennett has made a special study of
ammonium persulphate as a reducer, and his
special formula will be found imder the heading,
" Bennett's Reducer." The addition of ammo-
nium stilphocyanide has been recommended, this
causing the persulphate reducer to act in the
opposite way — namely, to dear the shadows
first after the manner of the ferricyanide and
"hypo" reducer, which makes it particularly
suitable for negatives of line subjects. The
formula for the persulphate reducer often re-
ferred to as " Puddy's reducer" is: water i oz.,
ammonium persulphate 25 grs., and ammonium
sulphocyanide (10 per cent, solution) 120 minims.
Namias advocates a 5 per cent, solution of per-
sulphate made acid with i per cent, of sul-
phuric acid for developing over-exposed carbon
prints. Ammonitim persulphate has also been
suggested as a " hypo " eliminator, stain
remover, and as an addition to the oxalate
developer for platinotypes ; i to 1 per cent, added
to the normal oxalate developer shortens the scale
of gradation and saves over-exposed prints.
AMMONIUM PHOSPHATE (Pr., Phosphate
d' ammonium : Ger., Ammonphosphat,
Phosphorsdures ammoniak)
Synonyms, hydrogen diammonium phosphate,
diammonium orthophosphate, dibasic phosphate
of ammonia. (NHjjjHPO,. Molecular weight,
132. Solubility, I in 4 water. Sometimes used
in emulsion making and in toning, but infre-
quently ; its chief use is in fireproofing fabrics.
It is obtained on drying the normal, or neutral
ammonium phosphate (NH4)3P04. The latter
is made by mixing phosphoric acid and ammonia
in concentrated solution ; on cooling, the normal
salt crystalUses out in short prismatic needles.
AMMONIUM AND POTASSIUM CHRO-
MATE {Fr., Chromate d'ammonium et
poiasse; Ger., Kaliammoniumchromat)
NH.KCrO.HjO. Molecular weight, 191. Solu-
ble in water. The pure salt occurs in bright,
yellow crystals, but is rarely used except in the
form of a solution which is made by adding
ammonia to potassium bichromate solution. It
has been suggested as an improved sensitiser
for carbon printing, etc., but it frequently makes
the tissue homy and reticulated.
In process work, when making up this bichro-
mate sensitising solution for carbon printing,
collotype, photo-Hthography, and zinc printing,
it is usual to add liquor ammoniae drop by drop
until the solution turns a hght lemon yellow,
and distinctly smells of ammonia. This forms
the double diromate of potassium and ammo-
nium.
AMMONIUM SULPHIDE (Pr., Sulfure
d'ammonium ; Ger., Schwef el- ammonium)
A yellowish solution, formula (NH4)2S, having
a most objectionable smell ; known also as sul-
phuret of ammonia. It is widely used for toning
bromides to a brown colour after bleaching, also
for toning P.O.P. Its evil odour and bad-keeping
qualities are reasons why some prefer to make
it as required, according to the following method :
A. Sodium sulphide, \ oz. ; water, 2^ oz. B.
Ammoniimi sulphate, 24 grs. ; water, 2I oz. Mix
A and B, and use at once or any time within
ten or twelve weeks ; in this form its odour is
not so bad. Ammonium sulphide should not
be kept in the same room as sensitive plates and
papers, as the vapour acts injuriously upon them.
In process work, ammonium sulphide has been
extensively used for blackening wet plate nega-
tives after lead or copper intensification, but is
now being largely superseded by sodium sulphide.
AMMONIUM SULPHOCYANIDE (Pr., Sulfa-
cyanure d'ammonium; Ger., Rhodan-
ammonium)
Synon3mis, sulphocyanate, thiocyanate, or
rhodanide of ammonia. NH^CNS. Molecular
weight, 76. Solubilities, i in o-6 water, very
soluble in alcohol. It is very hygroscopic, and
should be kept well stoppered. It takes the
Ammonium Sulphydrate
27
Amyl Acetate
fonu of colourless crystals, obtained from carbon
disulphide, strong alcohol, and liquor ammoniae.
It is used in toning printing-out papers. {See
" Potassium Sulphocyanide.")
A 5 per cent, solution of the sulphocyanide
will dissolve gelatine in the cold, and it has
therefore been used to develop over-exposed
carbon prints.
Owing to the highly deliquescent properties
of this salt, it is a common practice to make it
up into a nominal 10 per cent, solution as soon
as possible after buying, i oz. of the salt should
be dissolved in 2 oz. or 3 oz. of Water, and then
made up to a total btilk of 9 oz. Ten drops of
this stock solution will then contain i gr, so
that any toning formula may be made up from
it with less trouble than by weighing the damp
solid. Two drms. (120 drops) cont^ 12 grs.,
which is a good average quantity to mix with
I gr. of gold chloride and 8 oz. of water.
AMMONIUM SULPHYDRATE {ex., Sulphy-
drate d' ammoniaque ; Ger., Schwefelam-
mon)
Synonyms, ammonium hydrosulphide, ammo-
nium sulphide. NH^HS. Molecular weight, 50.
Soluble in water. The pure salt occurs in
colourless, crystalline masses, which rapidly turn
yellow on exposure to the air. The commercial
ammonium sulphide, which is generally used, is
prepared by passing sulphuretted hydrogen HjS
into liquor ammoniae NH4OH, and forms (NHi)^
S = 68, a colourless or slightly yellow solution
with disagreeable odour. It is used for blacken-
ing wet collodion negatives after intensification
with silver iodide, copper bromide, or lead nitrate.
AMMONIUM THIOCYANATE (See "Am-
monium Sulphocyanide.")
AMMONIUM THIOMOLYBDATE (Fr., Sulfo-
molybdate d' ammonium ; Ger., Ammoniah
thiomolybdanat )
(NHi)2MoS4. Molecular weight, 260. Solu-
bilities, soluble in water, insoluble in alcohol. It
takes Uie form of red scales obtained by boiling
molybdenum trisulphide in ammonium sulphide.
Its use has been patented for sulphiding bromide
prints in place of sodium sulphide.
AMMONIUM VANADATE (Fr., Vanadate
d' ammoniaque ; Ger., Vanadinsaures am-
moniah)
Synonym, ammonium metavanadate. NH^
VO3. Molecular weight, 116. Slightly soluble
in water. These colourless crystals have been
recommended as an addition to printing-out
emulsions to increase contrast.
AMPHITYPE
One of the many curious and interesting print-
ing processes invented by Sir John Herschel, but
of no practical value. It depends upon the
light-sensitiveness of ferric, mercuric, and lead
salts, and it gives a rich, vigorous print which
can be viewed from both sides of the paper, or
as a transparency. A sheet of paper is pre-
pared with a solution, either of ferro-tartrate
or ferro-citrate of protoxide, or peroxide of
mercury, and then with a. saturated solution of
ammonia-citrate of iron. Exposed in a. camera
for a time varying from half an hour to five
or six hours, according to the intensity of the
light, a negative is produced on the paper which
gradually fades in the dark, but may be restored
as a black positive by immersion in a solution
of nitrate of mercury, and ironing with a very
hot flat-iron.
Amphitype is also the name of a photo-litho-
graphic transfer process invented by W. H.
Shawcross, of Liverpool. The paper is sensi-
tised with an iron salt, and keeps indefinitely.
It is printed under a negative, then inked all
over with a special ink, and developed with a
solution of yellow prussiate of potash. The lines
of the print are thus covered with transfer ink
whilst the ground is a deep blue, which, however,
can be bleached away in a solution of common
soda. The transfers are applied to zinc or stone
in the usual way.
AMPLIFIER
A supplementary lens placed between a posi-
tive or image-producing lens and the focusing
screen for the purpose of producing an enlarged
image. Amplifiers may be positive or negative
in their form ; if positive, they must be placed
outside the principal focus of the primary lens,
as in the Dallmeyer photo-heliograph or as in
photo-micrography, where the eyepiece (usually
of special design) forms the amplifier. When
negative amplifiers are used, they may be placed
at any point between the back surface of the
primary lens and the principal focus ; the size
of image and the necessary camera extension
become greater as the negative lens approaches
the positive one. The earliest practical form of
negative amplifier was the Barlow lens, designed
for shortening the tube length of telescopes. The
principle is extensively employed in the con-
struction of the telephoto lens, in which the
amplifier is usually termed the " negative
element." (See " Telephoto I,ens " and " Photo-
heUograph.")
AMSTUTZ PROCESS (See " Aerograph.")
AMYL ACETATE (Vr.,Aatated'amyle ; Ger.,
Amylaceiat, Birnenol)
Synonjrms, essence of jargonelle pears, amyl-
acetic ester, isoamylacetate. CtHuCjHjOj.
Molecular weight, 130. Solubilities, insoluble in
water, miscible in all proportions with alcohol
and ether. It is a colourless ethereal Uquid with
characteristic odour, and is obtained by distilla-
tion from amyl alcohol, sulphuric and acetic
acids. It is used for making celluloid cold
varnish or zaponlack, a formuJa for which is —
Celluloid
Amyl acetate to
150 grs. I5g-
20 oz. 1,000 CCS.
This gives a hard, resistant film which can be
applied cold to negatives. The addition of
acetone gives a milky film. It is also used in
the amyl acetate lamp {which see).
In process work, amyl acetate is used as a
solvent for celluloid, and the resulting varnish
is used for stripping instead of collodion. The
varnish is used in aerograph retouching for
stopping out, and the amyl acetate for removing
the varnish after the colour has been applied by
the aerograph.
Amyl Acetate Lamp
28
Anamorphoscope
AMYL ACETATE LAMP (Fr., Lampe i
amylacetate ; Ger., Hefner Lamp)
A lamp devised by Hefner-Alteneck and
adopted by the latemational Congress of Photo-
graphy in 1889 as the standard light for sensi-
tometiy. The wick should consist of loose
cotton threads, and be held in a tube of 8 mm.
(about '32 in.) internal and 8'3 external diameter,
and of 25 mm. (i in.) length. The height of the
flame should be 40 mm. (i-6 in.), and this must
be gauged by a sight hole and cross wire. Out-
side the flame, at a distance of i cm. (-4 in.) from
its axis, is a metal chimney pierced with a hole
4 mm. (-16 in.) broad and 30 mm. (1-2 in.) long,
which can be shifted so as to bring it opposite
the brightest part of the flame. The amyl
acetate should be free from acetic acid and water,
and have a constant boiling point of 138° C.
(280-4° P-)- The standard English candle =
I -14 H.K. or Hefner-Kerze.
The great objections to the amyl acetate lamp
as a standard photographic light are its spectral
composition, which is very poor in violet and
blue rays, and its variability imder varying
heights of the flame (i mm. or -04 in. variation
in height produces an alteration of about 3 per
cent.), the influence of aqueous vapour and car-
bonic acid in the air, and also the state of the
barometer on the uniformity of the light. (See
also " Sensitometry.")
AMYL ALCOHOL (See
■Alcohol.")
Ger., Amy-
AMYLOTYPE (Fr., Amylotypie .
lotypie)
A photograph or print obtained by the action
of light upon vegetable matter or extracts. (See
"Anthotype.")
ANACHROMATIC
A name given to certain lenses, mostly of
French manufacture, which are uncorrected for
chromatic aberration.
ANACLASTIC (Fr., Anaclastique ; Ger., AnO'
clastisch)
Capable of refracting, or bending, rays of
light. Dioptrics, that branch of optical science
dealing with the phenomena of refraction, was
formerly called anaclastics.
ANAGLYPH (Fr., Anaglyphe; Ger., Anaglyph)
The name given to Du Hauron's stereoscopic
pictures. A pair of stereoscopic photographs is
taken and half-tone process illustrations prepared
from them. The picture belonging to the left
eye is printed in one colour — say blue ; and
the picture belonging to the right eye is printed
in another colour, usually red. The two impres-
sions are superposed, but owing to their stereo-
scopic dissimilarity they do not exactly register,
wim the result that a confused effect is produced.
To observe the pictures stereoscopicaUy, eye-
glasses (see "Anaglyphoscope") are provided.
If the left eye phase has been printed in
blue and the right-eye phase in red, the eye-
piece for the left eye wiU be red, and that for
the right eye will be blue. The eye looking
through the red glass will observe only the
phase that has been printed in the blue colour,
and vice versa. The result is that only one pic-
ture or stereoscopic phase reaches each eye and
the one rightly belonging to it. Fiirther, as both
images appear at the same place, unison takes
place in virtue of the laws governing binocular
perception, and stereoscopic reMef is observed.
The fundamental principle of Du Hauron's in-
vention has also been applied to lantern stereo-
scopic pictures.
ANAGLYPHOSCOPE
An appliance or arrangement for the inspection
of anaglyphs, usually made in the form of eye-
glasses or spectacles with a red and a green glass,
or red and blue. Tinted gelatine and other
transparent materials are also used. Perhaps
the simplest form consists of a card with two
circular openings, at a distance apart equal to
that between the average pair of eyes, oyer
which are glued pieces of gelatine of the requisite
tints. This is simply held up to the eyes in
viewing the anaglyph, which is then seen in
stereoscopic relief.'
ANALYSER (Ft., Analyseur ; Ger., Analysator,
Zerstreuungsprisma)
A prism of Iceland spar, divided diagonally
down its long axis, which receives the extra-
ordinary ray from the Nicol prism (which see).
The analyser enables the observer to study the
phenomena of polarised light. It is usually
mounted in a brass cell above the objective, but
may be placed above or in the eyepiece. (See also
" Polariscope " and " Polariser.")
ANALYTICAL PORTRAITURE
The taking of several properly adjusted por-
traits of different persons upon one plate, or the
printing of several different portrait negatives
upon one piece of paper ; the resialt is sup-
posed to give the type of the whole. Better
known as " Composite Portraiture " (which see).
ANAMORPHOSCOPE (Fr., Anamorphoscope:
Ger., Anamorphoskop)
A cylindrical convex mirror for reflecting the
iiuage of a distorted drawing and restoring it to
its proper proportions. Concave or convex
mirrors distort images in a singular manner, and
produce very interesting effects. Anamorphoses
constitute particular objects belonging especially
to the class of experiments relating to cylindrical
mirrors. They are images made according to
determined rules, but so distorted that, regard-
ing them fixedly, only confused strokes can be
distinguished. When they are seen reflected in
the curved mirrors, they present, on the contrary,
a perfectly regular appearance. In other words,
an anamorphose is a distorted diagram, the cor-
rected image of which can be seen in the mirror
of the convex anamorphoscope. It may be said
that distorted copies of photographs suitable for
inspection in an anamorphoscope may be pre-
pared in the following manner : Procure an
optically worked cylindrical concave mirror large
enough to reflect a half -plate photograph. Place
the photograph in a horizontal position upon
a table, and place the mirror at right angles
thereto, keeping it vertical. On looking into the
mirror from a given position, a distorted image
of the photograph will be seen. This image may
now be photographed by placing a camera lens
Anaplanatic
29
Anastatic Process
at the point previously occupied by the eye, a
position to be discovered by experiment, and
which will, of course, depend upon the curvature
of the mirror in use and the focal length of the
camera lens. The resultant photograph will
bear no apparent resemblance to the original ;
but if viewed in a convex cylindrical mirror whose
curvature corresponds to the curvature of the
concave mirror, a true copy of the original
photograph, in miniature, will be seen. The
order of things may be reversed with equally
true results. In taking photographs of this
character it is important so to arrange the
Ughting that the original photograph receives full
illumination, while the mirror is well shaded.
A curious effect may be produced by taking
a photograph with a plate placed very obliquely
to the axis of a lens or pinhole, the latter being
preferable. The image is of course terribly
distorted, but upon being viewed from, a position
similar to that occupied by the lens it Will
appear correct. A portrait painted in this
style may be seen in the National Portrait
Gallery, London.
ANAPLANATIC
Not aplanatic. The term has been applied
(incorrectly) to ordinary rectilinear lenses.
ANASCOPE (Fr., Anascope ; Ger., Anaskop)
A focusing glass or optical arrangement by
the aid of which the image on the camera screen
is seen right way up instead of being inverted.
ANASTATIC PROCESS (Pr., La Photo-
graphie Anastatique ; Ger., Anastatisch
Druch)
A method of copying line drawings by placing
a sensitive material with its film side in contact
with the drawings, and exposing to light through
the back of the sensitive paper or plate. This
process, originally invented by J. H. Player, has
been rediscovered and elaborated by B. B.
Foumier d'Albe, who has given it the above
name. As in Playertype, it depends on the
fact that the light passing through the plate
or sensitive paper is reflected back to the film
from the white surface of the plan or drawing,
whereas the dark lines of the latter reflect
hardly any light. If plates are used, the photo-
mechanical kmd is best. The exposure is about
the same as would be required to make a positive
transparency from an ordinary negative on the
same kind of plate. A quick-acting developer
giving contrast is to be preferred, as, for example,
hydroquinone with caustic potash, or a i in 15
solution of rodinal. The slight fog that occurs
in the lines may be removed by a brief immersion
in a ferricyanide and " hypo " reducer after
fixing and washing, following this by at least
half an hour's further washing.
A positive instead of a negative may be pro-
duced by soaking an imexposed dry-plate for
five minutes in a 10 per cent, solution of potas-
sium bichromate and allowing it to dry, of course
in non-actinic light. This is exposed to daylight
through the glass side, in contact with the draw-
ing to be copied, and is developed with a dilute
rodinal solution. The parts which have received
reflected light from the drawing are rendered
more insoluble than those parts in contact with
the darker portions, and the latter in conse-
quence alone absorb the developer. It follows
l3iat the lines of the original are developed out,
while the background remains white or nearly
so. The positive is fixed in "hypo" as usual.
Copies can also be produced by tiiis process on
bromide paper, and there are many other ways
in which the process may be applied. It is
immaterial if the drawing has printing or other
matter on the back. Distinctive points of this
process are that no camera or lens is employed,
and that the copy is exactly the same size as the
original.
Anastatic photography must not be confused
with the anastatic lithography process described
below.
ANASTATIC PROCESS OF LITHOGRAPHY
A process of lithography by which prints,
particularly old ones, may be treated so as to
yield a transfer, which may be inked up and
printed from. The essential features of the pro-
cess are that the ink of the print is softened and
made transferable by damping the back of the
paper with dilute acid ; or the print is so treated
that the ink can be reinforced by rolling it up
with an ink roller without soiling the paper.
The usual method, when the print is not too old,
is to wet the print with a weak solution of nitric
acid in water. It is then placed face downwards
on a, sheet of poUshed zinc and passed through
the press. Sometimes the plate is flooded with
turpentine, and, after allowing it to stand, the
surplus is squeegeed off. Then the print is laid
down before the turpentine has had time to
evaporate. Another procedure is to float the
print face upwards on a solution of i part of
sulphuric acid in 20 parts of water. When
damped through, superfluous moisture is removed
between blotting-paper, and the print is then
left in contact with the plate for some time.
The following is said to be a process employed
by a Paris firm, who make a speciality of litho-
graphic facsimiles of old and rare prints. Pre-
pare a bath as follows : —
Sulphuric acid
Alcohol
Water
3 to 5 parts.
3 to 5 „
100
The proportions are varied according to
antiquity of the print, thickness of paper, etc.
In this solution soak the print from five to fifteen
minutes, remove, spread face downwards on
glass, and wash thoroughly in a gentle stream
of running water. If the paper is heavy, reverse
the sides, and let the water flow over the print
as well ; remove carefully, and place on a heavy
sheet of blotting-paper, cover with a similar
piece, and press out every drop of water possible.
A wringing machine with rubber rollers is most
convenient for the purpose. The print, still
moist, is laid face upward on a heavy glass plate,
or hthographic stone, and smoothed out. With
a very soft sponge go over the surface with a thin
gum-arabic solution. The print is now ready
for inking, which is done with a lithographic
roller and hthographic ink thinned with tur-
pentine. The print is then appHed to a zinc
plate or a hthographic stone, and as many copies
as desired " pulled " — that is, printed by the
usual lithographic method.
Anastigmat
30
Animals
ANASTIGMAT
A lens free from the defect known as astigmat-
ism (see " Astigmatism " and " Lens"). Anas-
tigmatic is the adjective formed from this term.
ANGLE OF FIELD OR OF VIEW
The angle subtended by two lines drawn from
the node of emergence of any lens to the comers
of the plate in use. As a general rule, when the
angle of field of a lens is referred to, the extreme
angle which the lens is capable of covering is
meant, and it should be clearly stated in all
cases whether this angle is measured along the
longest side of the plate or diagonally from
opposite comers. It will readily be seen that a
much wider angle can be included in a circular
picture than in a rectangular one if the full
diameter of the image circle is taken as the base
instead of taking the longest side of the plate.
For example, when using a 6-in. lens which will
illuminate a 12-in. circle, the extreme angle is
90°, but the largest rectangular picture (say,
9i in. by 7^ in.) which could be placed within
this circle would include an angle of less than
77°. To cover a plate having a base line of
12 in. (12 in. by 10 in.) to the comers, an image
circle of 15-6 in. is required, giving an angle of
90° along the longest side of the plate. {See also
" View-angles, Table of.")
ANGLOL
An English trade name for eikonogen {which
see).
ANGULAR APERTURE
A synonym for focal aperture {which see). It
has no relation to the angle embraced by the
lens, being a measure of rapidity only. The
statement that a lens has a large angular aperture
means in simple language that it is very rapid
in its action.
ANHYDROUS (PT.,Anhydre; Ger., Wasserfrei)
A term applied to chemicals when deprived
of water ; literally, not containing water.
Anhydrous sodium sulphite is the most widely
used anhydrous salt in photography. It is said
to keep better in an anhydrous state than when
crystaUised. The anhydrous salt is double the
strength of the crystallised salt, so that i part
of the former may at any time be replaced in
a formula by 2 parts of the latter, or vice versa.
Anhydrous chemicals are not so popular in
England as in many other countries.
ANILINE (Fr., Aniline; Ger., Anilin)
Synonyms, aniline oil, phenylamine, amido-
benzene, amido-benzol. CgHuNHj. Molecular
weight, 93. Solubilities, insoluble in water, misci-
ble in all proportions with alcohol and ether.
It is poisonous, the antidotes being the use of
the stomach pump and emetics. Its sole use is
in the now obsolete aniline process {which see),
and as the starting-point for the manufacture of
numerous artificial colouring matters. It should
not be confused with aniline, or coal-tar,
colours {which see).
ANILINE, OR COAL-TAR. COLOURS
Under this generic name are included all the
artificial colouring matters or dyes, some of
which are of great interest photographically,
either from their sensitising properties or their
uses as colour screens or filters. Others, again,
are used for tinting prints, transparencies, etc.
It would be impossible to give information with
regard to all the dyes, but the principal ones
are briefly dealt with under their respective
names. {See also " Orthochromatism," " Fil-
ters," " Colour Sensitisers," etc.)
In process work, aniline dyes are extensively
used, especially in three-colour reproduction.
They are either applied to the plate by bathing,
or by adding to the emulsion as in the collodion
emulsion process. For the latter they are also
sometimes flowed over the plate before exposure.
Attempts have also been made to bathe wet
collodion plates, but the process has not
come into commercial use. Methyl violet is an
aniline dye that is largely used for dyeing the
fish-glue image in order to make it visible during
development. The dyes are also much used
for making colour filters, either by staining
gelatine and collodion films and allowing them
to dry (dry filters), or as aqueous or alcoholic
solutions, which are contained in glass cells and
placed in front of or behind the lens.
ANILINE PROCESS
A process patented on November 11, 1864,
by W. Willis, of Birmingham, for reproducing,
without a negative, drawings made on tracing or
other transparent paper. It is cheap, and the
results are fairly permanent, but it has never
come into general use. Paper is prepared with
a solution of potassium (or ammonium) bichrom-
ate, 30 grs. ; dilute phosphoric acid, 60 minims ;
water, i oz. — the paper being bru.shed over with
the mixture. When dry, a print is obtained by
exposure to daylight under the drawing on trans-
parent paper. It is then developed by exposure
to the fumes of i part of aniline dissolved in
16 parts of benzole, sprinkled upon blotting-
paper, and placed in a shallow box, the exposed
paper being pinned to the inner side of the lid.
When fully developed the picture is washed and
placed in water acidulated with i per cent, of
sulphuric acid and again washed. The finished
print is of a bluish-black colour. This process is
suitable for copying plans, etc., other methods
being the " Blue Print Process," " Ferrigallic
Process," etc. etc.
ANIMALCUL/e TANK (Fr., Cuvette des ani-
malcules ; Ger., Microskopischer Tierchen-
behdlter)
A shallow glass-sided tank for use as a slide
with the projection microscope and optical
lantern, in order to show animalcute and small
water insects on the screen. A good temporary
substitute is made by clamping together two
strips of glass, with a semicircle or ring of india-
rubber between them to form a cell.
ANIMALS, PHOTOGRAPHY OF
This branch of photographic work is one that
has received increasing attention as improve-
ments have been made in lenses, plates, appara-
tus, and special devices. The reflex camera and
the telephoto lens, especially, have been effective
helps to the uaturai history photographer. Animal
photography may be roughly divided into three
Animated Photography
31
Anthrakotype
sections : (o) that of domestic animals — the
horse, cow, sheep, dog, cat, etc. ; (ft) that of wild
animals in their natural habitat ; (c) that of wild
animals in captivity.
In the case of wild animals in their native
haunts, a very limited amount of work may be
done with the ordinary apparatus ; still more
may be accomplished by tiie use of telephoto
lenses ; while a good deal has been done by
special arrangements by means of which animals
have been made to photograph themselves, so
to speak, by flashlight.
The methods of dealing with domestic animals,
and with wild animals in captivity, are practically
identical. The work is greatly faciUtated by the
use of a reflex camera ; a lens of fairly long focus
in relation to the plate, and of large aperture ; a
rapid plate ; and a shutter working as quietly
as possible with high efiiciency and capable of
good speed. It is advisable to know something
of the animal to be dealt with, especially its
characteristic poses and movements. The reflex
camera enables the worker to keep the animal
accurately in focus and in position on the plate,
and to make the exposure at the most suitable
moment. The use of a large stop makes full
exposure possible even at high-shutter speeds,
and also bestows the important advantage of
being able to keep the background diffused while
the animal itself is sharply defined.
Selective focusing and a suitable lighting
of the animal itself are important factors in
obtaining an impressive result. It must be
remembered, however, that even when the back-
ground is diffused its character and suitability
must be carefully considered. If, for example,
it contains many points of bright light, these
may be exaggerated into " blobs " that are
unsightly and irritating. Another thing to
avoid is the use of a short focus lens at dose
quarters, especially when taking an animal
" head on," the result being an exaggeration of
the head and a dwarfing of the body. It is
generally advisable, particularly in the case of
small animals, to hold the camera low down.
An effort should be made in the case of wild
animals in captivity to keep out of the picture
any railings, network, or other evidence of their
not being in their natural haunts.
When the camera used focuses to scale, and
<x reflex camera is not available, failure is mini-
mised by not attempting work at very close
quarters, but rendering the animal on a smaller
scale and afterwards enlarging the result. The
most noticeable drawback to this procedure is
that the surroundings and background are ren-
dered too sharply, and so compete in importance
with the animal itself. {See also " Birds, Photo-
graphy of," and "Zoological Photography.")
ANIMATED PHOTOGRAPHY {See " Kine-
matography.").
ANIMATOGRAPH {See "Kinematograph.")
ANIME {See " Gums and Resins.")
ANOMALOUS DISPERSION (Pr., Dispersion
irregidiire; Ger., Abweichende Zerstreuung)
As a rule, light rays of short wave-length are
Infracted more than those of long wave-length
when passinjg from one transparent medium to
another of different density. With some refract-
ing media, however, this law is departed from to
a certain extent. When this occurs it is known
as anomalous dispersion.
ANTHION
A trade name for potassivun persulphate
{which see).
ANTHOTYPE
An obsolete " nature printing " process in-
vented by Sir John Herschel and founded upon
the sensitiveness of juices of plants. Chevrenl
and Hunt also experimented in the same direc-
tion. The expressed juices, and alcoholic or
watery infusions of certain flowers, more par-
ticularly papaver rhceas and corchorus japonica,
were spread on paper and printed upon under
a negative. Herschel found that the most
sensitive colour was the yeUow tint of the
japonica, and that the blue tincture of the
double purple groundsel completely bleached in
the smishine. According to his original instruc-
tions, published in 1842, the petals of fresh and
well selected flowers are bruised to a pidp in a
marble mortar, either alone or with a small
quantity of alcohol, and then are squeezed
tiirough fine linen. The paper to be treated is
moistened at the back with water, by sponging
and blotting off, and pinned to a board, moist
side downwards. The alcoholic tincture (mixed
with a very Utile water if necessary) is then
applied witii a brush, in strokes from left to
right. Then with a sweeping movement carry
the strokes up and down so as to cover the
paper completely and leave no spaces. The
paper is dried quickly, over a stove or otherwise.
Papers so prepared generally require an exposure
under a negative of about three or four weeks,
and the pictures are not permanent. Herschel
found that similar effects could be produced by
light on the gums, resins, and residues of essen-
tial oils, when thin films were spread on metal
plates ; also that a paper coated with an alcoholic
solution of guaiacum, and placed in an aqueous
solution of chlorine, acquired a beautiful blue
colour, and could be used for copying engravings.
All images by these processes quickly fade, and
are of no value except as curiosities while they
last. {See also " Nature Printing.")
ANTHRAKOTYPE (Fr. and Gei., Anthrakotypie)
A dusting-on process, suitable for copying
tracings or line drawings, first described by Dr.
Sobacchi, and elaborated by Captain G. Pizzi-
ghelli. Paper is coated with, say, a 10 per cent,
solution of gelatine, and when dry is sensitised
in a solution of potassium bichromate of about
5 per cent, strength. After again drying, the
paper is exposed under a tracing or other suit-
able positive imtil the ground assumes a light
brown colour, on which the lines are faintly
visible in pale yellow. The print is then soaked
in slightly warm water for about two minutes,
blotted off, and dusted over with a pigment.
The latter may be any finely powdered colour,
lampblack being suitable. The pigment adheres
to the unexposed parts (that is, the lines of the
drawing), which are sweUed by the water ; while
the portions on which Ught has acted are ren-
Anthraphotoscope
32
Antimony Sulphide
dered insoluble, and take only slight traces of
the colour. When dry, any of the pigment
adhering to the exposed parts is removed care-
fully with a damp sponge.
ANTHRAPHOTOSCOPE
An incorrect form of the word " anthrophoto-
scope " (explained below).
ANTHROPHOTOSCOPE (Fr., Anthraphoto-
scope ; Ger., Anthrophotoskop)
A kind of photographic peep-show, patented
in 1867 by Dr. Isaac Rowell and Francis E.
Mills, of San Francisco. Portrait photographs
are carefully cut out from their backgrounds and
placed in front of substituted backgrounds
attached to an inclined plane, diverging upward
from the plane of the portrait and intersecting
the latter at the feet. By this arrangement the
foreground is slightly nearer to the observer
than the middle distance, while the distance is
still further off, so that when viewed with both
eyes through a large magnifying lens of long
focus, the illusion of perspective and at least an
imitation of stereoscopic relief are obtained. By
means of a small toothed wheel the pictures may
be arranged into groups at pleasure, and the
scenery in the background may also be varied
as desired.
ANTI-CURLING FILMS
Rollable or flat films which do not curl during
developing and drying. The makers prevent
curling by coating the back of the film with
gelatine, or other substance, to counteract the
curling properties of the gelatine on the sensitive
side of the film. Previous to the introduction
of the above films, it was customary to soak
ordinary films, after developing, fixing, and
washing, for a few minutes in a solution of i part
of glycerine to 40 parts of water, and after-
wards to dry. This solution checks curling,
but keeps the film slightly moist, and at times
leads to stains and fading.
ANTIDOTES (See "Poisons and Their Anti-
dotes.")
ANTI-HALATION PLATES
Dry plates coated on the back (plain glass
side), or otherwise prepared, to prevent light
being reflected to the film when in the camera.
Such reflection causes the defect known as
halation (which see). Dry plates made of
green glass instead of white glass are said to
prevent halation perfectly (no backing being
necessary), but they are not articles of com-
merce.
The earliest forms of anti-halation plates were
made by staining the film. W. E. Debenham,
in 1 89 1, used saffron and logwood, but these
increased the exposure. Weir Brown advocated
dipping plates in ammoniacal erythrosine. A.
H addon suggested a thin coloured substratum,
and T. Bolas the coating of ruby glass with emul-
sion and then stripping the film, also the addition
of some neutral salt to the emulsion. Anti-
halation plates with a coloured substratum were
for a time articles of commerce, but the term now
generally refers to plates backed in the ordinary
way. (See also " Backings, Plate.")
ANTILUMIN
A special paper impregnated with a ruby or
orange dye and rendered semi-transparent. It
is used for covering dark-room windows and
lanterns, to make the light " safe."
ANTIMONY PROCESS (Fr., Photographie
<J V antimoine ; Ger., Spiessglas-Druck)
A printing process discovered by Francis
Jones, of the Manchester Grammar School, in
1876. When the gas stibine, or antimonietted
hydrogen (SbH,), is passed through a glass tube
containing sulphur, in the presence of suiJight,
a decomposition takes place, resulting in the
formation of the orange antimony sulphide : —
Sb,S, + 3 HjS.
Antimony Sulphuretted
Sulphide Hydrogen
2SbHj -1- 6S =
Stibine Sulphur
Since no change occurs in the dark, it was found
possible to utSise the reaction for photographic
purposes. Ordinary writing paper may be
treated with a solution of sulphur in carbon
disulphide and the solvent allowed to evaporate,
the loose grains of sulphur being then gently
brushed off the surface with a tuft of cotton-
wool. A special printing frame is used, having
a tube led into the back, so that the gas may be
conveyed into the felt with which ^s is lined
in order to impregnate the paper. A fern, a
piece of lace, or other suitable object having been
placed in the frame and the paper laid over it,
the frame is exposed to sunlight, and connection
is made with the gas. A print of an orange
red colour is quickly produced, the image con-
sisting of permanent metallic sulphide imbedded
in free sulphur. No fixing is required, the gas
being simply disconnected when printing is
sufficiently advanced. The operation should be
carried out in the open air, care being taken not
to inhale the fumes, whici are poisonous. To
obtain the gas, a small quantity of a solution of
antimony triciloride (butter of antimony) is
added to any hydrogen generating apparatus, as,
for example, a Woulff's bottle furnished with a
thistle funnel and a delivery tube, and contain-
ing dilute sulphuric add and granulated zinc.
The emerging gas then consists of a mixture of
antimonietted hydrogen and hydrogen. It is
advisable to dry the gas by passing it through
a calcium chloride tube before leading it into
me printing frame. Although of considerable
interest, this process appears to have certain
disadvantages, which have hitherto prevented
its use by the practical worker, not the least
of these being that the silver image of a negative
begins to be affected by the sulphur after several
impressions have been taken.
In process work, there is an antimony process
which consists in blackening a zinc plate with a
solution of antimony chloride in order that an
image transferred to the plate may show up after
the plate has been sHghUy etched. This allows
of an artist working on the plate by stopping-out
for re-etching.
ANTIMONY SULPHIDE (Fi., Stdfure d'anti-
moine ; Ger., Schwefelantimon)
Synonyms, antimonous sulphide, black anti-
mony. SbjSj. Molecular weight, 336. Solu-
bilities, insoluble in water, soluble in hydro-
Antiphotogenic
33
Aphengescope
chloric add. It is poisonous, the antidotes being
the use of the stomach pump and emetics. It
takes the form of a greyish black powder or
steel-grey metallic masses, occurring native. It
is occasionally advised as an admixture with
magnesiujn powder for flashlight work, but
its use is not to be recommended as the products
of its combustion are poisonous.
ANTIPHOTOGENIC (Pr., AniiphotogSnique ;
Ger. , A ntiphotogenisch )
Opposed to photographic or photo-chemical
action ; non-actinic.
ANTIPLANAT, OR ANTIPLANATIC
LENS
A lens introduced by Steinheil, of Munich, in
1881, and made in two intensities, //3 for por-
traits A and //6 for general work B. They difiered
An y\
A. Steinheil Antiplanat
F/3
B. Steinheil Antiplanat
F/6
from most contemporary lenses inasmuch as they
were composed of a positive front and a negative
back lens. In the more rapid form the anti-
planat may be regarded as a triple combination
lens, while in the slower one it is a doublex.
ANTIPYR
An Americzm trade name for formaline.
ANTISEPTICS (Pr., Antiseptiques ; Ger.,
Fdulnisswidrig Mittel)
Agents used to prevent putrefaction. They
find but very limited use in photography.
Thymol or phenol is used for gelatine emulsions,
and sahcylic acid in one or two aqueous solutions
which have a tendency to form fungoid growths.
ANTISPECTROSCOPIC (Pr., Antipectrosco-
pique: Ger., Antispectroshopisch)
An optical term applied to a lens to signifiy
that it does not split up white Ught into its con-
stituents. Achromatic (which see) has the same
meaning. '
APERTOMETER (Pr., Ouverture m&tre ; Ger.,
Oeffnungmesser)
An instrument for measuring the nunierical
aperture of a lens or objective. Of those forms
used in photomicrography, the best was devised
by Abbe, consisting of a semicircular glass plate
with the various apertures figured on the outer
edge. The straight edge of the glass is bevelled
to an angle of 45°, and in the centre of the bevel
is a metal disc pierced with a small hole. The
lamp must be placed opposite and in line with
this hole. The objective to be tested is focused
on the metal edge of the hole, the draw-tube is
removed, and a low-power objective, which
forms part of the apparatus, is screwed into the
lower end. The draw-tube with this second
3
objective is replaced, and the auxiliary lens is
focused by means of the draw - tube upon the
back of the objective which is being tested, by
sUding the draw-tube up and down till the images
of two metal pointers on the outer edge of the
apertometer are sharply defined. A band of
Ught should be seen across the field, and the
pointers are moved till they just reach the edge
of the luminous band, where it disappears from
the field of view. The readings given by the
outer edges of the metal pointers are added
together, and the half of the sum gives the
numerical aperture.
Cheshire's is an inexpensive and fairly accur-
ate apertometer, consisting of a glass disc with
concentric rings on the under surface. The
objective is focused on a mark in the centre of
the plate, and the eyepiece is then removed.
The observer looks down the tube and notes
the number of rings which are visible on the
back lens of the objective. The value of each
ring is o-i nwnerical aperture (N.A.), and the
total gives the N.A. of the objective.
APERTURE
The diameter of the beam of light admitted
by a lens, which may or may not coincide with
the diameter of the " stop " or " diaphragm "
(which see). A lens which can be used with a
comparatively large stop, or no stop at all,
without showing want of definition or other
defects, is said to be " rapid," and to have a
" large working aperture." When there is no
stop in the lens at all, it is (said to work at
" open apertitre " or " full aperture."
APHENGESCOPE (Pr., Megascope, Aphenge-
scope: Ger., Aphengeskop, Wunderhamera
fur Undurchsichtige)
In the aphengescope or opaque lantern, also
sometimes called the megascope, the images are
projected upon the screen by reflection instead
of by transmitting the Ught through transpar-
encies. The first magic lantern of this nature
appears to have been invented by Euler, the
mathematician, and was described in his " Letters
to a German Princess." In his letter to her of
A. Euler's Aphengescope
January 8, 1762, he gives diagram A, and says
that he had the honour of presenting her with
one of the lanterns six years previously.
The object to be optically projected was placed
in the back of the lantern at b, and opposite it
in a sUding tube in the front of the lantern was
the projection lens a. It contained two side
wings, with lamps and mirrors to illuminate the
object. In the "Encyclopaedia MetropoUtane "
Aphengescope
34
Aphengescope
is a plan of this or another lantern by Euler for
the projection of opaque objects. Prior to
Euler's invention it seems that the rays of the
sun were used to illuminate an object the image
of which was then thrown upon a screen. Really
practical instruments, however, were not con-
structed until about the year 1839, when Mr.
tongbottom used the oxyhydrogen light in
B. Diagram of Single Lantern Aphengescope
conjunction with opaque lanterns, with which
he gave exhibitions at the old Polytechnic
Institute, I/ondon. Twenty years later Mr.
Chadbum, of Liverpool, obtained a patent for
a lantern of the opaque class, in which he also
used oxyhydrogen illumination.
In all aphengescopes great illuminating power
is necessary if a large picture upon the screen is
desired. Fair results may be secured by using
an ordinary optical lantern for the purpose,
arranged as shown in B, in which A is the objective
lens, L the lantern containing the source of
illumination, and B the space in which to place
the picture or object to be projected. When very
large pictures are needed two lanterns may be
D. Foote's " Polyopticou " Aphengescope
used, as indicated in illustration C. The double
source of illumination makes the picture or object
B vsry bright, and the lens A transmits a brilliant
image to the screen.
A most ingenious form of aphengescope was
invented some years ago by an American, Dr.
Foote, of New York, who termed his instrument
the " Polyopticon Wonder Camera." Great
illumination is sectired by the use of a concave
mirror M, in illustration D, gathering up all the
rays from a lamp at D, and reflecting on to the
picture at B ; the objective lens is shown at A.
The reflector is pierced for the lamp-chimney,
and also for the object glass. The apparatus
may be compared to a huge egg, having one end
sliced off obliquely, against which opening the
picture to be projected is placed. There is no
condenser needed, and although the size of the
projected picture is necessarily of limited dimen-
C. Diagram of Double Lantern Aphengescope
sions, it is very popular in the United States
for projecting enlarged views of cartes, coloured
Hthographs, etc., of small size. Illustration B
represents a more recent form of aphengescopic
attachment. The objective lens is at A, the object
or picture to be projected at B, and a mirror at
M, the latter serving to divert the rays coming
from the illuminant D from a horizontal into a
more or less vertical direction. A biunial form
of this apparatus is shown in illustration F. Two
lanterns are used, and two mirrors M concentrate
the light to a common point b, where the picture
or object to be projected is situated. Naturally,
a much brighter picture is the result, and
accordingly a much larger image upon the screen
is permissible. The aphengescope suggested by
Mon. Trouve, and introduced by Mon. Molteni,
of Paris, was termed " I'Auxanoscope," and the
E. Recent Type of Aphengescope with
Adjustable Diverting Mirror
simplest form of this apparatus is provided with
a lamp on each side of the objective. The
incandescent electric lights are fixed in tubes,
the ends of which are provided with reflectors,
with a hole in each to allow of the insertion of
the conducting wires. In the pattern having
three illuminants, two are used as just described ;
while a third, at the back, is utilised for trans-
mitting light direct when inserting an ordinary
transparency in the groove provided.
Devices on the same principle have lately been
used for projecting the image of the diaJ of a.
watch upon the ceiling so Uiat a person lying
in bed may switch on the lamp and see the time.
Aplanat
3S
Arabic, Gum
A practicable fonn of aphengescope for attach-
ment to optical lanterns is hexagonal in plan,
and is made of either wood or metal. At the
back are two doors permitting of one object
being shown while another is being prepared. At
the front are three holes, the central one having
a flange to receive a lantern objective of long
focus and large diameter, and the side holes
being bushed with brass tubing to receive the
draw- tubes of two lanterns. The object to be
shown is placed in the aphengescope behind the
objective. •
Modem lighting facilities are responsible for
the recent revival in opaque lanterns. Incan-
descent gas, incandescent electric lamps, and the
more powerful electric arc, supply all that is
necessary with regard to illumination in order
F. Biunial Form of Aphengescope
to procure brilliancy of image upon the screen.
But with improved lighting facilities comes the
possible evil of overheating the subject, and
consequently damaging the originals. One pre-
caution against this evil suggests itself in the
form of an alum tank, interposed between
illuminant and subject, which performs the
function of absorbing heat rays without
unduly interfering with the coujrse of the iUu-
minant rays. Such a device has often been used
in conjunction with lanterns when projecting
transparencies, especially when the slide is
required to remain stationary for any length of
time. Moving panoramic pictures for the
aphengescope have been suggested, and in this
case it may not be necessary to introduce an
alum tank or heat absorber ; but for lecture
purposes, when the picture is fixed for a con-
siderable period, an absorber is a useftd adjunct.
" Mirroscope " is the name given to a recent form
of aphengescope, and it is designed separately for
electric, acetylene, and incandescent gas light.
APLANAT
A lens sufficiently well corrected for chromatic
and spherical aberrations to define well at a large
aperture. The name is now usually applied to
lenses of the rapid rectilinear type, although a
special lens called a" rapid aplanat " (//6-5) was
introduced by Steinheil in 1893. This somewhat
resembled the antiplanat of the same maker in
having a positive front and negative back lens,
but consisted of five glasses.
APLANATIC
Capable of working at fuU aperture, a term
first applied to photographic lenses by Thomas
Grubb, of Dublin, who introduced an " aplan-
atic landscape lens."
APLANATISM
The quality of being aplanatic.
APOCHROMATIC (Fi., Apochromatique ; Ger.,
A pochromatisch )
A term applied to lenses in which light of more
than two colours is brought to a focus. In the
ordinary achromatic construction, the green and
yellow rays near the d line in the spectrum and
the violet-blue rays near G are combined ; but
in the apochromatic lenses the red rays also
come to a focus on the same plane. This quality
is invaluable for three-colour work, as images
taken through blue, green, and red screens are of
equal size.
In process work, apochromatic lenses are
specially suitable for use in three-colour repro-
duction. The term is one specially used by
Carl Zeiss to describe lenses for colour repro-
duction ; for example, the " Apochromatic
Planar " and " Apochromatic Tessar."
AQUA FORTIS {I<atin)
Weak nitric acid. The term was once uui-
versally used by chemists for nitric acid, whether
dilute or not.
AQUA REGIA (Latin)
So called because it dissolves the noble
metals ; a mixture of 3 parts of nitric acid and
I part of hydrochloric acid. It is used for dis-
solving gold and platinum, as, for example,
when making gold chloride, the metals being
insoluble in the separate acids. Its solvent
action depends upon the fact that it contains
free chlorine, Hberated by the oxidizing action
of nitric acid upon the hydrogen of the hydro-
chloric acid.
AQUA VITAE (Latin)
An old name for alcohol [which see).
AQUARELL PROCESS
A combination of half-tone and chromo-
lithography for colour printing, practised
in Germany. Also known as aquareU fac-
simile reproduction, aquarell imitation, and
aquarell gravuie. The last - mentioned is
really a combination of colour plates with
collotype.
AQUATINT {See " Gum-bichromate Process.")
AQUATINT ETCHING PROCESS (Pr., Aqua-
tinte: Ger., Aquatint Manier)
An old method of forming a ground, or tint,
for etching on copper. Resin is dissolved in
alcohol, the proportion of the latter determining
the firmness or coarseness of the grain, and this
solution is poured on the polished copper plate.
As the alcohol evaporates the resin reticulates
into a granular structure. The plate is slightly
etched, and then certain parts are stopped out
corresponding to the tones of the picture.
Further etchings and stoppings out follow until
the complete picture is formed in graduated
tones. Usually the plates are printed from by
the intaglio method, but the method has also
been applied in connection with photo-processes
for typographic colour work.
AQUATINT, PHOTO {See "Photogravure.")
ARABIC, GUM {See " Gums and Resins.")
Arabin
36
Arc Lamps
ARABIN (Fr., Acide gummtc)
The pure, soluble principle of gum arable, and
existing in different proportions in difierent
samples. In good Soudanese gum the proportion
of arabin is between 78 and 80 per cent. ; in
Turkey gum about 40 per cent. It is used in
the arabin gum-bichi ornate process, under which
heading a method of preparing arabin is given.
ARABIN GUM-BICHROMATE PROCESS
A gum-bichromate printing process, worked
out by Nelson K. Cherril, and published in June,
1909. To prepare the arabin, a quantity of
best Soudan gum arable is sifted through a
40-mesh sieve. Place in a quart earthenware
jar 1 50 CCS. of water, 7^ ccs. of pure hydrochloric
acid, and then sift into the mixture, stirring the
while, 100 g. of the powdered gum. Keep the
whole at about 120° P. (about 49° C), and
stir frequently until solution is complete. Cool
and add 600 ccs. of the best methylated alcohol,
free from petroleum, and stir for half an hour or
so, or until the arabin is thrown down as a white
precipitate and has lost all stickiness or gum-
miness. Filter through two thicknesses of
cheese-cloth, gather the arabin in the cloth into
a ball, and squeeze it well, place it in a small
jar, cover with new spirit, stirring it and break-
ing it up well, and leave for several hours until
the spirit has absorbed all the water. Squeeze
again in cheese cloth, then put the arabin in a
towel and squeeze it in a press, with as heavy
pressure as possible. Break up the cake formed,
to allow the remaining alcohol to evaporate, with
gentle heat ; then break the remaining lumps in
a mortar and dry until all is a dry, gritty powder.
The formula in the English system would be
roughly as follows : —
Water . . . .
5i oz.
Hydrochloric acid .
. 127 mins.
Powdered gum
1540 grs.
Methylated alcohol
. 21 oz.
To prepare synthetic gum, take 20 g. of
arabin, 20 g. of heavy magnesium carbonate,
and from 40 ccs. to 75 ccs. of water, according
to the thickness of tie solution preferred for
coating. This formula in English is —
Arabin ..... 308 grs.
Magnesium carbonate . . 308 „
Water . . . . . i^ to 2J oz.
When mixed, stir occasionally until the froth
subsides, then filter through muslin.
To prepare the pigment, lampblack is used ;
wash it with repeated doses of mixed ether and
acetone until all fatty, gummy matters are
removed ; or, preferably, bum small pieces of
camphor slowly tmder a piece of porcelain — say
the bottom of a porcelain developing dish.
Scrape off the soot with a palette knife into a
test-tube and wash with mixed ether and
acetone until these solvents come away with
only slight discoloration. Pour off as much
as possible without losing the black, and dry
by stirring the test-tube in hot water, keeping
the water from the pigment. When dry, the
tube is inverted, and the black will fall out freely.
A special lampblack, known as No. 4, has been
prepared for this particular process. To mix
the gum and pigment for coating upon paper,
it is necessary to experiment with the particular
paper to be used, taking a normal temperature
— say 95° F. — for the developing water and a
normal time — say forty-five minutes — for devel-
opment. The mixture must be such as will just
soak clean from the paper in the development
time. With too little gum the pigment soaks
into the paper ; with too much, it washes away
before development is complete. In practice it
is best to make up an under-gummed and an
over-gummed ink, and experiment with these
wiU show the proportions for any paper. For
instance, Cherril recommends the making of one
ink containing gum in the proportion of 20 arabin
to 75 water, and the other in the proportion of
20 to 45 of water. If both these are pigmented
in the same proportion as to quantity — that is
to say, about 400 to 500 mm. of lampblack to
each 10 COS., the one will be found to give too
much penetration to Joynson's or Rive's paper,
and the other too httle ; a mixture of the two
will be found to give a good result. The
mixture is sensitised just before use by an
addition of an equal volume of bichromate
solution made by adding 15 g. (230 grs.) of
ammonium bichromate to 100 ccs. (3J oz.) of
water ; dissolve by heat, and neutralise by stir-
ring in a little chalk, decanting when effer-
vescence ceases and the solution settles. The
paper to be used is brushed over thinly with the
freshly-mixed gum and bichromate, the brush
marks being obliterated by crossing and recross-
ing the strokes. After drying, the paper is
ready to be exposed. Exposure should be by
actinometer after the manner of carbon, and
the paper is much more sensitive than the
average gum-bichromate paper prepared by
other processes. If the development of a print
from an ordinary negative is complete in about
forty-five minutes in water at a temperature of
95° F- (35° C.), the result wiU be perfect. Develop-
ment may be performed in a vertical tank by
floating face downwards on the water, only
" controlling " in the usual manner. (For par-
ticulars of gum work in general, see " Gum-
bichromate Process.")
ARAGO, DOMINIQUE FRAN9OIS
An eminent French astronomer and physicist
(6. 1786, d. 1853), to whom Daguerre showed and
explained his earUest results. Daguerre's dis-
covery was communicated to the Paris Academy
of Science by Arago on December 7, 1839, and
it was on the latter's recommendation that
the French government awarded Daguerre a
life pension of 6,000 francs, on condition that he
published the process.
ARC LAMPS (Fr., Lampes A arc ; Ger., Bogen-
lampen)
Lamps in which a powerful light is obtained
by passing an electric current through a pair of
slightly separated carbon pencils. Where the
current is interrupted by tiie gap an intensely
brilliant arc is created. Are lamps are of two
principal kinds : (a) open, in which the carbons
are exposed to the air, and. (6) enclosed, in which
the carbons are almost hermetically sealed in a
glass-covered ease, and bum in a mixture of
carbon monoxide and nitrogen formed by their
own combustion. The enclosed type is coming
Arc Launps
37
Archer
to be preferred, on account of its increased
actinic power, due to its larger arc, the greater
proportion of violet rays, and the fact that the
life of the carbons is much longer, owing to the
practical absence of air, and consequently slower
combustion. Some excellent open-type arc
lamps are, however, obtainable, in whidi several
pairs of carbons are used ; these obviously yield
a more powerful light than the single carbon
pattern.
The arc light is employed in studio portraiture,
printing, copying, enlarging, and photomicro-
graphy, also in the optical lantern and cinemato-
graph.
In studio work the lamp should be supported
on an adjustable tripod or bracket, so that it
may be raised as high as 8 ft. or 9 ft. or lowered
at will. The direct light of the arc is liable to
produce hard lighting and heavy shadows ; and
it is therefore advisable either to cut this off by
a small opaque disc placed in front of the carbons
A. Open Type Arc Lamp, with B. Enclosed
Diffusing Screen, etc. Arc Lamp
and to use only the light obtained from an
umbrella reflector or screen at the back of the
lamp, or, as an alternative, to use a translucent
difEusing screen of muslin or tracing doth in
front of the lamp. Sometimes these two plans
are combined. A illustrates the use of a diffusing
screen C with the Boardman multi-carbon arc
lamp (open type). The metal shield D screening
the direct light of the arcs will be noticed, and
also the large umbrella reflector E. B shows
an extensively-used pattern of enclosed arc (the
" Westminster ") designed for general photo-
graphic use. For low studios, a reversed
model is made, having the arc chamber on top
instead of beneath. Whatever kind of lamp
is employed, the lens must be shielded from the
direct rays by means of a projecting hood.
For printing, the lamp should not be too
near the frames, a good average distance
being 2 ft. or 3 ft. Various stands are obtain-
able to support a number of frames in circular
tiers, the lamp being suspended in the centre.
In lantern and cinematograph work the open
arc at present holds the field, though the enclosed
arc is coming into use. Lantern arc lamps are
so designed as to economise space, and are fitted
to a. sliding tray. A model having the carbons
at a right angle is claimed to give a better and
more direct hght, and to take up less room than
those types in which the carbons form a very
obtuse angle with each other.
In process work, arc lamps play an important
part, practically all work being done by electric
light, because of its uniformity and the certainty
of the exposures as compared with daylight.
The " open " arc has been almost entirely super-
seded by the " enclosed " arc. For copying,
a pair of lamps is usually employed taking
about 10 amperes, though for large work four
lamps may be necessary. The lamps are
enclosed with semi-cylindrical reflectors, which
are whitewashed inside. For colour work 15
ampere lamps are frequently adopted, and
coloured flame carbons utilised to aid the expo-
sure through the colour filters. Red flame car-
bons, for instance, are found beneficial with the
red filter for the blue printing plate. Search
lights of high amperage are also employed in
some studios for securing very powerful illumin-
ation. For printing on the metal, lamps of
from 15 to 20 amperes are employed. Arc
lamps for process work are usually run in
" parallel " ; and a high voltage — 200 volts or
more — is preferable with enclosed lamps so as to
obtain about 140 volts across the arc, by which
means a long fiaring arc of great actinic power
is obtained.
ARCHER, FREDERIC SCOTT
Bom at Bishops Stortford, 181 3, died in Lon-
don, May, 1857. He invented the wet collodion
process in 1848, and published working details in
The Chemist, dated March, 1851, his own
" Manual of the Collodion Photographic Pro-
cess " following in 1852. His process practically
displaced both the Daguerreotype and Tal-
botype (calotype) processes, and enjoyed popu-
larity from 1855 to 1880. Many historians have
coupled other names with Archer's, either as
assistants or co-inventors, but close study of all
the facts leads inevitably to the conclusion that
Archer deserves the whole of the credit. He
introduced pyrogallic acid (then sold at 6s. 8d.
per dram) as a developer ; a camera within
which plates could be exposed, developed, and
fixed ; a triple lens to shorten the focus of a
double combination lens ; and a method of
whitening collodion positives upon glass (see
" Alabaster Process "). Archer lived and died
a poor man ; and at his death a subscriptioh list
was opened and a sum of ^£747 raised for his
widow and children. Mrs. Archer died shortly
afterwards (March, 1858) and the amount was
settled upon his children, together with a Govern-
ment pension of £50 per annum. Punch, referring
to the testimonial, said (June 13, 1857): "To
the Sons of the Sun.— The inventor of collodion
has died, leaving his invention unpatented, to en-
rich thousands, and his family unportioned to the
battle of life. Now, one expects a photographer
to be almost as sensitive as the collodion to which
Mr. Scott Archer helped him. A deposit of
silver is wanted (gold will do), and certain faces
Archerotsrpe
38
Argentometer
now in the dark chamber will light up wonder-
fully, with an effect never before equalled in
photography. . . . Now, answers must not be
negatives."
ARCHEROTYPE, AND ARCHOTYPE
The early names (after Archer, the inventor)
of the collodion process.
ARCHITECTURAL PHOTOGRAPHY
In photographing architectural subjects,
whether for pictorial or record purposes, regard
must be paid to the fact that technical correct-
ness is absolutely essential. Many technical
points that can be ignored without any serious
disadvantage in landscapes become important
in architecture, and disregarding them would
involve serious loss of quality. The camera
back must be kept upright so as to secure vertical
lines in the photograph ; it should be tested with
a level or a plumb indicator. The one exception
to this rule is that in many old buildings the
walls lean outwards, the heavy pressure of the
roof, acting for centuries, having forced them
into that position. In that case, the camera
may be tilted slightly, the back leaning back-
wards, so as to bring the walls or columns vertical
in the photograph. Wide-angle lenses, or those
that include a large expanse of view, become a.
necessity in most architectural work. In exteriors
as well as interiors, the space is frequently too
limited to allow a distant point of view to be
taken, and a lens that will include sufficient of
the subject from a very short distance becomes
necessary. Although this is by some regarded as
a disadvantage, it cannot in every respect be so
considered. Photographing a subject from a near
point of view possesses one distinct advantage.
It conveys the impression of looking upwards in
a manner that cannot be attained by any other
means ; and this frequently adds impressiveness
to the picture. Small portions or details can be
effectively taken with a lens that would be suit-
able for general landscape work, but larger sub-
jects require the shorter focus instrument. The
most useful wide-angle lens Will have its focus
about four-fifths of the longer side of the plate ;
and if the worker has a second lens, its focus
should be about the same as the longer side of
the plate. And the ordinary landscape lens —
one and one-third the length of the plate — will
be useful for those subjects that provide suffi-
cient space. The lens, whatever may be its
focus, should be capable of covering a much
larger area than the plate in use. In many sub-
jects the lens has to be raised considerably above
the centre of the plate, and, unless the lens will
cover when it is so raised, dark empty comers
will appear on the negative. Tilting the camera
to accommodate a lens of limited covering
capacity is very undesirable ; the front and back
not being parallel necessitates the use of a very
small stop to secure sharp definition.
The camera should be simple and rigid, so
that long exposures may be given without any
risk of vibration. The rising front should allow
the lens to be raised well above the centre ;
almost as far as the top edge of the plate is
occasionally required. Within reasonable limits,
the greater the rise obtainable, and the greater
the covering power of the lens, the more useful
and adaptable will be the apparatus for archi-
tectural subjects. An anastigmat possesses so
many advantages that no other type of lens
should be employed.
In all subjects an oblique position rather than
a full front view should be chosen. The latter
destroys the effect of reUef, whereas the former
shows it effectively. It is very rare that a full
front view of any subject is effective ; the result
is almost always flat and lacking in interest, as
the projection of one part of a subject beyond
another is lost in the picture. A wide-angle
lens is frequently valuable in enabling the photo-
grapher to select a more oblique position than
would otherwise be obtainable.
A liberal proportion of foreground should
always be included in front of the nearest import-
ant vertical object ; it assists in conveying the
impression of space. The normal height of
vision — 5 ft. from the ground — ^is the best for
all large or high subjects ; it conveys the most
natural impression of size. Photographing from
a height dwarfs the effect of the building, and
should be adopted only for special purposes. At
times the camera may be much lower than 5 ft.,
especially for small subjects taken with a wide-
angle lens. {See "Interiors, Photographing.")
Symmetry in the arrangement of the subject
on the plate should be studiously avoided ; and,
equally, an arch, a column, or a doorway that
may form an important part of the subject
should never be shown almost but not quite
completed, broken by the boundary line of the
picture. It conveys the sense of incompleteness
and absence of support. Sunlight is very effec-
tive in some exterior work, especially in compre-
hensive views of large buildings. In smaller
subjects, too, it is frequently a valuable aid to
picturesque quality. At times, the sun shining
almost along the principal face of the building
photographed will produce exceptionally good
effect by throwing very long shadows of all pro-
jecting details. In many small details, direct
sunshine is best avoided in order to show the
form and surface of the details free from cast
shadows. When photographing in sunshine a
full exposure is absolutely necessary in order to
secure transparency and full detail in the
shadows. {See also "Interiors, Photographing "
and " Exteriors, Photographing.")
AREA SYSTEM OF STOPS
An obsolete system of marking lenses and
stops suggested in 1886 by George Smith. Every
stop and every lens had its own number, and
the relation of the stop number to the lens
number was supposed to indicate the correct
exposure.
ARGENTIC SALTS, OPALS, ETC.
Argentic salts are salts of silver ; argentic
opals are opals sensitised with silver. Argentum
is the Latin name, and Argent the French name
for silver. Sensitised materials of one particular
make are called argentic opals, paper, etc., but
bromide opals, paper, etc., are more popular
names.
ARGENTOMETER (Pr., Argentomitre, Pise
Nitrate : Ger., Argentometer, Silbermesser)
This instrument is used by wet collodion
Argentotype
39
Artificial Light
workers for testing the strength of the silver
bath. It consists of a hydrometer which is
floated in a tall glass jar. The hydrometer is
graduated either to show grains per ounce of
water, parts in a certain volume of water, or
percentages. The first-mentioned is most
A
Argentometer
commonly employed by English workers, and
the second or third by Continental workers.
The reading is only accurate in case of a new
bath, as by use the bath becomes charged with
iodising salts and alcohol from the coUodionised
plates, but for all practical purposes it forms a
sufficient test.
ARGENTOTYPE
A name for bromide paper, and widely used
in the early days of the bromide process.
ARISTOGEN
A concentrated one-solution hydroquinone
developer, introduced by I^iesegang, consisting
of hydroquinone, sodium acetate, sodium sul-
pliite, and citric add, for developing faintly
printed-out gelatino-chJoride and collodio-chlor-
ide papers. According to Sclmauss a similar
and suitable formula is : —
Hydroquinone (7 % alcoholic
solution) .... 4 parts
Sodium acetate (15 % solution) 8 „
Water . . . . . 70 „
ARISTOSTIGMAT (See " Lens.")
ARISTOTYPE
A gelatino-chloride P.O.P. The original aris-
totype paper was simply a paper prepared with
a substratum of barium, and coated with a
coUodio-chloride of silver emulsion, and the
term was first used early in the 'eighties, Ober-
netter, of Munich, being the first to introduce it.
The name is still used by some makers of P.O. P.,
both gelatino- and collodio-chloride, especially
in America.
AROMATIC CARBON COMPOUNDS
A very large class of chemical compounds
which are derivatives of benzene or contain what
is known as a closed chain or nucleus similar
to benzene. Generally, they contain a larger
percentage of carbon than the fatty or aliphatic
compounds, and are more frequency crystalline
at ordinary temperatures, and more easily
converted into substitution products, especially
by the action of nitric and sulphuric acids,
which produce nitro and sulphonic derivatives.
Most of the newer developers belong to this
class.
ARROWROOT (Fr., Arrowroot; Ger., Pfeil-
wurzelmehl)
A prepared pure starch obtained from vari-
ous plants, the finest being the West Indian,
of which the source is the rhizomes of Maranta
arundinacea. English arrowroot is the starch
obtained from potatoes. Arrowroot is used for
sizing papers before sensitising and also as a
mountant.
ARTIFICIAL IVORYTYPES
Photographs made in 1857, by Mayall, on a
paper substitute prepared by mixing barium
sulphate with albumen, and rolling the paste
into sheets. These, when dry, were printed upon
and used as paper.
ARTIFICIAL LIGHT
Thanks in no small measure to the introduction
of rapid plates, and of lenses working at very
large apertures, artificial light has become of
inestimable service in photography. It is used
for lighting the subject, for illuminating the dark-
room, and for printing. The actinic power is
obviously important, and the following table
gives the approximate comparative powers of
the illuminants in common use, a standard candle
being taken as i : —
Actinic Powers of Artimciai, Lights
Standard candle . . . i
Colza lamp, ^-in. wick . . 2
Paraffin lamp, ^-in. wick . . 4
,, „ i-in. wick . . 10
Paraffin duplex lamp . . 30
2-ft. gas burner . . .12
S-ft. „ „ • • • 35
i6-c.p. electric incandescent lamp 35
32-c.p. „ „ „ 70
Welsbach incandescent gas . 80
Sir WiUiam Abney gives the following table,
showing the photographic value of some artificial
lights in terms of the photographic value of a
standard candle, the photographic value being
taken as the effect on bromide of silver : —
Light of the Optical Value
of one Standard Candle
Photographic Value in
Terms of Standard Candle
Standard candle . . . i
Ordinary paraffin candle . . i-3
Oxyhydiogen light, blow-through
jet 2
Electric arc light . . .10
Magnesium burnt at the rate of
I gr. per minute. . -15
Bright sun at noon in summer 21 -6
Referring to the above. Sir William Abney says :
" It will be noticed how the optical and photo-
graphic values differ. It might be thought that,
although these differences do exist, yet, by
increasing the smaller number, the same effect
Artificial Light
40
Artificial Light
might be obtained. It must be recollected, how-
ever, that the electric light radiates from 1,000
to 10,000 candles from a very small area, and
that, to make the same photographic illumin-
ation, the number of candles would have to be
the same, but multiplied by 10. Thus, if an
electric arc light radiated 1,000 candles, the
number of standard candles that would have to
be employed would be 10,000, a number which
would never be concentrated in any reasonable
area. Sunlight may be taken as equal, optically,
to 5,600 candles placed at one foot from the
object illuminated."
The electric arc and the mercury vapour lamps
are the most powerful for photographic purposes,
and largely used by professional workers because
of their richness in those rays to which dry plates
are the most sensitive. The light from incan-
descent electric lamps is usually of a yellowish
tint, serviceable enough for printing, dark-room
illumination, etc., but hardly strong enough for
portrait work unless used in large numbers.
Acetylene gives a very serviceable and intensely
actinic light for most photographic purposes.
The artificial light that is most generally used
for printing, however, is the incandescent gas
mantle, which, when of an average quality
and full size, gives a light of between 60 and
70 caudle power. Magnesium, in the form of
either powder or ribbon, is extensively used for
portrait work outside the studio at night, its
use dating from 1863. Ribbon and powder,
weight for weight, give approximately the same
illumination ; and one inch of ribbon in contact
printing is equal to four minutes' exposure to
an ordinary flat flame gas burner at the same
distance {see also " Flashlight Photography ").
In 1882 a lamp was devised for burning magne-
sium ribbon in oxygen ; a number of improve-
ments followed, and the lamp is now an article
of commerce. Ordinary gas burners, oil lamps,
and candles give lights that are of poor actinic
value. As regards the cost of some iUuminants,
Leon Gaster, A.M.I.EI.B., has given the following
table : — ■
Cost
per 1, 000
hours
per candle
power.
Petroleum ....
9-o8d.
Alcohol incandescent
io-03d.
Auer burner, incandescent gas
3-i7d.
Pres.sure gaslight, incandescent
2-I2d.
Carbon filament lamp
i4-iid.
Nemst lamp .
8-82d.
Arc lamp.
S-i8d.
Flame arc lamp
i-o6d.
(See also " Acetylene," " Flashlight Photo-
graphy," " Candle Power," " Limelight,"
" Artificial Light, Portraiture by," etc.)
ARTIFICIAL LIGHT, PHOTOGRAPHY
BY
Photography by artificial light presents no
serious ififficulty if proper precautions are taken,
and a correct exposure given. It is imperative
that the source of light should be in such a
position that no direct rays reach the lens. When
it is unavoidable that the source of light is in
front of the camera, the lens may have fitted to
it a sky-shade or a large temporary hood, so
as to protect it from the light. Whenever pos-
sible, the source of light should be behind the
camera, not directly at the back, but at one side
or the other. Where the arrangement of the
light is under the photographer's control, and
the light is of such a nature that it can be divided,
the larger part should be placed at one side and
behind the camera, and the smaller part at the
other side. Bven where the light is fixed, but
divided, as with two or more electric arc lamps,
a similar result may be obtained by placing the
camera so that one light is almost directly
behind it, slightly to one side, and the other one
considerably towards the other side. When
practicable, the light should be diffused by a
screen of tissue paper. This softens the light,
and destroys the harshness of the cast shadows,
which would otherwise be very strongly marked.
When photographing an interior, or a small
object in a building, by electric arc lamps, the
strength or actinic value of the light may be
tested by means of an actinometer while the
camera and subject are being arranged. For
a room about 40 ft. by 25 ft. or 30 ft., with the
camera and a single arc light of about 2,000
candle power at one end, the exposure should be
ten minutes, using a lens aperture of //16 and a
plate of a speed of 200 or 250 H. & D. For a
small object photographed at a distance of 6 ft.
or 7 ft., illuminated by a single arc light of
2,000 candle power at a distance of 10 ft. or
12 ft., the exposure should be five or six minutes
for a light-coloured object, up to twelve or fifteen
minutes for one of dark colour.
Where arc lamps are not available, magnesium
ribbon or powder, or a mixture of magnesium
and aluminium, may be employed. The powder
is frequently burned in the form of a flash, and
though this may be desirable when groups of
persons have to be included, the methods in
which the powder is burned more slowly are
preferable. Magnesium alone produces consider-
able smoke in burning, and though this smoke
is only in evidence after the exposure is com-
pleted, it is a serious objection in many cases,
and quite prohibits making a second exposure.
(See Flashlight Powders.")
A convenient form of artificial light easily
obtainable is that sold under the name of
" Flash Candle." These candles consist of a
celluloid tube fiUed with a perfectly safe mixture
which bums for a few seconds and produces a
light of great intensity. They are obtainable in
various sizes, called two-second, four-second, and
seven-second candles respectively. Two, three,
or four of these may be placed in suitable posi-
tions for lighting an interior, and they may be
lighted in rapid succession by applying a lighted
taper to the touch-paper with which each caudle
is provided. Focusing and arranging must be
done before lighting the candles. A room or
space about 25 ft. by 16 ft. would be sufficiently
iUuminated if the camera and lights were at one
end and two four-second candles were burned,
using a lens aperture of //16 and a plate having a
speed of 200 or 250 H. & D. As in the expo-
sures given for electric light, it is assumed that
there is a wall near the lights, or an equally
well-lighted space beyond. If these candles
or an electric light were used to illuminate a
small space which formed part of a large room
Artificial Negatives
41
Artograph
or open space, in such a manner tHat there was
a large open dark space beyond the light, at
least half the illumination would be lost by
difEusion.
Still life and flower photography may be
carried out very successfully by artificial light,
using either magnesium ribbon or the flash
candles. One four-second candle at a. distance
of 3 ft. should be sufficient, using the lens at// 16
and a 200 H. & D. plate ; a screen of ground
glass or tissue paper for diffusing the light is
imperative, and a white reflector behind it.
Copying may be done in a similar manner, or
by means of Uie ordinary gas or electric house
lighting. Two lights should be used if possible,
one placed at each side of the camera, so as to
light the work to be copied as evenly as possible ;
or half the exposure may be made with a single
light at one side, and then the light placed at
the other side for the remainder of the time.
When copying a print with a glossy surface, care
must be taken to avoid the sheen that may be
produced by an improperly placed light. For
copying a photographic print, the same size as
the original, using a 50 candle-power gas or
electric light placed about 2 ft. from the print,
the exposure required for //16 and a plate 200
H. & D. would be about five minutes. For
copying a black print on plain white paper — a
line engraving, for example — two minutes would
be sufficient.
For rapid work by artificial light, see under
the headings " Flashlight Photography " and
" Flashlight Powders." For the application of
artificial light in the production of prints, see
under the headings " Bromide Paper " and ■
" Gaslight Papers and Lantern Slides."
ARTIFICIAL NEGATIVES
Hand-made, and not photographic negatives ;
known also as factitious negatives. An opaque
ground or varnish is spread on glass, and, when
dry, is scratched through with a needle point,
making a drawing after the style of an etching.
The process is also used for making lantern slides
(positives) of diagrams, writing, etc. Asphalt
varnish to which wax is added until a pUable
ground is obtained makes a suitable coating.
If the ground is sticky or is not dense enough it
may be dusted over and polished with fine
blacklead, such as is used by electrotypers.
White grounds may also be formed by dusting
with blanc d' argent. A wet plate may be fogged,
developed, and intensified to form a groimd ;
and there are numerous other methods of pre-
paring such plates.
ARTIGUE PROCESS
A modification of the carbon process, named
after its inventor, Mons. Artigue. No safe-
edge is necessary on the negative, there is no
transfer, and consequently the print is not
reversed. The paper for this J)rocess is sup-
plied coated with a mixture of a colloid sub-
stance and a very fine black pigment. It is
supplied insensitive, and requires to be sensi-
tised by floating on a 2 per cent, solution of
potassium bichromate. A thin negative is most
suitable for this process, and the exposure of
the print is timed by means of an actinometer
as in ordinary carbon printing. An essential
feature of the process is the method of develop-
ment. A very fine sawdust is supplied by the
makers of the paper ; this has to be mixed with
water to about the consistency of a thick soup.
The print is soaked in tepid water for a few
minutes, and then laid face upwards on a sheet
of glass. The sawdust and water mixture,
preferably tepid, is poured over the print from
a jug. The print is rinsed from time to time so
that the progress of development may be judged,
and the pouring of the sawdust mixture is con-
tinued until the print is sufficiently light, exactly
as the pouring of water in an ordinary carbon
print. As soon as development is completed,
the print is well rinsed to remove any of the
sawdust that may adhere, then placed in a
5 per cent, solution of altmi for five minutes,
rinsed in two or three changes of water, and
dried. The surface of the prints is exceedingly
delicate, and very great care has to be exercised
throughout to prevent injury. The prints pro-
duced by this process are characterised by very
great delicacy and rich quality. They have a
delicate velvety matt surface, the deepest
shadows are a rich black with full detail, and
the scale of gradation is good.
The Artigue process has never been exten-
sively worked in England. Suggested reasons
are the extreme tenderness and deUcacy of the
coating, which necessitates great care at all
stages, and the difficulty experienced in obtain-
ing the materials. The introduction of the gum-
bichromate process has lessened the demand for
a paper of the Artigue character, and several
attempts to introduce a paper somewhat similar
have met with very slight success. It must be
conceded, however, that none of the substitutes
has equalled Mons. Artigue's production in
delicacy of surface, in richness of quality, or in
gradation.
ARTISTIC PHOTOGRAPHY
A frequently used but somewhat vague term.
The idea underlying it is that the producer of a
given picture has aimed at something more than
a merely realistic rendering of the subject, and
has attempted to convey a personal impression.
Thus, a landscape may be rendered solely as a
topographical view or as the material for con-
veying the idea of, for example, solitude ; an
interior may be intended to show architectural
detail or to suggest, for example, grandeur The
results are consequently either realistic or
artistic. The artistic element becomes more
pronounced the more the merely mechanical
and thoughtless is subordinated to the deliber-
ate and intentional control of the producer.
ARTOGRAPH
An automatic machine, known also as the
electric artograph and telautograph, for sending
sketches or line drawings along a telegraph wire,
invented about 1891 by N. S. Amstutz, of Cleve-
land, Ohio. According to a description published
at the time, the picture was photographed on a
" stripping film " of gelatine and potassiimi
bichromate, which, after washing with luke-warm
water to remove the portions not hardened by
the action of the light, gave a picture in relief,
more or less high, according to tiie tones of the
original. The next step was to vary the strength
Artotype '^^
of CTUrrent in the telegraph wire according to the
variations of light and shade in the picture —
that is to say, according to the heights and depths
of the etched film. This was done by an arrange-
ment similar to the stylus which moves over the
indentations on the wax surface of the phono-
graph. The point of the stylus passed over every
part of the film, and tripped up and down accord-
ing to the degree of reUef. By a multipljring
lever its movements up and down were caused
to depress a series of keys which completed the
electric circuit. If the rehef was very low only
one key was depressed, and more keys were
closed in proportion to the depth of the relief.
The current was thus varied in strength accord-
ing to the degree of relief on the film. At the
receiving end the current passed through an
electromagnet, which bore with more or less force
on a travelling graver, according to the strength
of the current, and the design was cut in a surface
of wax, from which an electrotype could be
obtained for printing purposes. The results
published at the time of the introduction of the
system were crude.
ARTOTYPE
A name give to an early collotype process in
which the plate was given two separate coatings
of bichromated gelatine instead of, as at present,
Asphaltum
ASKAU PIGMENT PRINTING PROCESS
(Fr., Proc^dS Askau ; Ger., Askau-Druck)
A dusting-on process introduced in Germany
by Joseph Rieder, in 1909, in which pure india-
rubber (caoutchouc), with a small proportion of
asphalt added, is used as the sensitising material.
Paper coated with the mixture will keep for a.
mouth. It is exposed under a positive trans-
parency, as in otiier dusting-on processes, and
is " developed " with a mixture of sea-sand and
a suitable powdered pigment, the latter adhering
to the light-affected parts according to the
exposure each portion has received. A lac
varnish is then sprayed over the print by means
of an air brush to fix the pigment.
ASPHALT
The chief of the many synonyms for asphaltum
{which see).
ASPHALT PROCESS
A process of using asphaltum for photo-
etching. (See " Asphaltum.")
ASPHALTO-PHOTO-LITHOGRAPHIC PRO-
CESS (Fr., La Photoliihographie au
Bitume ; Ger., Asphali-Photolithographie)
An adaptation of the bitimien process of
Joseph Nicephore Niepce. A lithographic stone
is coated with a solution of bitumen in ether, or
other suitable solvent, and is exposed to light
under a negative. The light-affected parts are
Tendered insoluble, and the unexposed portions
may then be dissolved away by the application
of ether. After rinsing and allowing to dry, the
stone is wetted with gum water, which is applied
with a sponge. When dry, the surface gum is
washed off with a slightly-damp cloth and the
stone is lightly etched with a very weak solution
of nitric acid. It is then rinsed to remove the
acid, again gummed, and, when dry, wiped with
the damp cloth, after which it is ready for print-
ing from in the ordinary lithographic manner,
wetting the stone at each impression. The same
process can be employed with zinc or aluminium
plates. {See also "Photo-lithography.")
ASPHALTOTYPE
A name given to one of the processes for using
light sensitive asphalt for making typographic
printing blocks. {See also "Asphaltum.")
ASPHALTUM (Fr., Asphalte, Bitume de Jud^e :
Ger., Asphalt, Judenpech)
Synonyms, asphalt, bitumen, bitumen of
Judea, mineral pitch, and Jew's pitch. A
natural product of the decomposition of vege-
table substances.
The term asphaltum comes from the Greek
word for fossil pitch, i)a<r<pa\Tos (and a-ipaWofiat)
and signifies an unchangeable body. The
Latin word bitumen is derived from pix tumens.
Geologically, asphalt is, as stated above, a
natural product of the decomposition of vege-
table substances ; and it is found in all parts
of the world, most frequently in volcanic neigh-
bourhoods. The principal sources are on the
shores of the Dead Sea in Syria (whence comes
the name Syrian asphaltum), and in the Great
Pitch Lake of the Island of Trinidad ; but it is
also found in the Lake of Maracaibo (in Vene-
zuela), at Coxitambo (in Peru), at Barbadoes,
and in the island of Cuba ; whilst in Europe
there are deposits at Seyssel and at Bechel-
bronn (in Alsace). Small deposits have been
foimd in Cornwall, Derbyshire, and Shropshire.
For photographic processes, however, only the
Syrian and tie Trinidad asphaltum are con-
sidered, these having the characteristic pro-
perties of asphaltum — namely, brownish-black
colour, high melting point, and conchoidal frac-
ture. Bitimien has usually been considered to
be formed by the oxidation of petrolemn, and
according to the generally accepted analysis is
composed of carbon, hydrogen and oxygen, with
a small quantity of nitrogen, together with
sulphur and mineral substances (iron, man-
ganese and calcium). Syrian asphalt comes into
the market in large pieces, which frequently con-
tain small lumps of earthy substances consisting
of carbonate of lime, gypsum, clay, and sand.
Trinidad asphalt also comes into commerce in
large pieces, which, however, do not contain
the earthy particles found in the Syrian. The
commercial asphalt can be purified by boiling in
water, when the pure asphalt melts and floats
upon the surface while the impurities subside.
The Syrian asphalt begins to melt at 275° F.
(135° C), and the Trinidad at 266° F. (130° C).
The specific gravity of the former is I'I03, and of
the latter 1-96 ; both kinds behave the same in
relation to solvents. They are partly soluble
in alcohol and ether, more so in benzole, com-
pletely and easily soluble in chloroform, bisul-
phide of carbon, tetrachloride of carbon, tur-
pentine and the various mineral oils. They are
insoluble in solutions of caustic potash or soda,
weak or strong, hot or cold. With concentrated
sulphuric acid the Syrian asphaltum is decom-
posed, but only by the heat, with evolution of
sulphurous acid, and it dissolves into a dirty
Asphaltum
43
Aspirator
brown fluid. Concentrated nitric acid has but
very little action on it, even -with heat.
The results of analysis show that the Syrian
and Trinidad varieties are similar in com-
position. Each is found to contain lo per cent,
of sulphua', and this constitutes an important
factor in regard to photographic sensitiveness.
By successive treatment with boiling alcohol,
boiling ether and chloroform, it is found that
both kinds may be separated into three com-
ponents, difiering in their chemical composition
and photographic properties. The portion (o)
insoluble in ether shows the highest sensitive-
ness, (6) the substance soluble in ether is less
sensitive, and (c) an oily substance extracted by
alcohol is quite insensitive. The part that is
insoluble in ether is, as a rule, easily soluble in
chloroform and turpentine, and less so in benzole
and petroleum. Syrian asphaltum contains
52 per cent, of the sensitive component, while
Trinidad contains only 38 per cent.
Spectroscopically examined, solutions of Syrian
asphaltum of the most sensitive kinds show weak
absorption bands, whilst the less sensitive kinds
show the bands more strongly.
As obtained from dealers, asphaltum is gener-
ally fit to be used at once ; but, if necessary, it
may be purified by powdering it and digesting
it with (Ulute hydrodiloric add, which dissolves
the earthy particles. Some authorities recom-
mend a treatment with boiling water, by which
soluble and earthy particles may be separated
out. In order to obtain the most rapid results,
it is desirable to extract the least sensitive con-
stituent of the asphaltiun with ether, and use
the residue in making the sensitive solution.
The simplest way of doing this is to digest the
powdered asphaltum in a bottie with an excess
of ether, shaking it up from time to time, and,
if necessary, stirring it with a glass or wooden
rod. The ether is changed at intervals of a few
hours, till all or nearly aU the soluble constituents
are removed. The last ether is then poured off,
and the residue thoroughly dried. Husnik's
asphaltum, which is believed to be prepared in
some such way, is obtainable as an article of
commerce in the dry powder form. The solvent
used for making up the sensitive solution is
generally benzole, which should be quite free
from water. Sometimes chloroform is added,
and generally some essential oil, such as lavender
or lemon, which prevents the too rapid drying
of the coating, and so keeps it uniform ; the
addition of oil is said to increase sensitiveness.
The following is a practical formula for pre-
paring a sensitive solution of asphaltum for
coating zinc plates for etching : Dissolve 1 50 grs.
of finest powdered Syrian asphaltum in 2 oz.
of chloroform and 3 oz. of anhydrous benzole.
Add 30 grs. of Venice turpentine and 10 drops of
til of lemon or oU of lavender. The film should
be of a transparent golden yellow tint. The
coating should be done by means of a whirler
(which see). The exposure is best made under
stripped films, which may be treated with a
baUi of glycerine to make them adhere when
squeegeed down to the plates. It is not necessary
to use a printing frame. The exposure may vary
from half an hour in the sun to two or three
hours in the shade. In bad weather the exposure
may extend to days. Development is usually
done with turpentine, which dissolves the soluble
parts of the image. The scum is rinsed away,
and the greasiness removed from the surface
with soap and water or a weak solution of soda. ■
Prof. Valenta has published a process for
augmenting the sensitiveness of bitumen by
incorporating sulphur with it. By this process,
ICO g. (si oz. II grs.) of raw Syrian asphalt
are boiled in a retort with an equal quantity
of raw pseudo-cmnene — which has the formula
C jH5(CH5)3, and a boiling point of about 1 70° C. —
and 12 g. (186 grs.) of flowers of sulphur
which should have been previously dissolved in
the pseudo-cumene. When after about three or
four hours' boihng, the evolution of sulphuretted
hydrogen has ceased, the pseudo-cumene is dis-
tilled off and the black pitchy residue dissolved
in benzole in the proportion of 4 to 100, which
solution is used for the sensitive coating of the
plate or stone. The sulphurised asphalt pre-
pared in this way is almost insoluble in ether,
but dissolves fairly readily in benzole, toluene,
xylene, cumene, and turpentine, and is very
sensitive to light. Recentiy Prof. Valenta has
simplified his method by dissolving the asphaltum
in carbon disulphide and adding siilphur chloride.
A number of processes mosUy used for photo-
lithography take advantage of the fact that
when bitumen is dissolved in both alcohol and
ether in suitable proportions it wiU split up into
a grain on drying. The film can then be printed
under an ordinary continuous tone negative and
yield a picture in half-tones. The Prey process
is a successful method worked on this basis.
Bitumen processes are not much employed
nowadays, owing to the slowness and uncertainty
of the exposures. Bitumen powder is, however,
largely used for dusting on plates to strengthen
the resist for etching, and the solution is used as
a resist varnish for the backs and margins of
plates, and for stopping out.
Alberini's reversed bitumen process consists
in removing the exposed bitumen from the
metal plate instead of the unexposed bitumen as
in the ordinary process. This makes it possible
to expose the bitumenised zinc plate under an
engraving, print, or inked drawing on thin
paper, dispensing with the use of a negative. The
preparation of the plate and exposure follow
on the lines of the ordinary process, but develop-
ment is effected by immersing the plate in a
dish of 40 per cent, alcohol. The principle of
the process is that the alcohol dissolves the part
which has been acted on by light, and not the
unexposed part, which is usually developed with
turpentine.
ASPIRATOR
An instrument used to promote the flow of
gas or liquid from one vessel to another by
suction. In its simplest form it is a cylindrical
glass or other vessel having a pipe to admit air
at the top and a stop-cock at the lower end.
A shows a simple form of aspirator bottie. As a
container for solutions which must be kept in
bulk free from air, it is shown at B. The large
bottie C contains, say, a hydroquinone-metol
developer and has two glass tubes, one of which
F reaches to the bottom ; F passes through »
rubber stopper and is continued down below the
shelf, having a piece of rubber tubing with a
Aspray-Fisher
44
Astrophotometry
clip and a piece of drawn-out tube at the end.
The other tube E just pierces the rubber stopper,
and is connected with a small bottle d containing
about 50 grs. of pyro dissolved in 2 oz. of a
10 per cent, solution of caustic soda. The
tube from the large bottle just pierces the rubber
stopper in the smaller one, while a third tube G
goes to the bottom, its other end being open to
the air. This tube should be high enough to
prevent the pyro-soda mixture being forced out
of the bottle. To use the arrangement, vmdip
the rubber at the end of the tube F and blow
through G. This forces the developer up and
down the tube F and so creates a siphon, it
being then only necessary to unclip the tube to
obtain developer from the large bottle down the
tube. The solution in the small bottle filters
the air from both carbonic acid and oxygen,
and the developer keeps good indefinitely. If
A. Aspirator
Bottle
B, Aspirator for Solutions
to be kept from Contact
with Air
the depth of the liquid in the small bottle exceeds
3 inches, the tube F should be at least 6 inches
below the shelf.
ASPRAY-FISHER ANIMATED STEREO-
GRAMS (Fr., MSthode Aspray-Fisher de
la Stirioscopie Animie : Ger., Aspray-
Fisher Lebendige-Stereographie)
An invention patented in 1859 by C. Aspray
and R. Fisher. The two halves of a pair or
series of stereoscopic pictures are so taken as
to be views of the same person or object in
slightly different positions. By rapidly opening
and closing each eyepiece in turn with a revolving
disc, so that either eye is alternately eclipsed,
the illusion of motion combined with stereo-
scopic relief is obtained. This is the earliest
recorded attempt to combine apparent movement
with the effect of natural relief and modelling.
ASTIGMATIC CORRECTOR
A negative attachment for removing the
astigmatism of portrait lenses. It was invented
by T. R. Dallmeyer in 1897. Although highly
successful in producing a perfectly flat and non-
astigmatic field, the corrector was never placed
upon the market, as it was found necessary to
grind special glasses for each individual lens.
The focal length of the portrait lens was increased
by from 30 to 40 per cent, with, of course, a
corresponding decrease in rapidity.
ASTIGMATION
An old and practically obsolete synonym of
astigmatism.
ASTIGMATISM
A serious defect in many lenses by which they
are prevented from rendering vertical and hori-
zontal lines with equal degrees of sharpness. It
is more noticeable towards the edges of the field,
the centre being quite free from it. The defect
is best explained by a diagram. If, using a lens
defective in this way, a dearly defined cross is
focused in the centre of the field, it will go
evenly out of focus on moving the screen to and
fro, the edges being uniformly blurred as at A.
Upon focussing the same cross near the margin
of the plate, the vertical or horizontal line only
will be blurred, the other becoming sharper as
the screen moves to one side or the other of the
+
illlilPIBtPliili
Blurred Images due to Astigmatism
focal plane of the image, as at B. In like
manner, a drde is drawn out into an ellipse
either horizontally or vertically, as the case
may be. Astigmatism may be minimised by
the employment of a small aperture, but cannot
be entirely removed. It is usually found in
portrait and rectilinear lenses, and may be partly
cured by shortening the tube ; this, however,
has the disadvantage of increasing the curvature
of fidd.
ASTRO - PHOTOGRAPHY. (See " Stars,
Photographing," "Cdestial Photogra-
phy," " Comets, Photographing," etc.)
ASTROPHOTOMETRY
The use of the photographic plate for astro-
photometry is not unattended with disadvan-
tages, for whilst the correction of the instruments
may be good it is impossible to bring all the rays
to an accurate focus, and they are grouped in
rings around the actual image of the star. As
the brightness of the star increases, or the expo-
sure is prolonged, the image not only becomes
denser, but also widens; Uierefore it has been
suggested to estimate the magnitude of the star
both by the density and the increase in diameter,
or either. Unfortunately, the law breaks down
that increase of the exposure is equivalent to the
increasing of actinic luminosity, but it has been
found to apply to stars down to the eleventh
Atmography
4S
Aurora Yellow
magnitude. When tlie diameter of the star
image is used, an allowance has to be made for
the duration of exposure, and this has to be
determined for every plate and instrument, but
may then be taken as constant. When the
density of the image alone is used, Pickering and
Schwarzschild independently suggested that the
out-of-focus images should be photographed
when they no longer appreciably differ in size
but do in density. One of the chief diflSculties
to which attention has only been recently directed
is the effect of the different colours of the stars,
for obviously a blue star and a. red star photo-
graphed on an ordinary plate and then on a
panchromatic or red-sensitive plate would
present totally different images, not only as
regards size, but density.
ATMOGRAPHY
The name given to the curious effects on sensi-
tive plates and papers caused by emanations and
vapours from sugar, eggs, smoke, and other sub-
stances, sometimes referred to as effluviography
and vapography.
ATMOMETER (Pr., AtmomHre : Get., Dunst-
messer)
An instrument for measuring the quantity of
water passing into the air by evaporation in a
given time.
ATMOSPHERE, RENDERING
In the pictorial sense the word atmosphere
is generally used to indicate a certain amount
of visible vapour or mist in the air. The presence
of mist is frequently a valuable aid to picture
making, often imparting a suggestion of delicacy
and mystery to subjects that are less satisfactory
when the air is dear and the light bright. The
rendering of subjects under these conditions is
not always easy. The exposure must be carefully
timed, and development must be so adjusted
as to secure a negative of soft and delicate
gradation. The use of a colour screen, or light
filter, is generally a disadvantage, as it has a
tendency in certain conditions to make the
veiled distance clearer and brighter than it
appears. The best result is obtained with a
full exposure on an ordinary plate, followed by
development carried only far" enough to secure
detail and gradation without blocking up the
lighter tones. A deUcate grey print in bromide
or platinum is frequently the best presentment
of the effect.
ATMOSPHERIC ACTION
The atmosphere is a mixture of oxygen and
nitrogen containing always more or less car-
bonic acid and aqueous vapour. In the neigh-
bourhood of cities there is also more or less smoke
and traces of sulphur compounds, and occasion-
ally ammonia. AU developing agents when
exposed, either in the solid state or in solution,
to the air greedily absorb oxygen, and they
discolour and become less active, the oxidation
products not being developers. Silver in a
finely divided state, as it occurs both in nega-
tives and prints, is extremely liable to be attacked
by any sulphur compounds, particularly when
gelatine is the vehicle, as this readily absorbs
aqueous vapour and thus brings the deleterious
sulphur compounds into more ultimate contact
with the silver of the image.
ATOMIC WEIGHTS (Pr., Poids atomiques ;
Ger., Aiomgewichte)
A term relating to the nvimber of atoms form-
ing a molecule of any element, according to the
atomic theory. On the atomic weights are based
the molecular or equivalent weights, and a list of
these is given in a table to be found under the
heading "Solubilities."
ATZPINSEL (Ger.)
A round, mop-shaped brush {see illustration)
of soft hair, generally marten fur, bound to a
wooden handle by means of waxed string
varnished with shellac. It is used for brushing
Atzpinsel
the surface of the metal plate in etching, to free
the image from scum. It is also occasionally
employed in etching on copper with iron per-
chloride when the plate etches slowly and there
appears to be a deposit in the hollows.
AURAMINE (Pr., Auramine ; Ger., Auramin)
Synonyms, auramine yellow, amidotetra-
methyl diamido-diphenylmethane hydrochloride.
Solubilities, soluble in water, alcohol, and
ether. A sulphur-yellow-coloured aniline dye
which is sometimes used for making light filters
or yellow screens. It is unsatisfactory in this
respect, as it passes the bright blue, the extreme
end of the violet, and ultra-violet, absorbing only
the deep blue.
AURANTIA (Pr., Aurantia : Ger., Aurantia,
Kaisergelb)
Solubilities, slightly soluble in water, very
soluble in alcohol. An orange- coloured aniline
dye used for making light filters. Much superior
filters can be made with other yellow dyes —
that is, filters that do not absorb so much red
and orange as those made with aurantia.
AUREOLINE (See " Primuline YeUow.")
AURIC CHLORIDE (See " Gold Chloride.")
AURIN (Pr. and Ger., Aurin)
Solubilities, insoluble in water, soluble in
alcohol. A mixture of aurin^ methyl-aurin, and
corallin aniline dyes occurring in yellowish
brown lumps with greenish fracture. It is
occasionally used for making coloured spirituous
backing.
AURORA YELLOW
A fine yellow pigment used both as a water
colour and as an oil colour. It is cadmium
sulphide CdS, prepared by passing sulphuretted
hydrogen SH through a solution of cadmium
chloride CdClj, the precipitate being Washed
with hot water and dried. A final treatment
Aurotype
46
Autochrome Process
with carbon disulphide CSa is desirable, as this
removes free sulphur.
AUROTYPE (Pr. and Ger., Aurotypie)
A printing process made known in 1844 by
Robert Hunt, in which gold chloride was
used in conjunction with potassium ferricyanide
and ferrocyanide. Hunt pubUshed other print-
ing processes in which salts of gold were em-
ployed.
AUROUS CHLORIDE (See " Gold Chloride.")
AUTOCHROM, OR AUTOCHROM PRINT-
ING
A combination of typographic and litho-
graphic printing used for cheap colour work,
such as coloured postcards. The keyplate is a
half-tone typographic block, and the colours are
filled in with tint plates printed lithographically.
AUTOCHROME PROCESS
A process of screen-plate colour photography
invented by MM. I<umi^e [Eng. Pat. 22,077, 1904 ;
25,718, 1904; 9100, 1906], based on the use of
starch grains, as far as possible of a uniform size,
dyed to the necessary colours, red, green and
blue violet, mixed and sifted on to glass coated
with a tacky surface. The grains are then rolled
and any white interspaces filled with a black
pigment. The screen-plate thus formed is
coated with a panchromatic emulsion. (See
"Screen-plate Processes.")
The plate is placed in the dark-slide so that
the glass side faces the lens, and a black, smooth
card shoidd be placed in contact with the sensi-
tive emulsion to prevent any damage to the
latter. A yellow screen must be used to cut
down the excessive action of the blue violet
and blue, and the makers provide special screens
for this purpose, though the following, sug-
gested by Von Hiibl, has proved satisfactory in
practice : —
A. Tartrazine . . I5^grs. i g.
Distilled water . 17J0Z. 500 ccs.
B. PhenosafEranine . 1-5 grs. o-i g.
Distilled water . 24^ oz. 900 ccs.
C. Gelatine . . 93 grs. 6g.
Distilled water . 3 oz. 85 ccs.
640 minims or 38 ccs. of C should be mixed
with 168 minims or 10 ccs. each of A and B.
Immediately before use, 6-2 grs. or 0-4 g. of
Eesculine dissolved in 338 minims or 20 ccs. of
water with 3 or 4 drops of ammonia should
be added to the dyed gelatine ; it is important
to make the sesculine solution only just before
use, as it rapidly discolours. Of this dyed gela-
tine, 140 minims or 7 ccs. should be coated on
every 16 sq. in. or every 100 qcm. The exposure
must be determined by meter, or the speed of
the plate may be taken as approximately
2 H. & D. or 3 Watkins, but, unfortunately,
the speed varies practically both in sunlight
and shade, and in winter and summer, this
variation being dependent on the spectral com-
position of the light.
After exposure the plate should be developed,
and the developer first recommended was pyro-
ammonia, but a later recommendation is the
following : —
Quinomet (metoquinone) 62 grs. 4 g.
Sodium sulphite (anhydrous) 278 ,, 18 ,,
I/iquor ammonise (-880) 4 mins. 0-2 ccs.
Potassium bromide . 15 j grs. i g.
Distilled water to . 35 oz. 1,000 ccs.
The duration of development should be 2^
minutes at a temperature of 60° P. (iS"S° C).
Many other developers may be used, such as a
normal metol-quinol developer or rodinal i in 12
for six minutes, amidol, rytol, etc.
As the emulsion is very sensitive to red, the
plates must be worked in total darkness or in a
deep green light such as is obtained through
the following filter, and even then the plate
should be exposed to this light as little as
possible : —
New Bordeau R 3 %
solution . . 2j oz. 125 ccs.
Tartrazine 4 % solu-
tion . . . 3 „ 150 „
Light green S S %
solution . ■ 3i „ i75 .,
Glycerine . . i „ 5° ,.
Gelatine 10 % solu-
tion to . . . 20 „ 1,000 „
2 oz. or 56 ccs. should be coated on every
100 sq. in. or 645 qcm. Or, in place of the
above, fixed-out dry plates may be dyed in
tartrazine and methyl violet to form a red
screen, which should be placed in contact with
one stained with malachite green, and if a brilliant
light is used a sheet of tissue paper, stained with
tartrazine or malachite green, should be placed
between them.
At the conclusion of development the plate
should be rinsed for fifteen to twenty seconds,
and then immersed in the following reversing
bath:—
Potassium permanganate 31 grs. 2 g.
Sulphuric acid . .170 mins. 10 ccs.
Distilled water to . 35 oz. 1,000 „
The plate should remain in this for two or three
minutes and then be examined by a weak white
light, and if all the metallic silver has disappeared
it should be washed for about a minute. It is
advisable to keep the above reversing solution
in two separate solutions and mi-y as required.
After dissolving out the primary image of
silver and washing, the plate should be exposed,
emulsion side up, to white light and then re-
developed, which may be done by the following
amidol developer : —
Sodiumsidphite(anhydrous)i35 grs. 15 g.
Amidol ... 45 „ 5 „
Distilled water to .20 oz. 1,000 ccs.
The original developer, metol-quinol, rodinal
etc., may also be used. When the second
development has completely reduced the silver
bromide, and the picture now shows up in colour,
the plate is washed for three or four minutes and,
without fixing, set to dry. If the plate is seen
to lack brilliancy (due to over exposure) it may be
intensified with the following, first immersing
for not more than ten seconds in 192 minims of
the permanganate solution given above, diluted
with 20 oz. of water : —
Autochromedlascope
A. Pyro .
Citric acid .
Distilled water to
B. Silver nitrate
Distilled water .
26 grs. 3 g.
26 „ 3 ,,
20 OZ. 1,000 CCS.
39 grs. 2-5 g.
3i OZ. 100 CCS.
For use mix 50 minims or 11 ccs. of E with
I fluid oz. or 100 ccs. of A, and immediately
apply to the plate and allow to act for three or
four minutes, then rinse for a minute or two and
clear in the following : —
Potassium permanganate 8J grs. i g.
Distilled water . 20 oz. 1,000 ccs.
for about one minute, and wash. The plate can
then be fixed in —
"Hypo"
3 oz.
ISO g.
Sodium bisulphite lye
I „
50 ccs.
Water to
20 „
1,000 „
for two minutes and washed and dried by a
gentle heat. When dry it shoiUd be varnished
with —
Gum. dammar . .31 grs.
Copal . . . 77 „
Carbon tetrachloride to 3J oz.
Gum dammar
Benzole
I oz.
5 „
20 g.
SO „
1,000 ccs.
20 g.
loo ccs.
When properly treated, and with correct selec-
tion of the subject, particularly if glaring con-
trasts of colours are avoided, very exquisite
results can be obtained.
Autochromes have been successfully repro-
duced by the three-colour and four-colour block
processes by illuminating the transparency with
reflected light and copying through colour
filters, the same as in copying from a painting
or other coloured original. The frontispiece to
this volume is an example of four- colour repro-
duction.
AUTOCHROMEDIASCOPE
A reservoir viewing instrument for auto-
chrome and other screen-plate pictures. The
transparency is viewed, not directly, but reflected
Autochromediascope
in a mirror as at a. The plates are held in
grooves b, and any given one may be brought
from the grooves (by means of levers C) to the
open position d, and so receive illumination from
47 Automatic Photography
the sky. A grotmd-glass screen is placed over
the opening at the top, in order to difiuse the
hght. The viewing box is mounted on a rotating
head, by which it can be tilted to any con-
venient angle.
AUTOCOPYIST
A simplified process of collotype, in which the
glass plates for bearing the printing image are
replaced by parchment paper, whidi is coated
with gelatine, immersed in bichromate solution,
dried, and exposed under a negative, after which
it is washed, stretched over a bed-plate, inked
up and printed from in the usual collotype way.
The printing is done by means of an ordinary
letter-copying press, or similar means.
AUTOGLVPHIC PROCESS
A method invented by Dimcan C. Dallas, by
which a drawing was made on a metal plate by
means of a heated pen and a wax composition.
The plate could be printed from without etching.
AUTOGRAPHY
A process of hthographic printing simplified
for the reproduction of writing in facsimile.
The writing is done on a hard, smooth-surfaced
writing-paper with transfer ink, and then trans-
ferred to stone or zinc in a press. In some pro-
cesses the paper was damped on the back with
water ; in others with acid, and in one process
blotting paper soaked in turpentine was applied
to the back of the sheet. The process has also
been applied to type-written sheets, and to
crayon drawings on grained paper.
AUTOGRAVURE
A photo-mechanical process modified from
the well-known photogravure process, the resist
image being formed by a special carbon tissue
manufactured by the company that works the
system.
Autogravure is also the name of a process
worked by a firm in Vienna for reproducing
paintings. Negatives are made for yellow, red,
blue, and grey printings. Positives are made
from the first three, and from these half-tone
negatives are made. These are printed on to
stone, zinc, or aluminium for lithographic print-
ing. Further printings are added if necessary
from the same negatives in other shades of ink.
Prom the fourth negative an embossing plate
is made to give reUef to the picture.
AUTOMATIC PHOTOGRAPHY (Fr., La
Photographie Automatique ; Ger., Auto-
maiische Photographie)
A term frequently appUed loosely, and refer-
ring strictly only to apparatus that carries out
the entire operation of making a finished photo-
graph. To this class belongs the automatic
machine exhibited by M. Enjalbert at the Paris
Bxhibition of 1889. Full directions to the sitter
were shown in turn at the proper times on the
face of the machine, which was started by drop-
ping a specified number of coins into a cash-box.
The duration of the exposure was indicated by
the ringing and cessation of a bell, and a finished
ferrotype portrait was delivered in about five
minutes. Apart from the Uability to get out of
order, the great drawback to apparatus of this
Automatic Photography
48
Automatic Printing
description is that it cannot make allowance for
the sitter's possible inattention to instructions,
or for variations in light or temperature. Partly-
automatic machines, with an attendant or
operator, have in consequence enjoyed greater
popularity. The illustration shows a typical
so-called automatic camera of the kind used by
itinerant photographers and at exhibitions
Automatic Ferrotype Camera
The box in the centre of the upper shelf is filled
with forty ferrotype plates in sheaths, which
may be inserted in daylight, a. heavy hd being
then placed on top to keep them flat. On
drawing out and returning the rod A, which is
attached to a plunger, the bottom plate is pushed
into a horizontal holder. By turning a miUed
head at the side, the plate is raised into position
for exposure at the back of the small fixed-focus
camera shown to the left. Having ascertained
that the sitter is correctly placed by inspecting
the image in the finder — the small concave lens
seen at the top — the exposure is made by press-
ing the bulb, this being connected to a rubber
tube passing to the shutter through B. Any
exposure may be given according to the length
of time the pressure is continued on the bulb.
By means of another small rod in the side the
exposed plate is allowed to drop into a wire
cradle, controlled by the knob c. The cradle
is raised or lowered by turning the knob, while
on the attached rod are marked distances to
indicate how far it must be drawn out to bring
the cradle over each trough in turn. Having
allowed the plate to remain in the developer a
stated time, tiie knob is turned to raise the cradle
and the rod is pulled out to the distance marked
for the fixing bath, in which the cradle is left
till the plate is fixed. The knob is then again
turned and the cradle transferred in a similar
manner to the third or washing tank ; after which
the panel in the front can be let down to examine
and remove the plate. With a little practice
the apparatus is very easily manipulated, a
finished positive being obtained in about one
minute.
Another branch of automatic photography —
or, rather, automatic exposure — is that in which
a photograph is obtained by the action, although
without the concurrence, of the subject, as
when securing pictures of wild beasts in the
jungle, or in taking a flashlight portrait of a
burglar. The latter undertaking is quite feasible,
and various arrangements have been patented
for the purpose, in which, for example, the unwel-
come visitor is supposed to make an electric
connection by stepping on a mat or opening a
window, thus rendering a platinum wire red-hot
and firing a charge of magnesium flash-powder,
while at the same time actuating the exposure
shutter of a camera. The one thing against the
idea is the fact that the modem burglar would
undoubtedly prevent the survival of the record
by smashing the camera to pieces. The auto-
matic photography of animals, birds, and reptiles
in their natural surroundings is, however, an
accomplished fact, and some admirable results
have been obtained. The exposure— -or, _ at
night, the simultaneous exposiu-e and ignition
of flash-powder — is usually arranged by causing
the animal or other subject to disturb an elec-
trically connected cord, or to make a contact
by treading on a prepared stone, branch, or twig.
AUTOMATIC PRINTING (Pr., Impression
automatique ; Ger., Automatisch Druck)
As early as i860, Fontayne, of Cincinnati,
employed an automatic printing apparatus, by
which 200 exposures per minute were possible
upon a band of sensitive paper, a large con-
densing lens being used to concentrate sunlight
on the negative. Of later date is a very ingenious
clockwork printing machine, patented in 1885
by J. Urie, of Glasgow ; its internal arrangement
Automatic Printing Machine
is shown in the illustration. The bromide paper
is used in a continuous band, which, having once
been adjusted under the negative, is moved on
by the length of one print after each exposure.
The hght is furnished by a gas burner, and is
automatically lowered when the paper travels ;
while a flat dish containing water is interposed
between the burner and the negative, to prevent
the overheating of the latter. The correct
exposure having first been ascertained, the
IN WESTMINSTER ABBEY BY HENRY W. BENNETT, F.R.P.S.
ARCHITECTURAL PHOTOGRAPHY (Interior)
Autotype
49
Azotic Acid
machine may be regulated to repeat it inde-
finitely as long as it virill run, and may be left to
itself. Large automatic printing machines,
power-driven and electrically illuminated, have
of recent years been adopted for the production
in quantities of bromide prints, pictorial post-
cards, etc. Automatic pnnting machines of a
special description are also employed in making
the positive film from the negative one for the
kinematograph.
AUTOTYPE (See "Carbon Process.")
AUTOTYPOGRAPHY (Pr., Autotypographie :
Ger., Autoiypiegraphie)
A term sometimes used for relief printing
blocks. It has been particularly applied to a
process for the making of prints from the leaves
of plants and flowers.
A process called by this name was invented
by George Wallis, in 1859 and i860, by which
drawings made upon gelatine could be trans-
ferred to metal plates, and afterwards used for
printing from in the same way as an ordinary
copper plate.
AUX DEUX CRAYONS
A style of stained print once popular in
America. The print is immersed in a solution of
alcohol 3 oz., powdered aloes J- oz., until stained,
or toned, a lemon colour, is then well washed,
and placed in 3 oz. of water to which have been
added 4 drops of liquor ammonise. It remains
there until of a warm orange colour, and is then
washed, dried, and mounted. The high lights
are touched up with Chinese white and the blacks
with Indian ink, and the whole is finally coated
with a solution of plain collodion ij oz., castor
oil 4 drops. The process is now obsolete, but
for a time was a craze in the United States,
where carefully made and artistic examples
commanded good prices.
AUXILIARY EXPOSURE
A method used in the early days of photo-
graphy in connection with slow plates to assist
exposure. Before or after the proper exposure
was made, extra exposures were given on coloured
papers or through coloured glasses, as it was
thought that by so doing more detail was
obtained. In process work even to-day a piece
of white paper is often placed for a few seconds in
front of a photograph while it is being copied ;
while in France it is the custom with some expert
operators with modem dry plates to expose for
a second or so upon a piece of white paper
before photographing dark interiors. It is
doubtful if such auxUiary exposures are of any
real use in these days of extra rapid plates, and
there is always the risk of fogging. Auxiliary ex
posures have also been advocated for papers,
particularly when harsh negatives are used,
for the purpose of getting flatter, actually fogged,
prints. When photographing gloomy interiors,
the daylight is utilised as far as possible, and
sometimes an auxiliary exposure with mag-
nesium is given for the shadows.
AUXOMETER (Pr., Auxomitre; Ger., Auxo-
meter)
An instrument for ascertaining the magnify-
ing power of a lens or optical system.
AXIAL ACCOMMODATION OF THE EYE
In binocular vision, the converging or diverg-
ing of the axes of the eyes as required so that
they meet where the object of attention is
situated. The axis here referred to is the imagin-
ary line drawn through the centre of the eye from
the pupillary centre to the retina. In ordinary
vision, the axes meet at the point where the
object of immediate attention happens to be
situated, and as the attention is turned from one
object to another, the two eyes move by mus-
cular control, simultaneously, so that whatever
may be the position and distance of objects
looked at, the axes converge or diverge as the
case may require, bringing tiie attention of both
eyes to a common point. When the object
looked at is remotely placed, the eyes look
almost parallel with each other ; but if tiie object
is only a few feet distant from the observer, a
conspicuous convergence of the axes is noticeable.
The constant change in the direction of the eyes'
axes is known as axial accommodation, and
without this double images would be seen and
confusion of perception result. The term is
sometimes applied to the adjustment of optical
centres in binocular instruments, such, for
instance, as the adjustment of twin lenses in a
stereoscopic camera, binocular microscope, and
so on. {See "Stereoscopic Photography.")
AZALINE (Pr. and Ger., Azalin)
A mixture of chinoline red and cyanine,
introduced as a red sensitiser by H. W. Vogel,
the use of which has been superseded by the
newer isocyanines.
AZOL (Pr. and Ger., Azol)
A trade name for a concentrated one-solution
developer whose action resembles that of rodinal.
Por plates and films 20 minims of azol are added
to I oz. of water. Por over-exposure 10 drops
more of azol per i oz. of water are added, but
for under-exposure the original quantity required
is only i s drops per i oz. For bromide papers the
proportion is 1 5 drops of azol per i oz. of water,
adding a few drops of a 10 per cent, solution of
potassiuni bromide if the whites are not pure.
Gaslight papers need 40 drops of azol per i oz.
of water and potassium bromide as required ;
while for lantern slides the developer should be :
Azol, 25 drops ; bromide (10 per cent.), 5 drops ;
water to i oz.
AZOTATE
A term derived from the French and meamng
nitrate.
AZOTE
A French term for nitrogen.
AZOTIC ACID
An Anglicised form of the French term for
nitric add.
BACK FOCUS
A term used to denote the distance between
the back surface of a lens and the sensitive plate.
It bears no fixed relation to the true focal length
of the lens, and the old opticians inserted it in
their catalogues only as a guide to the camera
extension necessary. Many of the early cameras
were sliding boxes, and would not close up
enough to accommodate all lenses.
BACKGROUND (Fr., Fond; Ger., Hinter-
grund)
A term commonly appUed to the painted
sheets or screens used in studio portraiture ; but
actually the scenery, or anything else, whether
these. It is a common fact that many portraits
are spoilt by ugly and unsuitable backgrotmds,
but it is possible to take out these and print-in
more suitable ones.
The printing-in of backgrounds is easier with
print-out papers than with development papers,
such as bromide and carbon, where the progress
of printing cannot be seen. The simplest method
is first to block out the background on the original
negative with an opaque mixture, going care-
fially round the outHne of the figure with a finely-
pointed camel-hair pencil charged with the pig-
ment, which may be red water-colour. The
broad expanse of background may be gone over
with the pigment on the film side of the negative ;
'^ntfft^«iT"^V'^t1
■imlamdiMHvil^tuttn,
A. Roller Background
hung on Brackets
C. Background Cords
passed through Staple
B. Background with RoUer
at Bottom
nattiral or artificial, behind the sitter or object.
Studio backgrounds are of many kinds, to suit
different purposes and tastes ; as, for example,
vignette, full-length, interior, exterior, plain,
graduated, and doud backgrounds. They are
usually painted in oil or distemper on canvas
or stout paper, and are either attached to rollers
or stretched tightly on a wooden frame having
supporting feet. Backgrounds on rollers may
be hung on brackets like blinds, as shown at A,
with or without a spring roller, a pulley and cord
being provided for raising and lowering. In
another system B the background is fastened
at the top to a horizontal lath, and is made to
roll up or down from the bottom by cords passing
through staples C, or over pulleys, on the same
principle as theatre curtains are made to work.
BACKGROUNDS, PRINTING-IN
The art of using two or more negatives to
form one print has been widely practised for
many years. It is sometimes referred to as
double printing and as combination printing,
but the former term is generally understood to
mean the printing-in of clouds (which see), and
the latter term (fully described imder a separate
heading) the art of combining in one picture
pieces taken from a number of others. The
printing-in of backgrounds differs from both of
50
or Brunswick black, or red or black paper, may
be used on the glass side. It matters not how
it is done so long as the background is covered
up. In the illustrations, A represents a sitter
against a brick wall which, being quite unsuit-
able, it is desired to take out. The blocked-out
negative is printed in the usual way, and will
give the result indicated at B — that is, the figure
will have no background whatever. The print
must not be toned or fixed yet. The selected
backgroimd must next be printed in. To do
this, carefidly paint over the entire figure in
print B, by gas or lamp-hght, with red water-
colour paint C, well covering the image and care-
fully following the outline. When quite dry place
the print in contact with a suitable background
negative and print in the usual way. The image
will be printed upon the hitherto blank paper
only, and the figure will be unaffected owing to
the protection given by the red pigment {see D).
Washing the print in water removes the paint
and gives the result shown at F ; this should be
toned and fixed. Other prints may, of course,
be made in the same way, but if a number is
required it will save time to copy F in the camera
and so obtain a new negative. If a good water-
colour is used, the portrait image will not be
injured in any way. If the work has been care-
fully done, no joins will be apparent. Any slight
Backings, Plate
SI
Backings, Plate
overlapping may be touched out on the finished
print.
Another method of printing-in backgrounds is
first to block out the background, as in the pre-
vious case, so as to obtain result B. Print two of
these. From one the figure is carefully cut out
with scissors and laid face downwards on the
background negative. (A print from it would
which cause halation. Plates may be obtained
ready backed, many of the commercial back-
ings being secret preparations and of excellent
quality. Backings are of many kinds, more or
less difiicult to prepare, apply to, and remove
from, the plate.
Liquid Backings. — Any red or black mixture
will serve for ordmary plates, the latter being the
^
^®
/im
A, Print with Undesirable
Background
B. Print with Background
Blocked Out
C. Figure Painted Over
with 'Water-colour
resemble E, but this is not the result required. )
The second print B is now laid on the prepared
background negative in such a way that the
printed figure is covered by the cut-out figure.
The background is then printed in to give the
result shown at P. A variation of the process is
to print in the reverse way — that is, to make
a print from the background negative (with the
cut-out figure attached), so as to obtain a print
like E, and to use this over the original negative
with the background blocked out, so as to print
in the figure B. Either method gives result P.
Both of the chief methods here described
more suitable for isochromatic or colour-sensitive
plates. Such homely mixtures as red and black
currant jam and shoe blacking have been
advocated at various times, but there is no need
to use such uncertain materials. Brunswick
black is good for the purpose, but somewhat
slow in drying. A quick-drying backing is a
thin solution of bitumen in benzene, and this
may be left upon the plate until after the nega-
tive is developed, fixed and dried, being then
removed by the aid of benzene. As a general
rule, backings should be removed before develop-
ing, because otherwise it is difficult to judge the
D. New Background
printed-in ; Figure
Painted Over
E. Print from Background
Negative, with Figure
Blocked Out
F. Final Result. The Old
Figure with the New
Background
demand great care, and the first has the dis-
advantage that some Uttle difficulty is experi-
enced in getting the two separate printings to
the same depth. By any of these methods, it is
difficult to avoid false hghting of the figure.
BACKINGS, PLATE
A backing is a coating upon the plain (glass)
side of a dry plate in order to prevent reflections
progress of development and the density of the
image. One of the commercial backings dis-
solves in the developer without affecting the
working. Perhaps the best of the home-made
backings is : —
Crystal caramel powder
Water .
Methylated spirit .
Backings, Plate
52
Backings, Plate
The ingredients need to be mixed well together.
Another formula is : —
Caramel . . . . . i oz.
Powdered burnt sienna . . i „
Office gum . . . . I „
For isochromatic plates lampblack should
be used instead of the sienna. J. S. Teape
recommends the following : —
Caramel . . . . . i^ oz.
Saturated solution of gum traga-
canth . . . . . I oz.
Powdered burnt sienna . . 2 „
Methylated spirit . . . 2 „
The spirit is added after the ingredients have
been well mixed. The above are liquid back-
ings, which are in optical contact with the glass.
Instead of caramel, it is possible to use various
dyes and pigments, such as sienna, lampblack,
etc. The following are typical formulae : —
I. Powdered burnt sienna. . J oz.
Powdered gum arabic .
• i „
Glycerine
Water ....
• s „
2. Essence of cloves
Turpentine .
Lampblack .
6 parts
7 „
. q.s.
to form a paste that may easily be distributed
on the back of the dry plate.
3. Methylated spirit .
Soap ....
Erythrosin .
Aurin .
e^ . _ i1- J _11 li i._
. ID OZ.
. 200 grs.
I drm.
• I ,.
J- i. ' .. It
Scrape the soap, and allow it to digest in the
spirit for a week, shaking at intervals ; filter, and
add the dyes. This gives a good yellow backing
solution, which dries at once.
Paper Backings. — Backing sheets or papers are
not so effective as liquid backings. Red or black
paper is cut to size, one side smeared with glycer-
ine, and pressed into close contact with the glass
side of the plate. Special hacking pads, which
A. Plates Clipped Together for Backing
are preferable to the above, may be made by
coating strong paper with the following mix-
ture : —
Gelatine . . . . . i oz.
Water . . . . . 2 ,,
Glycerine . . . . i „
Indian ink, sufficient to colour.
Dissolve by heating, and apply when warm
to pieces of stout paper or calico, which require
to be squeegeed on to the backs of the plates,
and may be used over and over again if smeared
occasionally with glycerine.
B. Plate-holder for Use in Backing
Comparisons. — ^The following table shows the
effectiveness of the various backings, the test
subject being severe : —
Halation.
Unbacked plate . . . Very bad.
Plate backed with —
Caramel and water . . Very slight.
Bitumen . ... Very slight.
Sienna and water . . Very slight.
Black paper and water . Bad.
Black paper and glycerine . Not so bad.
Shoe blacking . . . Slight.
Red and black currant jam Slight.
Canada balsam and lampblack Nil.
Caramel and sienna . . Nil.
Films and lantern-slide plates are sometimes
backed, but they do not show halation so badly
as dry plates, and therefore the simplest backing
will serve, if needed at all. (See also " Hala-
tion.")
Applying Backings. — ^The work of backing
plates must be done in the dark-room, and varies
somewhat with the nature of the material used.
It is not absolutely necessary to wait until the
backing is dry, although it is desirable to do so ;
but if a plate is used with the backing still wet
it should be covered with paper, preferably the
oiled kind in which sensitive paper is sometimes
wrapped. The backing must be applied evenly
C. Light-tight Drying Box
and not in streaks, and should cover every part
of the plain glass side of the plate. The simplest
method for small plates is carefully to put two
plates film to film, and to clip them together at
both ends as at A. The backing may then be
appUed by means of cotton wool or soft flannel
(brushing causes streaks), and the plates then
Bag
S3
Balances
hung up or laid aside to dry. In this way, and
with ordinary care, the backing mixture is kept
from the films.
For very messy backings the worker may
prefer to use a holder as at B. In the centre of
a piece of flat wood d, stout enough to prevent
warping, is glued a piece of black velvet or other
soft-surfaced material of the size of the dry
plate. A piece of millboard or of thin wood E,
of the same thickness as the dry plate and the
same size as D, to which it is hinged, has at its
centre a space P of the size of the plate, so that
when the flap E is placed over the base D the
velvet is seen through the hole. The plate is
placed film side downwards upon the velvet,
and E is brought into position over D, the back
of the plate coming through F. The backing is
spread over the plate, any superfluity going on
to the card. The flap is then lifted up, and
the plate removed.
When using slow-drying backings, a dark
box is convenient, and this can be made with a
strong cardboard box i in. deeper than the
longest side of the plates to be coated ; the
corners and joints should be covered inside with
black paper so as to make the box light-tight.
Place corrugated paper G or strips of cardboard
along the bottom, as in illustration C, to prevent
the plates from slipping. The first plate leans
against the end of the box and supports the
next one, a piece of red or black paper being
interposed. The Ud is made light-tight in the
following manner : Under the edge of the lid
H glue a strip j, and on j glue another strip k,
covering over tiie edge of the lid of the box by
an inch or more. When the lid is put on, the
box will be quite light-tight, because of the light
trap formed by j and K.
In process work, it is found that backing the
plate gives greater freedom from grain between
the lines or dots, and is quite worth the extra
trouble. A good backing for this purpose is
Lichtenstein's caramel with a little water and
lampblack added.
BAG
(See " Camera Bag,"
etc.)
'Changing Bag,"
BAIN-MARIE (Fr.)
A hot-water bath which in its simplest form
is that of a jar in a saucepan of water, the
gelatine, etc., to be dissolved or melted, being
Simple Type of Bain-marie or Water Bath
placed in the jar. The ordinary gluepot is an
example of a bain-marie. The French cook has
a utensil of the same style and name. A water
bath of this kind (see illustration) is used by
photo-lithographers for coaiing transfer paper.
BALAGNY'S DEVELOPER
An early form of pyro-ammonium carbonate
developer for dry plates. The formula is : —
A. Ammon. carbonate . ij oz. 64' s g.
Water . . ■ 35 ,, 1,000 ccs.
B. Pyrogallic acid . . i „ 28-4 „
Ammon. bromide 90 to iSo grs. 5'8 to 1 1 6 g.
Alcohol . . . 18 oz. 500 CCS.
For use, mix 6 oz. of A with i to 2 drms. of B.
Under-exposed plates are soaked first in A alone,
and then in the mixture of the two.
More recently, Balagny has advocated an acid
mixture of amidol. (See " Amidol.")
BALANCE IN COMPOSITION (See "Com-
position, Pictorial.")
BALANCES (Pr., Balances: Ger., Wagen)
Weighing instruments. A high degree of
A. Scales
sensitiveness is not required in the photographer's
balances ; neither need the instruments be
expensive. A pair of scales A, or a spring balance
with pan to weigh up to about 4 oz. or J lb.,
B. Pharmacist's Balance
and a smaller balance B, of the kind used by
pharmacists, will suffice for most photographic
purposes. Glass pans, preferably removable,
are best, as it is easier to keep them clean. A
good balance should possess stability and
Balloon Photography
54
Barometer, Photographic
sensibility — that is, it should not oscillate long
when the two pans are equalised, while a very
trifling addition on either side should at once
disturb the equilibrium.
BALLOON PHOTOGRAPHY (See "Aerial
Photography.")
BALSAM (See " Canada Balsam.")
BALSAMO'S PROCESS (Pr., Precede Bahama ;
Ger., Balsamo's Prozess)
A printing process discovered by Prof. J. G.
Balsamo, of Lucca, in 1861. Phosphorus is
digested for a considerable time in hydrochloric
acid at the ordinary temperature, or, to hasten
matters, at a temperature of about 120° to 140°
P. (about 49° to 60° C). The solution improves
by keeping. When saturated with phosphorus,
the acid is diluted with copper acetate until the
liquid assumes an olive green colom:. Paper is
immersed in this solution in a flat dish for three
or four minutes, taking care that it is thoroughly
impregnated, and is then thoroughly dried. The
paper, which is very hygroscopic, is now exposed
behind a negative, with a piece of blotting-paper
at the back to absorb any moisture that may be
disengaged, until the parts acted upon by the
light become of a greyish colour, due to the pro-
duction of copper binoxide. After removal
from the frame, the print is exposed for about
five minutes to the vapour of sulphuretted
hydrogen, which converts the copper binoxide
into copper sulphide. The print is next washed
to remove the superfluous copper salts, and is
then toned in a dilute solution of bismuth nitrate
acidified with a little nitric acid, by which means
bismuth is substituted for copper, thus rendering
the print permanent.
BARIUM BROMIDE (Fr., Bromure de
baryum; Ger., Bafyumhromid)
BaBrj 2H2O. Molecular weight, 333. Solu-
bilities i^ in I water, soluble in benzole. All
barium salts are poisonous, and the antidotes
are sodium or m.agnesium siilphates followed by
emetics and the use of the stomach pump.
Barium bromide is in the form of colourless
crystals, which are prepared by dissolving barium
carbonate in hydrobromic acid, evaporating and
crystallising the solution. It is occasionally
used in collodion.
BARIUM CHLORIDE (Pr., Chlorure de
baryum; Ger., Baryumchlorid)
BaClj 2H2O. Molecular weight, 244. Solu-
bilities, I in 2-5 water, insoluble in alcohol.
Poisonous (5se " Barium Bromide "). It takes
the form of colourless flat-sided crystals, which
are prepared from barium carbonate and hydro-
chloric acid. It is occasionally used in emulsion
making, but chiefly in the preparation of barium
sulphate.
BARIUM IODIDE (Pr., Jodure de baryum;
Ger., lodbaryum)
Balj 2HjjO. Molecular weight, 427. Solu-
bilities, I in 0-5 water, i in 20 alcohol. It is
poisonous ; for the antidote, see under heading
" Barium Bromide." It is in the form of
colourless crystals, obtained by decomposing
ferric iodide with barium hydroxide^ It is
readily decomposed on exposure to the air,
giving off free iodine. Occasionally it is used
in making collodion emulsion.
BARIUM MONOXIDE, OR BARYTA (Pr.,
Monoxyde de baryum; Ger., Baryum-
monoxyd)
BaO. Molecular weight, 153. A grey, porous
mass, fusing at a high temperature. It is pre-
pared by decomposing barium nitrate by heat,
and is (or was) used in Brin's process for the
manufacture of oxygen — the method employed
in extracting the oxygen for compression into
cylinders as used by lantemists.
BARIUM NITRATE (Pr., Azotate de baryum;
Ger., Baryumnitrat)
Ba(N03)a. Molecular weight, 261. Solubilities,
I in 12 water, insoluble in alcohol. It is poison-
ous ; for the antidotes, see under heading
" Barium Bromide." It is occasionally used as
an admixture in magnesium flashlight powder
and for making barium monoxide.
BARIUM PEROXIDE (Fr., Bioxyde de
baryum; Ger., Baryumperoxyd)
Synonyms, barium dioxide or superoxide.
BaOa. Molecular weight, 169. Solubilities, insolu-
ble in water, soluble in dilute acids with de-
Composition. A heavy, greyish-white powder,
obtained by heating barium nitrate. It has
been suggested for dissolving the silver image
so as to obtain reversal, its action being due to
the formation of nascent oxygen. It also occurs
in a hydrated form, Ba(0H)2 8HjO, having the
molecular weight, 315, and being slightly solu-
ble in water.
BARIUM SACCHARATE (Pr., Sucrate de
baryum ; Ger., Zucherbaryt)
Soluble in water. It is poisonous ; for the
antidotes, see under heading Bariimi Bromide."
It occurs in white crystals, but a solution was
suggested by Mathet as a substitute for the alka-
lis in developers. Excess of barium hydrate is
shaken for several days with a 10 per cent,
solution of sugar and then filtered ; but it has
found no practical use.
BARIUM SULPHATE (Pr., Sulfate de baryum ;
Ger., Schwefelsaures baryt, Schwerspat)
Synonyms, barytes, synthetic barytes, blanc
fixfe, permanent white, baryta white, mountain
snow. BaSOj. Molecular weight, 233. Solu-
bilities, insoluble in water and alcohol. It is a
heavy. White, impalpable powder, occurring
naturally or prepared by adding sulphuric acid
or a soluble sulphate to a soluble barium salt.
It is used to prepare baryta paper (which see),
the very commonly used paper for silver print-
ing processes.
BAROMETER, PHOTOGRAPHIC
Photographic prints that act as weather
indicators ; known also as weather-glass prints.
Certain coloured photographs will alter with
the varying atmospheric conditions, owing to
the fact that cobalt chloride (CoClj) has been
used in preparing them, this salt being blue
when anhydrous (perfectly dry) and pink when
Baryta
55
Baskett's Reducer
damp. Cobalt solutions may be used as sym-
pathetic inks, the writing being almost invisible
until wanned before a fire and all moisture
driven out, when it becomes blue. A finished
but unmounted bromide print is soaked for ten
minutes in a 5 per cent, solution of formaline,
and then is washed and dried. The cobalt
solution is made as foUows : —
Gelatine
i oz.
68 g.
Glycerine
1 „
250 ccs.
Cobalt chloride .
. 40 grs.
23 g.
Water
4 oz.
1,000 ccs.
The gelatine (ordinary cooldng gelatine will
serve) is soaked in the water imtil swollen, and
is then melted by gentle heat ; then the glycerine
is added and next the cobalt chloride. The
warm solution is brushed over the bromide print
that has been previously treated with the forma-
line. The print is drained, dried, and hung up
unframed or in an unglazed fram^e. The print
is of a pinkish colour in wet weather, blue in dry
and fine weather, and of a lilac or lavender colour
in changeable weather.
BARYTA (See " Barium Monoxide.")
BARYTA PAPER (Pr., Papier haryti ; Ger.
Barytpapier, Kreidepapier)
Good raw paper stock coated with an insoluble
emulsion of baryta in gelatine and used princi-
pally for coating paper intended to take a gela-
tino-chloride emiision. A good baryta paper
must be coated with three films, the first two
serving to prevent the emulsion from coming
into contact with the paper and the third giving
the particular surface and tint desired. Both
glazed and matt surfaces, tinted red, blue or
violet, or white, can be obtained. It is also
used in surfacing paper for collotype and Wood-
bury type.
Its preparation requires costly machinery.
The baryta is either precipitated by the paper
coater, or bought in the form of powder and
mixed in a kneading machine with one-third its
weight of water till a perfectly uniform cream is
obtained, which is carefully sifted, divided into
two equal parts, and thoroughly mixed with
gelatine solution. To one part of the baryta
emulsion is slowly added, with constant stirring,
a. solution of chrome alum, which causes the
emulsion to become ropy, and at the moment
of this appearance the other half of the baryta
emrdsion is added. The mixture is again passed
through sieves, some glycerine added, and then
coated on the paper. The first coating is
so adjusted that there is about 12 to 15 g. of
dry baryta to every square meter (17 to 21 grs.
per square foot). The emulsion is picked up
by the paper, which is coated in long rolls,
by passing through a trough, or it is wiped on
by a roUer, and it then passes over a rubber-
coated cylinder ; evenness of coating is obtained
by seven brushes with reciprocating motion, the
first being hard and the others gradually in-
creasing in softness until the seventh is of the
very finest and softest badger hair, about 2 in.
long. The paper is then hung in festoons to
dry, rolled up, and given the second coating in
precisely the same way. Sometimes it is then
calendered, but usually again coated by the
same machine with another baryta emulsion
containing glycerine and chrome alum, and
more or less gelatine, according to the surface
desired. To this emulsion is also added the
colouring matter — Paris blue, ammoniacal car-
mine solution, etc., being used. After drying,
the paper is passed through calendering machines,
which are provided with heavy steel rollers,
which may, or may not, be heated, and exert
a pressure of about 10,000 lb. The paper is
sprayed with water before passing through the
calender rolls, and the surfaces of the latter are
highly polished, roughened, or grained respec-
tively, so as to impart a. special surface to the
baryta film.
The commercial baryta paper is usually obtain-
able in rolls of about 600 metres in length, and
is graded according to surface — matt, glossy,
rough or grained — and according to the weight
in grammes per square meter.
BASEBOARD (Pr., Base : Ger., Bodenbrett)
The board serving as the foundation of any
apparatus, particularly of a camera. Except in
studio and process cameras, it is generally
hinged to the body, in order to fold up ; and it
is provided with a bush to take the screw attach-
ing the camera to the tripod stand, or with a
circular turntable, which can be fitted on the
legs of the latter. The stability of the baseboard
is a vital consideration for serious work, especi-
ally that of a scientific or technical nature, and
for such the studio pattern of camera is pre-
ferable, where it may be used.
BASKETT'S REDUCER
A mechanical abrading reducer for negatives
and lantern slides, introduced by Robert Baskett
in 1 90 1 ; known also as the Globe polish reducer.
The formula is : —
Terebene
Salad oil
Globe metal polish
2 oz.
• 2 „
One 2d. tin.
The terebene is sold at oil and colour shops as a
paint drier at about eightpence per pint ; the re-
fined spirit, costing about one shilling per ounce,
is not required. The ingredients are well mixed
together and strained once or twice through fine
muslin into a bottie. When required for use,
shake up the mixture, put a few drops on a piece
of cotton wool or chamois leather, and rub
gentiy and evenly over the parts of the negative
(whidi must be perfectiy dry) to be reduced.
Rub with a circiUar motion and not too hard,
as it is easy to rub a hole in the film. When the
surface reduction has proceeded far enough and
the surplus grease has been wiped off with a piece
of clean cotton wool, a final rubbing with a pad
shghtiy moistened with benzene will give a
polished and nearly waterproof surface that is
with difiSculty distinguished from the glass side
of the negative. Alcohol wiU also clean off the
superfluous reducer. The reducer is particularly
suitable for local reduction when only a part of
a negative and not the whole is to be reduced.
Some kinds of liquid metal polishes, which are
put up in convenient metal botties, can be used
as reducers exactiy as bought.
Alcohol used in the same way as this reducer
acts similarly, but takes very much longer.
Bas-reliefs
56
Bas-relief Prints
BAS-RELIEFS
Plaster or wax casts in low relief produced
from photographs ; formerly they were popular
for brooches, cameos, etc. Generally, the relief
obtained is very small. The process depends
primarily upon the hardening action of light
upon gelatine impregnated with potassium
bichromate. A negative should be specially
taken for the purpose of the first experiments, a
suitable subject being a modelled bust or a
sculptured bas-relief. Landscapes are prac-
tically impossible subjects ; while portraits
should not be attempted unless the sitter's face
and hair have been powdered to imitate a bust,
great care has been taken with the lighting, and
the photograph has been taken in the brightest
possible Ught against a perfectly black back-
ground. Any heads attempted should not
exceed 3 in. in height, as the relief obtained is
not sufficiently strong for larger sizes. Success
depends upon the contrasts in the negative, and
if not sufficient these should be increased by local
intensification or by working on the back of the
negative.
Having obtained a suitable negative, a sheet
of No. 4 gelatine is soaked in a solution of i drm.
of potassium bichromate in 6 oz. of water. The
swollen gelatine is next squeegeed on to a well-
waxed glass plate and dried slowly in the dark,
it being then stripped from the glass and its
polished side printed upon from the negative.
An alternative method of preparing the
bichromated gelatine is to soak 5 oz. of gelatine
(Nelson's No. i) and 2 oz. of powdered gimx
arable for four hours in a mixture of 6f oz. of
acetic acid and 18^ oz. of water ; at the end of
the four hours dissolve by gentle heat, strain
through clean linen, and coat some polished
glass plates with it, avoiding air-bubbles and
dust. Dry the plates in a well-ventilated dark-
room as rapidly as possible, maintaining the
temperature at from 50° to 75° F. (10° to 24° C).
Either gelatine sheet or plate is printed by
daylight in contact with the special black and
white negative. Exposure depends upon the
strength of Ught and density of the negative,
the average duration being thirty minutes. The
gelatine &ows a faint image, which is a slight
guide.
The gelatine sheet, after printing, is cemented
firmly, face upwards, to a piece of glass, by means
of liquid glue or similar adhesive, and the whole
is then soaked in cold water for several hours,
at the end of which time the parts acted upon
by light are found to have lost their power of
absorbing water, while the other parts swell
considerably. If the relief is not sufficiently
pronounced, it may be increased by soaking in
a solution of i oz. of citric acid in 4 oz. of water
and transferring to water. When swelled as
much as possible the superfluous water is drained
and removed with blotting-paper, some oil
poured on and drained off, and it is then ready
for casting from.
In the case of a glass plate instead of the
gelatine sheet, after printing it is soaked in a
solution of 2 oz. of powdered alum and 30 drops
of glacial acetic acid in 40 oz. of water. At the
end of two hours a fairly good relief should be
secured. If the relief is not enough the negative
may have been unsuitable, the exposure under
the negative not long enough, or the plate
dried too slowly after sensitising. The .super-
fluous moisture is blotted off and the relief oiled.
Whichever method has been employed, the
result so far is an oiled gelatine mould, from which
a cast is now to be made in plaster-of-paris or
wax. The mould is placed in an old printing
frame or a tray ; or, instead, wooden sides
are built up round it to form a receptacle for
the plaster. All surfaces which the plaster will
touch, except the relief itself, should now be
smeared with vaseline. Mix up some perfectly
fresh plaster-of-paris to about the consistency
of cream, immediately strain through mu,slin, and
without losing time pour on to the oiled relief to
a depth of + in. When the plaster has set it
may be separated from the relief and the latter
used again after soaking in water and oiling.
In addition to plaster, stearine, spermaceti,
and even heavy brown wax, make excellent
casts. Coloured waxes may be made according
to the following formulae (given by H. E. Black-
bum) : Red. — Wax 500 grs., India red 64 grs.,
carmine lake 90 grs. Sepia. — Wax 500 grs.,
sepia 50 grs., lampblack 10 grs. Green. — Wax
500 grs., cobalt blue 10 grs., Indian ink 50 grs.
Blue. — Wax 500 grs., Frankfort blue 100 grs.,
alizarin blue 15 grs., Indian ink 50 grs. Warm
black. — Wax 500 grs., lampblack 50 grs., burnt
umber 60 grs., indigo 32 grs. If desired a thin
layer of wax of one colour may be brushed on
the mould, allowed to set, and the mould then
filled up with wax of another colour. The
plaster gives more permanent results.
BAS-RELIEF PRINTS
Photographic prints embossed in low relief.
Platinotype prints are the best for this purpose,
but others may be used if hardened in a 10 per
cent, solution of formaline. A folding wooden
frame A is required large enough to take an
unmounted print. The opening in the frames
B. Bas-reUef
Print in Folding
Frame
A. Folding Frame used in
making Bas-reUef Prints
must be as large as the actual portrait, but smaller
than the complete print. Profile portraits give
the best results. On a piece of cardboard the
same size as the print, is traced the outline of
the head and bust; to do this, trace the head
on a piece of tracing paper and transfer to the
cardboard by means of carbon (manifolding)
paper. Cut out the space inside the outline.
Baths
57
Bedford, Francis
and the card will then form a mask, which should
exactly correspond with the outline of the
portrait. The print is now mounted on thick
blotting-paper with starch or other slow-drying
adhesive, and is placed under heavy pressure
for ten or fifteen minutes, after which time it
should feel damp and pUant. Some workers wet
the blotting-paper to ensure this. The cut-out
mask is next placed over the face of the print
in register, and the whole put into the frame
and clamped. The arrangement is shown by B,
the bust being seen through the hole in the card.
By means of a bone or ivory paper-knife, or
the handle of a tooth-brush, carefully apply pres-
sure from the blotting-paper side and raise or
emboss those parts desured, holding the frame
in the left hand and working with the right, the
face of the print being nearest the operator.
First of all work the tool all over the back of
the portrait with a circling motion, and then
apply more pres.sure to the nose, cheeks, dress,
etc., which need to be given in prominence. The
work must be done very gently, as the blotting-
paper is damp, and the tool may go through
the picture and spoil it. Leave in the frame
until dry and mount on stiff card by the edges
only. (For imitation bas-reUefs, see " Plastic
Photographs.")
BATHS (Fr., Bains ; Ger., Bdder)
A name given both to the trays, dishes, or
troughs holding photographic solutions, and to
the solutions themselves. Thus, the dish used
in fixing is known as the " fixing bath," a term
also applied to the " hypo " solution which it
contains. Baths may be either upright (as, for
example, the silver bath in the wet collodion
process), or horizontal (as, for example, the
dishes or trays for developing, toning, and fixing).
Dishes and trays are made in many different
materials, such as porcelain, stoneware, " grani-
tine," glass, enamelled iron and steel, papier
niache, vulcanite, celluloid, zinc, lead, etc.
Glass dishes and dishes coated with vitreous
enamel have the advantage that they are unaf-
fected by chemicals, readily cleaned, and show
distinctly any lack of cleanliness. But porcelain
dishes are commonly preferred for most purposes,
although they will not resist all chemicals. For
developing, ebonite or celluloid dishes are pro-
bably most convenient ; for toning and fixing,
porcelain or glass ; while enamelled iron or steel
is used for hot-bath platinotype. Lead or stone-
ware troughs and trays are employed to resist
acids.
BAUDRAN'S COLOUR PROJECTION
METHOD
A method of projecting ordinary uncoloured
photographic prints on to a surface whereon
they are said to appear more or less coloured.
It was invented by Baudran, of Versailles, in
1 89 1. It is well known that some daguerreo-
type pictures show a trace of natural colour when
viewed at a certain angle, and Baudran thought
that by properly lighting ordinary pictures on
silver paper he could obtain colours m the same
way. An opening is made in the shutter of a
dark-room, and on a shelf outside is placed a
photograph, preferably an enamelled print on
albumen paper, facing the opening and cutting
off much of the light that would otherwise be
admitted. A mirror is so placed as to reflect light
upon the photograph, the object being to light
the image in the same way as the original sub-
ject was lighted. In the opening in the shutter
is placed a camera which projects an enlarged
image on a screen inside Uie dark-room. The
image is said to be coloured. All colours do not
appear equally well, but that of the flesh is
said to be visible mostly always, although not
very bright.
BEACH'S DEVELOPER
A pyro-potash developer popular at one time,
particularly in the United States, where it was
originally introduced by F. C. Beach. It gives
a dear negative and a fine black image, which
was considered preferable to the yellowish,
slow-printing negatives produced by the pyro-
ammonia developer. The inventor appears to
have modified his developer a number of times,
but the chief ingredients were always pyrogaUic
acid, sodium sulphite, acid and potash. The
best way to make up the two stock solutions is
described below, the actual formula being : —
No. I (pyro solution) —
Water . . . 5 oz. 142 ccs.
Sodiiun sulphite . 4 „ 124 g.
Sulphurous add . 4 „ 124 ,,
PyrogaUic acid . i „ 28-4 ccs.
No. 2 (potash solution) —
Potassium carbonate 3 oz. 93 g.
Sodimn sulphite . 2 „ 62 ,,
Hot water to . 10 „ 284 ccs.
For the pyro solution the water is boiled and
the sodium sulphite dissolved therein. When cold
the sulphurous acid (dilute, as sold by chemists)
needs to be added, and finally the pyro. Beach's
original method of making the potash solution
was to dissolve the carbonate in 4^ oz. of hot
water, the sulphite in 4 oz. of hot water, and
to mix the two. The above are stock solutions,
which will keep good for a long time. To make
a working developer, take i oz. of water, add to
it I drm. (60 minims) of the potash (No. 2)
solution, and from 20 to 30 drops of the pyro
(No. i) solution. Add bromide in cases of
over-exposure.
BEAUMfe DEGREES (See " Hydrometer.")
BECQUEREL RAYS
Very shortly after the discovery of the
Rontgen rays, H. Becquerel discovered that the
metal uranium, its earths and compoimds,
emitted rays which penetrated wood, glass, and
even some metals, and exerted an action on a
dry plate similar to that of light. He proved
that the richer an earth or compound was in
uranium the stronger were the rays emitted,
and this led to an examination of pitchblende
by M. and Mme. Curie, who finally isolated
radium from the uranium pitchblende and
proved that to this were due the Becquerel rays.
BEDFORD, FRANCIS
Francis Bedford (6. 1816, d. 1894) was asso-
dated with photography since its first practical
inception, and had such skill as a landscape
worker that he was invited to form one of the
Beechey's Process
53
Bennett's Carbon Sensitiser
party selected to accompany the late King
Edward (then Prince of Wales) when he visited
the East in 1863. His son William (6. 1847,
d. 1893) was President of the Bath Convention,
1891.
BEECHEY'S DRY PLATE (EMULSION)
PROCESS
A method of preparing collodion dry plates,
published by the Rev. Canon Beechey in October,
1875, further details appearing in 1879. The
plates were coated with a collodion made accord-
ing to the following directions : First prepare
a solution of cadmium bromide 32 grs., alcohol
I oz. Decant after standing for some time, and
add hydrochloric acid 8 minims. Next take
above solution -J oz., absolute ether li oz.,
pyroxyline 12 grs. The plates having been
coated with this are next sensitised in an
alcoholic silver nitrate bath (40 grs. to the ounce),
the plates being previously given a substratum of
gelatine or indiarubber. They are then soaked
in a solution of 20 grs. of pyrogallic acid in 20 oz.
of flat bitter beer, which acts as a preservative.
Great latitude is allowable in the exposure, from
thirty seconds to five minutes being common.
The following developer was specially recom-
mended : —
Potassium bromide (12 grs. per
I oz. solution) . . .15 drops
Pyrogalhc acid (96 grs. solu-
tion) . . . . 30 „
Ammonium carbonate (60 grs.
solution) .... 3 drms.
The plates were an article of commerce for many
years, and were very popular for transparency
work.
BEER DRY PLATES
Dry collodion plates at one time used chiefly
for positive (lantern-slide) work. The plates
were sensitised in the usual way, washed, coated
with beer, and dried. Further information will be
foimd under the following headings : " Albumen
Process," "Beechey's Dry Plate (Emulsion)
Process," and "Coffee Process." The beer,
coffee, etc., acted as preservatives.
BEESWAX (Fr., Cire ; Ger., Bienenwachs)
A wax obtained from the honeycomb of the
bee. Melts at 62° to 65° F. It is insoluble in
water and alcohol, but, if pure, entirely soluble
in hot oil of turpentine. The wax when pure
is a yellowish mass of a pleasing smell, and
breaks with a granular stru,cture. It is used in
some processes of carbon printing. White wax
should be ordinary beeswax bleached by exposure
to sunHght and air.
In process work, beeswax forms an important
ingredient in the composition of etching inks.
A dusting-on powder, known as waxed asphal-
tum, for photo-Uthographic half-tone transfers,
consists of beeswax and asphaltum melted
together and powdered. Beeswax (preferably
the best Gambia) is largely used in electrotyping^
for making the moulds from blocks or type.
BELITSKI'S REDUCER
A one-solution reducer for negatives, known
also as the " green " reducer. The formula is : —
Potassium ferric oxalate
150 grs
Sodium sulphite
125 ,.
Water ....
7 oz.
Shake until dissolved, and add oxalic acid 40
to 45 grs. Shake again until the solution turns
green, pour off the solution from any undis-
solved crystals, and add hypo if oz. Instead
of the potassium ferric oxalate, which is at
times difficult to obtain, 100 grs. of ferric
chloride crystals and 190 grs. of potassium
oxalate may be used. The reducer is usable
over and over again, does not stain, and keeps
well in the dark.
BELLOWS (Fr., Souf.et : Ger., Ba!g)
The light-tight, collapsible, or expanding con-
nection between the back and front of the
camera, usually made of leather or American
cloth hned with black fabric. There are various
shapes, as, for example, square A, oblong,
conical (or, more correctly, pyramidal) C,
stereoscopic B, truncated-cornered D, and others.
The square bellows is generally preferred for
studio, process, and scientific apparatus. The
lighter and handsomer pyramidal bellows, now
A. Square, Parallel
Bellows
B. Stereoscopic
Bellows with Division
C. Conical or
Pyramidal Bellows
D. Bellows with
Truncated Comers
almost universally seen on field and hand cameras,
may sometimes cut off a part of the view when
using the rising front, unless care is taken. The
oblong bellows is practically out of date, except
for stereoscopic cameras, owing to the intro-
duction of the reversing back. The stereoscopic
bellows, which may be either oblong or pjrra-
midal, is provided with a central partition fold-
ing in unison with the bellows. A bellows with
truncated corners has the advantages that it
closes in smaller space, is more elastic, and the
folds are less hable to cling together.
BENNETT'S CARBON SENSITISER
A solution for sensitising the carbon tissue
supplied in an insensitive condition ; intro-
duced by H. W. Bennett. The formula is : —
Potassium bichromate . 4 drms. 22 g
Citric acid . . .1 drm. 5-5 „
Strong ammonia (about) 3 drms. i6'5 „
Water . . .25 oz. 1,000 ccs.
The proportion of water may be varied, any
quantity from lo oz. to 25 oz. being used ; the
smaller quantity of water makes the tissue more
Bennett's Reducer
59
Bennett's Toning Bath
rapid, bvvt it gives less contrast in the print, and
the full quantity is better for ordinary work.
The quantity of ammonia is only^pproximate ;
it must be determined by the 3nount neces-
sary to change the colour of the solution from
the deep orange of the bichromate to a distinct
lemon yellow. To sensitise, the piece of tissue
should be immersed in the solution for two
minutes, withdrawn, laid on a piece of glass or
ferrotype, squeegeed to remove as much of the
solution as possible, and then lifted from the
glass and pinned to a lath by two comers, or
suspended from a cord by clips, so as to hang
freely exposed to the air to dry. Drying should
be accomplished in from four to six hours.
Sensitising may be done in full daylight, but
drying must take place in the dark.
Tissue sensitised in this solution will render
gradation much more perfectly, especially in
the lighter tones. A little gasUght in the drying-
room will have no effect on the quality or solu-
bility of the tissue ; even a considerable amount
of gaslight will be practically negligible. Details
of working are given under tie heading " Carbon
Process."
BENNETT'S REDUCER
A well-known reducer, introduced by H. "W.
Bennett, made by adding sodium sulphite to a
solution of ammonium persulphate, and acidify-
ing by means of sulphuric acid. Reducing by
means of this reagent is rehable and uniform in
its results ; the operation is free from the risk
of staining and other irregularities which pre-
viously made the ammonium persulphate reducer
uncertain. The formula is : —
Ammonium persulphate i oz. ii8 g.
Sodium sulphite . .85 grs. 21 ,,
Sulphuric acid . . 45 mins. 10 ccs.
Water to make . . 9i oz. 1,000 „
(For working details, see " Reducing Negatives
by Chemical Means.")
BENNETT'S TONING BATH FOR
P.O. P.
A combined toning and fixing bath that gives
rich purple tones on most brands of P.O. P.,
introduced in 1908 by H. W. Bennett. It con-
tains a sufficiently large proportion of " hypo "
to ensure perfect fixation of the prints, and the
bath is rendered slightly alkaline with ammonia.
Prints toned and &ed in this bath are as per-
manent as any sUver prints ; they preserve their
original richness and freshness unimpaired for
many years. A feature of the bath is the fact
that separate solutions are kept of each ingre-
dient, and they are so adjusted that equal
quantities of each are taken, excepting the
hypo " solution, and i oz. of that is required
for each dram of the others. No calculation is
needed, whatever quantity of solution may be
required. Five solutions are necessary : —
A. Sodium hyposulphite . . i lb.
Water, sufficient to make . 32 oz.
The " hypo " should be dissolved in boiling
w^ater.
B. Ammonium sulphocyanide .
2 oz.
Water to make .
H ..
C. I/ead acetate
I ,.
Boiling water to make
Si „
A dense precipitate will settle. The bottle
must be well shaken each time any solution is
required.
D. Gold chloride . . .15 grs.
Water . . . 2 oz. 7 drms.
E. Strong ammonia . . 120 mins.
Water to . . . . 10 oz.
Each solution will keep indefinitely. To pre-
pare the bath, mix together in the order given :
1 oz. of A, I drm. of B, i drm. of C, 2 oz. water,
I drm. of D, and i drm. of E. The measure
must be thoroughly rinsed after measuring
C and D. The solution is ready for use in five
minutes. This quantity is sufficient for ten
quarter-plate prints ; a suitable quantity for
any other number may be prepared by allow-
ing i oz. of A for every five quarter- plate
prints, and remembering that whatever number
of ounces of A solution are taken, the same
number of drams of each of the others will
be required. The prints are immersed in the
bath without previous washing, and they should
be put in the solution one at a time, and each
one thoroughly wetted before the next is added.
All the prints that are to be toned in one dish
should, however, be put into the solution as
quickly as possible consistently with covering
each with the solution evenly.
As soon as the last print is placed in the dish
the first should be taken from the bottom,
brought to the top, and quickly examined.
Should any air-bells have formed on the surface
they will show as dark marks ; but if they are
broken at once with the finger they will not show
on the finished print. The second print that
was placed in the bath will now be the lowest ;
this should be brought to the top, and so on with
each print in turn, imtil all have been changed
in position. Throughout the operation the same
method of procedure must be followed — the
lowest print brought to the top ; but after the
first changing the work should proceed more
leisurely, leaving each print a longer time at the
top of the solution. The minimum time of
immersion in the bath is twelve minutes in hot
weather if the temperature of the solution is
70° F. (21° C.) or more, and fifteen minutes in
cool weather, though the toning should not be
done in a room at a lower temperature than
about 60° F. (i5'5° C). This minimum time is
very important ; if less time in the solution is
given, imperfect fixing will result. Longer time
may be allowed if cooler tones are desired ;
twenty minutes will not be too long. If warmer
tones are required, the composition of the bath
must be varied, so that the desired tones are
not reached before the prints are fixed. The
amount of water used for making the B and C
solutions may be increased to 11 oz., and for
the D solution 3|- oz., and the bath still pre-
pared by taking i drm. of each for i oz. of A.
As soon as the minimum time has elapsed, or
the desired tone reached if longer than the
minimum time, the prints are taken from the
bath and at once well washed. If washed in
water that is frequently changed, from one to
two hours should be allowed, according to the
frequency of the changes and the quantity of
prints in one dish. Prints for this toning bath
require to be very deep.
Bennetto's Colour Photography ^ Berkeley's Sulpho-Pjrrogallol
BENNETTO'S COLOUR PHOTO-
GRAPHY
A process of three-colour photography in
which the three negatives were obtained at one
exposure in a camera, the positives being
made on red, yellow, and blue carbon tissues
and superimposed. It has not been commer-
cially introduced.
BENZENE (Fr., Benzol, Benzine crystalUsable ;
Ger., Benzol, Steinkohlenbenzin)
Synonyms, benzol or benzole, coal tar naphtha,
phenyl hydride. CeH,. Molecular weight, 78.
Solubilities, insoluble in water, soluble in alcohol,
ether, chloroform, acetone, and glacial acetic
acid. The vapour is extremely inflammable.
It is a colourless, mobile, volatile liquid, which
can be obtained from benzoic acid, but is usually
procured by distillation from coal-tar. It is
used in varnishes and for developing in the
bitumen process.
This substance must not be confounded with
benzine or benzoline {which see). A crystal of
iodine dropped into benzene turns carmine-
coloured, whilst with benzine a violet colour is
obtained. A drop or two of absolute alcohol
will not mix with benzine, but mixes at once
with benzene.
In process work, benzole is used for dissolving
indiarubber to make the solution used in edging
wet collodion negatives, and for coating the
latter as a preliminary to applying collodion for
stripping. It is the best solvent for asphaltum.
BENZINE (Fr., Benzine, Ger., Benzin
Petroleumhenzin)
Synonyms, benzoline, petroleum ether, naph-
tha, petroleum naphtha ; practically identical
with petrol and gasolene. It is a colourless
liquid obtained from petroleum by distillation.
It is rarely used in photography, and must not
be confounded with benzene (which see).
BENZOATE TONER
One of the many toners recommended in
bygone days for plain salted paper. The follow-
ing is a typical formula, and gives black-violet
tones : —
Ammonium benzoate
Gold chloride
Water .
30 grs. 4-2 g.
6 „ -8 „
:6 oz. 1,000 CCS.
BENZOIC ACID (Fr., Acide benzoique; Ger.,
Benzoesdure)
Synonym, phenylformic acid. CjHs COOH.
Molecular weight, 122. Solubilities, i in 15
boiling water, i in i -8 alcohol ; soluble also in
ether, chloroform, glycerine, benzole, fixed and
volatile oils. Borax or sodium phosphate
increases the solubility in water. It occurs as
white or faintly yellowish pearly plates 01
needles with agreeable aromatic odour and
taste, and is obtained by sublimation from gum
benzoin, or from toluene by oxidation with nitric
acid, or from the urine of herbivorous animals
by distillation.
BENZOLE {See " Benzene.")
BENZOLINE {See " Benzine.")
BENZOQUINONE, OR QUINONE
CjHiOj. Molecular weight, 108. Slightly
soluble in water, more so in alcohol and ether.
It forms volatile yellow prisms, plates, or needles,
having a pungent smell. It is procured com-
mercially by acting on aniline with a bichromate
and sulphuric acid. It is used in the preparation
of the developer hydroquinone (benzoquinol, or
quinol, C,H4(0H)j), a substance which is ob-
tained by the reduction of quinone with sul-
phurous acid.
BERGHEIM LENS
This lens was constructed in 1896 by T. R.
Dallmeyer at the suggestion of J. S. Bergheim,
a painter, who wished for a lens which would
give him correct drawing and soft definition
without sacrificing the natural structure of the
original. To obtain this end the inventor intro-
duced a large amount of both spherical and chro-
matic aberration, so that to obtain the maximum
sharpness possible with this lens an allowance
has to be made after focusing. Although prim-
arily intended for portraiture, the Bergheim
lens is constructed on the telephoto principle,
the front element B being a single uncorrected
positive lens, while the back is an uncorrected
negative lens C of similar focal length — that is
to say, when the two lenses are brought into
contact they neutralise each other, various
focal lengths being obtained by separating them.
1
A
Bergheim Lens
The greater the separation the shorter is the
resulting focal length. The diaphragm A is fixed
in the hood of the lens, and is marked for aper-
tures requiring certain fixed relative exposures,
no matter what the temporary focal length
may be. The characteristic feature of the
definition given by this lens when skilfully used
is a pleasing semi-sharpness through a very deep
field, no actual sharpness or offensive fuzziness
being visible.
BERKELEY'S SULPHO-PYROGALLOL
The first of the developing substances to be
preserved in solution by means of an acidified
sulphite ; it was introduced by H. B. Berkeley
in 1882.
Berkeley's solution consists of 4 oz. of sodium
sulphite with sufficient citric acid (about i oz.)
to render the solution distinctly acid ; i oz.
of pyro is dissolved in 9 oz. 55 minims of the
solution, so that every 10 minims contain t gr.
of pyro. The sulphite must be thoroughly
dissolved in the water, and the solution acidified
before the pyro is added. The introduction of
sulphite as a preservative of pyro in solution
has been of great service to photographers. The
sulphite not only preserves the developing sub-
stance in solution, but prevents the rapid
oxidation of the developer in use, thus keeping
Bichromate
6l
Bicycle
the plate clean and free from stain. Without
sulphite the use of pyro with the alkaline car-
bonates would be impracticable, on account of
the very rapid discoloration of the developer
and the excessive staining of the plate.
The use of an acidified solution of sodium
sulphite as a preservative has been largely super-
seded in the case of pyro by the introduction of
potassium metabisulphite, a strongly acid sul-
phite, though the sodium sulphite is still added
to the developer to ensure clean working and
freedom from staining. It is also used as a pre-
servative for most of the more recently intro-
duced developing reagents.
BICHROMATE
The bichromates commonly referred to in photo-
graphic Uterature are " Potassium Bichromate"
and "Ammonium Bichromate" {which see).
BICHROMATE DISEASE
A skin disease that afFects some workers who
use potassium bichromate extensively. It occurs
only when the skin is particularly sensitive and
the hands are brought much into contact with
the bichromate (dry or dissolved), and it takes
the form of small ulcers or an irritating " rash."
A preventive is to wear rubber gloves or finger-
stalls. The hands should always be well washed
in warm water after using bichromate, and wiped
thoroughly dry. The use of a carbolic soap will
often give relief from the itching, the hands
being afterwards rubbed with a cooUng oint-
ment or the following mixture : Glycerine
4 drms., carbolic acid i drm., alcohol S oz. For
very severe cases the following treatment has
been advised : Rub into the skin a little nitrate
of mercury ointment (obtainable from most
chemists, and called by the Pharmacopoeia
" Unguentum hydrargyri nitratis"). (See also
"Skin, Efiects of Chemicals Upon.")
BICHROMATE LAMP
A lamp for dark-room use in which a solution
of potassium bichromate serves as the light
filter. Howard Parmer found that the various
kinds of ruby and orange fabrics and glass in
common use transmit only 2 per cent, or less
of the light, whereas a 6 per cent, solution of
potassium bichromate gives quite as much
safety and gives more than 80 times the
amount of illumination po.ssible with orange
glass. "With other solutions the differences are
still greater, but the potassium bichromate
solution appears to be the best for general use.
Most bichromate lamps are based on the pattern
designed by Farmer, whose original lamp is
shown at A. It consists of two concentric
glass cylinders, about 4 in. and S in. in diameter
respectively, placed one inside the other, mounted
on a suitable soUd base and furnished with a
wooden cap, in which is mounted an incandes-
cent electric bulb. This is excellent as a central
light. A glass tank, for use with oil or gas lamps,
is shown at B and C, such tanks being filled
with a suitable solution and used in place of the
usual red glass. As either type of lamp may be
filled with any light-filtering solution, an oppor-
tunity is afforded of adapting the actinic quaUty
of the light to particular requirements. A 6 per
cent, solution of potassiiim bichromate is safe
for bromide papers, but not for dry plates,
especially isochromatic plates, a safe solution
for which is made as follows : Dissolve i oz. of
the bichromate in about 9 oz. of water. Take
about 4 oz. of the solution, and add i drm. of
A. Bichromate
Lamp
U
B. Tank Light C. Section
Filter of Tank
Light FUter
eosine, which is a strong red dye, and gently
heat imtil the colour is a deep red ; mix the two
solutions and pour into the lamp cell. Should
the solution have a muddy appearance, pass it
through filter paper.
BICHROMATE REDUCER
An acid solution of potassium bichromate
may be used as a reducer for dense negatives
in the same way as the more popular acid solution
of potassium permanganate. A suitable formula
is :—
Potassium bichromate 200 grs. 20 g.
Sulphuric acid . . J oz. i'2 ccs.
Water to . . . 20 „ 1,000 „
Dissolve the bichromate in water, and add the
acid. The solution keeps well, but is liable to
be irregular in action.
BICHROMATED GELATINE
A term fully explained under the heading
" Carbon Process." It refers to gelatine that
has beciu sensitised with potassium bichromate.
BICONCAVE LENS
A lens, either simple or compound, of which both
outer surfaces are concave. (See also " Lens.")
Biconcave Lens
Biconvex Lens
BICONVEX LENS
A lens, either simple or compound, of which
both outer surfaces are convex. (See also " Lens." )
BICYCLE (See "Cycle.")
Bi-gum Process
63
Black Line Process
BI.GUM PROCESS
A familiar designation for the " Gum-bichro-
raate Process " {which see).
BINDERS
For lantern 'slides and transparencies, binders
consist of narrow strips of gummed paper by
means of ■which the plate bearing the image is
secured to the plain glass which is placed over
the film as a protection. They are made in two
forms, short lengths sufficiently long for one edge
of the lantern sUde only, so that four binding
strips are required for eacii slide, and long strips
sufficiently long to bind all the four edges with
one piece. The former are very much more
easily applied.
BINOCULAR
Photographically, this is another name for
" stereoscopic " (which see).
BINOCULAR MICROSCOPE (See "Micro
scope.")
BIOGRAPH
A kinematographic instrument invented by
Herman Casler, of Canastota, New York, U.S.A.
In the early stages of kinematograph science the
size of the film pictures was (as now) only i in.
by f in., and owing to optical and chemical
limitations early results were unsatisfactory.
Casler considered that improvements could be
made if the film pictures were taken on a larger
scale ; and he proceeded to devise the biograph,
in which he arranged to take pictures measuring
2f in. by 2-^ in. and to utilise the whole surface
of the film, dispensing with side perforations, by
the introduction of an arrangement of roUers,
instead of sprocket wheels. Hence he presented
his invention to the public in America during
the autumn of 1896. The biograph projected
pictures at the rate of thirty to forty per second,
and flickering was thus largely overcome.
Further, Casler, claimed that inasmuch as the
film was carried forward by friction rollers
instead of by sprocket teeth, there was greater
steadiness of the images upon the screen. Against
the advantages indicated must, however, be set
the increased cost of production and the incon-
venience of cumbersomeness in both the taking
apparatus and the projecting machines. The
biograph enjoyed a season of popularity in the
United States and also in I<ondonj but it
failed to become universal, whilst time has
shown that small-size pictures and simpler appar-
atus could be improved to meet all requirements.
BIOSCOPE
A well-known type of kinematograph projector.
The name is derived from two words signifying
respectively life and to see, and was in use long
before the introduction of the kinematograph, to
which it was first applied by Charles Urban, at
that time associated with the Warwick Company.
The courts did not sustain the use of the word
as a trade-mark.
BIRDS, PHOTOGRAPHY OF
Most of the methods used in the photography
of animals (see " Animals, Photography of,"
" Zoological Photography," etc.) apply also in
the case of birds. There are other points, how-
ever, to be taken into account. Many birds are
not only small in size, but are difficult to approach
because of their natural timidity and wildness,
this being especially the case with birds in a
free state. The telephoto lens becomes of in-
creased value, even high magnifications having
often to be employed. Even more than in the
case of animals, it is necessary to possess con-
siderable knowledge of the haunts and habits of
biids, and frequently there must be added an
unboimded store of patience and perseverance.
It is frequently necessary to use all sorts of
elaborate and ingenious appliances to bring the
camera into workable proximity to the bird
without alarming it and arousing its suspicions.
In fact, no work of much value can be done in
the direction of bird photography without making
a special study of it and acquiring the necessary
knowledge and apparatus to make good results
possible. Particular attention should be paid
to eiTective and characteristic pose, and natural
surroundings, and the use of orthochromatic
plates and suitable screens is often imperative
to secure a true rendering of the colour values
of the plumage.
BIS-TELAR
A telephoto lens of fixed magnification, intro-
duced by Busch. It has a iocaX length of about
if times the camera extension required, and the
two kinds obtainable work at//9 and f/y respec-
tively. It is well adapted for hand-camera work,
and is largely used by press photographers when
photographing distant objects.
BISULPHITE LYE (See " Sodium Bisulphite.")
BITUMEN (See " Asphaltum.")
BITUMEN OF JUDEA (See "Asphaltum.")
BLACK CLOTH (See " Focusing aoth.")
BLACK. DEAD
Recipes for dead blacks are given under the
heading " Blackening Apparatus."
BLACK LINE PROCESS
A name given to the original ferro-gallic, or
Colas process, described under the heading
" Ferro-gaUic Process."
Another process known as " black line " is
a printing process worked out in 1894 by R.
Nakahara, of Tokyo. The sensitising solution
Gum arable .
3 oz.
93
Water .
22 „
625
Tartaric acid
192 grs.
12.S
Common salt
864 „
60
Ferric sulphate
2 oz.
62
Ferric perchloride
3 „
93
The gum is dissolved by heat in the water, and
the other chemicals added to the warm solution.
The solution is spread over well-sized paper
with a sponge, and, after allowing it a little time
to penetrate, all superfluous moisture is removed
with the sponge well wrung out, and the paper
dried as rapidly as possible. The exposure to
dayhght under a negative or plan is rather long.
The colour of the prepared paper is yellow, but
Black Mirror
63
Blackening Apparatus
during printing all but the lines turn to white.
The print is developed in a plain aqueous solu-
tion of gallic acid, the strength of which is not
important ; the print must not be left too long
in the developer or stains will result. The
developed print is rapidly washed and dried.
Success depends chiefly upon the sponging off
of the superfluous sensitising solution and rapid
drjdng.
BLACK MIRROR
A mirror formed of black glass and used for
photographing clouds by reflection
BLACK OXIDE OF MANGANESE (See
" Manganese.")
BLACK. PROCESS
A black water-colour pigment largely used in
retouching photographic prints with the aero-
graph and otherwise for process reproduction.
It is claimed that it has no blue in its com-
position. It may be diluted with water for pure
greys, or mixed with Albanine for the lighter
shadows. It dries a dull black and reproduces
well.
BLACK SPOTS
Black specks on negatives and prints, but
m.ore particularly upon ordinary P.O. P. Those
upon the P.O. P. are caused (a) by metallic
particles in the first washing water, these coming
from a pump, tap, pipes, cistern, etc. ; or (6) by
trimming the untoned prints upon a metal plate.
The spots cannot be removed, bat they are
easily prevented by immersing tie prints before
toning in a 10 per cent, solution of common
salt, so as to convert all the soluble salts of silver
into chloride, then washing again before toning.
The addition of a little washing soda to the salt
solution has also been recommended, the actual
formula being 2 oz. of common salt and i oz.
of washing soda to i pint of water. The prints
are left in this for from five to ten minutes, then
washed in running water for five minutes, and
toned as usual. The above method serves to
prevent spots, but when platinum is used as a
toner instead of gold, the washing soda should
not be used, only the plain salt and water.
Black specks upon negatives and developed
prints (bromide and gaslight papers) are caused
by imdissolved particles of the developer proper,
hydroquinone, amidol, etc., settling upon the
film. These particles may be present undis-
solved in a freshly made developer, or may be
flying about the room and settling upon the
sensitive surface in the form of dust.
BLACK TONES
Black tones are obtainable upon carbon and
other pigment papers, which already have a base
of black pigment, platinotype, bromide, and gas-
Ught papers with ease, and on print-out papers
with difficulty. The richness and quality of the
blacks on platinotype are characteristic of the
process and depend upon the state of the paper,
exposure, etc. The quality of the blacks upon
bromide and gasUght papers depends upon the
exactness of exposure and upon the state of the
developer, because if too much potassiimi
bromide is used in the latter the blacks are
greenish in tone, and if too little is used neither
the blacks nor the whites are of the best.
All tones upon P.O. P. largely depend upon the
quality of the negative ; and for black tones the
negative should preferably be rather hard — that
is, should have dense high lights and clear
shadows. Such a negative should be printed
under green glass and toned in any gold or
platinum bath, or in the following combined
toning and fixing bath : — A. "Hypo" 4 oz. ;
water 10 oz. B. Lead nitrate i oz. ; distilled
water 10 oz. ; glacial acetic acid 48 drops. Add
B to A gradually, and with shaking, until a
distinct cloudiness appears ; then filter. Take
10 oz. of the above mixture and add i grain of
gold chloride, and this forms the toning bath.
If black tones do not result, the negative was
not suitable, or the printing has not been suit-
ably carried out. Some workers obtain a rich
black tone on P.O. P. by using gold first and
platinum afterwards, but, as in all cases, much
depends upon the smtability of the negative.
BLACK VARNISH (See " Varnish.")
BLACK VIGNETTES
A style of portrait known also as " Magic,"
" Egyptian," and " Russian " vignettes, invented
in 1868 by a Russian photographer named
Bergamaso. The sitter's head is made to stand
out against a perfectly black background, the
edges of the picture all round being black
instead of white as in an ordinary vignetted
A. Black Vignetting
■with Serrated Card
in front of Lens
B. Black Vignetting
with Card inside the
Camera
portrait. The sitter is placed against a per-
fectly black background, and the light is pre-
vented from acting on the edges of the plate,
more particularly on the lower part (upper part
as it is seen on the focusing screen). The light is
cut off from the plate either by means of a ser-
rated piece of blackened card or tinplate on an
adjustable rod outside the camera, and before
the lens, as A, or by the insertion of a black card
with an opening in the centre, in the bellows
of the camera, as B. Either system, when
properly used, cuts off the light at the top or
bottom and gives a negative with plain glass
borders which print black, the well-lighted head
appearing in the centre.
BLACKENING APPARATUS
Only a dead black is suitable for the interior
of a camera, as a glossy black would give rise
to reflections.
Blackings should be tested upon pieces of
metal, wood, leather, etc., before applying to
the apparatus. Recipes are as follow :
Blacklead
64
Blisters
Brassworh. — To blacken camera brasswork,
clean with fine emery, rinse, and immerse in a
saturated solution of copper nitrate for about
two minutes. Then take out, heat over a
Eunsen burner or ordinary spirit flame, and
repeat the process several times. To make the
copper nitrate, dissolve i oz. of copper filings in
2 oz. of nitric acid ; do this in the open air, and
stir with a glass rod to assist dissolving.
Zincwork. — Clean and rinse as before, and
immerse in a solution of copper chloride 45 grs.,
zinc nitrate 30 grs., and water 4 oz., to which is
added -J oz. of hydrochloric acid. Finally, rinse
and dry.
Tin. — Use carbon black mixed with the least
possible amount of French polish. Excess of
polish makes it glossy. A dye can be used instead
of a pigment ; for example, boil together i oz.
of water, 1 5 grs. of borax, 30 grs. of shellac, and
15 minims of glycerine. Maintain the boiling
till dissolved, and then add 60 grs. of nigrosin.
Bellows Interiors. — Use a solution of shellac
in methylated spirit coloured with lampblack.
Camera Interior (Woodwork). — Dissolve \ oz.
of shellac and J oz. of borax in 10 oz. of hot
water, and add about ^ drm. of glycerine and
sufficient aniline black (soluble in water) to form
a good solid black. Two coats should produce
a rich velvety dead black. Another recipe is :
Aniline black 50 grs., gum shellac 100 grs.,
methylated spirit 2J oz. Negative varnish
mixed with powdered lampblack may also be
used.
Lampblack mixed with gold size and turpentine
makes a good dead black for general use.
BLACKLEAD (Fr., Plombagine; Ger., Graphit)
Synonyms, graphite, plumbago. Used for
lubricating apparatus and in retouching.
In process work, finely powdered blacklead
is sometimes rubbed on to wet plate half-tone
negatives in order to intensify the dots in certain
parts where additional density is required. It
is also used in the " Powder Process " or
" Dusting-on Process " for the duplication of
negatives. As an inert powder it forms an acid
resist, and is dusted-ou to an ink image for that
purpose. In electrotyping it is used to give the
wax mould an electro-conductive surface.
BLAKE-SMITH PROCESS
The modern method of toning bromide prints
by first bleaching the image or converting it
into such a form that treating with a sulphide
solution will convert it into sulphide of silver ;
largely due to the experimental work of R. E.
Blake-Smith. Various methods of bleaching
the image have been used, but the most simple
as well as the most satisfactory is to convert
the image into a bromide or chloride by means
of a solution containing potassium ferri cyanide
and either potassium chloride or potassium
bromide. (For details of this method, see "Ton-
ing Bromide Prints," etc.)
BLANC D'ARGENT
A pure white pigment water-colour of French
manufacture, largely used by process retouchers,
and preferred for aerograph work. Drawings or
retouching done with it should be reproduced
without delay, as it discolours.
BLANC FIXfe {See "Barium Sulphate.")
BLANCHARD. VALENTINE
Bom at Wisbech, 1831 ; died at Heme Common,
November 14, 1901. A famous portrait photo-
grapher in the 'sixties and the inventor of appar-
atus and processes. He was the first to recommend
making large transparencies from small negatives,
and the art of printing-iu clouds from separate
negatives, the latter being published on Septem-
ber 4, 1863. He was always opposed to micro-
scopic sharpness in definition, and the slight
diflfusion which he gained by the use of a single
lens caused much attention to be paid his work.
He was an advocate of long exposures and large
plates, giving about forty-five seconds' exposure
and using 15-in. by 12-in. plates for his por-
traits. His method of obtaining carbon prints
without transfer consists in immersing the
tissue for a minute in petroleum, the paper sup-
port being thus rendered translucent. The
tissue, after the removal of the surplus oil, was
placed in a printing frame with the support next
the negative, printed in the usual manner, and
developed from the front. He also invented a
brush, known as the Blanch ard brush {see
" Brushes "), which is widely used for sensitising.
BLEACHING NEGATIVES (See "Intensi-
fication.")
BLEACHING POWDER (See "Calcium
Hypochlorite.")
BLEACHING PRINTS (See "Drawings
Made iiom. Photographs.")
BLIND SHUTTER (See "Shutters.")
BLINDS, STUDIO (Sea " Studio.")
BLISTERS
Blisters appear at times upon all makes of
plates, films, and papers in the manufacture of
which albumen or gelatine is employed, but
the papers most subject to the trouble are
albumen and bromide. The principal cause of
blisters is the use of a too strong " hypo" bath,
rapid washing, excess of alkali in the developer,
and the difference in temperature between the
developing, toning, or fixing solutions and the
washing water. 'The blisters usually appear
when the plates or papers are being washed after,
fixing. It is a curious fact that fewer blisters
appear where ordinary tap water is used than
where soft water is employed. It is, however,
the fixing bath that ususUly needs attention when
bromide and gaslight papers are prone to blister.
The fixing bath, as freshly made with cold water
and " hypo," should not be used immediately, the
temperature of such a solution dropping almo.st
to freezing point, and of course many degrees
lower than the temperature of the washing water
used before and after ; hence the expansion o£
the wet gelatine, which is very susceptible to
temperature, in the form of blisters. If a fixing
bath is needed quickly it should be made with
hot water and used when the temperature has
fallen to the level of the washing water ; or,
if cold water is used, the bath should be mixed
some considerable time before use in order that
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Blisters
65
Blocking Out
it may have time to rise in temperature. When
care is not taken about the temperature of the
bath, blisters may be prevented by allowing the
■washing water to run gradually into the fixing
bath while the fixed prints remain therein. The
water gradually replaces the "hypo," the differ-
ence in temperature (if any) is gradually made up,
and the expansion of the gelatine is too slow to
do any harm ; this method, too, largely prevents
blisters due to the use of a strong fixing
bath.
The use of an add fixing bath is widely advo-
cated for the prevention of blisters on bromide
papers and negatives. Any formula will serve,
but that containing " hypo " and metabisnlphite
will be found best. Another plan is to soak
the prints previous to, or immediately after,
fixing in a 20 per cent, solution of formaline
and then to wash well. There is really no satis-
factory cure for blisters when once they have
appeared ; pricking the paper at the back with
a pin for the purpose of allowing the air to
escape from the bubble has been advised, but
the loosened film never becomes properly
attached to the paper, and frequently peels off
when dry. Another plan is to squeegee the
blistered print upon deaned ground glass and
strip when dry, but, as in the previous remedy,
the blisters invariably scale off later.
Information given above on preventing blisters
applies equally well to negatives and bromide and
gaslight papers. BUsters but rarely appear on
negatives, but when they do the negatives
should be soaked in methylated spirit and
dried ; a more genertil trouble with plates is
" frilling " {which see).
Alhurnen paper, as a rule, blisters very badly
if carelessly manipulated, the cause being the
unequal temperatures of the solutions employed.
Rives paper, which is now almost universal,
is thought to bhster more than the Saxe paper,
which is tougher, but not now so widely used.
Preventive measures are (a) to use solutions
of as even temperatures as possible ; (6) to soak
the prints in hot water or methylated spirit,
afterwards washing well, previous to toning ;
(c) to remove the prints from the ordinary alka-
line fixing bath (add baths must not be used
for albumen paper) to water to which has been
added one-tenth its weight of common salt,
allowing them to remain for ten minutes and
finally washing well.
Carbon prints show minute blisters when the
water used is too hot. Blisters may be also due
to free air in the water, greater trouble in this
direction being experienced when water comes
direct from the main than when it comes through
a dstem. It is advisable to boil suffident water
for the bath in which the tissue is to be soaked
before squeegeeing to the temporary or final
support. Fifteen minutes' boiling should be
suffident to expel all the air, and it is then cooled
in a jug in order that only a small surface may
be exposed to the air, of which water can absorb
a large quantity.
Gelatine (P.O.P.) prints rarely blister, but when
they do the cause is a too strong " hypo " fixing
bath, or the unequal temperatures of solutions
and water. An add fixing bath must not be
used for P.O.P. ; if hardening is thought
necessary, formaline should be used.
6
BLITZ-PULVER
The German name for flashlight powder. It
is occasionally used in English and American
literature. In the United States, a powder having
this name contains the mixed nitrates of barium
and strontium 5 oz., metallic magnesium 2 oz.,
and amorphous phosphorus 120 to 180 grs.
BLOCK (Pr., Clicks, Planche; Ger., Block, Auto-
typie-druckform, Autotypiehlischee, Galvano)
A block of wood or metal, or metal plate
backed by either wood or metal, and having a
typographic printing surface. It may be a pro-
cess block (produced photographically), a wood-
cut, in the production of which photography
may or may not play a part, an electrotype, or
stereotype. " Block Processes " include all
those processes in which, by the aid of photo-
graphy, a relief surface is produced, capable of
being printed from in an ordinary printing press
together with letterpress.
BLOCKING OUT. OR STOPPING OUT
A method of painting out undesirable details
upon a negative, the painted portions appearing
white upon the finished print ; parts of lantern
slides may also be blocked out, in which case
the blocking out appears black upon the screen.
Blocking out is extensively used on photographs
of machinery, furniture, etc., for reproduction in
catalogues, etc. It is generally desired that the
artide photographed should stand by itself upon
a white ground, in which case opaque pigment is
used as the medium for stopping out the rest of
the picture; but when a perfectly black back-
ground is required the best thing to do is to
make a transparency and block this out, and
from this to make a second negative, on which
the blocked-out portions will be dear glass,
which will, of course, print black. Whichever
method is adopted, the actual work of blocking
out is predsely the same. In order to do the
work properly, the following materials are
necessary: a retouching desk, one or two sable
or crow- quiU brushes with fiaie points, a mapping
pen, Indian ink, ruler, a bottle of black varnish,
and red water-colour or other opaque medium.
The negative is placed film side uppermost on
the retouching desk and the film worked on with
the opaque. A rough print to serve as a guide
should be taken from the negative before the
work of blocking out is begun. It is advisable
also to begin from the centre of the negative
and work outwards. A retoucher with a steady
hand may be able to do all the necessary work
with a brush, but many will need the rule, pen
and ink. The pen, if used, is charged with
Indian ink and held perfectly vertical to the sur-
face of the plate ; it should have a smooth and
well-rounded point, as otherwise it is apt to cut
the fflm. Any errors made with the pen and
ink may be removed by washing away the hne
by means of a camel-hair brush charged with
water ; but when this is done care must be taken
to wait until the gelatine film is perfectly dry
before going over it again with a pen, otherwise
the film wiU be torn. Having ruled all the
necessary lines, the rest of the blocking out may
be done with the black varnish diluted with
turpentine, or with any other opaque pigment.
Those pigments used with water are perhaps
Blood Albumen
66
Blue-Print Process
the easiest to use because, should any error be
made in the work, they may easily be washed
ofi, or wiped off with a damp sponge, whereas
black varnish is difficult to remove even with tur-
pentine ; the varnish, however, is the more durable,
and will stand any amount of wear and tear.
AU the fine work, if desired, may be done on
the film side with a pen and Indian ink, or with
a brush charged with opaque or red water-colour,
and the bulk of the stopping out on the glass
side with black varnish or Brunswick black,
taking care that the working on one side over-
laps the other.
Another method is to take a rough print from
the unblocked negative, cut out the part required,
and use the cut print as a mask, which may be
pasted on the glass side of the negative. This
serves as opaque, and but Uttle fine work may
be required on the film side, care, however, being
taken to let the working on the film side overlap
the paper mask. The latter may, if desired, be
wetted and placed on the film side, but it is
removed more easily from the glass side of the
negative. (See also " Camphor.")
Any of the above methods may also be
employed for transparency work, but in the case
of lantern slides it will be necessary to use a
stopping-out mixture which wiU not crack when
subjected to the heat of the lantern illuminant
concentrated by the condenser.
The present-day commercial practice is for
the photographer to make as good a photograph
of the subject as he can, supply a good print,
and leave the blocking out to the process
worker's artist, the work being done on the
print and not on the negative. The photo-
grapher can often assist matters by seeing that
the background is of such a nature that the work
of blocking out is faciUtated, as the merging of
the picture of a machine, for instance, into the
background makes it difficult to see where one
ends and the other begins. Frequently it is
sufficient to run a line of white pigment between
the subject and the background, and the process
worker then understands that the latter is not
to be included. The aerograph is largely used
for blocking out on prints, etc.
BLOOD ALBUMEN (See " Albumen.")
BLOTTING-PAPER
Used for blotting off water from negatives,
and for drying those papers not having a gelatine
or sticky surface. Inked and coloured blotting-
paper is not suitable. The paper should be as
fluffless as possible ; special blotting-papers for
photographic purposes are obtainable. Ordinary
blotting-paper may be freed from all impurities
likely to damage prints by pouring boiling water
and a hot weak solution of sodium carbonate over
it alternatively two or three times, ending with
the boiling water. This treatment removes the
acids and sulphites, which might otherwise affect
the permanency of the silver prints.
BLOW-THROUGH JET (See " I^imelight.")
BLUE GLASS. PHOTOGRAPHIC USES OF
Blue glass of good quality has several uses
in photography. By looking through a piece of
it at the view to be taken, or by fixing a sheet
of it over the focusing screen, the photographer
is enabled to see the subject with its colour con-
trasts toned down, and will be the better able to
judge what the effect will be in a photographic
monochrome print. Some years ago blue glass
was advocated for glazing studios, but exposures
under blue glass need to be longer than under
white glass, and the only gain to the photo-
grapher is that he is working in a light that is
less trying to his eyes. Blue glass is of service
if placed over a har.sh negative when printing
on P.O. P., it having the effect of giving a softer
print, inasmuch as certain organic salts are not
acted upon as they would be were the blue glass
absent. Blue glass is also of service when copy-
ing a faded or yellowish photograph ; a piece of
pale blue glass is held before the lens during the
exposure, and the resultant negative gives
increased contrasts, and in general is of better
all-round quality.
BLUE TONES
These are obtained most easily on blue-print
(ferro-prussiate) paper or by using blue carbon
tissue, in both cases a blue print being produced.
Good blues are difficult to obtain on P.O. P., a
blue-black (which see) being the nearest. Bromide
prints may be partially or wholly changed to a
Prussian blue. Ferric ferricyanide is usually
employed, it being made as required by mixing
together solutions of potassium ferricyanide and
ferric ammoniuna citrate, adding a little nitric
acid. The formula for the toner is : —
Potassium ferricyanide 4; grs. 10 g.
Nitric acid (pure) . . 24 mins. S ccs.
Ferric ammonium citrate 22 grs. 5 g.
Water . . . . 10 oz. 1,000 ccs.
If this works too quickly, add more water. Place
the prints, after developing, fixing, and washing,
in the above, until of the desired colour, and
wash in running water for twenty minutes, or
until the whites are clear.
BLUE VITRIOL (See " Copper Sulphate.")
BLUE-BLACK TONES
In silver printing these can be obtained only
by using a toning bath rich in gold, say i gr. to
5 oz. or 6 oz., and also a. liberal allowance for
the prints being toned, -^ grs. or more to each
full-size sheet of paper, or fifteen half-plate
prints. In addition, a rich print from a strong
negative is absolutely essential, the tone of the
shadows being very largely determined by their
depth. Some toning baths will give blue-black
tones much more readily than others ; with
some, these tones cannot be obtained. In
separate toning and fixing the sulphocyanide
bath, if strong, will give blue-black tones readily.
In combined toning and fixing Bennett's toning,
bath will give a similar result by increasing the
quantities of the B, C, and D solutions. One and
a half drams of each should be used to each
ounce of the A solution, in place of i drm., as
given under the heading " Bennett's Toning
Bath for P.O.P."
BLUE-PRINT PROCESS
Known also as " Cyanotype " (negative) and
" Ferro-prussiate " process, and largely used by
Blue-Print Process
67
Blue-Print Process
engineers, architects, etc., for leproducing
technical drawings. It is one of the oldest
photographic printing processes, having been
invented by Sir John Herschel in 1840. Paper
is coated with a mixture of ammonio-citiate of
iron and potassium ferricyanide dissolved in
water, then dried in the dark, and printed by
daylight in contact with a negative or drawing
on tracing paper, when an image in insoluble
Prussian blue (TumbiUl's blue) is produced. The
print is washed to remove the soluble coating
unacted upon by Ught, leaving a finished print,
blue on a white ground.
Another blue-print process is the positive
cyanotype, or Pellet's process [which see, imder
the latter heading), which gives blue lines on a
white ground, the opposite process to the above,
it being one in which blue is formed where the
light does not act. The negative cyanotype or
blue-print process proper is the one particularly
suitable for negatives, and is that to which
attention is here directed.
Blue-print paper, ready sensitised for imme-
diate use, may be purchased, but as it does not
keep well, and is so easy to prepare, it is better
to make it as required. A large number of
sensitising formulae have been pubhshed from
time to time, considerable latitude being per-
missible in the quantities of chemicals used as
well as in the methods of working. They all,
however, resemble one another, and yield prints
which are all very much alike. Almost any kind
of paper can be cpated with the sensitive mix-
ture ; fairly stout cream-laid notepaper, or a
real photographic paper such as Rives, is as
good as any ; it should be free from wood-pulp
or other impurities usually found in cheap white
papers, its surface should be fairly hard and not
too absorbent, and it should be tough enough to
withstand thorough washing. Common rough
papers are better if sized before sensitising,
because the size prevents the image from sinking
into the paper. For the size use the following
arrowroot mixture : — ^Take i oz. of arrowroot
and mix to a smooth stiff paste with a small
quantity of cold water. Add warm water to
make 22 oz. in all, and boil gently until dear.
Thin papers may be immersed bodily in the
warm mixtiire for a minute or two, and then
drained and dried. Thick papers should be
pinned by the comers to a flat board and the
warm size applied first up and down and then
across, by means of a soft sponge or a Blanchard
brush {see the heading " Brushes "). Then with a
clean soft sponge go over the paper again in order
to efface all streaks and make the surface smooth ;
hang up, and when quite dry it is ready to sensi-
tise. The two sensitising solutions are made
according to the following formulae : —
A. Ferric ammonium
citrate (brown) . 80 grs. 160 g.
Water . . . i oz. I,CX50 ccs.
B. Potassium ferri-
cyanide . . 60 grs. 120 g.
Water . . . i oz. 1,000 ccs.
Unless quite fresh and clear the ferricyanide
crystals should be washed before weighing, and
dried between blotting-paper, to free the crystals
from powder or crust. Mix the solutions, and
keep in a stone bottle or in a dark place. The
solution is usable at once, but works better
when a week or ten days old, but it must be
filtered just before using, and if older than this,
should be preserved by adding to every 2 oz,
of it I gr. of potassium bichromate. The sized
common paper or the plain good paper, with
blotting-paper underneath it, should be pinned
to a flat board, placed (as illustrated) at an
angle of about 20° to the horizontal in pre-
ference to being either flat or upright. Suffi-
cient of the sensitive solution should be poured
into a saucer and then applied to the paper
with a sponge. Buckle brush, or large soft camel-
hair mop. The coating must be done in artificial
light or very weak daylight, and the solution
should be spread upon the paper by strokes
across the sheet, beginning at the top and joining
the second stroke to the first. The strokes
should then be made vertically in order that the
paper may receive a perfectly even coat, without
any of the sensitive mixture running in rivulets
down the sheet. When evenly coated the paper
must be dried as quickly as possible, and in the
dark — a warm cupboard is a good place — but no
very great heat should be applied to the wet
paper to hasten the drying. The coated paper
Paper Ready for Coating in Blue-print Process
will not keep good for many days ; a heavily-
coated poor paper will not keep so long as an
rmsized or lightly sized good one. The colour
of the sensitised paper may be a dirty greenish
yellow tinge, but will vary according to the
sensitising formula. The paper is placed in
contact with a negative or drawing on tracing
paper, and printed by dayUght, preferably in
strong sunlight. On exposure to light the colour
of the paper gradually changes through bluish-
green and bluish-grey to a kind of dirty olive-
green, the image having a choked-up appearance
when fully printed. The print is washed for
about fifteen minutes in water, which should
remove the soluble salts and leave a brilliant
blue print. The water serves both as a developer
and fixer, the print needing no further treat-
ment. Prolonged washing weakens the image,
as will also water containing carbonate of hme.
Brighter prints are obtained by adding about
20 grs. of citric acid to the pint of water. A
solution of 5 parts of alcohol in 95 parts
of water has been advocated for improving
the whites, and a 2j per cent, alum solution has
been recommended for brightening the blue
coloupr ; but neither of these aids is necessary if
the water is free from lime, the negative or
tracing a suitable one, and the paper properly
prepared.
Blue-Print Process
68
Bolting Cloth
An alternative method is to use single solu-
tions, one for sensitising and the other for
developing the faint image, obtained by printing
in the usual way, to the desired blue colour.
The sensitising mixture is as follows : —
Ferric ammon. citrate (green) i lo grs. 220 g.
Urauic nitrate . . . 35 ,, 7° „
Water . . . . i oz. 1,000 ccs.
Paper is coated with this mixture and printed
in the manner already described. The faint
image is developed to its full strength by placing
in —
Potassium ferricyanide 22 grs. 44 g.
Water . . . . i oz, 1,000 ccs.
The print is completed by washing in water.
This process is more rapid than the one first
described.
The blue-print processes are used for printing
upon fabrics and for the making of blue trans-
parencies for window decoration. For the latter
it is necessary to use a plate coated with gelatine
to serve as a vehicle for the sensitiser.
-Toning Blue-prints. — Blue-prints may be
toned to several other colours, but the various
formula published are imcertaiu in their action on
home-made papers, two samples of which are
seldom alike ; they answer better with com-
mercial blue-print papers. Before toning, wash
the prints thoroughly. Green. — Make a satur-
ated solution of ferric protosulphate, acidify with
sulphiiric acid, and dilute with an equal quantity
of water. Immerse the blue-print until the
required tint is obtained, wash well, and dry.
A weak solution of sulphuric acid (acid 4 drops,
water i oz.) will also give the print a greenish
tinge. Lilac. — For lilac-violet, immerse in a
hot solution of lead acetate, or a cold solution
of borax. A 2 per cent, solution of potassium
sulphocyanide (10 grains in i oz. of water) gives
a pink-lilac tone, after obtaining which blot off
superfluous solution, expose to strong sunlight,
wash, and dry. Greenish Black. — Dissolve 30 grs.
of borax in i oz. of water and add sulphuric acid
drop by drop till the solution just reddens
litmus paper ; next add a weak solution of
ammonia till the red colour begins to change,
and finally add 4 grs. of catechu, shake well and
filter ; tone, wash, and dry. Brownish Black. —
Add 6 drops of liquor ammonias to i oz. of water,
immerse the blue-print, and allow to remain
until the colour has vanished ; then wash and
place in water i oz., tannic acid 9 grs., in which
the bleached print gradually assumes a brown
or brownish black colour ; wash and dry.
Purple Brown. — Add 30 grs. of tannic acid and
I gr. of pyrogaUic acid (or even less) to i oz.
of hot water, immerse the blue-print until toned
to a HIac, rinse, and place quickly into a weak
solution of caustic potash (potash 8 grs., water
I oz.) ; wash and dry. Black. — A good black is
difficult to obtain ; ' success depends upon the
quality of the negative and upon the depth of
the blue-print. The deep shadows tone to a
rich black, but there is a falling-off in the half-
tones. Of the many formulae, Lagrange's is the
best, but one of the most troublesome. Rinse
the print in distilled water and, in a yellow light,
bleach in a silver nitrate solution (9 grs. in i oz.
of distilled water). Wash well in distilled water.
expose to the fumes of ammonia, and afterwards
develop with an ordinary ferrous oxalate de-
veloper ; the print may then be washed and drie4.
Grey to Red. — Print darker than usual, wash
for ten minutes, and immerse in a solution of
copper nitrate (24 grs. to i oz. of water) to
which a little liquor ammoniae has been added
cautiously, a few drops at a time, until the pre-
cipitate first formed is just redissolved, leaving
the liquid a deep blue. This bath turns the
blue-print mauve, then grey, and after a time
red. Prints dry more blue than they appear
when wet. The bath does not act well on prints
showing great contrasts, since by the time the
dark parts have turned grey the half-tones and
lighter tones will become red. Most of the tones
obtained by the above methods are unsatisfactory.
{See also " Window Transparencies" and " Fab-
rics, Printing on.")
Bleaching Blue-prints. — Instructions are given
imder " Drawings Made from Photographs."
BLURRING
In a photographic image, the absence of sharp
or crisp definition, a point of light becoming a
nebulous circle, and a fine line a hazy broad
band. Blurring may result from several inde-
pendent causes. A large working aperture of
the lens may be necessitated by the nature of
the subject demanding a rapid exposure, and
the difference in the various planes of the sub-
ject may result in some being out of focus, and
consequently blurred. Or occasionally, the
entire image may be out of focus, either by
accident or design. Many lenses, when used at
full aperture, will not give sharp definition over
the entire plate, and while the central part is
crisp and well defined, the comers are blurred.
Or the camera may move during the exposure,
with the result that the whole image is blurred.
Or, again, in photographing moving objects, the
exposure may not be sufficiently short to pre-
vent the object showing movement on the plate.
A lens that has been tampered with and put
together incorrectly, may give a blurred effect.
BOLOMETER (Fr., BolomStre; Ger., Bolometer)
Practically an extremely sensitive thermo-
meter formed of one, two, or four metallic grids
or gratings so connected as to form a Wheat-
stone bridge, and carrying a. very sensitive
galvanometer mirror. It is used to measure
extremely small differences in temperature
(o-ooooooi°C.). S. P. Langley utilised this instru-
ment in conjunction with a series of rocksalt
lenses and prisms, and received the deflected
light from tke galvanometer mirror on a strip
of bromide paper. Thus he was able to meas-
ure further into the infra-red and map out
the absorption lines with remarkable accuracy.
BOLTING CLOTH (Fr., Etamine; Ger.,
Beuteltuch)
A material of fine regular texture, originally
made for bolting or sifting flour ; known also as
bolting silk and silk bolting cloth. It is used
for obtaining softness of definition in a print.
For use when enlarging upon bromide paper, a
piece of the cloth, shghtiy larger than the enlarge-
ment to be made, is stretched free from creases
on a light wooden frame. This is interposed
Bolton, W. B.
69
Borders, Fancy
■between the enlarging lantern and the sensitive
paper. It may be tacked over and in actual
contact with the paper, but in this case the grain
of the fabric shows as a canvas efEect in the en-
largement ; it is more often used away from the
paper, the greater the distance the greater being
the diffusion obtained and the less marked being
the grain. Different effects are obtainable by
moving the bolting cloth during exposure, also
by giving part of the exposure witii the doth
and the remainder without. The interposition
of the cloth increases the exposure by about
one-third, but this largely depends upon the
effect desired.
In contact printing, the bolting cloth is placed
in between the negative and the printing paper.
The doth may be obtained in various degrees
of texture and in sheets up to 39 in. by 36 in. It
must be carefully handled, as it is easily dam-
aged, and any tear shows upon the finished print.
In the hands of an artistic worker bolting doth
is a useful device for obtaining soft pictures.
BOLTON. W. B.
Bom 1848; died 1899. Editor of the British
Journal of Photography from 1879 to 1885. An
authority on photographic emulsions ; published
in September, 1864 (with B. J. Sayce), a formula
for collodio-bromide emulsion, and in January,
1874, particulars of a washed collodion emulsion
process, this amounting to an almost revolu-
tionary improvement on the unwashed collodion
process.
BONE BLACK (Pr., Noir animal; Ger.,
Knochenfohle)
The product formed in the retort by heating
bones in the absence of air ; animal charcoal.
It contains about 10 per cent, of carbon and
about 80 per cent, of caldum phosphate, the
remainder being caldum carbonate and other
substances. Used in photography as a pigment in
carbon and like processes, also in plate backings
and black varnish. Ivory black prepared from
ivory chips is a similar but superior pigment.
BOOK CAMERA (Fr., Chambre d. livre ;
Ger., Buchkamera)
An early form of detective camera, made to
Book Camera
resemble either a book, as shown, or several
books strapped together.
BOOKS OF KINEMATOGRAPH PICTURES
(See " Kinematograph Pictures in Book
Form.")
BORACIC ACID
Another name for boric add {which see).
BORAX (Pr. and Ger., Borax)
The common name for sodium borate {which
see). Also known as sodium biborate or pyro-
borate.
BORAX TONING
A certain and reliable method of toning sensi-
tised albumenised paper and some forms of
plain salted paper prepared and sensitised by
the worker. It is not very satisfactory as a
toning bath for gelatino-chloride of sUver emul-
sion papers that is, for the modem printing-out
paper. A good formula is : —
Borax . . .80 grs. 23 g.
Gold chloride . . i gr- '28 „
Water . . . 8 oz. 1,000 ccs.
The borax should be dissolved in boiling water,
and when the solution is cool the gold should be
added. The prints must be washed well before
toning, and when the desired tone is obtained
they should be rinsed in two or three changes
of water and then fixed in the usual manner.
BORDER PRINTING
This is an alternative to moimting a print.
A sheet of paper and a printing frame, both
larger than the actual picture, are used, and
by masking the negative the print appears in
its first stage with a plain margin. Masks are
next used to cover the picture itself, and also
the plain margin with the exception of an edge
all round the print. A second exposure then
gives a narrow border to the picture. This
method may be elaborated almost indefinitely,
and spedal printing frames are made to mini-
mise the difficulty of securing accurate regis-
tration. Used with discretion and taste, good
effects may be secured by surrounding borders
of varjring width and tint, the great advantage
being that the tone and quahty of the tints are
the same as in the picture itself. The great pit-
fall is over-elaboration, resulting in distracting
attention from the picture itself. {See " Borders,
P'ancy.")
BORDERS, FANCY
These are generally made by means of special
negatives (films, as a rule), which may be bought
commercially in considerable variety. The sub-
ject is first printed while the margin is masked
and then the border printed while the picture
is masked {see " Border Printing "). Some of
the more tasteful of these borders are effective
in making picture postcards, cards with Christ-
mas greetings, and so on. When a small sub-
ject is used, on a postcard, for example, a well
printed border of good design and tone is pre-
ferable to a bare expanse of white. At the same
time, however, a picture of real value will prac-
tically never gain in effectiveness by such an
addition, and the suitability or otherwise of a
fancy border for the purpose in hand needs
careful consideration.
Boric Acid
70
Box, Negative
BORIC ACID (Fr., Acide borique : Ger.,
Borsdure)
Synonym, boracic acid. H5BO3. Molecular
weight, 62. Occurs in shining scales or amor-
phous powder. It is used in pyro developers
as a restrainer and to prevent stains, and also
m the fixing bath as a stain preventer. A solu-
tion of 30 grs. of the acid in i oz. of water has
been recommended for stopping development
instantly. In cases of very great over-exposure
it works well as a restrainer, tie proportions being
3 drops of a saturated solution added to each
working ounce of developer. A formula for a
pyro-hydroquinone developer containing boric
acid is given under the heading " Developers,
Mixed." As a preservative, 10 grs. may be
added to each pint of developer, and it will
then also act as a restrainer. In a fixing bath
it may be added in the proportion of 70 grs.
to each ounce of dry " hypo " used, but should
not be vised after an acid developer. It was at
one time recommended as an addition to the
combined toning and fixing bath, but it is next
to useless employed in that way, and may
possibly harm the prints. However, Eder recom-
mends its addition to the " hypo " bath when
used before toning. (See " Toning after Fixing.")
BOTTLES (Fr., Bouteilles, Flacons ; Ger.,
Flaschen)
Narrow-mouthed bottles A are best for hquids,
and wide-mouthed ones, B and C, for solids.
Those with flat-topped stoppers are preferable,
it being then less easy for dust to collect in the
space between the neck and the stopper. A
useful and neat type of bottle has a space for a
label ground on its side, on which the name of
the substance may be written in pencil, or with
waterproof Indian ink. Corrosive and volatile
substances and solutions, and deliquescent or
moisture-absorbing chemicals require to be kept
in bottles provided with well-groimd stoppers.
The stoppers of acid bottles should be rubbed
round with vaseline, which renders them per-
fectly air-tight and prevents them from sticking ;
the same may be done to the stoppers of bottles
containing caustic alkahs or carbonates, which
have a slightly corrosive action on glass. Hydro-
fluoric acid, which attacks glass, must be kept
in a guttapercha or lead bottle. Dark or orange-
A. Narro'w-
mouth Bottle
B and C. Wide-mouth
Bottles
coloured bottles are used for substances that are
deteriorated by hght. Corked bottles are not
recommended for photographic purposes, except
for chemicals that will keep well and are not in
frequent use. They may be rendered air-tight
by melting wax over the cork and roimd the
neck. A convenient way of doing this is to hold
a hghted candle above the cork, allowing the
melted wax to run all over and around it. (For
special bottles of various kinds, as collodion
bottles, dropping bottles, etc., see under
separate headings.)
BOX, LANTERN-SLIDE (Fr., Boite aux
ipreuves pour projections ; Ger., Latern-
bilderkasten, Diapositivkasten)
A long wooden or metal box with a hinged
hd, grooved for the storage of lantern sHdes.
The ordinary pattern resembles a grooved
negative box, but some workers prefer plain
boxes without grooves, and for storage purposes
only these are sometimes of greater convenience,
since a number of sUdes can more readily be
Lantem-sUde Box
inserted or removed at once ; however, tor
reference or indexing requirements the grooved
type is preferable. TraveUing lantern - slide
boxes are designed with a view to the prevention
of breakage ; the example shown is fitted with
a rubber buffer at top and bottom to stop any
movement of the slides, and has strong brass
end fasteners and leather straps. The lid is
furnished with pegs fitting closely into holes in
the top edges of the box.
BOX, NEGATIVE (Fr., Boite aux cUcMs ;
Ger., Negativenkasten)
A box, usually either of wood or metal, for the
storage of negatives. The ordinary grooved
wooden type is shown at A, but there are several
other patterns. In one B there is a grooved
drawer shding in an outer case, and this offers
the advantage that any given negative can be
examined without disturbing other boxes above.
A. Grooved Box for Negatives
and possibly without even needing to remove
the drawer. Either single drawers, which can
be added to as desired, or drawer cabinets may
be obtained. Another type of negative box
has an outer shell made hke a book with a label
to indicate the contents, and having an inner
grooved case that slips into it from the back.
Box, Plate
Grooved metal boxes are also made, with slip-on
lids. One pattern is an adaptation of the
card index and vertical filing system, the nega-
tives being fcept in numbered envelopes, on which
B. Negative Box with Grooved Drawer
full particulars can be written, and an index
card is also provided. Guide cards may be used
to divide or subdivide the negatives, and as
there are no grooves a good deal of space is saved.
BOX, PLATE (Pr., Boite aux plaques ; Ger.,
Plattenkasten)
A light-tight wooden or metal box, usually
grooved, for the safe custody of unexposed or
undeveloped plates. Such boxes are made in
various patterns. Some resemble grooved nega-
tive boxes, but are more carefully constructed,
with a deeper lid and rebate. Others A have an
outer sliding lid, together with an inner lid
furnished with a spring, which keeps it pressed
B. Metal Plate Box with SUp-on Lid
tightly down over the plates when the outer
lid is in position. Metal boxes with slip-on lids
and spring dips fastening over the latter B are
also obtainable.
BOX-FORM CAMERA (Fr., Detective; Ger.,
Kasten-Kamera)
A non-folding hand camera in the shape of
a box. It is generally of fixed focus, though
sometimes there is a focusing adjustment. The
majority of box-form hand cameras have a
magazine to hold a number of plates in sheaths ;
or provision is made for carrying roU films, or
a pack of flat films. (See " Hand Camera.")
71 Breath Printing
BOUDOIR
A commercial size and style of mount largely
used by professional photographers. The aver-
age size of a boudoir print is 8 in. by 5 in. — that
is, a trimmed whole plate, and the mount may
measure anything from 8| in. by 5 J in. upwards.
Boudoir midget mounts measure about 3f in.
by 2 in.
B.P.
The initial letters of the words " British
Pharmacopoeia," which is an official catalogue,
published from time to time by the General
Medical Council, giving the standards of purity
of drugs, etc. The Pharmacopoeias of different
countries vary slightly. The initials, when found
in a formula, mean simply that the chemical
named should be of the standard strength and
purity.
BRASS, BLACKENING
Recipes for dead blacks for application to
brass are given under the heading " Blackening
Apparatus."
BRASS ETCHING
Brass is etched in intaglio or relief by means
of ferric chloride, the same as in copper etch-
ing. The resist image is generally applied by
the enamel process.
BRASSES, PHOTOGRAPHING
Memorial brasses are frequently difficult to
photograph owing to their position, but unfixed
brasses may be arranged so that a suitable light
(preferably a side light) falls upon them. When
the light or reflections are troublesome, it is a
good plan to dab the brass with a rag dipped
in whitening. If the camera is pointed upwards
or downwards to the brass, take care to have
the focusing screen — and, of course, the plate —
vertical. The stop should be small and the plate
should be a slow or medium one of the isochro-
matic variety. As a rule, rubbings from old
brasses make better photographs than the brasses
themselves.
BREATH PRINTING (Fr., Impression d.
I'haleine ; Ger., Atemhopieren)
A curious process, due to Sir John Herschel,
by which invisible, or latent, photographs may
be produced, capable of development by the
breath or by a moist atmosphere. A solution
of silver nitrate (sp. g. 1-200) is added to ferro-
tartaric acid (sp. g. i'023), a precipitate falling
which is nearly redissolved by a gentle heat.
A yellow liquid is thus obtained in which the
further addition of silver nitrate causes no
turbidity. The total bulk of the silver nitrate
solution used should amount to half that of the
ferro-tartaric acid. Paper sensitised with this
liquid, thoroughly dried in the dark, and exposed
under a negative or engraving in sunshine for
from thirty seconds to one minute, does not yield
any visible impression unless over-exposed. To
develop the latent image it is only requisite
to breathe upon the paper, when a vigorous
picture appears as if by magic. Or the print
may be laid in a blotting-book, some of the
outer leaves of which have been damped by
holding them over warm water.
Brenzcatechin
72
Bromide Process
BRENZCATECHIN
One of the names of tie developer popularly
known as " Pjrrocatechin " {which see). Known
also as ortho-dihydroxybenzene, catechol, and
oxyphenic acid.
BREWSTER, SIR DAVID
Bom at Jedburgh, 1781 ; died at AUerly,
1868. Knighted, 1832. He made many dis-
coveries in optics, investigated polarisation of
light, invented the kaleidoscope, and in 1844
designed the Brewster stereoscope. In 1836 he
visited Pox Talbot and became interested in
the latter's method of producing paper negatives ;
he also corresponded with Claudet, Ross, Hill,
and other faliiers of photography. He wrote
many articles and books (about 400), several of
■mhida. dealt with photography.
BRILLIANCY
A term implying that a print is bright and
clear in quality. It generally accompanies a
long range of tones with strong shadows and
bright high lights.
BRISTOL BOARD
A fine kind of pasteboard made by pasting
down successive layers of thin paper and having
a smooth or glazed surface. Its thickness is
indicated by the terms 6-sheet, 8-sheet, etc.
BRITISH GUM {See " Bextriae.")
BROKEN NEGATIVES
These must not be confused with cracked
negatives {which see), as they are not treated in
the same way. Broken negatives are generally
understood to be those in which the film is broken
as well as the glass. If the glass only is broken
the film can be transferred to another piece of
glass, but this method is not suitable when the
film as well as the glass is broken, because of
the danger of distorting or losing the pieces
during the process of stripping. In man}' ways
a mended broken negative is more satisfactory
than a film that has been stripped and put on a
new glass backing, and some photographers
advocate the breaking of the film purposely when
the glass is cracked in order that it may be
treated as a broken negative. To mend a nega-
tive which has been broken into two or more
pieces, take each piece and clean the edges free
from dust and dirt. The largest portion is then
laid upon a dean and perfectly level glass plate,
and Canada balsam diluted with xylol applied
to the edges very thinly with a small camel-hair
brush. Xylol (or xylene) is a coal-tar product,
and if it is not obtainable benzene can be used
in its place. The remaining pieces of the
negative are also touched all round the edges
with the cement, and are then carefully joined
so as to fit exactly. The addition of xylol
enables one to use the balsam without heating,
and as it has about the same index of refraction
as glass, the internal surfaces of the glass, if
correctly placed together, will no longer reflect
light, and the breaks will hardly be perceptible.
The surface of the film is afterwards cleaned with
a piece of cotton-wool dipped in benzene. Nega-
tives carefully mended in this way show no sign
of breakage if printed slowly in the shade.
BROMEOSINE {See " Eosme.")
BROMHYDRIC ACID {See " Hydrobromic
Acid.")
BROMIDES
Salts formed by the action of bromine on a
metal, with the characteristic formula MjBr.
BROMIDE EMULSION {See "Emulsion.")
BROMIDE ENLARGING {See "Enlarg-
ing.")
BROMIDE PAPER (Fr., Papier au bromure;
Ger., Bromsilber papier)
Paper coated with an emulsion of silver
bromide in gelatine, for contact printing and
direct enlarging by natural or artificial light. It
is prepared with a variety of surfaces. Made
and introduced commercially about 1874, but
not on a large scale until 1880. Working details
are given under the heading " Bromide Process."
BROMIDE PAPER NEGATIVES
Bromide paper may be used in place of dry
plates for negative making. The process is
described under the heading " Paper Negatives."
BROMIDE PENCILS (Fr., Crayons au bro-
mure : Ger., Bromidptnsel)
Black crayons used in workiug-up bromide
enlargmeuts and prints, platinotypes, etc. They
are obtainable either in cedar pencils or as
points for adjustable holders, and are sharpened
by rubbing on a piece of No. o glasspaper. White
crayons are also procurable. For a blue-black
enlargement it is important not to employ a
brown-black pencil, or the work wiU show too
much ; and it should be remembered that
ordinary black chalk drawing pencils have
frequentiy a tendency to brownness.
BROMIDE PROCESS
The essential feature of the bromide process is
its suitability for obtaining either contact prints
or direct enlargements by artificial light, and
the consequent facilities that it gives for secur-
ing any desired result with absolute certainty.
If a print is produced which is not exactly in
accordance with the result desired, a second
exposure may be made while all the conditions
remain absolutely constant, and the time of
exposure may be so modified that the second
print will give exactly the effect desired. In
adopting the bromide process, the following
conditions are desirable. A Ught that can be
kept as uniform as possible, a means of fixing the
relative positions of light and printing frame
so that the distance between them is always the
same, and the exclusive use of one brand of bro-
mide paper. The distance between the light
and frame should be so adjusted that exposures
will vary from ten seconds for a moderately thin
negative up to forty or fifty for a strong or
dense plate. It is impossible to work accurately
if exposures are as short as two or three seconds ;
such exposures cannot be timed vrith certainty,
whereas longer exposures can be timed with an
inappreciable percentage of error. Correctness
of exposure is absolutely essential in bromide
Bromide Process
73
Bromine Water
printing if good results are desired ; there is no
more fruitfid source of imperfect prints than
incorrect exposure, and the consequent attempts
to compensate by incomplete or forced develop-
ment. A perfect bromide print is one that has
been so exposed that full development with a
normal solution will give the contrast and depth
required. In order to expose a print in this
manner, it wiU be found desirable to make a
preliminary trial exposure on a small slip of
paper, selecting a portion of the plate that has
part of the densest tones. An ordinary piece of
paper may be cut into six or eight trial slips, and
several may be exposed on different negatives
and developed together. The development of
these trial slips should be fuU, in order that the
correctness of the exposure may be judged
from the final appearance when in the fixing
bath.
Another proUfic source of loss of quality in
bromide work is the system of using one portion
of developer for several prints in succession.
The prints last developed are inferior in colour
and general qnaUty, and if toning is afterwards
performed, the colour is very poor and weak.
For prints of moderate size, sufficient developer
shoi^d be taken for one print, the solution used
once and then thrown away. For smaU prints
this is also the preferable plan, but as the quan-
tity of solution necessary is much larger relative
to the size of the print, it may be permissible
to use the same solution for two prints in suc-
cession, or, better, to develop two prints together.
But this should be the limit.
Where practicable, as in the case of an incan-
descent electric light or an inverted incandescent
gas burner, the frame should be placed hori-
zontally below the hght for making the exposiyre.
It will facilitate shielding parts of the negative
during the exposure, and also the making of the
exposure by uncovering and recovering the
frame, using a sheet of card.
Biamidophenol and amidol are good developers
for bromide prints, but they cannot be kept in
solution satisfactorily for more than three days.
The seriousness of tlus objection is realised when
only two or three small prints are required, and
then no more wanted for perhaps a week.
Amidol is, however, a favourite with many
workers, on account of the fine blue-black colour
of the prints produced with it. Ortol is also a
good developer for bromide paper, and it keeps
for a long time in solution. Metol and hydro-
quinone form a developer that is a favourite
with many workers, as it keeps well in solution.
Excellent formulae are as follow : —
Diamidophenol Developer for Bromide Paper
Biamidophenol (or amidol) i6 grs. 4"4 g.
Sodium sulphite . . l6o „ 44 „
Potassium bromide . 4 „ I'l ,,
Water . . . . 8 oz. 1,000 ccs.
The sodium sulphite must be dissolved in the
■water first. This solution is used without dilu-
tion.
Ortol Developer for Bromide Paper
A. Ortol . . 4 drms. 54 g.
Potass metabisulphite 2 „ 27 „
Potassium bromide i „ I3'5 „
Water . . 10 oz. 1,000 ccs.
The potassium metabisulphite must be dis-
solved in the water first.
B. Sodium carbonate
Sodium sulphite
Water
2 oz. 218 g.
2 .. 218 „
10 „ 1,000 ccs.
To develop, take 40 minims of A, 80 minims of
B, and add sufficient water to make i oz.
Metol-Hydroquinone for Bromide Paper
A. Metol . . . lo grs. 2'3 g.
Sodium sulphite .120 „ 27 „
Hydroquinone • 30 „ 7 „
Potassium bromide 10 „ 2' 3 „
Water . . 10 oz. 1,000 ccs.
Dissolve the constituents in the order given
in the formula.
B. Sodium carbonate . J oz. 55 g.
Sodium sulphite . J- „ 27^5 „
Water . . . 10 „ 1,000 ccs.
Mix equal parts of A and B to form the work-
ing developer.
All these formulae produce rich prints of a
good, pure colour, which will tone quite satis-
factorily. Full development wiU take about
three minutes with the diamidophenol and metol-
hydroquinone formulae, and four minutes with
the ortol. The print should be soaked in
water for about half a minute, the water then
drained off, and the developer flowed evenly
over the surface, the dish being rocked until
development is completed. Then the print
should be rinsed and immersed in the fixing
bath, taking care that the prints do not cling
together and that the solution has free access
to their surfaces. An acid fixing bath is prefer-
able, containing i oz. of potassium metabi-
sulphite to I lb. of " hypo," the solution being
so mixed that i pint shoidd contain 3 oz. of
" hypo." The prints should remain in the fixing
bath for fifteen minutes, and should afterwards
be thoroughly washed. From one to two hours,
in water frequently changed, according to the
frequency of the changes, and the number of
prints in the dish, should be sufficient.
Daylight can also be used for bromide work
if desired, and many prefer it for enlarging pur-
poses, though it is not suitable for contact
printing. {See also "Enlarging.")
BROMIDE OF URANIUM PLATES
Plates coated with a silver bromide collodion
emulsion containing a small quantity of uranium
nitrate to keep it free from fog ; these plates
are now obsolete.
BROMINE (Fr., Brome ; Get., Brom)
Br. Molecular weight, 80. Solubilities, i in 28
water, very soluble in alcohol, ether, and solu-
tions of alkaline bromides. A deep reddish
brown liquid giving off at normal temperatures
an extremely irritating orange vapour. It is
rarely used in photography except in its salts,
though bromine water has been suggested for
bleaching bromide prints prior to sepia toning.
BROMINE WATER (Fr., Eau bromie ; Ger.,
Bromwasser)
An orange-yellow solution, formed by shaking
bromine with water and decanting from the
excess which settles at the bottom of the bottle.
Bromised Collodion
74
Brush Development
BROMISED COLLODION, OR BROMO-
lODISED COLLODION (See " CoUo-
dion.")
BROMISER
A solution of alkaline or metallic bromides
usually kept in a separate solution and added
to collodion just before coating the plate there-
with. {See "CoUodion, Wet")
BROMO-ARGENTOTYPE
An obsolete name for bromide paper.
BROMOIL PROCESS
A process of obtaining pictures by bleaching
and pigmenting bromide prints ; suggested by
E. J. WaU in 1907. Working details were first
published by C. Welbome Piper in August of
the same year, and the modified process, as now
worked, was introduced in the following month.
Prints for the ordinary oil-pigment process
{which see) are made by contact, and as the pig-
ment process is generally more suitable for prints
of fairly large size it follows that users of small
plates must make an enlarged negative before
they can produce an ordinary oil print. It was
to obviate this that the bromoil process was
devised. Essentially, it is a means by which
a bromide print (which, of course, may be an
enlargement from a small negative) can be pre-
pared for pigmenting. Special bromide papers
for this purpose are obtainable, although many
of the ordinary brands are equally suitable.
The print should not be too old, and it should
possess certain qualities. A flat print, or one
whose development has been curtailed, will
seldom give a satisfactory result. The exposure
should be so adjusted that when the developing
action has been carried to its fullest extent the
result is a clean, strong print, rather more vigor-
ous than would be desirable if it were intended
to remain unaltered. Amidol is a good developer
for the purpose, a suitable form being ;o grs. of
dry amidol added to 20 oz. of water in which
I oz. of sodium sulphite has been dissolved. The
print is fixed in plain " hypo " solution, and very
thoroughly washed. At this stage the prints
may preferably be dried. Subsequently they are
re-soaked for a few minutes to facilitate the even
action of a bleaching solution. A suggested
formula is : —
Citric acid
120 grs.
12-5 g.
Potassium bromide
120 „
12-5 „
Potassium ferricyanide
120 „
12-5 „
Potassium bichromate
240 „
25 ,,
Alum
480 „
50 „
Water to .
20 oz.
1,000 CCS,
Dissolve in the order given. It is weU to
crush the crystals, dissolve in hot water, and use
when cold. This is applied to each print separ-
ately until the black image is entirely changed
to a yellowish brown colour. The prints are
then washed until the bichromate stain is
removed, and they are then placed for about
five minutes in a bath containing i oz. pure
stilphuric acid to 20 oz. of water. This is pre-
pared by adding the acid slowly to the water,
and as considerable heat is generated it should
be made some time before use, or blistering of
the print will result.
After a short washing, the prints require five
minutes' immersion in a solution of 2 oz. of
" hypo " crystals and -J oz. of sodium sulphite
in 20 oz. of water. A further washing to elimin-
ate most of the " hypo " brings the prints to the
stage where pigmenting may be proceeded with.
There are many variations of the routine of
preparing the print. For example, many workers
prefer to dry the prints again, and re-soak them
for pigmenting. Others omit the acid bath from
the preliminary stage, and use it immediately
before this second soaking instead. When the
prints are only soaked in water before pigment-
ing it is generally advisable to see that the
temperature of the water is at least 65° F. (about
18° C.) in order to secure the necessary swelling
and reUef in the gelatine. (For an outline of the
method of finishing the prepared print by pig-
menting, see the heading " Pigmenting.")
A modification of the bromoil process has been
made for the preparation of Uthographic transfers,
especially in large sizes for poster work. The
bromide paper used should be the so-called
" carbon " or velvet surface, and should be of
a good substance. An enlargement of a half-
tone negative is made on to the paper, which
is then developed with amidol, though sorne
workers prefer pyro-ammonia. The print is
fixed and washed as usual. It is next bleached
in the usual bromoil bleaching solution at a
temperature of 75° F. (about 24° C.) for two
minn,tes ; soaked in a 5 per cent, soltition of
sulphuric acid for six minutes ; washed in several
changes of water for five minutes ; fixed in
" hypo " or toned with sodium sulphide for one
minute ; washed in water for five minutes ; and
dried thoroughly. It is inked all over with a
composition roller charged with lithographic
printing ink thinned with turpentine, until a
thin even coating is laid upon the surface ; five
minutes or so is allowed for the turpentine to
evaporate completely, and the print is then
immersed in water at about 70° F. (about 21° C),
and after soaking for about half an hour the
transfer may be developed in exactly the same
way as an ordinary bichromated gelatine transfer.
BROMO-IODIDE OF SILVER (See "Silver
Bromide.")
BRONZED PRINTS
Prints on certain makes of papers which have
a metallic appearance when held at a suitable
angle. The effect occurs chiefly upon self-toning
papers and sometimes upon platinum prints,
more particularly when the print has been
over-exposed or made from a negative having
very clear shadows. The more sensitive the
paper the more likely are the deep shadows to
be bronzed. Bronzed shadows may be elimin-
ated usually by applying a print varnish, or
rubbing with wax or encaustic paste.
BROWN TONES {See "Sulphide Toning,"
etc.)
BRUSH DEVELOPMENT
The development of negatives, bromide prints
and platinum prints by applying a suitable
developer by means of a brush instead of immers-
ing in the developer. For negatives the slower-
Brush Development
75
Brushes
working developers, such as pyro, are more suit-
able than the rapid kinds, such as rodinal, metol,
etc. It is usual to soak the plate in a very weak
developer until the image just begins to show,
and then to rinse in water and apply the weak
developer, or even a normal developer, by means
of a camel-hair mop, giving the partially devel-
oped negative repeated rinses in water in order
that there may be no distinct line of demarca-
tion. Where a sharp line is wanted, glycerine
may be mixed with the developer. The brush
method enables parts of the negative to be
subdued or accentuated in a wonderful manner.
The process is perhaps of the greatest service
in portrait work where white dresses are likely
to give undesired effects. It is more widely
used in the United States than in England, and
R. W. Phillips, an American, recommends the
following method of brush development for por-
trait work; a three-solution pyro-soda formula
is used : A. Water 20 oz., sodium sulphite
^ oz. ; when dissolved add enough pure acetic
acid to turn blue litmus paper red, then add i oz.
of pyro. B. Water 16 oz., sodium sulphite
4 oz. C. Water 16 oz., sodium carbonate 4 oz.
To make a normal developer add i oz. of each
of the three solutions to 8 oz. of water. For
brush development two working solutions are
made up, one the normal developer given above,
the other beiag the same, except that the car-
bonate is omitted. Then use a separate solution
of one-half carbonate and one-half water, or
two-thirds carbonate and one-third water, which-
ever is found to suit the strength of the negative
desired. In the case of a plate exposed on a
sitter in white drapery, develop until the image
shows faintly, then pour off this regular developer
and wash the plate. Next pour on the pyro and
sulphite solution previously made up, hold the
negative horizontally up to the light in the hand,
and with a camel-hair mop saturated with the
carbonate solution rub over that portion of the
negative which is to appear the most pro-
minently. This must be done the first time very
quickly, putting the negative back into the
solution immediately. The operation is then
repeated, the carbonate being well blended over
the plate so as not to show streaks and defined
lines.
The principle involved is this : the negative
is developed only to a slight extent in the first
immersion, and as soon as the pyro and sulphite
solution is poured on development practically
ceases. Then the high lights are controlled
absolutely with the carbonate solution. Some
little practice is necessary in order to get a per-
fect result. Over-exposed negatives are unsuit-
able for brush development, the control being
so difficult.
It is found rather difficult to carry out delicate
work of this character in the dark-room, and
there is a very serious risk of exposing the plate
too freely to the Hght, and so producing fog and
loss of quaUty.
In bromide printing, brush development is
very frequently adopted for large prints. A
smaller quantity of developing solution can be
employed than most workers coidd use satis-
factorily in a dish, though the results produced
by the brush method are almost always inferior
in richness and quality to those obtained in the
ordinary manner. The print is thoroughly
wetted, so that it wiU lie perfectly flat on a
sheet of glass, and the developing solution
brushed rapidly over its entire surface in the
manner described under the heading " Brush
Toning "
Platinotype prints may be developed with
a brush if glycerine is mixed with the developer.
[See " Platinotype Process.")
BRUSH TONING
A method of toning in which the solution is
applied by means of a brush. This method is
occasionally adopted for large prints. A con-
centrated solution is employed and the print,
after washing, is laid on a sheet of glass and the
solution rapidly brushed over its entire surface.
It is desirable to cover the print with the toning
solution as quickly as possible, and each stroke
of the brush must sughtly overlap the part
wetted by the preceding stroke ; also, no part
of the print must be left uncovered in the first
application, or uneven toning will result. The
brush strokes are first made along the print, then
across, and then diagonally, continuing the work
until the toning is completed.
Prints, particularly those on bromide paper,
can be brush-toned to two or more colours.
The method is widely used for the rapid toning
of ordinary gelatine or collodion P.O. P., and
almost every formula can be adapted, but the
following is considered to be the most suitable.
Four stock solutions are necessary : —
No. I. Ammonium sulphocyanide I oz., water
to 9 oz.
No. 2. Sodium phosphate i oz., water to 9 oz.
No. 3. Saturated solution of borax.
No. 4. Gold chloride solution i gr. to i drm.
To make up a working mixture take 14 minims
of No. I and make up to i drm. with water ; then
add 12 drops of No. 4 very slowly, shaking the
mixture after each drop is added. Then add
6 minims of No. 2, and finally 16 minims of No. 3.
Each ounce of the working solution referred to
above contains practically 7 grs. of sulpho-
cyanide, I gr. of gold chloride, 5 grs. of phosphate,
and 7 grs. of borax, and the bath, if desired, may
be made up by adding these quantities to each
ounce of water used. By this method, the print
exactly as it comes from the printing frame, is
placed on a sheet of glass or pinned to a board,
and the working solution brushed quickly and
evenly over it with a camel-hair mop. Toning
should be complete in about two minutes, after
which it is washed and fixed as usual.
Great care should be taken not to expose
the print to a strong hght during the process
of toning as otherwise there will be a risk of
discolouring the whites.
BRUSHES (Pr., Brasses; Get., Pinsel)
The most suitable brushes for mounting,
colouring, and other photographic operations will
be found described under their respective head-
ings. The two brushes (always home-made)
most widely used in the dark-room are the
Blanchard and the Buckle brushes. The Blan-
chard brush A is made by taking a strip of glass
about 6 in. long and 2 in. wide, and attaching to
one end one or two thicknesses of swan's-down
Bubbles in Lenses
76
Bullets, Photographing
calico, wrapping it round the end and fastening
by means of an elastic band or thread. The
Buckle brush B is made by drawing some cotton-
wool, by means of a loop of silver wire or strong
thread, partially through a glass tube, so that
a tuft protrudes. Both these brushes are con-
A. Blanchard Brush
B. Buckle Brush
venient instruments for all kinds of photographic
uses, as either the cotton-wool or the swan's-
down may easily be renewed. The Blanchard
brush is mostly used for applying sensitising
solutions.
The Atzpinsel {which see) is a special brush
used by process workers.
BUBBLES IN LENSES
Small bubbles (or air-bells) are occasionally
seen in even the best of photographic lenses,
but generally they are no detriment. Their
presence, even under the most unfavourable
conditions, does not occasion a loss of light
exceeding -^ per cent., and their influence upon
the optical efficiency of a lens system is there-
fore of no moment whatsoever. The efforts of
opticians during recent years to improve lenses
in their higher optical characteristics have led
to more extended use of glasses that differ widely
in their optical properties and chemical com-
position from the crown and flint glass hitherto
employed, and still used for commoner lenses.
Their manufacture is attended by greater
technical difficulties, and it is no easy matter
to secure perfect freedom from air bubbles.
BUBBLES ON PLATES AND PAPERS
Bubbles or air-bells frequently form on plates
and papers during development, and they have
the effect of preventing the developer acting
on the spots covered by them. The result is
clear glass spots upon the negative or white
spots upon developed prints. Bubbles invariably
arise from stale or frequently used developer,
particularly pyro, or they are caused by a care-
less and uneven flowing of the solution over the
surface to be developed. Soaking the sensitive
material in water previous to development also
causes bubbles to form on the film. A huge crop
of tiny clear spots — the result of bubbles — of an
irregular form and appearing mostly at or near
the edges of the negative, is generally due to
an old or oxidised developer, or to one that has
been allowed to stand even for a short time after
mixing. Larger, round spots are caused by
bubbles which attach themselves firmly to the
sensitive surface during a preliminary soaking in
water, or when the developer is poured on rashly
and unevenly. Spots with small black centres
are also caused by bubbles ; these form during
development and cause the gelatine under them
to be harder than the developed portions, and
therefore slower in fixing, the result being the
small specks of unfixed silver bromide in the
centres of the spots. The methods of preventing
bubbles are obvious. The plate or paper should
not be soaked in water before the developer is
applied ; the developer should be freshly mixed,
and poured on to the sensitive surface in an even
sweep, first along one edge, and the dish then
tilted so as to cover the surface as quickly as
possible ; the dish should be rocked slowly and
regularly, and not violently and in sudden jerks.
Many workers pass a clean broad camel-hair
brush, a pad of cotton-wool, or a Buckle brush
over the film as soon as the developer is poured
on, so as to break up and remove any possible
bubbles ; the brush must, however, be quite
clean and soft, or the remedy will be worse than
the disease.
BULLETS IN FLIGHT, PHOTOGRAPHING
The first attempt to photograph a projectile
in flight is said to have been made at Woolwich
Arsenal in i860. Owing to the slow wet-plate
process used, the results were unsatisfactory.
In 1884 some experiments were made at Prague
by Mach and Wentzel which were far more
successful ; these were on the lines described
below. In 1887 an improvement on the Prague
results was made by Drs. Salcher and Riegler,
of Fiume.
Probably the most important experiments in
the photography of flying buJlets were those
published in 1892 by Prof. C. V. Boys, a full
account of which will be found in the Journal
of the Royal Photographic Society (April 30,
1892). His procedure was partly suggested by
Lord Rayleigh's methods of obtaining photo-
graphs of drops, breaking soap bubbles, etc.,
which were taken by the light of an electric spark.
The following description of the two chief
methods employed by Prof. Boys are due to the
above-mentioned publication.
The first is shown diagrammatically at A.
J is a fulminating pane or condenser of small
capacity, which may be charged on its two sides
respectively, positively -I- and negatively — ,
by means of any kind of frictional or induction
machine. This pane is allowed to discharge
through a very short circuit in which are two
gaps S s'. The spark at S is allowed to shine on
the photographic plate P without the intervention
of lenses of any kind. The spark at s^ is hidden.
A second condenser, the jar ;' (of very small
capacity compared with the pane j), is con-
nected to J, one coating by means of wire, as
shown by the full lines, and the other by means
of a string wetted with a solution of calcium
chloride, as indicated by the dotted line. Its
coatings, therefore, till the time of discharge
arrives, are kept at the same potentials as
those of the pane j. The discharge circuit of
/ includes the gaps s^ and n. The potential is
so chosen that neither condenser is able to
discharge across the two gaps S S' or n s'
as the case may be, but that either
would go off if either of its gaps were
Bullets, Photographing
71
Burgundy Pitch
made conducting. This is effected by the
passage of the bullet across «, which immediately
causes a feeble spark at s^, due to the discharge
there of ;'. The air here, being now conducting,
no longer prevents the pane j from discharging
across the gap s, and Uierefote a spark is pro-
duced which casts upon the photographic plate
a shadow of the bullet, and in effect an image
of any atmospheric phenomena accompany-
ing the bullet The ifficulty in photographing
bullets is to obtain a spark which, while it
is bright enough to act on the plate, is yet
of such short duration that the bullet has
not time to move more than a hundredth
of an inch or less while it is yet in existence.
If glass lenses are used a large proportion
of the actinic rays are absorbed (in the case
of a spark between magnesiimi term.inals, four-
fifths of the whole); but in the case of a
true image any spark formed by the bullet at
••J N
A. Arrangement for
Photographing Bullet
inFUght
B. Modification of
of Method A for
Photographing BuUet
n is properly focused by the camera lens, and
does not much interfere with the result. If
lenses are not used the whole of the rays (except
such as may be absorbed by the air) are effective,
but any spark at n, being near the plate, would
fog it so completely as to make the more dis-
tant spark at s almost, if not quite, inoperative.
This difficulty is completdy avoided by the use
of the jar /, of very small capacity, which is
unable to produce a spark of any appreciable
photographic effect. Moreover, the spark at
s is brighter, and should last less time when a
very short discharge circuit is employed than
the corresponding spark produced in the dis-
charge through a greater length of wire, such,
for instance, as wotdd be necessary if the
main discharge were taken to the bullet and
back.
The second method is a modification of the
first, and was arranged to meet those cases
where difficulty might arise in closing the gap n.
In the first arrangement the gap n must be more
perfectly closed than is the small space s, in
order to make the action of what may be called
the " spark relay " certain. By the introduction
of a second pane or jar (see B) J^ in series with j',
the potential of the little iar 7 may be made
n + 1 times that of j^ if the capacity of j^ is
that of
In the discharge, only j^ is
affected, so it .will be necessary to discharge j^
also before beginning a new experiment.
The above sufficiently indicates the principle
of the electrical arrangements. With regard to
the practical details, tiie apparatus mostly used
consisted of a box lined with black cloth, in
which the photographic plate was placed. The
large condenser was a plate of glass about a foot
square, and the small condenser was a jar or
bottle to act as a starter for the spark. The
bullet enters and leaves the box by two holes
covered with paper to exclude the light, and
in passing in front of the plate it touches the
terminals of two thin lead wires, thus completing
the circuit and causing two flashes — a small one
which does not affect the photographic plate, and
a larger one which does affect the plate, and has
a duration of less than one-millionth of a second.
BULL'S-EYE CONDENSER
A plano-convex (almost hemispherical) lens,
mounted upon a stand and fitted with a universal
joint. It is used in microscopy to focus the light
upon the object, or upon the substage mirror.
Bull's-eye Condenser
and is almost indispensable when examining or
photographing opaque objects. Also it is useful
for improving the illumination of transparent
specimens.
BURETTE
An apparatus used in volumetric analysis to
deliver accurately measured quantities of liquids.
It consists of a glass tube of uniform bore,
graduated, and usually fitted with a stop-cock
at the bottom from which any desired quantity
of a hquid can be allowed to flow from the tube.
A modified form working after the manner of a
fountain-pen filler is used for measuring small
quantities of photographic solutions.
BURGUNDY PITCH (Fr., Poix blanche de
Bourgogne; Get., Burgunderpech)
The resin of Abies or Pinus excelsa, the spruce
fir, purified by melting in hot water and
Burnett's Process
78
Burton, W. K.
straining. True Burgundy pitch is not easy to
obtain, and a fictitious article is often sold for
it. The true resin is translucent and has a dull
yellowish brown coloujr, and the fracture is
shining and conchoidal ; some examples contain
much water, and are opaque and of a duU grey
colour ; they require straining to free them
from impurities. The odour is peculiarly aro-
matic and characteristic. It is not wholly
soluble in alcohol of -838, a little flocculent white
matter being left ; much the same happens if
placed in contact in a vial with twice its weight
of glacial acetic acid. It is very soluble in
acetone. The false Burgundy pitch is usually
brighter in colour than the true, with a weak,
scarcely aromatic odour ; it is less soluble in
alcohol, and in glacial acetic acid it forms a
turbid mixture separating into two layers, a
thick, oily liquid above and a bright soliition
below. Burgundy pitch is used in process work
in the preparation of photo transfer inks. In
solution with spirit of wine it forms an excellent
aquatint etching ground.
BURNETT'S PRINTING PROCESS
One of the many printing processes employing
uranium ; invented by Burnett in 1857.
BURNISHER (Fr., Presse cl satiner & chaud ;
Ger., Heisssaiinirmaschine)
A machine for imparting a glossy surface to
prints by pressure and friction against a heated
and polished bar or roller. The bar burnisher A
— the older type — has a poli.shed steel or nickelled
must be avoided. The prints should not be
quite bone drv, and if kept too long they do
not burnish so well. On the other hand, they
must not be damp, or they may blister and stick
to the bar or roller.
When a bar burnisher is used, the prints will
require, before burnishing, to be lubricated by
rubbing with a mixture consisting of 4 grs. of
Castile soap dissolved in i oz. of alcohol, appHed
with a tuft of cotton-wool. To dissolve the soap,
the bottle containing the mixture is placed in hot
water. The print is passed through the burnisher
face downward, pulling it upward in a slightly
curved direction from the back as it goes through.
This is done three or four times. "When the print
is passed through flat, without pulling it, whether
in a burnisher or a rolling press, hot or cold, the
operation is known as " rolUng " ; but this term
is frequently applied indiscriminately to burnish-
ing also.
With a roUer burnisher, n. lubricant is not
required. SoUd rollers take some time to get
hot and require to be rubbed lengthwise with a
soft cloth vmtil heated, meanwhile revolving the
roUer backwards ; this is to prevent the deposi-
tion of condensed moisture from the air, due to
the lower part of the machine getting warm first,
while the roller is still cold; this moisture,
if allowed to settle and dry on, would make
the roller dull and streaky, and might cause
rust.
The more modem burnishers have a hollow
roller with the gas burners inside it ; this gets
hot in a much shorter time, and the heat is also
A. Bar Bumishei
bar and merely a single roller ; while the roller
burnisher — or, as it is sometimes called, " enam-
eUer " B— has two rollers, one or both being of
polished nickel. The bar burnisher is said to
give the better gloss, but has the disadvantage
that the prints need lubricating, and they occa-
sionally get scratched. Both kinds are heated by
spirit or gas, or with hollow rollers steam is
sometimes employed. RoUing presses, properly
so-called, have a large flat steel plate and a
single polished roller, and are used either with
or without heat.
Burnishers of agate or other stone have had
in the past a few photographic uses. (See " Agate
Burnisher.")
BURNISHING (Fr., Satinage ; Ger., Satini-
ren)
The method of obtaining a glossy surface on
P.O.P. and albumenised prints by drawing them
through a heated bumi.sher. For P.O.P the
bar or roller of the burnisher should be just too
hot to be touched with the finger, and for albu-
menised prints a trifle hotter, but excessive heat
B. EnameUer or Roller Burnisher
more even. A screw adjustment is usually pro-
vided for regulating the distance between the
rollers, bar burnishers having instead nuts under
the plate, or some similar arrangement. Should
the steel bar of a bar burnisher become scratched
it should be rubbed carefully with a sKp of fine
oilstone having a little sweet oil on it, until
uniformly .smooth and bright. The oilstone
should be held flat on the bar and drawn
from end to end only, not across. Nickelled
rollers are difficult to repoHsh satisfactorily
when worn, and generally require sending to be
replated.
BURNT-IN PHOTOGRAPHS (See "Cer-
amic Photography.")
BURTON, W. K.
Bom in Scotland, 1853 ; died at Tokio, Japan,
1 899. Author and experimentalist ; first became
prominent in the early 'eighties as an authority
on the theory and practice of emulsion making.
Burton was an engineer by profession, and early
in 1887 left for Tokio, where, at the Imperial
Buttonhole Camera
79
Buttons, Photographic
College, he was appointed to a professorship. He
compiled an exposure table and published an
"ABC of Photography."
BUTTONHOLE, OR VEST, CAMERA (Pr.,
Chambre d houtonnUre ; Ger., Knopfioch-
Kamera)
A small detective camera of circular form,
somewhat like a large watch, and worn under
Button-hole Camera
the vest, as shown in the illustration. The lens
protruded through a buttonhole. Six round
pictures about the size of a penny were taken
in succession on a circular plate. The device
was invented by Stim.
BUTTONS, PHOTOGRAPHIC
Celluloid buttons containing photographs.
Ordinary prints are first prepared, these being
albumen, P.O.P., or bromide, and after fixing,
washing, and drying, they are mounted face
down with starch or gelatine on sheets of cellu-
loid sold for the purpose. If necessary, the
photographs may be mounted before they are
dried. When dry the photographs are cut out
with a. punch or die, placed in a machine with
the metal discs, and stamped into buttons. The
bent pin, strut, or frame is then attached.
Gas-heated Roller and Metal Plate
Professional workers use a gas-heated roller
and metal plate, as shown. The dry print is
immersed in alcohol till both sides are moistened.
A sheet of blotting-paper is placed on the plate,
then the celluloid, next the print, face down, and
finally a piece of tissue paper. The roller,
sufficiently hot to sizzle when touched with
water, is now passed over all, uniting the print
and celluloid.
"C. DE V."
The abbreviated form of " carte-de-visite "
{which see).
"CABINET" SIZE
A popular size of professional portrait, having
a mount measuring 6f in. by 4^ in. The actual
print may be $^ in. by 4 in., 5-J in. by 4 in., or
6 in. by 4J in., these being known in the
trade as "No. i," "No. 2," and "Special"
cabinet sizes respectively. Cabinets were in-
troduced in 1867 by P. R. Window, of
Baker Street, London, who, as a professional
photographer, fouJid the then popular carte-
de-visite too small for groups and for ladies'
dresses, possibly crinoUnes, which were fashion-
able between 1856 and 1867.
CACHET, ROUGE ET VERT
Names once given to some French isochrom-
atic plates, "rouge" being of medium rapidity
and "vert" special rapid. A French chemist
(Tailfer) was the first to make a successful
isochromatic dry plate (1882). The British rights
to the patent were secured in 1886 by B. J.
Edwards & Co.
CADMIUM BROMIDE (Fr., Bromure de cad-
mium : Ger., Bromcadmium)
CdBrj, or CdBrj 4H2O. Molecular weights,
272 and 344. Solubilities, i in 0-94 water, i in
3 alcohol, I in 250 ether, i in 16 alcohol and ether.
A yellowish crystalline powder, obtained by
heating cadmium to redness in bromine vapour.
It is used to bromise collodion.
CADMIUM CHLORIDE (Pr., Chlorure de cad-
mium ; Ger., Chlorcadmium)
CdClj, or CdCla 2H2O. Molecular weights, 183
and 201. Solubilities, i in 0-71 water, i in 8
alcohol. It occurs as small white crystals, which
are occasionally used in collodion emulsions.
CADMIUM IODIDE (Fr., lodure de cad-
mium ; Ger., lodcadmium)
Cdl,. Molecular weight, 366. Solubilities, i in
I -08 water, i in i alcohol, i in 3-6 ether. It
takes the form of colourless flaky crystals.
This salt is preferred for iodising collodion for
process negatives, generally in conjunction with
ammoniimi iodide.
CADMIUM-AMMONIUM BROMIDE (Pr.,
Bromure double de cadmium et d' am-
monium ; Ger., Zweifach-ammonium-cad-
miumbromid)
2CdBr2 2NHiBr HjO. Molecular weight, 758.
Solubilities, i in 073 water, i in 5-3 alcohol, i in
24 of equal parts alcohol and ether. A double
salt suggested by Eder on accoimt of its greater
stability for collodion processes. It can be pre-
80
pared by dissolving 344 parts of crystallised
cadmium bromide and 98 parts of ammoniimi
bromide in water and then crystallising.
CADMIUM-AMMONIUM IODIDE (Fr., lo-
dure double de cadmium et d' ammonium ;
Ger., Zweifach-ammonium-cadmiumiodid)
Cdlj 2NHjI 2H2O. Molecular weight, 692.
Solubilities, i in 0-58 water, i in 070 alcohol,
I in I -8 equal parts alcohol and ether. A double
salt suggested by Eder, as it gives greater
sensitiveness to collodion than the single salts.
It can be prepared by dissolving 145 parts of
ammonium iodide and 183 parts of cadmium
iodide in water and then crystaUising.
CALCIUM BROMIDE (Fr., Bromure de cal-
cium; Ger., Bromcalcium)
CaBrj. Molecular weight, 200. Solubilities,
I in 07 water, very soluble in alcohol. Very
deliquescent. Should be kept well stoppered.
A white, granular powder, obtained by neutrahs-
ing hydrobomic acid with chalk. It is used in
making collodion emulsion.
CALCIUM CARBIDE (Pr., Carbure de cal-
cium; Ger., Calciumkarbid)
CaCa. Molecular weight, 64. It is decomposed
by water, and extreme care must therefore be
exercised in storing free from moisture. It
occurs in greyish-black, irregular lumps, or
sometimes in coarse granules, and is obtained
by direct union of lime and carbon in the electric
furnace. On being added to water acetylene
gas {which see) is evolved, slaked lime being left
as a residue : Ca C^ 4- HjO =Ca Hj 4- CaO.
CALCIUM CARBONATE, OR CHALK (Fr.,
Carbonate de chaux ; Ger., Kreide,
Kohlensaures Kalk)
CaCOj. Molecular weight, 100. Solubilities,
insoluble in water, alcohol, or ether. Prepared,
or drop, chalk 1 occurs as a white amorphous
powder or small cones, and is obtained by wash-
ing native chalk. Precipitated chalk is obtained
by precipitation from a soluble calcium salt by
a carbonate, and should alone be used in photo-
graphy, as it is freer from impurities ; it is an
impalpable white powder, and is used to neutral-
ise toning baths.
CALCIUM CHLORIDE (Fr., Chlorure de cal-
cium; Ger., Chlorcalcium)
CaClj (anhydrous), CaOj eHjO (crystal).
Molecular weights, anhydrous iii, crystal 219.
Solubihties, i in 1-4 water (anhydrous), i in 0-25
water (crystal), soluble in alcohol. It is extremely
deliquescent, and must therefore be kept well
stoppered. The pure anhydrous salt occurs as a
white, granular powder, in sticks or lumps ; the
hydrated salt as white crystals ; both are used
occasionally in emulsion making.
Calcium Chromate
8l
Calotype Process
The commercial granulated dry chloride
(CaClj 2H,0) occurs in greyish-white porous
masses about the size of a pea, and is used as
a desiccating agent for platinotype and other
papers. When from absorption of moisture it
becomes a pasty mass, it can be easily dried
in an ordinary oven.
In process work, calcium chloride is used in
iodisers for collodion. The dry commercial variety
of calcium chloride in hard lumps is used for
placing in drying boxes for carbon tissue, gela-
tine films, etc. Also it is used in calcium tubes
for storing sensitised paper.
CALCIUM CHROMATE (Fr., Chromate de
calcium ; Get., Calciumchromat)
CaCrOi 2HaO. Molecular weight, 192. Solu-
bilities, soluble in water and alcohol. It is a
yellowish powder, prepared by neutralising
chromic acid with chalk. It was suggested by
Valenta as an addition to printing out emulsions
to obtain greater contrast, and he gives the
following method of making a 10 per cent.
solution : —
Chromic acid (pure)
Distilled water to
386 grs. 25 g.
3|- oz. 100 CCS.
Dissolve, and add sufficient precipitated chalk
to make the solution permanently milky after
weU stirring. Filter, and wash ttie filter with
sufficient distilled water to make 8f oz., or
250 CCS., in all.
CALCIUM HYDRATE. OR HYDROXIDE
Ca (OH)2. Molecular weight, 74. A synonym
for slaked lime, a substance which has been sug-
gested as an addition to the gold toning bath,
but is very rarely used.
CALCIUM HYPOCHLORITE (Fr., Chlorure
de chaux, Chlore A blanchir ; Get., Chlor-
kalk)
Synonyms, bleaching powder, chloride of
Ume. Solubilities, i in 400 water, i in 7-5 alcohol.
It is poisonous, the antidotes being ammonia
vapoiir, steam, ether vapour, and dilute sul-
phitretted hydrogen. It occurs as a white or
greyish-white powder with powerful chlorine
smell, and is obtained by passing chlorine gas
over slaked Ume. Its composition is doubtful,
but may be considered to be approximately
Ca(OCl)Cl. It is used for preparing Labar-
raque's solution and Eau de Javelle (which see).
CALCIUM SULPHATE (Fr., Sulfate de cal-
cium; Get., Calciumsulfat)
Synonyms, sulphate of lime, gypsum.
CaSO, 2HaO. Molecular Weight, 172. Solu-
bility, I in 380 water. It occurs naturally as
the mineral anhydrite CaSO^, and, in combina-
tion with 2H2O, as alabaster, gypsum, satin-spar
and selenite. Gypsum when heated moderately
loses its water, becoming What is knowM as
plaster-of-paris, which, when mixed to a paste
with water, again takes up 2H2O and sets to a
hard solid with expansion. Plaster-of-paris is
used for making casts and moulds in some
photo-mechanical processes, and for photographic
bas-reliefs. It Is sometimes useful for stopping
leaks and repairing broken articles. It should
be kept in air-tight stoppered jars, and only the
6
finest quality should be used for photographic
purposes. Calcium sulphate is a common
impurity in spring water, causing what is known
as permanent hardness, which is not removed
by boiling.
CALCIUM TUBE
A tube or box, usually of " tin " (tin-plate),
divided into two parts, the larger for storing
paper and the smaller for containing calcium
chforide. The illustration shows a good home-
made pattern. The larger tin holds the sensitive
paper, which rests upon a smaller tin having a
perforated top and containing the chloride.
Such tins may be used for all kinds of paper
Ukely to be affected by damp, and, indeed, are
necessary for keeping platinotype paper dry
and in a good printing condition. The calcium
chloride absorbs the moisture. Platinotype
paper is sold in air-tight tins, each of which
contains a twist of paper or cotton-wool hold-
ing a small piece of asbestos, which has been
saturated with calcium chloride ; this may be
used over and over again by heating on a red-
hot shovel to drive out the moisture. Should a
Calcium Tube
new piece be required it may be prepared by
taking a saturated solution of calcium chloride,
adding to it coarse commercial asbestos, and
knea(&g the whole into small cubes, afterwards
drying them in an oven. Calcium chloride may
be purchased in the anhydrous form and used
in place of the asbestos ; it should be tied up
in fine muslin or placed in a small perforated tin,
care being taken to prevent any particles of it
getting on to the sensitive paper,
CALMEL'S POWDER
A mixture of resin, pitch, and asphaltum
melted and ground to fine powder for use as
an acid resist in photo-etching.
CALOMEL (See "Mercurous Chloride.")
CALOSCOPIC LENS (Fr., Objectif caloscop-
ique; Get., Caloskopische Linse)
A landscape lens made in the late fifties and
early sixties of the nineteenth century. It was
designed on the same principles as Petzval's
orthoscopic lens.
CALOTYPE, OR TALBOTYPE, PROCESS
A negative process upon paper, invented by
Fox Talbot and patented by him on September
Camarsac's Process
82
Caunera
20, 1 841. It was the third British patent for
photography, the two previous ones being for
the Daguerreotjrpe process. The patent was
afterwards disputed by the Rev. J. B. Reade,
but Talbot's claim was upheld in the law coiyrts,
mainly for the reason that Reade's previous dis-
covery was not properly published or made
known. Pox Talbot's process weis afterwards
considerably improved by C. Cundall. The
original process is briefly as follows : Paper of
close texture was washed over with a solution of
100 grs. of silver nitrate in 6 oz. of water. When
dry, the paper was immersed in a solution of
potassium iodide, 25 grs. to each ounce of water,
for two or three minutes, then rinsed in water
and dried. Paper in this condition was called
" iodised paper," and could be stored in a port-
folio for use as required. Sometimes the double
operation referred to above was performed at
one time by brushing a solution of iodide of
silver and potassiimi over the paper with a.
Buckle brush. In order to prepare the paper for
exposure in the camera two solutions were
necessary : A. 100 grs. of silver nitrate dis-
solved in 2 oz. of water, to which is added one-
sixth of its volume of strong acetic acid. B.
A saturated solution of crystallised gallic acid.
Equal parts of A and B were mixed together, the
mixture being called gallo-nitrate of silver. The
iodised paper was brushed over with this solution,
or the paper floated upon it for half a minute,
then rinsed in water or blotted off, the operations
being carried out in the dark-room. The paper
was then placed, either wet or dry, in the dark
slide and exposed in the camera, the exposure
necessary being, under good conditions, about six
minutes. The paper was developed by washing
over with gallo-nitrate of silver (as above), and
was fixed, after washing in water, by a minute's
immersion in a solution of 100 grs. of potassiujn
bromide in 8 oz. of water. Finally it was washed,
dried, and printed from.
Modifications of the process consisted in slight
alterations in the sensitising bath, the use of
ferric protosulphate as a developer, and of
sodium hypo.sulphite as a fixer, and the making
of the paper negatives more easily printable by
waxing or by immersion in almond oil. The
calotype process was popular between 1841 and
1 8 5 1 , but was superseded by the collodion process
CAMARSAC'S PROCESS (Fr., Proad6
Camarsac ; Ger., Camarsac' s Prozess)
Lafon de Camarsac was the first, in 1855,
to discover the method of making bumt-iu
photographic enamels, now known as ceramic
photographs, or photo-ceramics, and the process
was in the beginning named after its originator.
{See "Ceramic Photography.")
GAMBOGE {See "Gamboge.")
CAMEO (Pr., Camie ; Ger., Kamee)
Photographically, a bas-relief portrait finished
in plaster-of-paris or coloured waxes. (For
working details, see " Bas-reliefs.")
CAMEO PRINTS
An old type of professional carte-de-visite
portrait, popular between the 'sixties and
'eighties. It was the invention of Messrs.
Window & Grove, and in its earliest form, called
" diamond cameos," consisted of four positions
on one card, as A, and raised as medallions.
I,ater, one position took the place of four, and
it became even more popular. After mounting
A. Cameo Print,
Medallion Style
B. Convexity C. Cameo
of Cameo Print backed
Print -with Cotton-
wool
the print in the ordinary way upon a flat card,
it was put in a press and made convex, as B.
Another and a more expensive plan was to make
only the print convex, and to fill the concave
part with cotton-wool before pasting it upon
a flat card, as C.
CAMERA (Fr., Chambre, Chambre noire ; Ger.,
Kamera)
The photographic camera is essentially a light-
tight box, having a lens at one end and provided
at the other with a suitable arrangement for the
insertion and withdrawal of the sensitive plate
or film. To ensure that the required amount
of subject is included, a ground-glass focusing
screen, or some kind of finder or sight, is employed.
The prototype of the photographic camera is
the camera obscura {which see). The first
camera used for photography was that of
Nic^phore Niepce, who, writing in 18 16, describes
it as a box about 6 in, square, furnished with a
sliding tube carrying a lens. In Daguerre's fiarst
camera A the only means of focal adjustment
A. Daguerre's First Camera
was a rack and pinion on the objective. Charles
Chevalier, of Paris, introduced some improve-
ments, among them the method of making the
loody in two portions, one shding within the other
and clamped by a screw working in a slot on
the baseboard, as seen in Daguerre's later appar-
atus B ; this arrangement is still met with in
Camera
83
Camera Bag
some ferrotype cameras. The mirror E at the
back, to erect the image in focusing, -will be
noticed. The next step forward was the inven-
tion of the bellows, which was probably sug-
gested by that of the accordion, and seems to
an inclined mirror and using it both for focusing
and as a shutter. D will serve to explain the
various fittings and movements of a modem
triple-extension field camera, each part being
named and indicated by an arrow. The different
B. Daguerre's SUding-body Camera
have been known as early as 1839, though it
was not in general use till the 'fifties. It
was originally square or oblong, and the only
■way of reversing the plate was to turn the entire
apparatus on its side. The pyramidal, or so-
called " conical," bellows was first made in
1861, and at about the same period were intro-
duced the swing front, swing back, and side-
shifting movement. Since Qien progress in
camera construction has been rapid. The
reversing back, rising and falling front, turn-
table, and many other conveniences, have been
added, until the elaborate and beautifully-
finished outfits of to-day bear scarcely any
resemblance to the heavy and clumsy apparatus
of earlier years. Yet, to give a curious instance
of how ideas tend to repeat themselves, the
C. Box-form Camera Obscura : Early
Anticipation of Reflex Principle
kinds of cameras are described in this work
under their separate headings as " Studio
Camera," " Field Camera," " Hand Camera,"
" Reflex Camera," " Enlarging Camera," etc.,
and any not so found should be looked for under
Handle
Bel Iowa
Reversing
Back,
Plumb Indicator
Rising Front
Cross Front
Shutter
Lens
Wide-Angle
Mouement
Swing Back
Bach
Extension
Frame
Front Focusing
Pinion
Front
Extension
Frame
Turntable
Let into Baseboard
D. Fittings and Movements of Modem Triple-extension Field Camera
latest refinement of mechanical sldll, the reflex
or reflector camera, is strikingly similar in design
to an early pattern of box-form camera obscura
C described by the Abbe Nollet in his " Le9ons
de Physique," published at Paris in 1755.
Thomas Sutton, in 1861, was the first to adopt
the reflector principle in exposure by hingeing
the particular branch of work for which it is
used.
CAMERA BAG, OR CASE (Fr., Sac A
chambre ; Ger., Schnappsack, Sack)
A receptacle for the carriage and protection
of the camera, lens, and slides, commonly of
Camera Carrier
84
Camera Obscura
canvas or leather, and generally provided with
a strap to sling over the shoulders. The better-
dass bags are Uned with baize, felt, or velvet,
and have suitable partitions. A lock and key-
is a useful precaution against the dark-slides
being tampered with when traveUing.
CAMERA CARRIER (Fr., Porte-chambre ;
Ger., Kameratrdger)
An attachment for carrying the camera, etc.,
on a bicycle or tricycle. Various patterns are
made, with screw clamps to fit on the front,
back stays, or handle-bar of the cycle, and
furnished with straps or spring clips to secure
the apparatus. There is a general opinion, how-
ever, that the camera is best carried when slung
on the rider's back. (See also " Cycle.")
CAMERA LEVEL (Fr., Niveau ; Ger., Nivelle)
A device to enable the back of the camera to
be kept truly vertical or the base horizontal, as
the case may be. For the first purpose, a plumb
A. Circular Spirit
Level
Long Spirit Level
C. Quadrant or Two-way Level
indicator hung at the side is ordinarily employed,
though a circular spirit level A let into the top is
sometimes preferred. For the baseboard, either
a long spirit level B or a circular one is used.
There are many patterns of levels, some working
with spirit, others having a small ball enclosed.
A quadrant or " two-way " level is illustrated
at C.
CAMERA LUCIDA (Fr., Chambre claire ;
Ger., Die Helle Kammer)
An instrument used for delineating views from
nature and copying drawings. It was a camera
ludda that Fox Talbot was using when, in
October, 1833, he began to think out a plan for
fixing the images seen by its aid, but he at a
later date put it aside in favour of the camera
obscura. The camera lucida proper was invented
by Dr. WoUaston, who died in 1828, but the name
was originally given to an instrument, invented
by Dr. Hooke, analogous to the microscope.
The best form of the camera lucida consists
of a four-sided prism having the vertical cross
section A B c D as shown in the diagram. The
side A B is at an angle of 22^ deg. with the hori-
zontal, while the side B C makes the same angle
with the vertical. A horizontal ray of light from
an object B is twice totally reflected at F and g,
and emerges vertically from h to j. The eye
at J refers the ray to a point vertically beneath
at K, and at the same time is able to look over
the edge C of the prism at a sheet of white paper
Optical Principle of Camera Lucida
placed below, on which the image of the object
is seen, and on which it may be traced with a
pencil. The prism is mounted in a brass case,
and is fixed by a movable joint to an upright rod
about I ft. high, provided with a damp at its
outer end to attach it to a drawing board.
CAMERA OBSCURA (Fr., Chambre obscure :
Ger., Die Dunkelkammer)
Literally, " dark chamber " ; an optical
instrument invented by Baptista Porta in 1569,
although there is evidence of an even earlier
knowledge of its principle and properties. This
simple instrument depends in principle on the
fact that if a tiny hole is made in the shutter of
a room from which light is otherwise excluded,
a small reversed image of the view outside will,
under favourable drcumstances, be thrown on
the opposite wall. This experiment appears to
have been known to philosophers from time
immemorial, but only comparatively recently was
discovered the improvement effected by using a
convex lens in place of the hole. Baptista Porta's
box-form of camera obscura appears to have been
used as an entertaining toy, or as a ready means
of tradng landscapes and views, for nearly three
centuries prior to the discovery of photography.
A quaint form of camera obscu.ra, designed by
A. M. Guyot, for outdoor work in tradng land-
scapes, is sho\vu in section at A. It resembles
an ordinary table, the camera being situated
between the legs and the top being formed by
a sheet of plain glass M, on which is laid a piece
of tradng paper. The image formed by the
convex lens K is thrown upwards on the screen
M by being reflected from an inclined mirror r,.
A modification of this device is shown at B, the
projected image being viewed under cover of a
dark chamber, at the top of which the optical
system is arranged. A double convex lens is
placed in a sliding moimt at K, and over it is a
mirror L, set at an angle of 45° rdative to the
horizon. As the lens is uncorrected for spherical
aberration, the image would suSer in definition
at the margin if received upon a perfectly plane
surface. Therefore the surface M is made con-
cave, and part of a sphere whose radius is the
focal distance of the convex lens K.
The best form of camera obscura is that in
which internal instead of specular reflection is-
employed, to prevent the loss of light attendant
Camera Obscura
85
Camera Obscura
on the latter. The optical system then con-
sists of a rectangular prism C, having one of its
faces convex and another concave, such a com-
bination doing away with the necessity of a
mirror to change the direction of the rays from
V
~V-
V V
A. Guyot's Camera Obscura
a horizontal to a vertical course. The rays from
a distant object or landscape will be made to
converge after impinging on the convex surface,
and being reflected in the interior of the prism,
will pass into the dark chamber to the surface
upon which the picture is to be received. The
picture thus obtained wiU be extremely vivid.
With an optical system of this character, the
surface on which lie picture is formed may be
plane and not concave. As these meniscus
prisms are dif&cult to procure, they may be
replaced by a triangular prism N (see illus-
tration D), having a plano-convex lens o and a
plano-concave lens P, both of proper focal length,
cemented by Canada balsam on two of its faces.
Spherical aberration is sometimes guarded
against by using a plano-concave lens E in place
B. Camera Obscura, with Concave Surface to
receive Image
of the more complex combination, in which case
the lens is placed at the top of the dark chamber
with its concave surface uppermost. With this
latter arrangement a plane surface suffices to
receive the picture, but the mirror l, in illus-
tration B wiU still be needed to turn the rays
from the horizontal to the vertical direction.
The box-form camera obscura is shown at P,
and it will be seen that the principle here
employed is practically the same as that of
Guyot's table-form apparatus, with the addition
of a shade q. This device is sometimes used by
Prisms and Lenses of Camera Obscura
employing Internal Reflection
artists in sketching or, rather, tracing outline
pictures of landscapes, k is the lens, i, the
mirror, and M the sheet of tracing paper, or
ground glass with the matt surface uppermost.
The modem photographic camera obscura —
which will be readily recognised as the reflex or
reflector camera — is arranged in the same way
as P, but the lens used at K is of the compound
type, in which spherical aberration, achromatism,
and all the other defects of a simple lens are
corrected ; so that when the mirror i. is mechanic-
ally moved out of the path of the rays a perfect
negative image is received upon the sensitive
plate, suitably placed at the back of the camera.
A sterescopic camera obscura devised by
Theodore Brown is a half-plate instrument fitted
with a mirror for reflecting the rays on to
a horizontal screen where the stereoscopic images
are seen. Unlike an ordinary stereoscopic
camera, in which a pair of lenses side by side are
used, only one lens is used, but it is supplemented
with a double reflecting device (the " Stereo-
photoduphcon," which see), to be used on the
hood of the single lens. The effect is very
..-m
F. Diagram of Box-form Camera Obscura
charming, especially when the face of the
observer is properly enclosed within the hood or
shade placed above the screen on which the dis-
similar images are projected. By turning the
camera on its axis during inspection of the images
a panoramic, as well as a stereoscopic, natural
colour effect is produced.
Camera Screw
86
Camera Stand
CAMERA SCREW (Pr., Vis du pied: Ger.,
Stativschraube)
The screw attaching the baseboard of the
camera to the head, or top, of the tripod, in those
cases when a turntable is not fitted. The loose
screw is very liable to get lost, and is difificult to
insert without several ineffectual attempts, in
which the bottom of the camera frequently gets
scratched. Several special forms of tripod screws
have been introduced to avoid these objections,
among which may be mentioned Renbold's,
which is permanently attached to the camera
and folds into a recess in the bottom when not
in use. It is tightened on the tripod head by
means of a nut.
The Royal Photographic Society recommend
that all screws fitted to cameras either for
attachment to the stand, for fixing rising fronts,
or for other movable parts, be either A in., J in.,
fV in., or f in. in external diameter, and in pitch of
thread and other details in accordance with the
generally recognised Whitworth standards for
these sizes.
CAMERA STAND (Pr., Pied: Ger., Stativ)
A raised support for the camera, to keep it
steady during focusing and exposure. There are
several varieties, differing m construction accord-
ing to their purpose. In the older but still very
common form of studio camera stand B the top
is raised or lowered by rack and pinion, or by
a counterpoise and weight, while the table has a
tilting movement. The better class of studio
stand is, however, much more ornate and elabor-
ate (see "Studio Camera"). The Hana studio
stand C is novel in construction, having a counter-
ease and smoothness of movement, the camera
may be raised as high at 7 ft. or lowered to only
2 ft. from the ground. The tripod stand A for
A. Tripod Stand for Field Camera
balanced platform travelling on two upright
pillars, to which it may instantly be clamped
by pulling a lever. Besides the advantages of
B. An Ordinary Form of Studio Stand
C. Studio Stand with Counterbalanced Platform
field cameras is usually made to fold up, the three
legs being then strapped together for carrying.
Camera, Vertical
87
Camera, Vertical
The bottom joint should have a sliding move-
ment to aUow of adjustment on uneven ground.
The top, or head, is detachable ; it is covered
D. Telescopic Stand
with felt to avoid scratching the camera, and it
has a hole for the screw by which the latter is
secured. Many tripod legs, however, are made
to fit a turntable at the bottom of the camera.
The tripod head must be sufficiently large for
the apparatus which it is to support, or vibration
wHl occiir. Steadiness and rigidity should be
the distinguishing characteristics of a tripod
stand, and should be considered before lightness,
though the two quaUties are not necessarily
antagonistic. Telescopic stands D of brass, steel,
or aliitnitiinm are very portable, but are suitable
only for Hght cameras.
CAMERA, VERTICAL
Cameras are used vertically for the purpose of
photographing ceilings, floors, or articles laid
upon a horizontal surface. Vertical fittings are
A and B. Hinged and Strutted Table for
Vertical Camera
obtainable commercially, but most are home-
made. A and B show a very simple arrange-
ment, the exact size of which will depend upon
the camera used. The accessory takes the form
of a narrow hinged table, which is screwed to the
ordinary tripod top, the camera being screwed
to the hinged portion, which, in use, is supported
vertically by a strut, as shown. The camera
can be pointed upwards or downwards in a
perfectly vertical position, or, if the strut con-
tains various holes to pass over the screw,
at any angle. The late T. C. Hepworth's
method (described first in 1894) allows of the
camera being pointed downwards but not
upwards, and it is largely used for photographing
precious stones, medals, illustrations from books,
etc. One advantage of such an arrangement
(see figure C) is that it may be used in an
ordinary room against a window, and the sub-
jects will probably be as well hghted as in a
studio. This arrangement has been used for
photographing a baby lying in a cradle. The
camera is fixed at the top end of a skeleton stand ;
upon the glass platform E can be placed a coloured
card, paper, or other medium to serve as a back-
ground on which the opaque objects, flowers,
etc., may be laid and photographed from above.
By employing a glass platform shadows are
obviated, and this in some cases is of great
advantage, while at the same time it is possible
to use at any distance below the glass a back-
ground of any colour, which, by screening the
Bght, can be lightened or darkened as may be
required. A useful addition is a bhnd V to shut
ofi all hght from the upper surface of the plat-
form ; another is a mirror G to reflect the hght
upwards. By placing a negative upon the glass
platform a reduced or enlarged transparency
can be obtained more easily than by any other
plan. Should the negative be a film it can be
kept flat by placing a piece of glass over it.
C. Vertical Camera
In process work, stands holding cameras
vertically are frequently used when copying
small objects supported on a horizontal surface
and these stands are also of advantage when
copying from open books.
Cameron, Julia Margaret
Candle-light Effects
CAMERON, JULIA MARGARET
Bom in Calcutta, 1815 ; died in Ceylon, 1879.
Came to London in 1848, started photography
in 1865, and became famous for her admirable
portraits of celebrated persons.
CAMPHOR (Pr., Camphre : Ger., Kampfer)
Common camphor is known also as Japan
camphor. A colourless, translucent, crystalline
solid with characteristic smell ; melts at 175° P.
(nearly 80° C), is soluble i in 700 of water, and
is readily soluble in alcohol, oils, etc. It is
used in the manufacture of celluloid, varnishes,
and retouching mediums. Skies may be blocked
ou,t of a negative by holding the latter glass-side
downwards over a piece of hghted camphor, and
wiping away the soot from the parts of the nega-
tive it is desired to print.
CANADA BALSAM (Pr., Baume du Canada ;
Ger., Canadabalsam)
Known also as Canada turpentine. A resin-
ous fluid, transparent, and of a greenish yellow
tint, very viscous, and hardening into a clear
transparent solid, whose refractive index is about
equal to that of glass. It is obtained from the
Balsam Fir of North America, Abies halsamea
(Coniferse). In its conmiercial state it has the
consistency of honey ; it may be hardened by
exposing to the air or rendered more liquid by
heating or by the addition of turpentine, ether,
or chloroform, but is insoluble in water. It
has several uses in photography — for the cement-
ing of lenses together, making varnishes, and
rendering paper negatives and prints for the
crystoleum process translucent.
In process work, Canada balsam is used for
sealing together the two halves of the ruled
screens and for sealing colour filters. A further
use is for sealing a thin microscope cover glass to
the centre of the ground-glass focusing screen,
so that a transparent spot is provided for
focusing by means of a magnifying eye-piece.
CANARY AND ORANGE MEDIUM
A yellow or orange non-actiuic fabric used for
screening the light in dark-rooms ; yellow paper
and glass may also be used in place of the usual
red light for some photographic purposes. It
is less tiring to the eyes than red and gives more
illumination. A yellow light, however, is not
safe for modem rapid dry plates and isochro-
matic plates, but it is admirable for bromide
papers and lantern plates. It is more suitable
for use with artificial light than with daylight,
and when the latter is used two thicknesses of
canary medium may be necessary. Orange
medium or paper cuts off more green and blue
light than canary mediiun, and allows more
orange and red to pass, and it may therefore
be used for the slower brands of plates providing
the light is not particularly strong. According
to Sir William Abney, the total illuminating
value of the orange is nearly twice that of
the canary.
CANDLE BALANCE (Pr., Balance A chandelle ;
Ger., Kerzenwage)
An instrument employed in photometry to
ascertain the loss of weight undergone by a
candle after burning 3 given time.
CANDLE-LIGHT EFFECTS
Lighting effects in a photograph, apparently-
due to the use of a candle as the illuniinant.
Actually the candle pictured plays no part
whatever in the real illumination of the sub-
ject. This branch of work was made popular
by Newson Gibson, who, during the years
1 90 1 to 1904, produced many remarkable
candle-light effects which were puzzling at the
time, as it was well known that a candle did not
give a sufficiently actinic hght for ordinary
photography. The secret consists in using a
piece of lighted magnesium wire hidden from
the lens, but placed as near as possible to the
candle flame, so that the light from the magne-
sium appears to come from the candle, the back-
C D
A. Magnesium Wire Holder Over Candle
ground immediately above and behind the
candle being quite black. A blackened holder
supports the magnesium wire above the caudle,
and is invisible against the black background.
Proper arrangements must be made for carrying
ofi the smoke. In the illustration above, A B C D
represents the amount of the subject taken in
by the lens, the candle being placed as shown
and the remainder of the picture being filled with
suitable objects. The blackened shield or tube,
with the wire behind it, is shown at E, and is
lowered until the wire ignites, the smoke escaping
up the tube and not showing in the picture.
Another arrangement B is also recommended
by N. Gibson. A strip of wood G 30 in. long and
if in. wide is faced on the side that goes nearest
the camera with black velvet ; to the top is
loosely fastened a long rod H as a handle for the
operator, so that the light shield itself hangs
vertically, whilst its weight prevents any motion.
On the reverse side of the wooden strip is fast-
ened a triangular chimney j made of tinplate,
its bottom being about i-J in. from the lower
end of the wooden strip. At the bottom of the
chimney the magnesium K is placed, in such a
way that the wire may be easily lighted when
lowered on to the candle, and the smoke may
escape up the chimney and out of the picture.
When the magnesium ignites, the shield is raised
to expose the flame of the candle and the
exposure is made. The long chimney is necessary
when the candle is low down in the picture, but
when near the top and the smoke has not far
to travel a shorter chimney may be used.
Another worker uses a platinotype tin, as shown
at E, one half at the bottom being cut away and
the magnesium wire f suspended from a wire
Candle-
power
89
Ceuivas, Enleirgements Upon
running across the centre, the whole arrange-
ment being suspended on wire and let down on
the candle. It matters little what method is
adopted as long as the magnesium is hidden
and burned as near as possible in the position
of the flame. The flame of the candle must also
be kept steady during the exposure. A little
dayUght may at times be used to light up the
dark comers of the room, but it must not be
too strong, as the light must appear to come
from the candle itself. The necessary exposure
can only be found by trial ; as a basis for experi-
ment, expose for the whole of the time during
which I in. of magnesium wire is burning and
after it has burnt out allow another second for
B and C. Arrangements for Buming Magnesium
for CandleUght Effects
the candle flame, the stop being //ii and the
plate extra rapid. The "lamps " described have
an effective radius of only 2 ft. or 3 ft., so that
subjects must be arranged accordingly.
CANDLE-POWER
The unit for photometric work in England.
The light emitted by a standard candle. (See
" Unit of Light.")
CANDLES, FLASHLIGHT
Magnesium made up in the form of candles
with a wick of " touch " material. The commer-
cial candles are of various sizes, buming for and
giving exposures up to about half a minute, the
.most popular being the 2, 4, 7, 12, and 20
seconds sizes. The candles shoiUd be kept in a
dry place, as otherwise they wiU bum and
splutter badly when fired, and they should be
burnt on a metal tray or iron shovel. Service-
able flash candles of a kind may be made at
home according to the following formula : — •
Magnesium powder . . 20 parts
Barium nitrate. . 30 „
Flowers of sulphur 8 ,,
Beef tallow (or suet) . 7 ,,
Melt the suet or tallow, carefully knead in the
other ingredients, place in smaU metal boxes,
mould the top to a point like that of a candle,
and fire by means of a torch. They should be
burnt on an iron shovel. This preparation gives
a good hght, and may be used out of doors in
large quantities for street work at night, and
in small quantities in a room. (See also " Flash-
light Mixtures.")
CANVAS EFFECTS
Photographs having the appearance of being
printed upon canvas. Negatives may be printed
upon canvas-grained paper, which is obtainable
commercially, or a piece of thin canvas or
bolting cloth (which see) may be interposed
between the negative and the sensitive paper.
Negatives for producing canvas effects direct
upon the paper may be obtained by exposing
in the camera in the ordinary way, and then
making a second exposure, this time with the
lens focused on canvas, so adjusting the expo-
sures that the grain of the canvas does not pre-
dominate over the original exposure. Another
method is to make a separate negative of the
canvas, and to print from this before or after
using the same piece of paper for printing from
another negative ; this is probably the easiest
and most economical method, as the one negative
of the canvas may be used for any number of
pictures, and the canvas effect printed light or
dark over the original print as desired. A good
strong sidelight should be used when making a
negative from the canvas in order to emphasise
the grain. Any suitable fabric may be substi-
tuted for the canvas.
In process work, a canvas grain is often
imparted to the highly glazed "art" papers
used for three-colour printing, so as to give a.
more artistic effect imitating the painter's canvas.
This graining is done by running the paper
between a pair of embossing rollers, one of which
is steel, bearing the pattern, and the other of
paper, to take the impression.
CANVAS, ENLARGEMENTS UPON
Enlargements are made direct upon canvas
for the use of artists, either for finishing direct
or as a basis for oil-colours. The canvas must
first be cleaned with a mixture of i oz. of liquor
ammoniae ('880), and 4 oz. of methylated spirit,
this being rubbed on with a clean rag or sponge
until all greasiness is removed. Three solutions
will then be required for sizing, sensitising, and
developing.
Sizing
Distilled water . . 10 oz. 1,000 ccs.
Ammonium bromide . 35 grs. 7 g.
Ammonium chloride . 10 „ 2 „
Potassium iodide . 80 „ 16 „
Gelatine . . . 60 „ 12 ,,
Dry albumen . . i oz. 100 ,,
Mix and warm the mixture until the gelatine is
dissolved, but avoid overheating or the albumen
win be coagulated.
Sensitising
Distilled Water . . 6 oz. 500 ccs.
Glacial acetic acid . i „ 40 g.
Silver nitrate . . } „ 80 „
Mix and filter.
Developer
Distilled water .
Lead acetate
Gallic add
The cleaned canvas is sponged over with the
sizing mixture as evenly as possible. When
dry it is ready for sensitising. Take the canvas
into a dark-room, pour over it some of the silver
sensitising mixture, and spread evenly with a
5 oz.
500 ccs
5 grs.
I s-
30 „
6 „
Canvas, Mounting on
90
Carbon Process
pad. of cotton wool. Wet or dry it is ready for
exposing in the same way as bromide paper,
but it is slower than most bromide papers. The
developer is applied with the sponge previously
used for sensitising, the residue of silver assisting
development. The canvas is fixed in a bath of
" hypo " I oz., water 5 oz., and washed well.
During aU these processes the canvas may
remain on its stretcher.
CANVAS, MOUNTING PRINTS ON
The canvas needs to be strained on a frame.
The print or enlargement is placed on a. table
face downwards, and coated with any good
mountant, starch paste being as good as any-
thing. The paste should be rubbed in well with
the brush or sponge until the print is limp. Then
the stretched canvas is lowered upon it, picked
up with the adhering print, and laid right way
up on the table. The print needs to be rubbed
into close contact, special attention being given
to the edges, which may need treatment with a
paper-knife.
CANVAS, PRINTING ON [See "Fabrics,
Printing on.")
CAOUTCHOUC {See " Indiarubber.")
CAP, LENS (Ft., Bouohon : Ger., OhjecHv-
Deckel, Linse Kappe)
A circular, closely-fitting covering for the
lens, lined with blaci velvet. At one time all
exposures were made by taking off and replacing
the cap, but for this purpose a shutter is now
commonly used. The cap is still, however, often
resorted to for time exposures ; and caps are
generally provided on stand cameras for the
protection of the lens, even when a shutter is
fitted behind the lens.
CARAMEL (Fr., Caramel: Ger., Karamel)
A deep reddish-brown, sticky Uquid, made by
heating loaf sugar. It may be obtained in
liquid form from chemists, who call it sac-
charum ustum. It is used in photography as a
backing for plates to prevent halation. A rough
and ready method of making a small quantity
at home is to place loaf-sugar in a dry iron sauce-
pan over a slow fixe and stir with an iron spoon.
At about 400° F. (204° C.) caramel will be
formed, but it requires a considerable amount
of care to make it properly, as over- or under-
heating will spoil it. The superiority of caramel
over other backings is due to its non-actinic
colour and to the fact that its refractive index
is nearly the same as that of glass. {See also
" Backings, Plate.")
CARBOLIC ACID (Fr., Acide pMnique ;
Ger., Karbolsdure)
Synonyms, phenyhc alcohol, phenol, phenic
acid, and hydrate of phenyl. CgHsOH. Mole-
cular weight, 94. It is soluble in water, alcohol,
ether, benzine, chloroform, etc. ; it is volatile
and extremely poisonous, and causes bums on
the skin. It is colourless when fresh and pure,
but gradually turns pink on exposure to light.
It is used to preserve moimtants, emulsions, and
many other mixtures. It is the starting-point
of many photographic chemicals.
CARBON BISULPHIDE {See " Carbon Bisul-
phide.")
CARBON DISULPHIDE (Fr., Sulfure de car-
bone ; Ger., Schwefelkohlensioff)
Synonym, carbon bisulphide. CS^. Molecu-
lar weight, 76. Solubilities, insoluble in water,
soluble in alcohol and ether. Its vapour is
inflammable. It is a colourless, highly refractive
liquid with characteristic odour, which in im-
pure samples is extremely unpleasant. It is used
as a solvent for unvuJcanised indiarubber in
making rubber solution.
CARBON ENLARGEMENT
An enlargement made by the carbon proce.ss.
As this process of printing is much too slow for
making direct enlargements in the camera, an
enlarged negative has to be made, and prints
taken from that by daylight in the ordinary
manner. For printing in carbon, an enlarged
negative should be reversed, so that the print
can be made by the single transfer method and
still be non-reversed. The most simple and
satisfactory manner of obtaining a reversed
negative when reproducing or enlarging is to
reverse the transparency in the carrier, putting
the glass .side towards the lens instead of the
film. {See also " Enlarged Negatives " and
"Carbon Process.")
CARBON PROCESS
The idea of the carbon process as it is known
to-day is credited to A. 1,. Poitevin, who, in a.
patent dated December 13, 1855, describes
the action of light upon a chromated gelatine
mixed with a. pigment. J. Pouncy is supposed
to have been the first actually to produce carbon
prints, his patent being dated April 10, 1858.
In these early processes the half-tones were
mostly unsatisfactory, and modifications were
made by J. C. Burnett (1858) and Fargier (i860) ;
but it was not until J. W. Swan's improvement
in 1864, when he patented carbon tissue, that
the process became of any practical use to
photographers. J. R. Johnson made further
improvements in 1869, and in 1874 the flexible
support used in the process was patented by
J. R. Sawyer.
The carbon process differs essentially from
all other methods of photographic printing. It
depends for its working on the fact that gelatine,
to which has been added a suitable proportion
of an alkaline bichromate, becomes insoluble
when exposed to hght, but retains its solubility
if kept in the dark. A sheet of paper is coated
with a mixture of gelatine, colouring matter, and
potassium bichromate, and then exposed to day-
light under a negative. The portions of the
gelatine film that were protected by the high
lights or dense parts of the negative retain their
solubility, while those that receive the full force of
the light through the shadow portions become
insoluble. Parts exposed under the intermediate
tones become partially soluble. By treating the
film with hot water the soluble portions are dis-
solved away, while the insoluble parts remain,
and form the picture. Any colouring matter
may be employed, and consequently a picture
may be produced In any desired colour.
Carbon tissue is a dark-surfaced paper, the
Carbon Process
91
Carbon TUsue
colour corresponding to the deepest tone that
can be obtained in the picture. No visible
image is produced by exposure to light, and
consequently, the exposure in the printing frame
must either be timed or gauged by an actino-
meter. Carbon tissue sensitised in H. W.
Bennett's sensitising bath requires about half
the exposure necessary for printing-out silver
paper to the full depth necessary for toning,
or rather less than the printing-out paper
requires to give a visible image resembling a
finished result. The prints should be developed
as soon as possible after taking from the frame
(see "Continuing Action"). A piece of single-
transfer paper, slightly larger than the exposed
print, is also required. The exposed film must
be developed from the back, for the reason that
the whole of the face has been rendered insoluble,
excepting the extreme high-Ughts, while all the
surface in contact with the paper has remained
soluble. The film is so thick that the strongest
shadow does not penetrate right through. In
the deep shadows the insolubility penetrates
deeply ; in the medium tones there is a moder-
ate thickness of insoluble gelatine, while in the
very hght parts there is simply a slight super-
ficial insolubility. This layer of soluble gelatine
of varying thickness underlying the insoluble
image necessitates transferring the film so that
the soluble portion becomes the surface. Any
attempt to develop the film on its original paper
would result in its floating right off as soon as
the soluble gelatine commenced to dissolve.
Transferring and developing the exposed print
are simple matters. The piece of transfer paper
is soaked in cold water imtil limp. The exposed
print is then immersed in cold water for a few
seconds, untU it begins to become flat, and its
face is then brought into contact with the pre-
pared surface of the transfer paper, preferably
under water, the two papers brought out together,
squeegeed firmly into contact, and then partially
dried between blotting-paper under moderate
pressure for ten or tw5ve minutes. The print
is now ready for development. It is placed in
water that has been warmed to 105° to 110° P.
(40'5° to 43-3° C), and kept below the surface.
In about twenty or thirty seconds some of the
colour wiU be seen oozing from the edges. This
is the object of the safe edge, to preserve a mar-
gin of soluble gelatine ; without it the next
operation would be impracticable. As soon as
the colour is seen to be oozing out, the corner
of the paper bearing the film is lifted, and if it
comes away easily it is pulled steadily away,
leaving the film on the transfer paper. This film
is allowed to soak for a few minutes in the hot
water, and from time to time the water is
gently splashed over it, and it is taken from the
water and partially drained. This treatment is
continued until the print is sufficiently hght,
when it is drained thoroughly and then rinsed in
cold water to wash off any loose gelatine and
colour that may adhere. It is next immersed
for about five minutes in an alum bath (i oz.
to 20 oz. water), washed in about three changes
of water, and dried. With the exception of the
developing bath, all the solutions should be cold.
Care must be taken to avoid touching the sur-
face of the fihn during the working.
An objection to this method of working — the
single transfer method — is that the picture is
reversed, the left side becoming the right. When
it is desirable to avoid this a second transfer is
necessary, and the method is known as " double
transfer." Instead of using the single transfer
paper, a temporary support is substituted (see
"Flexible Support"). The method of working
is exactly the same as described for single transfer,
excepting for the preliminary waxing of the sup-
port. After development, treatment in the
alum bath, and drying the print on the temporary
support, it is ready for the second transfer. The
drying on the temporary support must not be
rapid, and the transfer should take place as soon
as po.ssible after drying, or else the print should
be kept in a cool place, moist rather than too
dry. A piece of final support or double transfer
paper is soaked in cold water for at least half an
hour, and then the temporary support bearing
the print is similarly soaked until quite limp.
Both are then immersed in warm water, about
90° P. (32° C), for about fifteen or twenty
seconds, face to face. Then they are withdrawn
clinging together and squeegeed into good con-
tact. When thoroughly dry the two papers
may be pulled apart, and the image will be firmly
and permanentiy attached to the double transfer
paper. The necessity for the second transfer is
frequently obviated by the employment of a
reversed negative. (See also " Carbon Tissue,"
" Carbon Transfer Papers," " Flexible Support,"
" Bennett's Carbon Sensitiser," etc.)
CARBON TETRACHLORIDE
Synonym, tetrachloromethane. CClj. Molecu-
lar weight, 156. A colourless, oily substance,
resembUng chloroform, volatilising completely
without odour, having a boiling point of I70'6° P.
(77' C), and a specific gravity of 1-593 at 68" P.
(20° C). It is obtained by acting upon chloro-
form with chlorine, and in other ways. It has
no action on metals, fabrics or colours, and it is
an excellent solvent of shellac, asphalt, fats, etc.
CARBON TISSUE
The paper prepared for printing by the carbon
process. It consists of a stout paper thickly
coated with a mixture of soft, soluble gelatine
and finely ground colour. As gelatine is colour-
less, any suitable and permanent colouring
matter may be employed, and this determines
the colour of the print. In preparing carbon
tissue, it is necessary that the film should be
appreciably thicker than the depth of the strong-
est shadow of the finished print in order that a
thin layer of soluble gelatine should remain
between the insoluble shadow and the. paper
support. Carbon tissue is prepared in two forms,
sensitive and insensitive. In the former, a
certain proportion of potassium bichromate is
mixed with the gelatine and colour when pre-
paring the film ; in the latter, the bichromate is
omitted, and the tissue requires sensitising by
immersion in a bath of potassium bichromate
before it can be used.
In process work, carbon tissue is used to a
considerable extent, the photogravure process
being, for example, solely worked with a carbon
resist' developed on the copper plate. The
special autogravure tissue is generally employed,
but some workers prefer the ordinary standard
Ccurbon Transfer Papers
92
Caricature
brown. It is also used as the resist in engraving
copper rollers for the rotary intaglio process of
printing. It may also be used as a resist for
relief grain blocks (an inverted photogravure).
In the Government Survey Offices an electro-
typing process for the reproduction of maps is
worked by developing a carbon print on a silvered
copper plate, and then depositing copper on it
so as to form a duplicate plate.
CARBON TRANSFER PAPERS
Transfer papers for receiving the film or
image in the carbon printing process. Two
kinds of such paper are used, called respectively
" single transfer paper " and " double transfer
paper." The former are those employed when
the film or image is transferred from its original
paper to one on which it is to remain perma-
nently ; the latter are used when the film is
transferred to a temporary support for develop-
ment, and re-transferred to a final support as its
permanent basis. Single transfer paper is pre-
pared by coating any suitable paper with gela-
tine that has been so hardened as to be prac-
tically insoluble and impermeable. Double trans-
fer paper bears a thicker coating of soluble
gelatine. Both kinds of paper are easy to
prepare ; any carbon worker can therefore
obtain his favourite paper by preparing it
himself.
The easiest method of working for the single
transfer process is to coat the paper first and
harden the gelatine coating afterwards. A
solution of gelatine should be prepared, i oz.
being soaked until soft and then dissolved by
heat and made up to about 25 oz. The gela-
tine solution should be appUed to the paper as
evenly as possible, by means of a flat brush or
a spouge. The brush should be taken first along
the sheet of paper, then across, and then diagon-
ally, so as to avoid ridges and to render the
coating even. Many workers prefer to give two
thin coatings rather than one of medium thick-
ness, the second being applied after the first
is quite dry. AVhen the gelatine coating is
thoroughly dry it should be hardened by immers-
ing the prepared paper in a solution of chrome
alum, 12 grs. to each t oz. of water. Three or
four minutes should be allowed for immersion,
and the paper should then be rinsed in two or
three changes of water and dried.
For double transfer a thicker coating of
gelatine is required, this being obtained by
two or three coatings of the solution given
for single transfer ; and no hardening solution
is employed. Both kinds of paper will keep
indefinitely if stored in a. dry place. The
methods of using are given under the heading
" Carbon Process."
The double transfer paper is often used by
photo-lithographers as a photo-transfer paper,
and is foimd to be very suitable for this purpose
.when sensitised with bichromate.
CARBONATE
A salt derived from the hypothetical dibasic
acid HjCOj, or carbonic acid; for instance,
Na^COa carbonate of soda. Carbonates are of
three kinds, normal, acid, and basic ; all are
decomposed by dilute sulphuric or hydrochloric
acid, with the production of carbon dioxide.
CARBOXYLIC ACIDS
Acids derived from the aromatic hydrocarbons
by the substitution of one or more carboxyl
groups (COOH) for a corresponding number of
hydrogen atoms ; they are named mono-, di-
carboxyUc acids, etc., accordingly. Examples
are formic and acetic acid.
Hydroxycarhoxylic acids are carboxylic acids
containing also a hydroxyl group (OH). An
example is lactic acid.
Amido-carhoxylic acids contain the amido or
amino group (NHj) as well as COOH.
CARCEL LAMP (Pr., Lamps carcel ; Ger.,
Carcel-lampe)
A lamp adopted at the Paris Electrical Con-
gress of 1881 as the French unit of illumination
in photometry. It bums 42 g. of colza oil per
hour, has a flame 40 mm. in height, and gives a
light equal to about gj standard candles.
CARICATURE (Pr., Caricature: Ger., ZerrUld,
Karikatur)
A freak portrait obtained by using special
backgrounds and foregrounds, distorting the film,
copying, etc. Some of the methods of producing
caricatures are described below, and others will
be found under such definite headings as
" Doubles " and " Trick Photography." Large
heads on small bodies. — These may be produced
in many ways, one of which is to draw the neces-
sary figure, without a head, upon a sheet of
A and B. Caricature Cards
white cardboard, the coUar, or neck, being at the
extreme top, as at A, or a circle may be cut out
for the insertion of the head, as at B. If the
former is used, the model sits upon a chair and
holds the design under the chin. The bap>:-
ground should be of the same colour as the
caricature card, and the junction between the
two is spotted out so as not to show upon the
finished print. An objection to the above plan is
that only the head of the sitter is photographed
and the following method may be preferable :
Two negatives, one of the head of the size re-
quired and one a smaller picture of the body,
are made ; the larger head is cut from the print
and pasted over the smaller head in the other
picture, the whole being then copied in the
camera. Distorted heads and bodies. — Distorted
images may be obtained by warming a partially
dried negative before a fire or over a gas flame,
the heat causing the gelatine to melt ; tie picture
can be made to " run," and can be distorted,
therefore, to any extent. When dry, the nega-
tive can be printed from in the usual way ; but.
Carmine Tones
93
Casein
of course, it cannot be restored to its original
state. Another plan is to strip the film from
the negative, and to attach it to another glass,
stretching it during the process, and allowing it
to dry in its stretched position upon the new
Y
J
C. Obtaining Thin-face Caricature
support. Broad, and. long faces. — Excessively
long or broad faces may be produced by the use
of convex or concave mirrors. The sitter is posed
in front of the mirror, and the distorted image
in the glass photographed ; but great care is
necessary to avoid reflections. Another, and a
much easier, plan is to copy an existing and
proper photograph ; for example, the portrait
print is placed in front of the camera, with one
edge nearer to it than the other, as in C. The
result will be that the width of the face is partly
lost, the effect being a lengthening of the face.
If an excessively broad face is desired, the print
is copied while lying at an angle to the horizontal
plane (the less the angle the shorter wUl be
the resulting figure) ; T) shows the idea, the
bottom edge of the pictiire being nearer to the
D. Obtaining Broad-face Caricature
camera than the top edge. Many firms sell
specially painted comic backgrounds for making
caricatures, also negatives of comic scenes into
which the head from any existing negative can
be printed.
CARMINE AND CRIMSON TONES
If a negative is of good contrasts P.O. P.
prints from it may be toned to a good carmine,
as follows : Print and wash as usual, and tone
in —
Ammonium sulpho —
cyanide .
20 grs.
45 g-
Potassium iodide
4 ,.
9 ,,
Gold chloride
I gr-
2.25 „
Water
I oz.
1,000 CCS
Toning takes, from twenty to thirty minutes,
and the tone as well as the time may be altered
by varying the amount of iodide. The bath has
a slight intensifying action. Any discoloration
on the back of the paper and in the high lights
will disappear in the fixing bath. Wash and
fix in " hypo " as usual.
CARRAGEEN {See "Iceland Moss.")
CARRIER (See "Camera Carrier," "Plate
Carrier," etc.)
CARTE-DE-VISITE (Pr.)
A popular size of professional studio portrait.
Size of mount, 4^ in. by 2J in. ; size of print,
3i in. by 2J in. or 3f in. by 2^ in., the latter
being " No. i C. de V.," and the former " No. 2
C. de V." The carte-de-visite was at the height
of its popularity in England in the sixties of
the nineteenth century. Its origin was due to a
fancy of the Duke of Parma, who, in 1857, had
his portrait gummed on his visiting-cards in the
place of his name. Perrier, a professional photo-
grapher of Nice, is supposed to have produced
the first of this popular size ; but it was Disderi,
of Paris, the Court photographer to Napoleon
III., who made it popular.
CARTON DURA
Hard waterproofed cardboard, formerly used
for making photographic dishes. It was made
by coating Bristol board with linseed oil, varnish
and asphalt, but has now been superseded by
papier mach6.
CARTRIDGE FILM (Pr., PelHcule enrouUe ;
Ger., Patronfilm)
A daylight-loading roll-film, consisting of an
emulsion on paper or celluloid, wound on a
wooden spool, together with a length of opaque
black paper. Cartridge films are used in roU-
holders — a kind of dark-slide — and in various
forms of hand cameras made to take the films
direct. A winding key is employed to pass the
film, as exposed, on to another spool. The first
roU-film on a paper support was introduced, in
1875, by L. Wamerke, and the first celluloid
roll-fihn in 1 889, by the Eastman Company. The
non-curhng film — that is, a celluloid film with a
thin layer of plain gelatine on the back — ^was
placed on the market by the latter firm, now
known as Kodak, Ltd., in 1903.
CASEIN. OR CASEINE (Fr., CasHne ; Ger-
Kasein)
Solubilities, insoluble in water, soluble in
alkaUs and organic acids. It is obtained from
milk by acidification, and is commonly known
as curds. It has been introduced as a vehicle
for the silver salts in printing-out paper, as it
gives a film which does not become sticky, does
not curl up, and is not easily scratched.
In process work, caseine has been advocated
for some years past by Prof. Namias and others
as a substitute for albumen and fish-glue enamel
to form a resist for etching zinc or copper. It
has not, however, come into general use. The
casein solution is made up as follows : —
3i oz.
• 15 „
• * „
Liquor ammomse
Potassium carbonate
Caseine .
Allow the whole to stand some hours to dis-
solve, and sensitise the solution with a saturated
solution of ammonium bichromate. The whole
is mixed and filtered into a clean bottle, which
has to be kept closed. The plate is coated in
the usual way, and after exposure under a
Caseine Pigment Printing
94
Catatype
negative is inked and then immersed in water.
Afterwards it is rinsed without rubbing with
cotton-wool. The caseine image is highly resist-
ant to the mordants usually employed, without
the necessity of burning-in.
CASEINE PIGMENT PRINTING (Pr., Tir-
age en casSine et pigment ; Ger., Kasein
Pigmentdruck)
A process patented by the Neue Photograph-
ische Gesellschaft, in 1908, for obtaining prints
in caseine and pigment from bromide or other
silver prints. The caseine is employed either
in the form of " curd," or in an acid or alkaline
solution. In a typical formula, 2,200 grs. of
pressed-out curds and 440 to 520 grs. of water-
colour are ground together, Oie mixture being
brushed over the bromide print and allowed to
dry. The print is then immersed for ten to
fifteen minutes in : —
Potassiimi bichromate
Potassium ferricyanide
Potassium bromide
Water to
88 grs. 9 g.
88 „ 9 „
88 „ 9 „
20 ,, 1,000 CCS.
This has the effect of rendering the pigment-
incorporated caseine insoluble at those parts
where the silver image is present, the action
varjring in degree according to the depth or
gradation of the latter. The picture may there-
fore be developed in water at from 105° to
125° F. (41° to 51° C), after the fashion of a
carbon print, a little potassium oxalate or
sodium bicarbonate being added to ensure
clearness of the lights. The original black silver
image fades to a faint brown during treatment,
and is practically invisible under the final pig-
mented picture.
CASKET LENSES
In their original form casket lenses were put
upon the market by Darlot, of Paris. His set
consisted of a portrait lens (covering 7 in. by
6 in., or with a smaller stop and adjustment of
the tube 8 J in. by 6f in.) and six single achro-
matic lenses fitting into the same tube, which
could be used alone or in pairs, giving fifteen
double lenses varying in focal length from 2f in.
to 9 in., each covering a plate whose lengtii is
considerably greater than the focal length of
the lens. Other makers have since produced
similar sets, amongst them being caskets of
simple uncorrected "spectacle" lenses for artistic
photography. The highest development of the
casket idea is found in tiie Zeiss Satz-anastigmats.
These consist of three or four perfectly corrected
anastigmatic lenses working at//i2-5. The D
set gives, in the single combinations, focal lengths
of I if in. to 19 in., and as doublets four com-
binations working at //6'3, the focal lengths
varying from 7 in. to 10 in. The casket system
was very popular some years ago.
CASSETTE (Ger., Kassette)
A French term occasionally used in early
British photographic works, and meaning the
plate-holder or dark-slide.
CASTILE SOAP
A pure soap made from olive oil and soda,
■and obtainable in two varieties, one a pure white
or yellowish white, and the other marbled or
veined with bluish-green ; the former is the
better for photographic purposes. It is used for
making encaustic pastes or for waxing glasses to
be used for stripping, also, when mixed with
methylated spirit, as a lubricator for prints to be
passed through a bar burnisher.
CASTOR OIL (Pr., Huile de ricin ; Ger.,
Rizinusol)
Solubilities, insoluble in water, soluble in
alcohol, ether, and glacial acetic acid. It is a
pale yellow, non-drying oil, obtained by expres-
sion from the seeds of Ricinus communis. It is
used in some varnishes and enamel collodion,
and to render paper translucent. Also, it is
used for temporarily cementing lenses, and as a
lubricant.
In process work, castor oil is used in two very
useful ways. It is added to collodion to make
it more flexible for the stripping process, and it
is used for treating the surface of an albumen
or fish-glue coating on zinc or copper, so as to
cause a negative film to adhere temporarily
whilst printing is in progress.
CATALYSOTYPE (Fr. and Ger., Cataly-
sotypie)
A variation of the calotype process, invented
in 1844 by Dr. Woods, in which the paper is
coated with a syrupy mixture containing
ferrous iodide instead of with potassium iodide.
The coated paper, having been sensitised by
brushing over with a silver nitrate solution, is
exposed in the camera, and the image either
develops itself, or is caused to appear by merely
keeping the paper moist. Its name was given
under the erroneous impression that the develop-
ment was due to a catalytic action — that is, a
chemical change brought about by an agent which
remains itself apparently unaffected. It is now
known, however, that this is not the case, since
ferrous nitrate, an energetic developer, is pro-
duced when the paper is treated with the silver
nitrate solution, by the same decomposition that
forms the sensitive silver iodide. The process
is not very satisfactory, the silver solution being
soon blatiened by the iron, and the ferrous
iodide mixture itself being inconstant in com-
position.
CATATYPE (Fr. and Ger., Catatypie)
A process depending on catalytic action, which
is defined in the preceding article. In the
original catatype process patented by Messrs.
Ostwald & Gros in 1901, a negative image
consisting either of silver or platinum is immersed
in a solution of hydrogen peroxide in ether, being
then withdrawn and the ether permitted to
evaporate. The peroxide is decomposed where-
ever it comes in contact with the metal, but in
various degrees according to the different grada-
tions of the picture. The negative so treated is
now pressed into contact with a gelatine
film for a few seconds, an invisible hydrogen
peroxide image being thereby taken up by the
latter. If the gelatine film is then immersed in
an alkaline solution of a manganous salt, brown
manganese peroxide is formed wherever hydrogen
peroxide is present, a brown positive image
being thus obtained. Or, if an alkaline silver
Catechol
95
c.c.
solution is i;sed instead of a manganous salt,
a black image in metallic silver results.
Another method is to place an ordinary
negative in contact with hydrogen peroxide, as
before, and to bring it for about thirty seconds
into contact with a gelatine paper in which a
pigment is incorporated, the paper being then
immersed in a solution of a ferrous salt. The
invisible hydrogen peroxide image taken up by
the gelatine will oxidise the ferrous salt to the
ferric state, in which it is able to render the
gelatine insoluble, the insolubilisation exactly
corresponding to the various degrees in which
the peroxide is present. The print can then be
developed with warm water, as in the carbon
process. There are many other variations of
the catatype process, mostly patented.
CATECHOL
Another name for the pyrocatechin developer.
CATECHU OR CUTCH (Fr., Catechou ; Ger.,
Katechu)
Solubilities, soluble in water and alcohol. It
occurs in irregular, brittle masses of dark brown
colotiT, sUghtly porous and glossy when freshly
broken ; it is an extract obtained from the wood
of a species of acacia.
There are several varieties of catechu known
in commerce, the principal being ordinary or
brown catechu, yellow lump catechu, and cubical
or yellow catechu, but all are of practically the
same composition. Bengal or Bombay catechu,
of the ordinary or brown variety, is the best
for photographic purposes, it being rich in
tannin. It is of a dark reddish-brown colour
with a brilliant fracture, and is almost entirely
soluble in water, giving a highly coloured brown
solution. It is used for toning platinum prints,
the process being known as " Packham's," also
for toning blue (ferro-prussiate) prints to a green-
ish-black colour, the latter being known as Roy's
process. (See " Blue-print Process.")
CATECHU TONING
A method of toning prints on platinum paper
to various shades of brown by means of a solution
of catechu was introduced by J. Packham in
1895. The stock toning solution is made up as
follows: Place 120 grs. of catechu in 5 oz. of
water and boil for five minutes ; allow to cool,
and then add i oz. of alcohol. To make up a
working solution add 30 to 40 drops of the stock
solution to one pint of water, and heat to a
temperature between 130° and 150° P. (54° to
66° C). The washed black and white platinum
pictures are immersed therein, and toning wil
be complete in about fifteen minutes, the colour
being a rich mellow brown. Within one minute
of immersion the prints will probably begin to
change, and thereafter pass through various
shades of brown in succession ; immediately
the desired brown is reached, the print is put
into cold water which at once stops the toning
action. A few minutes' washing completes the
operation. When the water with which the
toning bath is made contains a considerable
amount of hme, the solution becomes pink and
sUghtly stains the whites of the picture. This
may be counteracted by adding 2 grs. of potas-
sium oxalate to each pint of the toning bath, the
addition tending to give tones of a warmer
colour. J. Packham also states that after
toning with catechu and washing, the per-
manency and brightness of the image are aided
by immersing the print for about five minutes
in a solution of very weak potassium bichromate
of a light straw colour. The prints must not be
allowed to remain too long in the catechu toning
bath, or the whites wiU be degraded, as the
process is really that of staining. If desired, the
bath may be used cold, in which case toning is
very slow indeed. As the catechu-tannic acid
in the catechu combines to form an inky com-
pound with iron, it is important that the latter
be entirely removed from Uie prints before toning.
Chapman Jones has stated that catechu toning
is due to the action of the extract upon the iron
compound left in the print, which it is difficult,
if not impossible, to remove completely, and
that other substances which give colours with
iron salts would give similar results, though
perhaps not such desirable colours. The fact
that tlie image is toned appears to be due to the
fact that platinum holds the minute residue of iron
more tenaciously than the paper alone, and that
the residual iron compound is therefore roughly
proportional to the thickness of the platinum
deposit. (See also " Platinotype Process.")
CATHODAL RAYS (See "X-ray Photo-
graphy.")
CATHODOGRAPHY AND CATHO-
GRAPHY
Names at one time given to radiography, or,
as it is more commonly caUed, " X-ray " photo-
graphy.
CATOPTER (Pr., Catoptron ; Ger., Katopter)
An optical instrument in which reflection is
made use of ; a mirror. A concave mirror was
employed by some of the early Daguerreotypists
instead of a lens.
CAUSTIC (Fr., Caustique ; Ger., Atz)
Synonyms, hydroxide or hydrate. Caustic
compounds are those in which it may be con-
sidered that a metal has replaced one of the
hydrogen atoms in water, thus HjG = water,
KHO = potassium hydrate, or caustic potash,
NaHO= sodium hydrate, or caustic soda,
CaHO = calcium hydrate, LiHO = caustic
lithia. They are all powerful alkalis. Caustic
potash and soda are used in some developers as
accelerators, especially with hydroquinone, but
must be employed sparingly as they tend to
cause frilling.
CAUSTIC LITHIA (See " I^ithium Hydrate.")
CAUSTIC POTASH (See "Potassium
Hydrate." )
CAUSTIC SODA (See " Sodium Hydrate.")
C.C.
Cubic centimetre, a measure used in the
metric system. The Enghsh equivalent is
17 minims (nearly), or -035 fluid ounce.
C.C. is also used to indicate collodio-chloride
paper.
Cedar Oil
96
Cementing Lenses
CEDAR OIL (Fr., Huile essentielle de cHre ;
Ger., Zedernholzol)
Synonym, oil of red cedar wood. A yellowish,
volatile liquid with pleasant odour, obtained
from Juniperus Virginia, and other species of
cedar. It is used in microscopy as a clearing
agent and with oil immersion lenses.
CELESTIAL PHOTOGRAPHY (Pr., La
photographie astronomique ; Ger., Astrorio-
mische photographie)
This is described fuUy under the heading
"Cosmical Photography."
CELLOIDIN (Fr. and Ger., Celloidin)
Solubilities, insoluble in water, soluble in a
mixture of alcohol and ether. A specially pure
form of pyroxyline {which see), made by
Schering. Usually it occurs in the form of thin,
yellowish, transparent shavings.
In process work, celloidin is largely used by those
who make up their own collodion. The sub-
stance comes on the market either in large dry
flakes or in small dry chips, or in chips moist-
ened with alcohol. It is used in the proportion
of from I to 2 per cent.
CELLS, LENS (See " Lenses, Brasswork of." )
CELLS FOR MICROSCOPICAL SPECI-
MENS
Cells for mounting preserved specimens or
sections in glycerine, etc., are made by tracing
a circle of Brunswick black on a glass sUde and
attaching a cover glass.
In the photo-micrography of living objects one
of the most convenient materials for cell making
is plasticine ; a small piece of this is rolled out
between the hands, bent into a circle, placed on
the glass sUde, and flattened out by pressure with
another glass slide, until the cell is of the required
depth. The cell is filled with water and the
object placed inside ; then a cover slip pressed
down keeps the liquid in the ceU. Another
common form of cell for living objects is an
indiarubber ring cemented by Canada balsam or
rubber solution to the glass sUde, a cover glass
being placed on top when the object is in position,
CELLULOID (Pr. Celluloide ; Ger., Celluloid)
Solubilities, insoluble in water, soluble in
acetone, alcohol, and ether. It is obtained by
casting on metal cylinders a viscous solution of
pyroxyline {which see) in naphtha, amyl acetate,
fusel oil, and camphor in varying proportions.
This gives the tlun sheets used in roU-film
cameras, and the thicker strips used in kinemato-
graphy. Thick sheet celluloid is usually obtained
by casting the celluloid in blocks and shaving
off to the required thickness. Its principal use
is for the support of films of all kinds and for
making celluloid varnish or zaponlack.
A great objection to celluloid is its inflamma-
bility. A non-inflammable variety {see "Cellu-
lose Acetate") has been placed on the market.
A formula for a celluloid varnish is: —
Celluloid or pyroxyline
Acetone
Amyl acetate
Benzole . .
90 grs. b g.
10 drms. 35 CCS.
20 „ 70 „
20 „ 70 „
Old and spoilt films with the gelatine cleaned
off wiU provide the celluloid ; more or less is
used to regiilate the consistency of the varnish.
In process work, a celluloid varnish made by
dissolving celluloid in acetone is sometimes
used as a substitute for stripping collodion. The
celluloid solution is flowed over the negative,
after the application of rubber solution.
CELLULOID, CEMENTS FOR
The best cement for celluloid is a solution of
celluloid in amyl acetate or acetone. In joining
a kinematograph film, for example, the two ends
are scraped thin, lightly coated with cement,
and placed between glass plates to dry ; grease
on the glass will prevent the pressed-out cement
adhering to the glass. Many other cements are
available for mending broken celluloid goods.
A solution of i part of shellac in a mixture of
I part spirit of camphor and 3 to 4 parts of alcohol
(90 per cent. ) will answer ; as will also a marine
glue consisting of pure indiarubber, shellac, and
naphtha. Canada balsam may also be used in
the form of a solution in benzine.
CELLULOSE (Pr., Cellulose; Ger., Zellulose)
(CeHioOs)^. Molecular weight, (i62)„. Ob-
tained from the cell walls of plants and usually
in the form of cotton-wool, which is the material
from which cellulose acetates and nitrates are
made.
CELLULOSE ACETATE (Pr., Cellulose ace-
tate ; Ger., Celluloseaceiat)
(CdHioOs)*, 3COOH. This is obtained by the
action of acetic anhydride on cellulose, usuajly in
the form of cotton or cotton-wool, in the presence
of glacial acetic acid and some condensing agent
such as sulphuric or phosphoric acids or acetyl
and zinc chlorides. jThe cotton may be mer-
cerised or not, or previously converted into hydro-
cellulose, or the hydroHsing may be effected in
the acetylising bath. It occurs as a granular
powder of white or faintly yellowish colour, or
in the form of the original cellulose itself. It is
of special interest, as it forms the basis of the
non-inflammable celluloids that have been placed
on the market. Films prepared with it fuse
and char, but will not bum. It is insoluble in
alcohol and ether, and nearly all the solvents of
pyroxyline, but soluble in phenol, tetrachlor-
ethane and alcohol, acetone and alcohol, etc.
CELLULOSE NITRATES (See "Pyroxylme.")
CELLULOTYPE
Etching on celluloid with the needle point for
intaglio printing.
CELLUTYPE
Printing blocks cut in celluloid with the object
of superseding woodcuts.
CELSIUS THERMOMETER {See " Thermo-
meter.")
CEMENTS {See " Moimtants " and various
substances, " Ebonite," " Glass," etc.)
CEMENTING LENSES {See "Lenses, Cement-
ing." )
Centigrade Thermometer
97
Ceramic Process
CENTIGRADE THERMOMETER {See
" Thermometer." )
CENTIGRAM, CENTIMETRE, CENTI
LITRE, ETC. {See "Weights and
Measures.")
CENTRAL SPOT {See " Flare.")
CENTRE OF ADMISSION {See "Nodal
Points.")
CENTRIFUGAL SEPARATION (Fr., Sipara-
tion centrifuge ; Ger., Separiren mittels
einer Zentnfugalmaschine)
A method introduced by Plener in 1881 for
separating the sensitive silver salts from the
gelatine used during the manufacture of emulsions.
The fluid emulsion is poured into a gunmetal
receptacle, which is rotated at a speed of from
4,000 to 6,000 revolutions a minute, the silver
salts being thrown on to the walls of the con-
tainer, whilst the gelatine and water escape by
an orifice at the bottom. It is claimed for this
method that the emulsion is very rapidly freed
from the nitrates, formed as by-products, and
the decomposed gelatine. The method has fallen
into almost complete desuetude.
CENTRING OF LENSES
When a lens is correctly centred the axes of
all its surfaces are in a straight line ; otherwise,
good definition cannot be obtained. Faulty
centring gives a distortion to the image similar
to that of astigmatism or coma, and is easily
detected by fixing the lens upon a. camera or
optical bench and focusing a brightly illuminated
object, such as a small lamp flame or mercury
bulb. The position of the image is carefully
noted, and the lens gently rotated in its flange,
when, if the centring be perfect, the image wiU
remain quite stationary, but if not it will move
in more or less of a circular direction upon the
screen. The fatUt may be in the flange, or rather
the body ring of the lens tube, or it may be in
the thread upon the lens cells, in the cementing
of the separate components, or the surfaces of
one or more of the single glasses of the combina-
tion may not be correctiy adjusted. In any case,
it is a matter for an experienced optical work-
man to put right.
The centring of the actual components of the
lens is a simple process, but one requiring con-
siderable skill. When a lens leaves the pohsher's
hands it has a more or less rough edge, and is a
little larger than the cell it is destined to fit. It
then goes into the hands of a workman for
" edging " and " centring," which operations
are performed simultaneously. The lens is
stuck with pitch upon a revolving chuck, and a
gas flame is so adjusted that two images of it
are seen by reflection from the inner and outer
surfaces of the lens. These will be found to
" wobble " as the lathe head rotates, and the
workman slides the lens upon the soft pitch until
they are quite steady. The pitch is then allowed
to set and the edge of the lens is ground to correct
size upon the lathe by the appUcation of a copper
plate fed with wet emery powder. A similar
process is gone through after cementing two or
more glasses together while the balsam is suffi-
7
ciently soft to allow the surfaces to be moved
upon each other.
CERAMIC PAPER
A paper at one time used for the production
of ceramics ; invented by Guerot in 1891. It
was sensitised with a solution the constituents
of which were kept a trade secret. The paper
was printed upon, washed, squeegeed in contact
with the vitrifiable plaque, and stripped. The
image was then treated with a solution of potas-
sium permanganate, washed, dried, and finally
fired.
CERAMIC PROCESS
The art of obtaining a bumt-in impression of
a photograph on earthenware, china, or porcelain.
Such pictivres are permanent because the image,
formed by a vitrifiable powder, is protected by
an imperishable glaze. The material of which
the picture is composed must obviously be of a
special nature. The process is based on the
dusting-on or powder process, in which a bichro-
mated film loses its tackiness in different degrees
by exposure to light under a negative, so that
on brushing it over with a suitable powder an
image is obtained ; but in ceramic photography
the powder used is a vitrifiable colour which
stands firing without injury.
The transparency used must be bright, vigor-
ous, and of the highest quality. The image for
firing is not produced at first on its final support.
A poUshed glass plate forms a temporary sup-
port, the print obtained on it being afterwards
coated witti coUodion, stripped and transferred.
The glass plate is cleaned and coated with a mix-
ture of the following two solutions : —
Organifier
Le Page's fish-glue . 2 oz. 62 g.
Glucose . . . 8 ,, 248 ,,
Glycerine . . . 20 mins. i'2ccs.
Water . . . , 21 oz. 600 „
Sensitiser
Ammonium bichromate 900 grs.
Water . . . . 21 oz.
58 g.
600 CCS.
If a smaller quantity is desired, keep to the
same proportions. Mix together in equal parts
and filter as required. Such solutions may be
purchased ready prepared. The coated plate is
dried by gentle heat, not greater than that which
can be borne comfortably by the back of the
hand. A whirler is useful for rapid drying. A
thin, even coating should be aimed at, and the
film ought to be quite glossy when dry. The
exposure under the transparency varies with the
quality of the latter and the light, and it is better
to use an actinometer ; it may range from forty
seconds to three minutes in the sun, or to as
much as fifteen minutes in diffused hght. With
a correct exposure the image will be faintly
visible on the film. Development is performed
as in the dusting-on process {which see), but
the plate is held in an inclined position resting
on a sheet of white paper, sensitive side towards
the light, so that progress may be viewed by
both transmitted and reflected hght ; and vitri-
fiable powders must be employed. These con-
sist of metallic oxides and other fusible sub-
stances, and they are obtainable in a number of
Ceramic Process
98
Ceramic Process
dififerent tints. Sift the powder through silk,
but it may be necessary, before doing this, to
re-grind it with water, using a muller on a glass
slab. The powder must be thoroughly dried
before sifting. Firing alters the colours of the
powders to an extent that only experience will
show. When the image possesses about the
same vigour and transparency as a good lantern
slide, the surplus powder is dusted off, and the
picture coated with collodion (either plain or a
special preparation), which is flowed over the
plate like a varnish. When the collodion has
set, a sharp penknife is pressed downward
through the edges of the film on three sides of
the plate, cutting through to the glass ; the plate
is then immersed in several changes of water,
preferably filtered, to remove the bichromate
salt. The film will separate from the plate,
except on one side. When the bichromate seems
nearly all removed, the film is placed in a solu-
tion of fused borax for about ten minutes,
finally washing in a fresh bath of filtered water
for an equal period. To prepare the fused
borax solution, place 2 oz. of the fused borax
in an enamelled saucepan with water, boil
rapidly for five minutes, decant, add fresh water,
and repeat until aU the borax is dissolved. For
use, take three parts of the saturated solution
(cold) and add one part of water. For trans-
ferring, fih a large basin or dish with the borax
solution. The plate, after its final washing, is
stood in a rack for a few minutes to drain off
the surplus moisture. The penknife is then very
carefully passed along the fourth edge of the
film, which must not be cut through by drawing
the blade along, as that would pucker or tear
the film. The plate is now placed in the basin,
and the film will float off the glass, which can
then be withdrawn. With a camel-hair brush
turn over the fijm in the solution so that the
collodion side is downward ; if the fingers were
used there would be a risk of damaging the loose
film or of abrading the powdered side. The
plaque or other support is next introduced under
the floating film, which is guided into its correct
final position. The support is then slowly, and
by degrees, lifted out of the water with the film
adhering, powder side uppermost, and placed
on blotting-paper to dry, after whidi loose pieces
of fihn may be removed with a damp sponge,
and the image should be very carefully examined
for any black spots or imperfections, the former
being removed with a fine needle-point set in
a wooden handle. The delicate powder is next
protected by flowing over it —
Patty oil of turpen-
tine . . .10 mins. 20 CCS.
Oil of turpentine . i oz. 1,000 „
Oil of turpentine oxidises by exposing for some
time to light and air. The mixture should be
filtered and kept from the dust. When dry, the
plaque coated with this medium should appear
uniformly dull. Any white spots on the picture
may now be filled in with a little of the powder
colour mixed with the medium above mentioned.
If the plaque is given a light firing, just sufficient
to attach the powder to the surface, it can be
spotted or worked upon with facility.
Firing is the next process. The work will be
fired at any pottery for a moderate charge ;
but by the aid of a gas muffle the worker can
easily do his own. For tiles and plaques the
heat must be appUed very carefuUy, gradually
increasing the consumption of gas. When the
furnace is fully heated the gas is immediately
turned out, the chimney covered up, and the
whole left to cool, or, instead, the work can be
transferred to an annealing chamber. Enamel
plaques or medallions on a metal base need not
be cooled with such extreme care.
Dust is especially to be avoided in ceramic
work ; it is advisable to sprinkle the floor of the
room with water, which will probably suffice to
lay the floating dust, and on no account should
any sweeping or dusting be done immediately
preceding any of the manipulations. Charging
the air with moisture by means of a spray
difiuser or vaporiser prevents the dust nuisance,
but makes the room too moist for developing.
It may be said that the image may be printed
direct on perfectly flat surfaces, instead of using
a temporary support.
There are many possible modifications of the
above process, (i) Instead of using the dusting-
on process, a film prepared with ferric chloride
may be employed. The film is exposed under a
negative to obtain a plate of various degrees of
tackiness, which is then brushed over with
powdered enamel colour as before. No trans-
parency is required. The picture so obtained is
coated with collodion, stripped, and treated as
before described. (2) Printe obtained by the
carbon process, simply substituting enamel
colours in the preparation of the film, may be
developed upon porcelain as a final support,
forming excellent pictures for firing. (3) A
method that is useful where numbers are re-
quired is to obtain a photo-mechanical impres-
sion in the usual manner on a special transfer
paper prepared with a collodion substratum.
A suitably tacky ink is used for printing, and
the ceramic powder is dusted over this. The
paper is then moistened and removed, while
the film and picture, collodion side downwards,
are transferred to the porcelain support or
plaque, which is first treated with an adhesive
medium. (4) The following procedure may be
taken as representative of the substitution pro-
cess. A collodion positive is obtained in the
camera by the wet process, fixed, washed,
bleached in a 5 per cent, solution of mercuric
chloride, again washed and placed in the sub-
stitution bath, which is to replace the original
image, unsuitable for firing, with one of platinum
or iridiimi. A gold and platinum bath, as
follows, gives a purple-brown colour : —
Potassium chloro-
platinite . . 8 grs. 1.5 g.
Gold chloride ( I in 60) 4J drms. 43 ccs.
Water (distilled) . 4I oz. 345 „
Lactic acid . . 5 mins. -9 „
An iridium and gold bath gives a warm black
tone :—
Iridium chloride . 8 grs. 1.5 g.
Gold chloride ( I in 60) 4J drms. 43 ccs.
Water (distilled) . 4I oz. 345 „
Lactic acid . . 6 mins. i „
After the deepest shadows of the picture have
been toned tliough, wash for a few minutes to
Cerate Paste
99
Chalk
remove the free toning solution. Cut round
the margins of the film, immerse the plate in a
I per cent, solution of sulphuric add, wash the
eim after it strips off, transfer to the final sup-
port of porcelain, collodion side up, and dry.
Then remove the collodion film by gently rub-
bing with a sponge moistened with ether and
alcohol, again dry, and dust the image with
flux, when it is ready for firing. (5 ) It is possible
to obtain a bumt-in picture in natural colours
by the exact superposition of a blue, a red, and
a yeUow picture printed from three negatives
obtEiined through suitable screens. The yellow
film is first transferred and fired, allowed to cool,
and the blue image very carefully superposed
on this in exact register and burnt in. After
again cooling, the red film is transferred and fired.
CERATE PASTE
A paste or waxy mixture for surface applica-
tion to finished prints. Better known as
encaustic paste, under which heading formulae
will be found.
CERIC SULPHATE (Fr., Sulfate de cirium.
Sulfate cirique ; Ger., Cerisulfat)
Synonym, sulphate of ceriiim. Solubilities,
shghtly soluble in water, more soluble in dilute
sulphuric acid. Ce(S04)2 4HjO. Molecular
weight, 404. It occurs as reddish yellow crystals,
and was suggested by Lumi^re as a reducer, the
formula being : —
Ceric sulphate . 2 oz. 100 g.
Sulphuric add . 384 mins. 40 ccs.
Distilled water to . 20 oz. 1,000 „
This acts very energetically, and can be diluted
for prints and lantern slides. A 5 per cent,
solution acts more strongly on the high lights of
a negative than the shadows.
CERIO PRINTING
A term commerdally appUed to the kallitype
process (which see).
CERIUM SALTS, PRINTING WITH
There are two series of cerium salts, a cerous
and a ceric, the former being stable, but the
latter extremely unstable ; tiiis fact induced
Lumiere and Seyewetz to examine their photo-
graphic properties, and they found that ceric
sulphate and nitrate, when used for sensitising
gelatinised paper with exposure under a positive,
were reduced to the cerous state, and became
pale coloured. The print, being then treated
with certain organic substances, gave coloured
images, due to the formation of dyes through
the oxidation of the developers by the unre-
duced ceric salts, and the dye images thus formed
were insoluble in water. In an add solution
phenol gives grey images ; aniline salts give
greens ; naphthylamine gives blue ; amido-
benzoic add, brown ; parasulphanilic add,
red ; and ortho-toluidine salts, brown images.
With ammoniacal solutions other colours are
obtained ; for instance, aniline gives violet and
naphthylamine reddish violet images. Paper
sensitised with these cerium salts is far more
sensitive than with iron or manganese salts and
the range of colours is far greater, but no com-
mercial application of tliis process has yet been
m.ade.
CEROGRAPHY
The art and process of engraving on wax.
{See "Wax Engraving.")
CEROLINE (Pr., Caroline: Ger., Ceroline)
A solution of white wax in benzole, used in
the early days to render paper translucent.
CERTINAL
A highly concentrated liquid developer in one-
solution form, introduced by Ilford I<td., March,
1909. The best proportion for developing plates
and films which have received normm exposure
is certinal 24 drops, water i oz. At a tempera-
ture of 60° P. (nearly 16° C.) the image appears
in a few seconds, and development wiU be com-
plete in from 4 to 8 minutes, according to the
plate and the class of negative desired. The
rapid appearance on dry plates must not be mis-
taken for signs of over-exposure, and the image
will need to be developed for density. As a rule,
the image on a properly exposed plate appears
in 15 seconds, and development is complete in
6 minutes. With under-exposure the best
results are obtained by using the developer
weaker (16 drops of certinal to each ounce of
water) and developing longer. Over-exposed
plates need a stronger developer and the addition
of potassium bromide (certinal 48 drops, water
I oz., 10 per cent, solution of bromide 48 drops) ;
development will then take about one-fourth less
time than would be required when exposure and
developer are normal. For tank or stand
development J oz. (120 drops) of certinal should
be added to 25 oz. of water ; development will
be complete in from 30 to 60 minutes, according
to temperature, plate, subject, and type of
negative desired. For lantern plates and
bromide paper the best strength is 16 drops to
each ouaice of water, but gasHght papers and
plates need double that strength. More con-
trast may be obtained on papers and lantern
plates by using a stronger developer, and still
more by adding potassium bromide, while softer
results are obtained by diluting the developer.
Additional bromide gives warmer blacks, esped-
ally on gaslight papers and plates.
CHALK (Fr., Crate; Ger., Kreide)
Precipitated chalk, a fine white substance, is
a pure form of carbonate of lime. It is often
used for neutralising gold toning baths, for which
purpose common whiting (prepared from chalk
by grinding and levigating) is sometimes used ;
chalk is also used for dearing varnishes.
In process work, predpitated chalk or washed
whiting is largely used for deaning glass, for
giving a final polish to copper and zinc plates,
so as to remove grease (the chalk being made
into a paste with ammonia), and for rubbing in
an engraved plate, so that the image may show
up and enable the engraver or fine etcher to
do any retouching that may be required. Mag-
nesia is, however, more generally used now for
the latter purpose, the chalk often tending to
grittiness.
Lithographic chalk is somewhat a misnomer,
this substance being the black, greasy, crayon
used for drawing on grained lithographic stone,
zinc, or aluminium, and for drawing on grained
transfer papers. The term no doubt originated
Chalk, French
lOO
Charcoal, Wood
from the similarity of the crayons to ordinary
black and white chalks used for drawing on
paper.
Chalk ink is a stiff black lithographic ink used
for inking-up lithographic drawings in chalk on
grained surfaces.
Chalk transfer paper is a grained paper for
drawing upon with lithographic chalks.
CHALK, FRENCH (Pr., Talc, SaronAmarguer;
Ger., Talk, Franzosische Kreide)
Synonyms, talc and steatite. French chalk is
a hydrous silicate of magnesia, a typical analysis
being : silica 62, magnesia 33-1, and water
4-9 per cent. ; i or 2 per cent, of iron often
occurs as well. It has the appearance of a fine
white or greyish white powder, and is used
chiefly for polishing glass, to which prints are
squeegeed for the purpose of glazing.
In process work, it is used for polishing glass
for stripping purposes, and also as a resist for
etching, for which latter purpose it is dusted
upon an ink image. It is especially useful in
this way in lithographic work on stone, and it is
sometimes employed in admixture with black-
lead.
CHALK PLATE
An iron plate thickly coated with a chalky
substance, through which a drawing is scratched
with a pointed stylus. The plate is then used
as a matrix for stereotyping.
CHALKINESS (NEGATIVES AND
PRINTS)
" Hardness " or excessive contrast ; chalky
negatives and prints show a very great differ-
ence between the high lights and deep shadows.
The fault is due to under-exposure and over-
development, and a partial remedy is the ammo-
nium persulphate reducer. Softer prints may
be obtained from such negatives by bleaching
with, say, a mercuric bichloride solution as
used for intensifying, and printing from the
negative in its bleached or whitened condition.
There is no complete remedy for chalky or
hard prints.
CHALKINESS (WATER)
Water, particularly hard water, is some-
times chalky, and although it rarely does any
harm to solutions it is better to boil it before
use (see "Water"). Dr. Hauberisser has
described a chalkiness which comes over the
negative in a kind of fog, and is due to impurities
in the water, these giving rise to an insoluble
calcium compoimd. When water containing not
only sodium chloride, but a calcium salt as well,
is used, there is the risk of calcium oxalate being
formed should a ferrous oxalate developer be
employed. Similarly, with water containing
organic agents, the use of potassium carbonate
may cause calciimi carbonate to be precipitated
as a sediment in the gelatine, thus producing a
calcic fog. A simple remedy for such a deposit
consists in the application of a weak solution of
hydrochloric acid to the negative, this convert-
ing the calcium carbonate to soluble calcium
chloride, which, of course, washes out. There
may, however, be a risk of the Uberated carbon
dioxide causing blisters.
CHANGING BAGS AND BOXES
A changing bag is a device to allow of reload-
ing dark-slides or sheaths without the necessity
for a dark-room. It is generally a bag of several
thicknesses of black and red material, provided
with sleeves which tighten round the arms by
means of elastic, so that the hands are inside
the bag. In some forms the changing has to
be effected by the sense of touch alone ; in others
there is an eye-piece to fit on the face so that
the interior of the bag can be seen, light being
admitted through a panel of red fabric or cellu-
loid in one side of the bag. The utility Cjf such
a bag as a makeshift dark-room is obvious.
A changing box is a magazine holding plates
in sheaths, and is generally detachable from the
camera. An exposed plate can be moved from
the front to the back, or an unexposed plate
taken from the back and placed in front of the
one last exposed. The usual method of accom-
plislung this is to raise the plate into a bag of
flexible leather and place it in position by hand,
but in some cases the transfer is made mechanic-
ally. The front of the changing box is fitted
with a draw shutter, which is opened for expo-
sure and closed when the box is to be removed
from the camera. The back of the box can be
opened for the removal of exposed plates and
for reloading the sheaths. Hence there is some
advantage in those types in which the exposed
plates find their way to the back of the box,
as they may be removed without disturbing
unused plates. Many boxes are constructed to
take cut films instead of plates, their capacity
thus being doubled. Obviously the niunber of
plates or films available may be increased by
the use of additional changing boxes. (See also
" Dayhght Changing.")
CHARBON VELOURS (Pr.)
The name originally given to the paper intro-
duced by V. Artigue, of Bordeaux, in' 1892
(see "Artigue Process"). A recipe for making
a similar paper is given under the above
denomination by H. Schneeberger. The pig-
ment may be any ordinary water-colour ; or
moist colours may be used, provided they do not
contain a tanning ingredient. The colour is
rubbed up in a stiff paste of starch and applied
to the paper in a thin uniform coating. Too thin
a coating, or one containing insuflScient pigment,
does not give the desired velvety appearance ;
while, if too thick, the half-tones and other parts
where the hght has not penetrated to the support
are apt to wash away in developing. The coated
paper will keep indefinitely. It is sensitised, for
flat negatives, in a 2 per cent, bath of potassium
bichromate, or, for hard negatives, in a 5 per
cent. bath. Development is with a warm saw-
dust mixture, as in the Artigue process, a temper-
ature of about 80° P. (about 27° C.) being recom-
mended.
CHARCOAL, ANIMAL
Known generally as bone black (.which see).
CHARCOAL, WOOD (Pr., Charbon de hois:
Ger., Hohkohle)
Wood charcoal is the residue from the destruc-
tive distillation of wood. Wood having been
heated to a high temperature out of contact with
Chardon's Process
Chemiglyphy
the air, the volatile portioas are driven ofi, and
the yield is very Jiearly pure carbon. Sticks of
charcoal made from vine or willow wood are
used as crayons for working up enlargements.
In process work, blocks of charcoal are used
for polishing the metal plates. Formerly,
selected sticks of willow charcoal were used, but
of late years this has been superseded by char-
coal made of trimmed blocks of soft pine.
Such charcoal comes from the United States,
and is known as " American charcoal." It is
beautifully soft and even in texture, and can
be had in " hard " and " soft " qualities.
CHARDON'S PROCESS (Pr., ProcSdS Char-
don; Ger., Chardon's Prozess)
A collodion emulsion process due to Alfred
Chardon, who won with it the prize of i,ooo
■ francs offered jointly, in 1876, by the Photo-
graphic Society of France and A. I,iebert, of
Pans, for the best and most reliable dry process
for outdoor use. It was, as its author stated,
more a well-judged selection and combination of
the best points of other processes than an original
or new method, although possessing some novel
features : as the use of two different kinds of pre-
cipitated pyroxyline; washing the emulsion by
pouring it into the water, instead of the reverse,
as was formerly done ; the employment of
glucose in the developer to obtain density, etc.
CHEMICAL FOCUS (Fr., Foyer chimique ;
Ger., Chemischer Brennpunkt)
The plane on which the actinic rays are brought
to a focus. In simple periscopic or non-achro-
matic lenses, the focal plane for the actinic rays
lies nearer the lens than that of the visual rays ;
it follows, therefore, that the sharp image
obtained by focusing, which is affected by the
visual rays, is not reproduced by the sensitive
film on which the actinic rays act most. This
defect, which is rarely met with now, can be
remedied either by reducing the distance between
the lens and plate, after focusing and before ex-
posure, by from -^to-^oi the extension of the
camera, or by the temporary insertion, only
whilst focusing, of a weak supplementary lens
which reduces the focal length.
CHEMICAL FOG (See "Fog.")
CHEMICAL RAYS {See "Actinic")
CHEMICAL RETOUCHING (See " Re-
touching, Chemical.")
CHEMICALS
A list of the chemicals used in photography,
with their formulae and solubilities, appears under
the heading " Solubilities."
CHEMICALS. STORING
Chemicals need careful storing if they are to
be kept good and in a proper working condition.
Those given below are the chemicals mostly
used in photography, and the remarks apply
generally to the chemicals themselves, as bought,
and not to made-up solutions, as developers,
intensifiers, etc., for information as to which
see under the heading " Solutions." Photo-
graphic chemicals may be divided into four
classes — ^namely ; —
(i) Chemicals that keep well and need no
special precautions, other than being stored in
a dry place : —
Alum (ordinary and Potassium bichromate
chrome) Potassium bromide
Borax Potassium ferricyanide
Boric acid Potassium oxalate
Caramel Sodium acetate
Citric acid Sodium carbonate
Mercuric chloride Sodiimi hyposulphite
(2) Chemicals that must be kept in bottles
with tight-fitting corks (not glass stoppers)
because of their deliquescent nature or oxidising
properties : —
Adurol Magnesium powder
Amidol Potassium carbonate
Ammonium carbonat Potassium cyanide
Ammonium sulpho- Potassium hydrate
cyanide Potassium iodide
Eikonogen Potassium metabisul-
Ferric chloride phite
Ferrous sulphate Pyrogallic acid
Formosulplute Sodium hydrate
Glycin Sodium sulphate
Hydroquinone Sodium suilphite
Metol Uranium nitrate
and all other dry developers not mentioned
above, as metoquinoue, pyro-catechin, etc.
(3) Corrosive and volatile substances, which
should be kept in bottles having accurately
ground glass stoppers, not corks : —
Acetic acid Collodion
Acetone Bther
Alcohol Formaline
Ammonia (liquor) Hydrochloric acid
Ammonium persul- Iodine
phate Nitric acid
Amyl acetate Sulphuric acid
(4) Materials that should be kept in a dark
cupboard, or in black botties when not in use : —
All kinds of liquid aniline dyes.
Gold chloride in solution.
Potassium chloroplatinite in solution
Silver nitrate, dry and in solution.
Chemicals that are poisonous, or otherwise
dangerous, should be stored in a cupboard or
some out-of-the-way place where they cannot
be got at by persons unacquainted with their dan-
gerous properties. Such chemicals include : —
Acetic acid Sodium oxalate
Hydrofluoric acid Chromic acid
Nitric acid Hydrochloric acid
Chrome alum Sulphuric acid
Ammonium bichro- Ammonia
mate Ammonium oxalate
All soluble barium Bromine
salts Formaline
Soluble copper salts Lead acetate
Lead nitrate Potassium oxalate
Potassium bichromate Caustic soda
Caustic potash Sodium bichromate
Silver nitrate All developers
These are in addition to the scheduled poisons,
all of which must be kept in a safe place.
CHEMIGLYPHY
Another name for " Glyphography " (which see).
Chemigraphy
I02
China, Photographs on
CHEMIGRAPHY
A general name, not often used now, for zinc
etching. {See also " Chemitype." )
CHEMITYPE
Before the appKcation of photography to zinc
etching, lithographic transfers or drawings direct
on zinc were etched into relief for letterpress
printing. This process was generally called
" Chemitype " or " Chemigraphy."
CHIAROSCURO (It.)
A word adapted from the Italian chiaro, clear,
and oscuro, dark, and indicating the light and
shade in a picture. The suitable placing" of the
highest light and the deepest shadow is of great
importance. Scattered high Ughts and disjointed
shadow masses are fatal to harmonious effect.
The portraits of Rembrandt are good and familiar
examples of effective knowledge of the value of
proper chiaroscuro.
Chiaroscuro is the name of a class of colour
prints in which the varying effects of light and
shade are represented, not by lines or cross-
hatching, as in ordinary engraving on wood or
metal, but by tones in the shape of broad masses
of colour, produced by surface printing from
wood-blocks. These were usually employed for
the purpose of colouring an outline woodcut.
CHILDREN, PHOTOGRAPHY OF
The success or failure in photographing a
child is nearly always dependent on the ability
of the operator to gain the confidence of his
juvenile sitter. In the case of amateur work,
the child is often personally acquainted with the
photographer, but in professional work the child
is probably a complete stranger to the operator.
It is useless to treat a child in the same manner
as an adult, and simply request it to assume
the desired position. Particiilar art is necessary
in getting the child to adopt the pose required.
Too many friends of the child should not be
allowed into the studio, one being quite enough ;
otherwise difficulties are likely to ensue, especi-
ally in the case of very yotmg children whose
attention is very easily diverted. Children
differ so much in their disposition that it is
possible to make friends easily with some,
whilst others are shy and require quite diplo-
matic handling. In some cases it is better to
ignore the child at first, and to engage in con-
versation with whoever is in attendance on the
child, and then, by opening a picture-book,
operating a mechanical toy, introducing a. dog
or cat, the child becomes interested and gradu-
ally its confidence is won. Some of the most
successful child photographers have cultivated
an ability to bring themselves down to the
children by playing games and in other ways
giving them the impression " that they are one
of themselves." By this means they engage a
child's attention, until both the desired position
in the studio and the happy expression are
attained, at which juncture an assistant makes
the exposure.
The introduction of modem high-speed plates
has given new possibilities to child photography.
Some few years ago it was necessary to draw up
all the studio blinds so as to admit as much light
as possible, bu,t although this allowed a quicker
exposure to be made, the picture was devoid of
all light and shade gradations. The plates at
present available allow of a more subdued light
being used ; and proper attention should be
given to the arrangement of blinds for con-
trolling the hghting.
The studio reflex camera is at present but
very little used, but for child photography it
possesses very great advantages, as it frequently
happens that when the child has been correctly
focused and the dark-slide inserted for exposure,
the child moves to some other position, necessi-
tating re-focusing. With a reflex camera this
trouble is avoided, as it is possible to focus the
sitter right up to the moment of exposure.
The dress of the child often makes or mars
a picture, and some photographs owe their
charm almost entirely to dainty garments. On
the other hand, quite young children usually
make more pleasing pictures when photographed
either nude or with only a single garment on.
Amateur work takes place under varied con-
ditions, some workers possessing lofty rooms
with abundant light in which it is possible to
obtain pictures equal to those produced in a
studio ; but for those not so fortunate special
arrangements must be made so as to obtain
sufficient light for the quick exposures necessi-
tated. In an ordinary room with a bow window
it is often an advantage to take away all existing
bUnds and hangings, as these, when drawn up
or to the side, frequently cut off much light.
The window-panes may be covered with tissue
paper, as this gives a more equal diffusion of
light ; on the shadow side a screen should be
used with a sheet thrown over it for use as a
reflector, but care must be exercised not to move
this reflector too close to the child, otherwise
too flat a lighting is obtained, and there is great
risk of producing false lights in the eyes. As
childien are usually taken so as to show the
entire figure, it is necessary to see that the light-
ing reaches well down to the groimd ; to accom-
plish this it is sometimes useful to build up a
platform some 12 in. or 18 in. from the floor.
Care must be taken to prevent the Ught coming
too much from the side, and so to arrange the
light that the strongest portion of it falls from
a point higher than the child's head. This can
be attained by covering the lower panes of the
glass with three or four thicknesses of tissue
paper. In photographing children out of doors,
good hghting is possible if care is taken to choose
a position where the Ught is screened from one
side ; this is easily done by utilising the side of
a house and arranging the sitter near to it, so
that the main direction of light falls from the
side and front. If a head screen is available it
should be used to cut off the immediate top
light. An entrance doorway or portico is very
often suitable for such portrait work. {See also
"Home Portraiture," "Studio Portraiture," etc.)
CHINA CLAY {See " Kaohn.")
CHINA, PHOTOGRAPHS ON
There are several methods of printing photo-
graphs upon china, crockery, opal, etc. For
objects where the picture is to be viewed by
reflected and not transmitted light, ttie carbon
process {which see) is perhaps the best ; tissue of
China, Photographs on
any colour may of coxirse be used, and the pic-
ture, after being printed upon the tissue, is
transferred and developed upon the china sup-
port, after the latter has been properly prepared
with a suitable substratum. By this process it
is an easy matter to transfer photographs upon
curved surfaces. The ceramic process {which
see) is more difiBcult, but the results are abso-
lutely permanent and wiU permit of any amount
of washing.
_ The blue-print (ferroprussiate) process is
simple, and is often employed for producing
pictures upon china and glass. It will be neces-
sary to give the article a coating of gelatine to
serve as a vehicle for holding the sensitive solu-
tions, the blue-print being a direct printing and
not a transferring process, as carbon. A suit-
able gelatine substratum may be made by
soaking 22 grs. of Nelson's No. 1 gelatine in
I oz of water and melting by the aid of heat,
afterwards filtering while hot. The solution,
when warm (i 30° P. or 54° C), is coated as evenly
as possible upon the part of the article to be
printed upon, and then set aside to cool. The
prepared part is then sensitised as if it were
paper, and when dry it is ready for printing upon.
103
Chloral Hydrate
Printing on Vase
Collodion has also been recommended as a
rehicle for the blue sensitising solution, and the
results are perhaps more permanent. The
formula is : pyroxyline (high temperature)
120 grs., methylated alcohol (-820) 6 oz., and
methylated ether 5 oz. Mix a day or two before
using, allow to settle, coat the article with the
mixture, and when set sensitise with the " blue-
print " mixture. Substratums of collodion have
been known to peel off, and to prevent this the
places where the edge of the collodion is to come
should be treated before coating with a solution
of indiarubber in benzole.
Ordinary glass negatives can only be employed
for printing when the surface is flat ; on curved
surfaces film negatives may be kept in contact
by means of elastic bands, as shown in the illus-
tration, or by means of gummed paper at the
comers. As it is not desirable to remove the
negative from the vase for the purpose of exam-
ing the progress of printing, there must be
something l^t to chance, or an actinometer
must be used. It is advisable to varnish such
pictures when dry. Blue pictures may be toned
to a different colour by any of the methods
advocated under the heading " Blue-print Pro-
cess," sub-heading " Toning Blue-prints."
CHINA, PHOTOGRAPHY OF
The principal difficulties in photographing
china arise from the highly glazed surface and
the consequent reflections. These may be
minimised, if not altogether destroyed, by
attention to two points. The lighting should
never be from the front, but well towards one
side — almost a side lighting. An inspection of
the pieces being photographed from the position
of the lens wiU show when the Ughting produces
no direct reflections. In addition, a plain,
dark-coloured cloth should be hung immediately
behind the camera, so that no light or bright
objects may produce reflections. A colour-
sensitive plate and a yellow screen shotild also
be employed. In addition to giving a better
and a truer rendering of the ornamentation,
this also assists in reducing the effects of
reflections.
CHINA SILK
A soft material, recommended for cleaning
lenses, prisms, screens, and other optically-
worked glass surfaces. In using china silk for
cleaning ruled screens, merely breathe on the
surface before rubbing.
CHINESE WHITE
This white water-colour pigment, which con-
sists of zinc oxide, though formerly much used
for retouching photographs for reproduction,
has been largely superseded by Albanine, Blanc
d'Argent, and UlCnanine. The objection to
Chinese white is that it photographs darker than
paper ; it may, however, be used for mixing
with other pigments to form a body colour.
R. W. Wood has shown that Chinese white
photographs black in ultra-violet light.
CHINOLINE BLUE {See " Cyanine.")
CHINOLINE RED (Fr., QuinoUine rouge ;
Ger., Isochinolinerot)
Synonym, isochinoline red. A complex,
organic dye, obtained by heating benzole
trichloride with cbinaldine and isochinoline. It
is extremely sensitive to Ught, and this induced
Vogel to test it as a sensitiser {see " AzaKne").
It has now been almost entirely replaced by the
isocyanines, but Dr. Miethe has stated that a
small addition to an isocyanine bath keeps the
plates free from fog ; and the following is a
typical formula :—
Isocyanine dye sol. (1:1,000
water 4- alcohol) . . .10 parts
Chinoline red (i : 1,000 w. -(- ale.) 50 „
Water to ... . 500 „
The chinoline red also helps to fill up the usual
gap in the green.
CHLORAL HYDRATE (Pr., Chloral hydrate;
Ger., Chloral hydrat)
Synonym, trichloraldehyde. Ca,CH(OH),.
Molecular weight, 165-5. Solubilities, very solu-
ble in water, £cohol, and ether. It is poisonous,
the antidotes being ether, cocaine, and camphor.
It occurs as transparent, colourless crystsus or
flat crystalline masses, obtained by the action
of chlorine on aldehyde, with pecidiar pungent
odour and taste. It has been recommended as
Chlorates
104
Chromatic Aberration
a solvent of gelatine for making a mountant,
and has been suggested for making a non-
inflammable film.
CHLORATES (Pr., Chlorates; Ger., Chlor-
saures)
Salts formed by the action of chloric acid.
HClOj, such as potassium chlorate, KCIO3.
CHLORHYDRIC ACID
Acid.")
(See " Hydrochloric
CHLORIDE OF LIME TONING BATH
A toning bath, suitable for albumenised paper.
Fifteen grains of chloride of gold should be dis-
solved in I oz. of water, a few grains of prepared
chalk added, the solution well shaken, allowed to
settle, and then filtered, the clear solution being
used for making up the bath. The formula is : —
Sodium acetate
30 grs.
23 8-
Chloride of lime
li „
■II „
Gold chloride (i or. of
solution as described) .
15 mins.
1-2 CCS.
Water ....
30 oz.
1,000 ,,
This forms a stock solution which improves by
keeping. For use, take 2 oz. and add 8 oz. or
10 oz. of water, this being sufficient for eight
whole-plate prints.
CHLORIDE PLATES AND PAPERS
Plates or paper coated with a slow gelatino-
chloride emulsion intended for development.
(See " Emulsion.")
CHLORIDES (Fr., Chlorures ; Ger., Chloride)
A salt formed by the action of hydrochloric
acid, HCl, on metal, such as sodium chloride,
Na CI. (See respective names of metals.)
CHLORINATED LIME OR CHLORINATE
OF LIME (See "I<ime.")
CHLORINE (Fr., Chlore ; Ger., Chlor)
CI. Atomic weight, 35-5. A yellowish green,
gaseous element, obtained commercially by
heating manganese dioxide with hydrochloric
add. A solution of chlorine has been employed
as a " hypo " eliminator.
CHLOROBROMIDE EMULSION
An emulsion containing both chloride and
bromide of silver, the former being in excess.
(See " Emulsion.")
CHLOROCYANINE
Eder stated tiiat ordinary (iodo-) cyanine acted
better as a sensitiser and that it gave plates
freer from fog if it was treated with hydro-
chloric acid ; but K6nig has pointed out that
this process only purifies the cyanine, and does
not form chlorocyanine.
CHLOROFORM (Pr. Chloroforme ; Ger., Chloro-
form)
Synonyms, trichloromethane, (improperly)
formyl trichloride. CHClj. Molecular weight,
119-5. Solubilities, i in 200 water, miscible with
alcohol, ether, and benzole. It is poisonous, the
antidotes being emetics, the use of the stomach
pump, fresh air, cold douche, strychnine hypo-
dermically. It must be kept in the dark. It
is a heavy, colourless liquid, with characteristic
sweet smell and taste, and is obtained by the
action of bleaching powder on alcohol or acetone.
As a solvent of amber, etc., and indiarubber, it
is useful for varnishes.
CHLORO-IODO-BROMIDE EMULSION
An emulsion containing chloride, bromide,
and iodide of silver.
CHLOROPHYLL (Fr., Chlorophylle ; Ger.,
Chlorophyll)
Solubilities, slightly soluble in water, soluble
in alcohol and ether. The green colouring matter
from plants, which was used as a red sensitiser
for gelatine plates.
CHLOROPLATINITE OF POTASSIUM
(See " Potassium Chloroplatinite." )
CHLOROPLATINOUS ACID (See "Plati-
num Perchloride.")
CHONDRIN (Fr., Chondrine ; Ger., Chondrin)
One of the constituents of gelatine (which see).
CHOREUTOSCOPE
A fitting for the optical lantern, designed by
Beale, of Greenwich, to illustrate persistence of
vision. It consisted of a circular glass plate
with images drawn upon it, which rotated in the
lantern, zoetrope fashion. In a later and more
simple form the images were drawn on a strip of
glass, which was used in a special carrier.
CHRIPOTYPE
One of the many printing processes invented
by Sir John Herschel, who named it " Chryso-
type " (which see).
CHROMATED GELATINE (See "Bi-
chromated Gelatine.")
CHROMATES (Fr., Chromates ; Ger., Chrom-
sauresalz)
Salts formed by the action of chromic acid,
HjCrOj, on a metal, and having the formiila
M"Cr04. These salts are most of them highly
coloured and sensitive to light in the presence
of organic matter.
CHROMATIC ABERRATION (Pr., Aber-
ration chromatique ; Ger., Chromatischt
Abweichung)
To arrive at a proper understanding of the
cause of chromatic aberration, it is necessary to
remember that a lens is practically a prism with
the power of refracting or altering the direction
of rays of light and, in an uncorrected form, of
refracting rays of different colours to a different
extent. Diagram A indicates the effect of
passing a ray of white light through a prism ;
the bending of the rays will be noticed. The
most active in their chemical action are the blue
and violet, and these are diverted from their
original path more than on the others ; B shows
two prisms placed base to base so that in the
case of each colour the rays are directed to a
common point. The effect of this arrangement
more nearly approximates to that of a simple
Chromatic Aberration
los
Chromic Anhydride
lens as in C, where only three colours are in-
cluded for the sake of simplicity. Such a lens
is in fact a circular prism With the power of
bending the rays of one colour so that after
pEissing through it they meet at one point. This
point is called the focus, and it will be seen that
the focus for the blue-violet rays to which
ordinary photographic plates are most sensitive
is much nearer to the lens than the luminous
rays, green-yellow, which are those that form
the visual image upon the focusing screen.
This is chromatic aberration in its simplest form.
If the image produced by such a lens upon the
double concave flint one {see D). In ordinary
photographic lenses the optician combines the
most visually powerful region of the spectrum,
namely the green and yellow near the D line,
and the most chemically active, namely the blue
and violet near g. It will b6 seen that the red
rays are neglected, but in ordinary photography
this is of little moment. In three-colour work,
in which one of the images is made through a
red screen, a higher degree of correction is
necessary, and by the use of a third variety of
glass it is possible to bring the red rays to a
focus in the same plane as the green and blue.
A. Ray of White Light Passed through Prism C Rays Passing through Lens or Circular Prism
ground-glass screen be examined with a magnifier,
it will be found that the outline of any bright
object, such as that of a white china knob, is
surrounded with a fringe of colour, either blue
or orange. If a photographic plate be substituted
for the focusing screen there will be obtained
a blurred outline, the image being " out of
focus." On moving the plate nearer the lens by
one-thirtieth to one-fortieth of the total distance
between the lens and the visual focus, there will
be obtained on a plate an image which is prac-
tically sharp. When using ordinary spectacle
lenses, a course that is possible where extreme
definition is not required, the precaution above
mentioned must be observed.
The avoidance of chromatic aberration in a
photographic lens is effected by the use of at
so that images taken through screens of these
colours are identical in sharpness and size. A
lens of this description is called apochromatic
{which see). Recent advances in glass manu-
facture have rendered the old terms " crown "
and " flint " somewhat meaningless, as the
dispersive elements are now frequently made
of special forms of crown glass.
CHROMATISM
A lens that possesses the defect of chromatic
aberration, described in the previous article,
is said to suffer from chromatism.
CHROMATYPE {See "Chromotype.")
CHROME ALUM (Se«"Alum.")
Iflolet fellpm
' Green / Bell
B. Rays Passing through Prisms Placed Base
to B£ise
least two kinds of glass possessing different
degrees of refraction (or bending power) and
dispersion (or power of spreading out the various
colours). These glasses, in the case of ordinary
landscape and portrait lenses, were usually
( 1 ) crown glass, which, if made to suitable curves,
cotdd be caused to give any desired degree of
refraction with the minimum of dispersion ; and
(2) flint glass, which had a higher degree of re-
fraction, but relatively a much greater dispersion.
The simplest form of single achromatic lens is com-
posed of a double convex crown element and a
^ 7
\
1
D. Simplest Form of Single
Achromatic Lens
CHROME PIGMENTS
Under this term are classified lemon chrome,
which is chromate and sulphate of lead ; chrome
green, a mixture of chrome yellow and prussian
blue; chrome yellow, a normal lead chromate;
and chrome orange and chrome red, which are
basic lead chromates. They are occasionally
used in colouring prints, but possess little photo-
graphic interest.
CHROMIC ACID {See " Chromic Anhydride.")
CHROMIC ANHYDRIDE (Pr., Acide chro-
mique ; Ger., Chromsaure Anhydrid)
Synonyms, chromic acid, chromium trioxide.
CrO,. Molecular weight, 100. Solubilities,
I in 0-6 water, decomposed by alcohol. It is
poisonous, the antidote being emetics, then
Chromium Intensifier
io6
Chrono-photography
milk, white of egg, and calcium saccharate. It
must be kept dry. It violently explodes when
It comes in contact with organic substances. It
is in the form of deep, reddish brown acicialar
crystals, and is obtained by the action of sul-
phuric aci^ on potassium dichromate. It has
been suggested for bleaching prints, but the
potassium salt is more generally used.
Jn process work, chromic acid is used as an
addition to the fish-glue enamel solution. It
increases sensitiveness and hardens the film,
making it hold better on the metal. The acid
should be pure, in fine, needle-like, purple
crystals, not the red efflorescent variety used
for electric batteries. Chromic acid is also used
with sulphuric acid for " clearing " the fish-
glue image before etching, by which means it
removes any scum from between the half-tone
dots.
CHROMIUM INTENSIFIER
For this intensifier two stock solutions should
be prepared ; each wiU keep indefinitely.
A. Potassium bichromate. -J oz. 55 g-
Water . . .10,, 1,000 ccs.
B. Hydrochloric acid
Water to .
ioz.
55 g.
1 ,000 ccs.
The working solution is prepared by taking
I part A, I part B, and 2 parts water. The
mixed solution will not keep. The plate,
after being well soaked in water, is immersed in
this solution until thoroughly bleached, and is
next well washed until the yellow colour of the
bichromate quite disappears, exposed to day-
ight for a few minutes, and then redeveloped.
Any alkaline developer may be employed, but
pyro is not so smtable as those that are used for
making bromide prints. Both amidol and me-
tol-hydroquinone are good. A moderate degree
of intensification is secured, the printing value
being multiplied by 1 5 ; but if this should be
insufficient, the operation may be repeated, and
increased intensity will be obtained each time.
The result is quite permanent.
CHROMIUM POTASSIUM SULPHATE
Commonly called chrome alimi {which see,
under the heading "Alum ").
CHROMO-COLLOTYPE
A process of collotype printing in colours.
The term is also applied to a method of com-
bining collotype with chromo-Uthography for
colour printing.
CHROMO-CRYSTAL
A type of coloured photograph similar to
crystoleum and popular in the early days of
albumen prints. The print was pasted face
downwards on a piece of thick plate glass,
coloured at the back, and backed up with another
piece of thick glass, the coloured picture having
the appearance of being embedded in crystal.
The method is now employed, with or without
the back glass, for producing ornamental paper-
weights and other fancy articles.
CHROMOGRAM
The name given by Ives to the three consti-
tuent pictures for his Kromskop.
CHROMO - PHOTOGRAPHS
An early name given to photographs coloured
from the back, now known as crystolemns (which
see).
CHROMOSCOPE
The earlier name of the Ives Kromskop
{which see).
CHROMOTYPE
A process of reproduction in colours by means
of half-tone blocks, either by three-colour or
four-colour printings.
CHRONOMETRIC SHUTTER (Pr., Obtura-
teur chronomitrique ; Ger., Chronometrischer
Verschluss)
A shutter mechanically geared to give a pre-
cisely timed exposure, or successive e^^posures
at accurately recurring intervals.
CHRONO-PHOTOGRAPHY
The art of making photographic records of
the motion of an object in chronological order.
In the year 1870, Prof. B. J. Marey, of
Prance, commenced his researches on the analysis
of motion, and the advance in sensibility of
photo-surfaces has lent continual aid from that
time onward. The object of chrono-photo-
graphy is to discover the successive attitudes
which collectively make up a given motion, and
to embrace phases of a swiftly-moving object
otherwise escaping the notice of the unaided
human eye. From a physiological point of
view, this branch of the photographic art has
proved of inestimable value, and it has served
to dispel from the minds of artists certain
erroneous ideas hitherto held regarding the
various poses assumed by animals, birds, and
the like, during the evolution of their movements.
In the year 1865, Messrs. Onimus and Martin
exposed the bared heart of a living animal before
an open lens for the purpose of photographing
it while in motion. With the low degree of
sensibility then obtaining among photo-surfaces,
the exposure necessarily extended over one or
more pulsations of the heart, but as a pause
takes place at each extreme of the heart's beat
the outline of these positions was better defined
than the space between, and a record was there-
fore obtained of the maximum and minimum
limits of a pulsation. Clearly it is only necessary
to secure outlines of several intermediate posi-
tions in order that the experiment should attain
this character of chrono-photography, properly
so-called. A photograph of a man lifting his arm
would (if the exposure lasted during tte whole
movement) result in a blur, but if a number of
separate exposures was made in the same time
a series of overlapping images, equal in number
to the exposures, would occupy the place of one-
exposure blur, and the outlines of these images
would in addition form a perfect record of Qie
successive positions of the arm. An ocular
demonstration of these phenomena may be
readily produced by means of any ordinary photo-
graphic camera, supplemented with a disc per-
forated with a number of holes, and so attached
to the lens that by rotating the disc each of the
apertures comes opposite Uie lens in succession.
By pointing the apparatus to cover a man walking
Chrono-photography
107
Chrono-photography
along the footpath, and observing the inverted
image on the ground-glass screen of the camera,
meanwhile rotating the aperture disc, successive
and clearly defined images of the man will be
seen. Marey's clirono-photographs were obtained
somewhat in this way, and diagram A shows his
of a seagull. One of them is remarkable for
showing the wings in a downward position. It
is a curious fact that European artists seldom
or never represent this downward stroke of the
wing, but that the Japanese frequently do.
Two years after Marey started his researches in
A. Marey's Device for Obtaining
Chrono-photographs
D and E. Pictures
Obtained with Marey's
Photographic Gun
B. Subject in Special
Suit for Chrono-
photography
precise apparatus. A sensitive plate was placed
in a slide at p. A disc with apertures revolved
between the lens and the plate. On turning the
handle at the side, which communicated the
necessary motion to the disc, a rapid succession
of images was secured. Marey found that the
images, which were almost superposed, made it
difficult to distinguish individual phases. To
overcome this defect the subject, as shown at B,
was attired in a black velvet suit, with dots and
white lines marked thereon. During the act of
photographing, the subject ran, jumped, or
walked against a black background, in a direction
at rigjit angles to the axis of the lens. The
result was a (negative) image, as represented at
C, in which each separate attitude of the head,
left arm, and leg can be easily distinguished.
Such pictures provide valuable data in physio-
logical research. In order to secure complete
and detached pictures of birds in flight, Marey
contrived a photographic gun (see " Gun and
France, Muybridge, of California, began to in-
vestigate the progressive movements of animals,
his operations being carried out in the open air.
C. Chrono-photograph of Subject Attired
as at B
as shown at P. In 1877 Ii^ erected a long shed
containing a battery of cameras, and stretched
in front of it, at right angles, a series of threads,
which became broken as the subject (a man on
\ \ Mi.
°°Hlrm
^OD
K^
^fe^-.
Hpa
^M^
F. Muybridge's Arrangement for Obtaining Chrono-photographs
Revolver Cameras "), which was of real value
for analysing motion in such a way that the
record could be subsequently re-compounded
by means of the zoetrope (which see), h and B
are enlargements from two of a series of pictures
obtained with this gun, representing the flight
horseback) proceeded along the course. The
breaking of each thread communicated elec-
trically with the corresponding camera in the
shed, and effected the necessary exposure just
at that moment when the horseman was oppo-
site the lens. A slanting fence-reflector formed
Chrysoidlne
Io8
Circle of Illumination
a suitable background for the subject, which
was silhouetted against it, and the ground was
covered with indiarubber to prevent dusty
clouds flying from the horse's hoofs. Muybridge's
chrono-photographs of animals in motion, espe-
cially of the horse, gave rise to much contro-
versy. The first thought on looking at some
of the attitudes portrayed is that they are
unnatural and impossible ; but the matter is
explained when it is remembered that the eye
has a certain peculiarity not shared by optical
instruments, namely, persistence of vision. An
impression of everything looked at remains
upon the retina for about one-eighth part of a
second ; and it is obvious . that movements
occurring in less time than the period named
cannot be appreciated by the eye. In looking
at a galloping horse the general effect of the
movements is observed, and they are involun-
tarily commuted into three or four positions.
Such positions have been adopted by artists from
time immemorial, and we have thus come to
regard them as being correct.
The Muybridge system of chrono-photography
G. Marey's Final Chrono-photographic
Device
was modified by Anschiitz, of Lissa, in Prussia,
who added many new features to the apparatus
and secured results superior to those of the
earlier investigator. Prof. Marey, already
alluded to, later devised a camera in which a
roll of sensitised paper coujd be used, and finally
substituted transparent celluloid film. His final
apparatus is shown at G. A clamp H is sup-
ported by a spring frame j. A cam K effects the
feed motion of the film F, which is woimd upon
rollers or spools i, and M. By means of this
instmment Marey was able to secure a much
longer series of pictures than was possible with
his earlier machmes. (See also under the head-
ing " Kinematography.")
CHRYSOIDINE, OR DIAMIDO-AZOBEN-
ZENE (Pr., Chrysoidine : Ger., Chry-
soidin)
An orange aniline dye used as a light filter
in orthochromatic and tiiree-colour photography.
Its formula is CsHjNa CeH3(NHa)j. The hydro-
chloride of the base crystallises in brown octa-
hedrons. According to Frederick Ives, it is
possible to employ a chrysoidine filter for ortho-
chromatic work without colour-sensitising the
plates, but extremely long exposures are then
necessary.
CHRYSOSULPHITE (Pr., Chrysosulfite : Get.,
Chrysosulfit)
A preparation of magnesium picrate intro-
duced by Lumi^re as an addition to developers,
so that plates coidd be used in dayUght. Chryso-
sulphite No. i contains lOO parts of anhydrous
sodium sulphite and 50 parts of magnesium
picrate. No. 2 contains 100 parts anhydrous
sodium sulphite and 1 5 parts magnesium picrate.
This preparation has found but Uttle general
use. The normal strength ia developers varies
from 8 to 12 per cent.
CHRYSOTYPE
An obsolete process analogous to the blue-
print process, invented by Sir John Herschel in
1842; known also as " chripotype." It can be
best described iu the inventor's own words :
" Paper is washed with a moderately strong
solution of ammonia- citrate of iron, and dried.
The strength of the solution should be such as
to dry into a good yellow colour and not at all
brown. In this state it is ready to receive a
photographic image, which may be impressed on
it either from nature in the camera or from an
engraving (or positive) in a printing frame in
sunlight. 'The image so impressed, however, is
very faint and sometimes hardly perceptible.
The moment it is removed from the frame or
the camera, it must be washed over with a neutral
solution of gold of such strength as to have
about the colour of sherry wine. Instantly the
picture appears, not, indeed, at once of its full
intensity, but darkening with great rapidity up
to a certain point, depending upon exposure
and strength of solutions. At this point nothing
can surpass the sharpness and perfection of
detail of the resulting picture. To arrest this
process and to fix the picture (so far at least as
the further agency of light is concerned) it is
to be thrown into water very slightly acidified
with sulphuric acid, and well soaked, dried,
washed with hydrobromate of potash, rinsed,
and dried again."
Herschel later recommended developing with
a solution of nitrate of silver instead of gold,
and fixing in sodium hyposulphite ; and other
workers advocated the use of a solution of
potassium iodide after developing with gold.
The finished chrysotype pictures were of a
purphsh colour.
CHRYSTOLOTYPE
An early and secret process of making paper
negatives, invented by a Mr. Whipple. He
afterwards published an albumen process in
which glass was used, giving similar, if not
identic^ results, this leading to the supposition
that the negatives were on a kind of ^bumen
paper.
CINEMATOGRAPH {See "Kinematograph.")
CIRCLE OF ABERRATION
The spreading of the image of a point of light
into a disc of appreciable size. This may be
due to spherical aberration or to diffraction.
CIRCLE OF ILLUMINATION
A term used to express the diameter of the
largest circular picture produced by a lens Working
Circle of Least Confusion
109
Clamp
at its " mfinity focus," irrespective of definition
or eg^uality of illiumnation. A lens having a
relatively large circle of illumination as compared
with its focal length is knovm as a wide-angle
lens. The extreme range in lenses commerciaJIy
obtainable is from a circle having a diameter
five times the focal length of the lens, as in the
Goerz " Hypergon," to a circle barely equal to
the focal length, as in the Petzval portrait lens.
CIRCLE OF LEAST CONFUSION
The theoretically perfect lens is capable of
sharply reproducing a point or a Une, no matter
how small or fine. In telescope and microscope
objectives, where only rays near the axis of the
lens are used, this condition is nearly fulfilled,
but in photographic lenses, where approximate
sharpness over an extended field is desired, this
critical definition at the centre of the field is
sacrificed in order to obtain other qualities.
The size of the disc to which the image of a
theoretical point is spread out by any lens is
called the circle of least confusion, and is a
measure of the defining or " resolving " power
of the lens ; in British practice, ^ of an inch
is the maximum diameter of such a disc of which
a " sharp " picture can be composed, but latterly
on the European Continent tStt of an inch is
often taken as the standard of sharpness. To
realise what this means assume that an engraving
is composed of lines and dots ^^ of an inch in
width ; with a lens having a disc of confusion of t^tj
of an inch a full sized copy would have the Unes
and dots broadened out to more than ^hr in-,
but at 10 in. distance from the eyes the whole
picture would appear to be sufficientiy sharp.
By stopping down the lens the sharpness can
be increased until almost any desired degree is
attained. The circles of confusion at the true
focus are due to spherical aberration (which see),
but they are also found in portions of the image
which are " out of focus " and are easily recog-
nised in the backgrounds of portraits. In tlus
case they are due to the plate cutting the cone
of rays at some distance from the point of sharp
focus.
CITOCHROME (Ger., Ciiochromie)
A process of four-colour printing from half-
tone blocks, invented by Dr. Albert, of Munich.
The black or grey plate is printed first, and then
the yellow, red, and blue, but the soUd parts of
these colours, which would in the ordinary process
print over each other and imperfectiy produce
black, are cut out during the process of making
the plates, so that the black first printed shows
through the three-colour impressions and prints
as pive black. The inventor claims that by this
means more rapid colour printing can be done,
as there is no waiting for the solid colours to dry
before each successive colour is superimposed.
In carrying out the process continuous tone
negatives of the colour separations are made,
and also an orthochromatic negative of the black.
A positive is prepared from the latter. The con-
tinuous tone negatives for the colour separations
are put in a special printing frame, together with
the positive of the black plate and a ruled screen,
the whole being in contact with a sensitised zinc
plate. Either the frame or the arc light is made
to describe a circular path in a vertical plane so
as to spread the light passing through the ruled
screen. The positive of the black plate has the
efiect of stopping out the dark parts of each
negative. The negative of the black plate is,
of course, made without the positive plate being
superposed.
CITRATES IN DEVELOPMENT
Alkaline citrates have been recommended as
restrainers in dry-plate development in place of
potassium bromide. The consensus of opinion
is that bromide is better than any citrate if
added to the developer before it is applied to
the plate, but that citrates (particularly ammo-
nium citrate) act better as restrainers when
once development has begun. If added in suffi-
cient quantities, citrates correct over-develop-
ment better than bromide, and have the advan-
tage that, after they have been added to the
developer, density can be obtained without
further fogging, though the development of
detail has stopped. If ammonium citrate itself
is used — or, in fact, the citrates of either potash
or soda — the usual quantity required to be
effective is from 6 to 12 grs. per ounce of
developer ; but obviously m.ore or less can be
used. The ammonium citrate is the most
widely used and appears to work well with all
developers, but when potash or soda is used
as the alkali in a developer the citrates of potash
and soda are to be preferred.
CITRIC ACID (Pr., Acide citrique : Ger.,
Citronensdure)
Occurs in colourless and odourless crystals, or
amorphous powder, and has a strong acid lemon-
Uke flavour. CsHsOrHaO. Molecular weight, 210.
Easily soluble in water, either cold or hot, slightiy
soluble in ether, and still less so in alcohol. It
is hygroscopic, and should be kept in a well-
corked bottle. Aqueous solutions of citric acid,
and all other alkaline citrates, develop in course
of time a fungoid growth, du,e to Saccharomyces
mycoderma, with decomposition into carbonic
acid and water. Citric acid is used in some
developers as a preservative and in others as
a restrainer, for making acid fixing and clearing
baths, and as a preservative in emulsions.
CITRO-CHLORIDE PAPERS
Another name for gelatino-chloride printing-
out papers (which see).
CLAMP (Fr., Crampon, Agrafe: Ger., Klampe)
There are several kinds of clamps used in
photography. The lantern -slide clamp is in-
tended for holding the sHde and cover glass firmly
Clamp for General Use
together while binding. The etcher's clamp is
used when etching copper plates face downwards
in the ferric perchloride bath ; it is made of oak
thickly varnished. Various kinds of clamps are
Claryifying
110
Cleaning Dishes
employed ia chemical opetations, for supporting
burettes, test-tubes, retorts, etc. Fretwork
clamps [see illustration) are cheap and are often
useftii to seaire photographic apparatus in
unusual situations, to support backgrounds, or
to improvise temporary accessories. Clips {which
see) are occasionally wrongly referred to as
clamps.
CLARIFYING
A term applied usually to the mechanical
clearing of a solution by allowing a precipitate
to settle or by caitsing more rapid precipitation
by the addition of some inert substance to carry
down a precipitate which does not easily sub-
side. It is occasionally used to obtain clear
solutions of varnishes, when an inert powder
like pumice or chalk is added.
In process work, the fish-glue that is used must
undergo a process of clarifying, and " clarified
fish-glue " IS obtainable as a commercial pro-
duct. Formerly, process workers had to clarify
the glue themselves, and some still prefer to do
so. It is done by adding an equal quantity of
albumen and heating the glue to boiling-point,
stirring well the whole time, and boiling for one
minute. The albumen coagulates and holds the
suspended matter, which can then be filtered
out.
CLAUDE LORRAINE GLASS
A convex mirror of black glass, commonly
known as a " I<orraine mirror," or " Claude glass."
It was used by Qaude Lorraine, the famous French
painter, nearly three centuries ago as a means
of reducing the view and at tiie same time
modifying the colours. Used in photography, it
is of service in showing how a view will look
when reduced and, to a certain extent, when
reproduced in monochrome. Used in doud
photography, it facilitates the obtaining of the
necessary contrast between the clouds and the
blue sky, owing to the fact that the black glass
does not reflect the whole of the ultra-violet
light. A convex glass, silvered but not black-
ened, is used on the reading desk by lecturers
to reflect the lantern pictures shown on the
screen, and to reproduce them in miniature for
personal reference while speaking.
CLAUDET, ANTOINE JEAN FRANCOIS
Bom in France, 1796 ; died in London, 1867.
One of the earliest workers and improvers of
the Daguerreotype process in Fngland, and one
of the last to use it professionally. In 1840
there were oiily two photographic estabUsh-
ments in London, those of Beard and Claudet.
Claudet was also a partner in the firm of Claudet
and Houghton (1834). In addition to improving
the Daguerreotype process by the employment
of chlorine vapour to increase the sensitiveness,
he, in 1844, took out a patent for the use of red
light in the dark-room. One month before his
death his studio in Regent Street was burned
down, and all his valuable daguerreotypes, pic-
tures, and papers destroyed.
CLAYBOARD
A cardboard thickly coated with a chalky
enamel and used by artists for drawing upon.
The chalk surface permits of high hghts to be
scraped out and white lines to be cut through
the blocks. This board may be sensitised with
silver nitrate for printing under a negative so
as to form a basis for drawing on. The surface
is first prepared with arrowroot and ammonium
chloride in the usual way adopted for sensitising
plain papers.
CLEANING BOTTLES
The methods employed for cleaning bottles
will depend upon what the bottles have contained.
The simple and old-fashioned method of half-
filling the bottle with water and adding sand,
cinders, or shot may serve in some cases, as
may the use of a Uttle vinegar and broken-up
egg-shell. Generally, however, the best bottle-
cleaning solution is one made in the proportion
of from 2 oz. to 4 oz. of hydrochloric add to
one pint of water. This mixture is allowed to
remain for a time in the bottle, shaken frequently,
poured into another one, and the bottle rinsed
well with clean water. Bottles that have contained
oil should be rinsed first with a strong solution of
household washing soda, caustic soda or potash,
or liquor ammoniae, and finally with weak hydro-
chloric acid. Commercial benzole may also be
used for greasy bottles, followed by a strong
solution of washing soda, finally rinsing with
plenty of water.
Bottles which have been used for varnish may
be cleaned by rinsing with liquor ammonia
I part, methylated spirit 10 parts, and finally
witli weak ammonia and water. It is better
to use Hquid than mechanical cleaners (sand,
shot, etc.), which are apt to roughen the insides
of the bottles, such roughness causing them to
become dirty and unsightly very quickly.
Bottles used for gold toning solutions qxiickly
become dirty owing to the gold depositing itself
upon the inside of the bottle ; if the deposit is
not removed the gold in fresh solutions will be
attracted by it, to the detriment of the solu-
tions. Weak hydrochloric acid should be used
as a. cleaner for such bottles, and if this fails
aqua regia should be used.
CLEANING DAGUERREOTYPES {See
" Daguerreotypes, Cleaning and Restoring.")
CLEANING DISHES
Dishes used for " hypo " should not be put to
other photographic purposes, even after clean-
ing, as any print treated thereiu is liable to be
stained. Dishes used for developing and toning
soon become dirty, particularly when the de-
veloper oxidises quickly, as pyro, for example.
All dishes require to be cleaned at intervals, but
those made of porcelain appear to require the
most cleaning. There are two kinds of stains,
those which appear on the surface of the glaze,
and those which find their way under the glaze
into the very substance of the dish, from which
it is almost impossible to remove them. A
solution of hydrochloric acid will remove most
surface stains without damaging the dish, the
method being to pour water into the dish and
add hydrochloric acid until the solution is strong
enough ; commercial spirit of salt will do equally
weU and is cheaper. An old tooth-brush, or
a rag tied to a stick, may be used for the comers,
it not being advisable to use the fingers. Fresh
Clesuiing Lenses
III
Clips
stains will not require to be rubbed. For obsti-
nate stains, mix together 8 oz. of pearl-ash, 40Z.
of quicklime, and i pint of water, stir up and
place in the stained dishes ; allow to remain for
one hour, pour out, rinse witii very dilute hydro-
chloric acid in order to destroy the last braces
of the pearl-ash and lime, and finally wash well.
However, spirit of salt is more generally used,
and it makes dishes chemically clean enough,
even if it does not entirely eliminate the stains.
To remove slight stains from fragile dishes,
rub damp salt on them with a piece of flannel,
or rinse with very dilute hydrodiloric acid and
then rub with salt.
CLEANING LENSES
It is easy to damage a lens by improper
dean in g, optical glass being generally much
softer than other kinds. Apart from actual
scratches the surface is liable to become dulled,
a condition that afiects the " rapidity." The
necessity for frequent cleaning is obviated by
fitting all lenses with caps to both front and
back combinations, or by keeping them in air-
tight cases. When a lens requires cleaning it
should first be dusted with a camel-hair brush or
tuft of cotton-wool, and then carefully Wiped
with a very soft sili or linen handkerchief, or
with a soft wash-leather. If the surface still
appears cloudy, a single drop of pure alcohol
should be put on each of the surfaces, which should
be carefully wiped until quite dry. The spirit
must not be sJlowed to run between the lens
and its brass ceU, and care must be taken not
to remove the dead black coating from the lens
cell. The edges of the leas in contact with the
cell are best cleaned with the pointed end of a
bit of soft wood over which the rag is stretched.
Dr. Miethe recommends the use of pith, such
as that of the rush or elder, for this purpose.
A lens that has become scratched or dulled
should be sent to the maker to be repoUshed.
The greatest mistake an amateur can make is
to attempt to repolish a lens with rouge, putty-
powder^ etc. ; even the maker cannot repolish
a badly scratched lens so that it will work qtiite
as well as when it was new, therefore the result
of unskilled work can easily be anticipated. A
lens should not be wetted iJE it can be avoided,
and in the case of condensation of steam or dew
upon the surfaces, the moisture should be re-
moved as quickly as possible.
CLEANING NEGATIVES
The films of negatives are best cleaned when
wet. Usually they are merely wiped over with
a piece of wet cotton-wool ; but to remove a
dirty or messy appearance from a dry negative
use cotton-wool soaked in methylated spirit,
rubbing very h'ghtly to avoid reducing the den-
sity. The metal-polish reducer {see " Baskett's
Reducer") may also be used for cleaning the
dried film, but must be used very gently.
It is generally the glass side, not the film
side, of a negative that requires cleaning. In
the process of manufacture some stray emulsion
may get on the glass side, which, if allowed to
remain, would show in the print. Emulsion
streaks are best removed when wet by rubbing
with damp table salt ; but the same method
answers when the negatives are dry.
To clean ofE the films from " waster " nega-
tives that have been varnished, soak them in
a hot solution of soda or potash, and then rub
with a stifi scrubbing-brush, finally rinsing ; if
potash is used, do not let it touch the fingers.
Soaking in water containing a little nitric acid
answers for unvarnished negatives, scrubbing
or scraping afterwards if necessary. The follow-
ing solution is also recommended for removing
unvarnished films : Citric acid i oz., hydro-
chloric acid 2j oz., water 20 oz. Soak in this
for an hour or two, scrub, and finally rinse.
An excellent cleaning and polishing mixture
for glass consists of the following : —
Rain or soft water . . . i oz.
Powdered pumice-stone . . i „
Whiting or prepared chalk . ij „
Liquor ammoniaB . . . ^ „
Apply with a piece of chamois leather or flannel,
and poUsh with a clean rag or soft paper.
CLEARING SOLUTIONS
Used for removing development stains from
negatives or prints. When the staining is due
to insufficient sodium sulphite in the developer
the following formula is recommended : —
Alum . . . I oz. 55 g.
Hydrochloric add . i „ 12 ccs.
Water . . . 20 „ 1,000 „
The plate should be well rinsed from the
developer, immersed in this clearing solution
for two or three minutes, and then washed for
fifteen minutes and fixed as usual. The use of
an acid fixing bath renders a clearing solution
unnecessary. For clearing development fog, or
chemical fog, or staining caused by the plates
or paper being stale, a solution of thiocarbamide
is the best to employ. {See under the heading
of " Fogged Negatives, Treatment of." Lantern
slides are treated as described under their own
heading, )
In process work, clearing solutions are used
to remove any deposit of silver from between
the dots of half-tone negatives, and also to
sharpen up the dots. This process is called
" cutting." For dry plates, ferricyanide and
"hypo" (Farmer's reducer, which see) is used,
and for wet plates, iodine and cyanide.
CLERK-MAXWELL, JAMES
Bom at Edinburgh, 1831 ; died at Cambridge,
1879. First Professor of Experimental Physics
at Cambridge (elected 1871). He made re-
searches into the composition and vision of
colour, the kinetic theory of gases, electricity,
etc., and was associated with the early experi-
ments in colour photography, with regard to
which he made, about 1861, many suggestions.
CLICHfe
The French term, now anglicised, applied to
electrotypes, stereotypes, and process blocks.
Also used sometimes to indicate negatives and
positives. (See also " Block.")
CLIPS (Pr., Pinces ; Get., Klammern)
Spring clips of various kinds are used for
hanging up wet prints or films. The American
wood cSp A is useful for many purposes; clothes
Clip Copyboard
112
Clouds, Printing in
" pegs " of practically identical shape are obtain-
able at a very cheap rate. Metal dips B are
obtainable in variety. Such clips are especially
useful for suspending sensitised carbon tissue
or photo-lithographic paper for drying. Split
A, Wooden Clip
B. Metal Clip
corks with rubber bands make good clips for
some purposes (see an illustration referred to
under the heading "Film Manipulation"). Nega-
tive dips, or plate-holders, are used for holding
and lifting negatives during development, wash-
ing, etc., to avoid touching them with the
fingers. Film-developing dips are intended for
holding the ends of roll-fihns when developed
in the length.
CLIP COPYBOARD
A board used in process work for holding the
original for copying ; it is provided with spring
dips instead of with pins. In one type the
clips sUde in grooves, whilst in another they
are inserted in holes, and large dips to hold
books and small dips to hold paper or card-
board are provided.
CLOCK, DARK-ROOM (Pr., Horloge de
laboratoire ; Ger., Dunkelzimmer Uhr)
A dock specially made to fadhtate the timing
of photographic operations. The Watkins dark-
room dock, a former pattern of which was
known as the eikronometer, is primarily designed
for factorial development. It has two hands,
one completing a revolution in one minute,
while the other takes ten minutes. A stop
motion permits both hands to be started from
zero as the developer is poured on the plate, and
an outside indicator marks the completed time.
The Welbome Piper stop dock is for factorial de-
vdopment, and for timing numerous other mani-
pulations, in addition to which it has various
novel and useful movements.
CLOTH. BOLTING (See "Bolting Cloth.")
CLOTH, FOCUSING (See "Focusing Cloth.")
CLOUD NEGATIVES
Clouds that are to be added to landscapes must
be taken under similar conditions to those of
the landscapes for which they are required. A
large common or open space should be selected
for photographing, so that a low horizon line
may be induded on the plate. And this low
horizon line should be as unbroken as possible.
The formation of douds near the horizon is
different from that at higher altitudes, and it
is therefore necessary that douds near the
horizon should be induded on the plate so that
they may appear correct if the formation of
the landscape picture necessitates showing
sky near the horizon. Clouds taken right
opposite the sun, or directly towards it, are
quite useless for adding to the large majority
of landscape pictures, as most landscapes are
taken with an obhque front lighting. Oouds
should therefore be photographed with a similar
lighting. If the sim should be in the south at
the time of photographing douds, those about
the north-west and north-east will be the most
useful. As opportimities offer, doud negatives
should be taken with different lighting, and of
varied character ; briUiant pUed-up masses, rain
douds, broken-up skies, quiet, calm, summer
effects, etc., so that a suitable negative can be
be sdected when it becomes necessary to add
douds to a doudless landscape. It is necessary
to study the arrangement or grouping of the
douds on the plate so as to get the prindpal
point of light, or the priadpal feature in the
grouping, towards one side of the plate. The
grouping must be such that it can be utilised in
assisting the formation or composition of a pic-
ture whenever practicable. The prindpal doud
masses should form an angular line across the
plate. The exposure for doud negatives must
be very short, ranging from one-sixtieth of a
second for very light douds, up to one-fortieth
for heavy masses, using a rapid plate (200 H.
andD.), and lensaperture//i6 at mid-day in late
spring or early summer. Development may be
normal. With such short exposures the nega-
tive will be thin, and suitable in every way for
printing into landscapes.
CLOUD SHUTTER (See "Foreground
Shutter.")
CLOUDS, PRINTING IN
The landscape or marine picture should be
printed first and the douds added subsequentiy.
No attempt should ever be made to block out
the sky on the landscape negative, even if it
should print to a pale grey tone. Painting out
a sky leaves the outlines of the distance hard
and crude, instead of delicate and soft, as they
invariably appear in a landscape print, even if
sharply defined throughout. It is no disad-
vantage to print a sky over a pale tone of grey ;
the douds are softened in their contrasts, and
frequentiy harmonise better with the tone of the
landscape. At times, the grey tone of a sky
may be a disadvantage when it is desired to
add a sky that should be as brilliant as possible
for a spedal effect. In that case the sky may be
kept white by shidding. A card is roughly cut
to the shape of the outline of the landscape, and
supported over the sky part of the picture during
printing, the edge of the card being directly over
the outiine of the landscape. This plan allows
the landscape to print fully, but the sky will be
vignetted off from its full printing, where it joins
the landscape, to a pure white for the greater part
of its area. The suddenness or Uie gradual
nature of this vignettkig will be determined by
With Ordinary Plate
With Isochromatic Plate and Medium ("Three Times")
Screen
With Isochromatic Plate, but Without Screen With Isochromatic Plate and " Six Times " Screen ;
over-corrected
VARIOUS RENDERINGS OF DAFFODILS IN BLUE VASE
Clouds, Printing in
"3
Clouds, Printing in
the distance of the card from the surface of the
negative. When the landscape print is obtained,
a mask is also required, to be used to shield it
from the action of the light while the clouds are
printed. The most satisfactory method of
obtaining this mask is to take a rough silver
A and B. Landscape Negative and Mask
print of the landscape, and cut it carefully to
the outline of the subject. Any small dark
objects, such as a church spire, the branches
and twigs of a leafless tree, may be disregarded
in cutting this mask, as the clouds may be printed
over them. But the mask must be cut so as to
shield any light object, excepting in special
cases which must be determined on their merits.
The landscape and mask are shown at A and B.
The landscape print must be placed in position
behind the doud negative, care being taken that
the horizon of one is near the horizon of the other,
so as to ensure that the cloud forms are in correct
relation to the landscape. The clouds must be
printed in a frame one or two sizes larger than
the landscape, the frame being provided with a
sheet of plain glass so that the smaller negative
can be printed without difficulty. The large
frame allows space for arranging the landscape
print in the correct position on the cloud negative
irrespective of the extent to which it may project
in any direction.
K a large number of prints are required from
one negative, the most satisfactory manner of
using the mask is to attach it permanently to a
piece of glass the same size as the print. If only
a few are wanted, the mask may be wetted
sufficiently to render it quite limp ; it will cUng
to the glass thoroughly satisfactorily, without
risk of movement, while the sky is printed. In
either case, the mask is adjusted in position on
the outside of the plain glass in the printing
frame when everything is ready for printing the
clouds. The frame should be in a horizontal
position.
The mask should be carefully adjusted so that
it overlaps the landscape very slightly, about
one-sixteenth of an inch, or less in small work
C and D. Diagrams Showing How Carbon and
Bromide Prints are Marked for I^Iasking
The fact that there are two thicknesses of glass
between the mask and the print — the plain glass
of the frame and the sky negative — ^Will cause
the mask to print with a soft or vignetted outline,
and this slight overlapping is to compensate for
the manner in which the light diffuses under the
8
mask, and it prevents the print from showing
any hard jimction. In addition, a card should
be supported over the landscape portion, as
shown at E, while the clouds are being
printed ; this card should project over the sky
to a small extent to soften off the depth oi
printing near the horizon. The extent and
nature of this softening will be determined by
the extent to which the card projects beyond
the landscape and its height above the surface
of the negative. The edge of the card may be
either straight or cut approximately to the out-
line of the landscape, according to the subject.
This vignetting off towards the horizon becomes
absolutely necessary when a grey sky has been
vignetted into a plain white, as described
earlier.
All preliminary work in cloud printing should
be on silver printing-out paper. Working by
daylight in a process that gives a very strong
image enables the work to be followed easily.
The mask can be adjusted to the correct position
without any difficulty, and any, error in adjust-
ment or in arranging the card shield can be seen
at almost the beginning of printing, and rectified
immediately. The experience gained by print-
ing clouds in silver will enable any photographer
to place the masks and shields correctly without
difficulty when adding clouds to platinotype
E. Shielding Part of Negative when Printing
carbon, or bromide prints, though in these pro-
cesses there is no strong image to act as a guide.
The method of working in platinotype and
carbon, inasmuch as they are daylight processes,
will be similar to that described for silver print-
ing, but there is no image that can be seen
sufficiently well through the cloud negative to
assist in correctly placing the mask. In plat-
inotype, the image is an assistance, but it cannot
be utihsed in tiie same manner as in silver.
When the landscape print is taken from the frame,
a small pencil mark is made at each end of the
print, at the exact point to which the mask
has been cut ; and about an eighth of an inch
above each mark, a second one is made to serve
as a guide in placing the mask. These pencil
marks are shown at E E. When the landscape
is being arranged under the doud negative,
these pencil marks are of great assistance in
securing the correct position. But their great
value consists in the manner in which they
enable the correct pladng of the mask to be
determined. They are plainly visible through
the doud negative, and the mask can be fitted
to them as easily as to the strong image of a
silver print. It is self-evident that if the mask
is in the correct position at the two margins it
must be in the correct position throuighout its
length. The exposure should be timed by
means of an actinometer.
In carbon prints there is no image whatever
Coal-tar Colours
114
Coating
to serve as a giiide for marginal marks, and their
position must be determined differently. A
little water-colour is required — ^white or hght
yellow — and a fine brush. When the print is in
the frame, either before or after the exposure,
one-half of the back of the frame is opened, and
a fine mark is made on the margin of the negative
at the spot corresponding with the mask. That
half of the back of the frame is at once closed
again so as to press the tissue on to the negative,
and the moist colour wiU set ofi on to the margin
of the print. While this half remains closed, the
other half is opened and a similar mark made on
the margin of the negative at the correct position
for the mask. The precaution should be taken
of opening each half separately a second time to
ascertain that the colour has been transferred
to the face of the tissue ; and, before removing
the print, a mark should be made on the back
to indicate which is the top. The exposed tissue
should then be removed from the frame, the
marks strengthened, and a second mark made
just above each to correspond with the pencil
marks in platinotype. With these marks the
correct placing of the mask is easy, and this and
the printing will be the same as described for
platinotype. The appearance of the carbon
print is shown at C, the white brush marks F F
corresponding to E E in diagram A.
In bromide printing, the method of working
is the same as in carbon, but a dark colour must
be used for the brush maisks, black or dark-brown.
Diagram D illustrates a bromide print to be used
with the mask B, the brush marks being indicated
at G G. In bromide printing, the card shield
must be kept moving during the exposure, to
prevent a sharp liue from appearing.
In enlarging by means of a lantern, pencil
marks can be made on the enlargement, the
image thrown by the lens forming the guide.
The card shield may be held in any convenient
position between the lens and <i.e enlarging
easel so as to shield the landscape, and it must
be kept in motion throughout the exposure of
the cloud negative.
COAL-TAR COLOURS (See "Anihne, or
Coal-tar, Colours.")
COATING
It will be found somewhat easy with a little
practice to coat plates if the operation is prac-
tised first in daylight or gaslight, and for this
purpose it is advisable to start with whole
plates, assuming that one wishes subsequently
to obtain quarter plates. A pneuniatic holder
{which see) should be obtained, and the sheets
of glass thoroughly cleaned and stacked, with
the surfaces to be coated away from the operator.
The emulsion should be at a temperature of
95° P- (35° C.) in Slimmer and 98° F. (36-6° C.)
in winter ; and if the room is cold the glass
itself should be warmed. The pneumatic holder
is taken in the left hand, the bulb well squeezed,
and the lip of the holder just wetted and then
pressed on to the back of a sheet of glass in the
centre and the pressure relaxed. The suction
— really the pressure of the atmosphere on the
surface of the glass — ^holds it firmly against
the holder, wherein there is a partial vacuum.
The glass should then be held horizontally, and
the emulsion poured on to the middle, prefer-
ably from an earthenware teapot which has a
spout that starts from near the base, as this
avoids the air bubbles which rise to the top of
the emulsion. Failing a teapot, the ordinary
invalid's feeding cup would be a good sub-
stitute.
The pool of emulsion should be poured on
to the centre of the plate, and, as soon as it
covers about half the area, the plate should be
tilted so as to cause the emulsion to run to the
top right-hand comer, then to the top left-hand
comer, then to the bottom left-hand comer,
and finally to the bottom right-hand comer,
and the excess drained off here. This must be
done slowly, otherwise the emulsion will run
over the edges ; and it is advisable to practise
over a good-sized dish so as to catch any spUlings.
As soon as coated, the plate should be slid on
to a sheet of plate glass accurately levelled, and
allowed to set.
The coating of paper is not so easy, but it
may be done by pouring the emulsion into a
dish, tilting this, and drawing the paper over
the top of the emulsion. At least a yard of
paper can be coated in this way, and with care
but few bubbles will arise. But by far the
simplest plan is to use one of the film develop-
ing dishes provided with a roller. Having the
paper cut in long lengths, pass one end round
Tilted Dish of Emulsion for Coating Paper
the roUer, and, keeping it tightly strained against
the latter, pour in enough emulsion to cover a
little less than half the diameter of the roller.
Then the paper can be drawn through the emul-
sion and straight up, and enough wiU cling to it
to give good results. Naturally, the emulsion
must be kept hot.
Commercially, of course, special machinery is
used both for plates and papers, and in the
former case the cleaned glasses are fed on to
the bed of the machine and coated with emulsion
by various devices. Thence the glasses pass
through an ice tunnel, which thoroughly sets the
emulsion, and at the other end of the machine,
which may be 30 ft to 40 ft. from the coating
end, they are stacked in racks by hand and
thence conveyed to the drying-room.
The commercial paper-coating machinery is
usually arranged so that the paper, which is in
long reels, passes round a roller through the
emulsion. The coating is chilled either by a
cold roller or by cold air; the paper then
passes on, is formed into loops or festoons,
and traverses the drying-room, being again
reeled at the other end.
In process work, coating is an important
operation. For collotype, the gelatine coating
is applied by levelling tie glass plate and pour-
ing on a measured quantity of solution, guiding
it to the edges by means of a catgut bow or a
Co-axial
115
Cockling of Prints
glass rod. For coating zinc or copper a -whirler
{which see) is invariably used, the coating being
evenly spread by centrfiugal force, while the sur-
plus is thrown off. In the case of very volatile
mediums, such as bitumen, it is sometimes the
practice to coat by pouring on the solution with
a sweep of the bottle along the top edge of the
plate, taking care to incline the plate so as to
allow the solution to run down and the stirplus
to run ofi.
CO-AXIAL
Having a common axis. Thus the positive
and negative elements of a telephoto lens or the
eyepiece and object glasses of a telescope or
microscope are said to be co-axial.
COBALT BLUE (Pr., Bleu de cobalt; Ger.,
Kobaltblau)
A compound of alumina and oxide of cobalt
used in painting ; of slight photographic interest.
COBALT CHLORIDE (Pr., Chlorure de cobalt ;
Ger., Kobaltchlorid)
Synonym, cobaltous chloride. CoClj 6H2O.
Moleciilar weight, 238. Solubilities, soluble in
water and alcohol. Ruby red crystals, obtained
by dissolving cobalt carbonate in hydrochloric
acid and evaporating. The addition of small
quantities of cobalt chloride to printing-out
emulsions produces greater contrast.
COBALT SALTS, PRINTING WITH
Cobalt belongs to the same group of metals
as iron and manganese, and, like these, many of
its salts are sensitive to light. Although no
practical process has so far been founded on
this fact, it is as well to record briefly the
researches of A. and Iy. I<umi4re on the subject.
The most promising salt is obtained by dis-
solving cobaltic oxide, COaOj, to saturation in
oxalic acid solution, or by precipitating cobaltic
oxyhydrate from a cobaltous salt solution by
means of sodium peroxide and dissolving the
precipitate, after careful washing, to saturation in
oxalic acid solution, the cobaltic salt being kept
all the time in excess. This operation must be
performed in the cold, and takes some hours. A
green solution is obtained which can be used
to sensitise gelatinised paper, and, after drying,
on exposure to light under an ordinary negative,
a pale rose-coloured image of a cobaltous salt is
obtained. The action is extremely rapid, taking
but a fraction of the time necessary to print
under similar conditions with a silver salt. The
print, when ready, should next be immersed in a
5 per cent, solution of potassium ferricyanide
and washed. The image thus obtained is a pale
rose colour and not very intense, consisting of
cobalt ferrocyanide. This may be toned with an
alkaline sulphide, which produces dark brown
cobalt sulphide. By treatment with an iron salt,
a blue image is obtained ; a nickel salt gives a
red image. Attempts to develop the cobaltous
image with organic compounds (see " Manganese,
Printing with") were not satisfactory, in all
cases it being fotmd much more difficult, and
the only substances proved to be of any value
were hsematoxyline, which gave a violet blue
image that was changed to reddish by hydro-
chloric acid, and benzidine, toluidine, and their
hydrochlorate salts. These produced on the
places not affected by light, so that they would
give a negative print from a negative, an intense
blue image, which was turned brown by ammonia
and pale yellow by hydrochloric acid.
Further researches with the citrate, stannate,
nitrite, tartrate, gallate, and sulphocyanide of
cobalt have been made, but the results were still
less promising.
COBALT-LEAD TONING
A process for toning bromide and gaslight
prints to a green colour, introduced by MM.
Lumiere and Seyewetz in 1905. Two solutions
are required : —
A. Potassium ferri-
cyanide . .144 grs. 65 g.
Lead nitrate . 96 „ 44 „
Water . . 5 oz. 1,000 ccs.
B. Cobalt chloride . J „ no g.
Hydrochloric acid i^ ,, 330 „
Water . • 5 „ 1,000 ccs.
Por vigorous greens fully developed prints
must be used. The print is placed in A imtil
bleached, is next washed very thoroughly, and
then immersed in bath B. The image on the
finished print is made up of lead, silver, iron, and
cobalt in the form of a ferrocyanide and of the
chlorides of silver and lead. If the toning action
is prolonged, the cobalt will completely replace
the silver and lead.
COCKLING OF PRINTS
Photographs mounted in a wet state upon thin
cardboard, or upon the leaves of an album,
invariably cockle or curl when dry, whereas
prints moiinted surface-dry do not cockle so
badly. The defect is due to uneven expansion
caused by the wet mountant, and can be made
worse by unskilful manipulation. Careful selec-
tion of the mountant minimises the trouble, and
the following formula is as good as any in this
respect : —
White dextrine
Powdered alum
Sugar
Hot water
360 grs. 82 g.
16 „ 3"6 „
60 „ 13-6 „
I oz. 100 ccs.
This, when thoroughly mixed, should form a
thick cream, which should be allowed to stand
a day before use. Take the trimmed dry print
and lay it face downwards on a sheet of glass,
and with a fairly stiff brush apply the smallest
possible quantity of mountant to the back of
the print, distributing evenly and quickly ;
before the mountant has had time to soak
through, place the print upon the mount and
squeegee or rub down. Place two or three
thicknesses of fluffless blotting-paper over the
picture and moimt, and put into a copying press
and screw down hard, or put under heavy pres-
sure for several hoiirs. When dry, there should
be Uttle or no cockling.
Another plan is to brush the back of the dry
print over with a strong solution of gelatine or
soft glue, and to damp slightly the mount before
placing the print in position, drying under
pressure.
The theory of the subject is to prevent
Coddington Lens
Ii6
CoUimating Lens
expansion of the print before pressing it in
contact with the mount ; or, if this expansion
is unavoidable, to expand the mount, as in the
preceding paragraph, and let mount and print
contract together. Another point is to use a
thoroughly even mountant, because should one
part of the print get wetter than another, cockling
is almost sure to occur.
Photographers may learn something from the
draughtsman's method of stretching drawing
paper, and even if it is dangerous to mount
prints in this way, they can adopt it when pasting
brown paper on the backs of photograph frames.
The draughtsman slightly damps the back of
the paper, thus evenly expanding it all over,
touches the margin all round with paste, and
" lays " the paper on the board, thoroughly
pressing the margin into contact. The paper
contracts in drying and becomes as tight as a
drum-head.
CODDINGTON LENS
A biconvex spherical lens with a deep groove
fiUed with an opaque substance running round
the centre. The groove acts as a diaphragm.
This lens is used as a hand magnifier, and gives
a large, bright field, but its working distance is
short.
COERULINE S (Pr. and Ger., Cceruline S)
Synonyms, coerulein, ccerulean. A compound
of alizarine blue and sodium bisulphite, which
has been occasionally used for colour-sensitising
plates.
COFFEE PROCESS
A mixture of coffee, advocated by Colonel
Baratti, used as a preservative in the early days
of the dry collodion plate. About 1855 there
were numerous announcements of new pre-
servatives wherewith the sensitive surface of
collodion plates could be covered, so as to enable
them to be dried and kept ready for use. Among
the many substances recommended and widely
used were beer, tea, treacle, gum arable, brown
sugar, white sugar, raspberry vinegar, wort,
malt, and tobacco.
COINS AND MEDALS, PHOTOGRAPHING
The difficulty presented by subjects of this
character is solely due to the low relief of the
image and the consequent absence of contrast
in light and shade. This difficulty may be
entirely overcome by suitable lighting. The
coin or medal should be placed so that it receives
a strong light from one side, the direction of
the light being parallel with the face of the coin
and striking the edge strongly. There may be
a little diffused light in front, but as large a
proportion as possible should be across the face,
just skimming the surface. However slight the
relief, it will be shown by strongly marked lights
and shadows if this method of lighting is adopted,
and the production of a successful negative wiU
present no difficulty. The exposure must be
short.
COINS AS WEIGHTS
Enghsh silver coinage is minted exactly by
weight in proportion to its value — namely,
436A grs- for every five shillings ; thus a new
threepenny-piece weighs 21-8 grs., a sixpence
43'6 grs., and so on, the sixpence and three-
penny piece being almost exactly one-tenth
and one-twentieth respectively of the avoir-
dupois ounce. The list gives the approximate
avoirdupois weights obtainable by the use of
coins just slightly worn : —
20 grs. = one threepenny-piece.
40 ,, = one sixpence.
43 ,, = one farthing.
61 ,, = half-sovereign.
88 „ = one halfpenny.
123 „ = one sovereign.
145 „ = one penny.
175 ,, = one florin.
218 ,, = half-crown.
J oz. = one halfpenny and one threepenny
piece.
^ „ = florin and sixpence.
I „ = three pennies, or five halfpennies.
I lb. = forty-eight pennies.
The United States five cent nickel coin is
exactly 5 g. (77 grs.) in weight and 2 centimetres
in diameter. The English halfpenny-piece is
exactly i in. in diameter and weighs, when
new, exactly one-fifth of an ounce ; the penny
is of less convenient weight— one third of an
ounce. No halfpenny-piece is issued that is more
than -2 per cent, wrong in weight, one-fifth of
I per cent, being what is known as the legal
" remedy " in weight, and this does not amoimt
to I gr. per ounce.
French coins are particularly suitable as
metric weights, namely : —
25 g. =5 francs (silver)
10 „ = 2 „ „
5 n ^^ ^ »» »»
^f >> — Z )> . J>
10 „ = 10 centimes (bronze)
5 >» ^^ 5 )» I)
2 )» = 2 ,, I,
I If ^ I >i i>
COLAS'S PROCESS
A ferro-gaUic printing process perfected by
Colas, a German. It is described under the
heading " Ferro-gaUic Process."
COLD BATH PROCESS (See "Platinotype.")
COLD, EFFECT OF
The action of photographic chemicals is seri-
ously retarded by cold, as explained under the
heading "Temperatures."
COLD EMULSION (See " Emulsion.")
COLLIMATING LENS (Pr., ColUmateur : Ger..
Kollimatorlinse, KoUimator)
An achromatic biconvex lens placed in a
tube at its principal focal distance from a narrow
slit or small aperture. A collimator is used in
lens -testing apparatus to produce a parallel
beam of Hght, and in conjunction with the
spectroscope. Another form of collimator is a
small fixed telescope having cross-wires at its
focus ; this is employed for adjusting the optical
axis, or line of sight, in astronomical instru-
ments.
CoUinear Lens
117
Collodion
COLLINEAR LENS
An anastigmat lens introduced in 1894 by
Voigtlander, and made in intensities varying
from //4- 5 tof/i2-$. The illustration shows the
construction of the original type.
COLLOCHROME
Coloured collotype printing.
COLLODIO-ALBUMEN PROCESS
An obsolete process, which gave most beautiful
transparencies. A plate is first coated with
bromo-iodide collodion, then sensitised in a silver
bath and washed to remove excess of silver
nitrate. Next it is coated with a mixture of
albimien, bromide, and iodide of potassium,
which destroys the sensitiveness of the plate
so that it can be dried in daylight. When
required for use, the plate is resensitised with
silver nitrate and thoroughly washed and dried.
A gallic acid and silver nitrate developer is
generally used. (For working details see Albu-
men Process," sub-heading " Positives.")
COLLODIO . BROMIDE
Emulsion.")
(See
' Collodion
COLLODIO - BROMO ■ CHLORIDE EMUL-
SION (See " Collodion Emulsion.")
COLLODIO-CHLORIDE
An emulsion of silver chloride suspended
in collodion. Generally used for printing- out
papers. {See also " CoUodion Emulsion.")
COLLODIO-GELATINE (Fr. and Ger., Collo-
dio-gelatine)
H. W. Vogel suggested that dry gelatino-
bromide emulsion should be dissolved in glacial
acetic acid and alcohol, and mixed with a solu-
tion of pyroxyline in similar solvents, with the
object of combining the advantages of the two
processes. The process has foimd no practical
use, as the sensitiveness is very low. Husnik
gave the following formula : —
Dry gelatino-bromide
emulsion .
Glacial acetic acid
Alcohol
I oz.
I >.
• 1 ,.
30 g-
30 CCS.
30 „
Dissolve, and add —
Pyroxyline .
dissolved in —
2 oz.
60 g.
Glacial acetic acid
Alcohol
I oz.
. 800 mins.
30 CCS
50 „
COLLODION (Ti., Collodion; Ger., Kollodium)
A solution of pyroxyline in a mixture of equal
quantities of alcohol and ether ; it should be
kept in a well-stoppered bottle. It is a coloiu:-
less, syrupy liquid, being more or less fluid
according to the quantity and nature of the
pyroxline used. It will keep indefinitely if made
with a good pyroxyline ; the pyroxyline should
be first well saturated with the ether and then
the alcohol added, and, on shaking, the cotton
should completely dissolve. The solution should
now be set aside in the dark and allowed to
stand two or three days to allow any mechanical
impurities to settle, this being preferable to
filtration, as in this process some of the solvents
are lost. The ether used may be the so-caUed
methylated ether, and should have a specific
, gravity of -720 ; the alcohol may be the indus-
trial methylated spirit, but it is preferable to
use the pure alcohol ; aqueous alcohol should be
used when aqueous solutions of salts are to be
added to the collodion, as is often the case in
making collodio-chloride printing-out emulsion.
Collodion is used for enamelling prints {see
" Collodion, Enamel ") and as the vehicle for the
silver salts in the wet-plate process, dry collodion
plates, collodion emulsion, and coUodio-chloride
paper.
It is important that collodion should always
have that degree of viscosity which has been
found the most satisfactory for the particular
purpose. Viscosity may be defined as the
thickness or syrupy nature of the collodion. A
very thin collodion — that is, one with less
viscosity — is apt to allow the silver salts to
deposit at the bottom of the bottle ; on the
other hand, for some purposes — such as enamel-
ling— a less viscosity is advisable. The simplest
method of testing the viscosity is by means of
Von Hiibl's viscosimeter, a glass tube 6 in.
(15 cm.) long, I -2 in. (3 cm.) internal diameter,
with one end drawn into a fine aperture of
about ,^ in. (i imn.). About Jin. (8 cm.) from the
wide end, and on the outside of the tube, should
be scratched a line. This tube should be filled
up to the mark with distilled water, the small
aperture being covered with the finger, and
by means of a stop-watch the time taken for
the water to flow out should be noted. The
mean of six tests should be taken. Then the
same process should be gone through with the
collodion to be tested ; the time taken by the
collodion divided by that taken by the water
gives the viscosity of the collodion. For in-
stance, assimie the mean for six tests for dis-
tilled water at a certain temperature to be
84 seconds, and the time for a specially thick
4 per cent, collodion to be 187 seconds; then
187^84 = 2.226, the viscosity of the collodion.
The proportion of alcohol and ether is not a
fixed quantity. In summer more alcohol should
be used, and thus the loss from evaporation
slightly checked. For coating large plates a
coUodion rich in ether is difficult to work, as the
solvents evaporate before the plate is covered ;
on the other hand, a film produced by a collodion
rich in ether is tougher. In the wet coUodion
process excess of alcohol produces greater sensi-
tiveness, whilst in the dry coUodion process the
ratio of the solvents is of less importance, and
certainly in those emulsions washed by precipi-
tation an excess of alcohol is an advantage. The
solubility of the silver nitrate and the salts has
also considerable bearing on this point, and it
may be considered as a general axiom that all
Collodion Bottle
Il8
Collodion Emulsion
salts are more soluble in alcohol than in ether.
More particular details will be found under the
special headings.
In process work, collodion is an important
factor on account of the facility and cheapness
with which, by its help, negatives suitable for
the various reproductive processes can be made.
The comparative slowness of wet-plate exposures
is no drawback where exposures are invariably
made by electric light ; and the development,
fixing, intensification, clearing, and drying are
all executed much more quickly than on gelatine
plates. The silver deposit being on the surface,
the image is more susceptible to intensification
and reduction than an emulsion fflm. Finally,
on the ground of cheapness, wet collodion holds
the field. It has been calculated that the
average cost of making negatives in half-plate
size is : Wet collodion, id. ; collodion emulsion,
ijd. ; dry plate, 2jd. Collodion is also largely
used in process work for stripping. {See also
conclusion to article "Collodion Process
(Wet).")
COLLODION BOTTLE (Fr., Flacon d collo-
dion ; Get., Kollodiumgiessfiasche)
A long, narrow bottle for holding and pour-
ing coUodJon in the wet-plate process. The
earlier patterns had merely an ordinary stopper,
but in the modem " cometless " collodion bottle
A, so called because its peculiar construction
A. "Cometless"
Collodion Bottle
B, Collodion Pouring
Bottle and Filter
ensures practical freedom from the comet-
shaped spots and other markings incidental to
wet-plate work, a closely-ground cap is sub-
stituted. A combined pouring bottle and filter
is shown at B. A piece of muslin or cotton is
tied over the lower end of the inner tube, through
which the contents must pass before being poured
out. The surplus is returned to the bottle
through a notch at the side of the tube. For
a third type of bottle, see imder the heading
" Collodion Filter."
COLLODION EMULSION
A suspension of various silver salts in collo-
dion, and used for printing-out papers, trans-
parencies by development, and negative work.
The simplest of all collodion emulsions to make
is that for printing-out paper, or, as it is some-
times called, coUodio-chloride paper. There are
numerous formulse, but those given in the next
column and in the first column of p. 119 have
been found of great practical use.
0-9
g-
1-8
*f
10
CCS
10
it
Valenta's Formula
Lithium chloride .
Strontium chloride
Absolute alcohol .
Glycerine
Dissolve by the aid of a gentle heat, and add to—
CeUoidin collodion (3 %) . 95° ccs.
Then add—
Citric acid . . . . 5 8-
Warm alcohol . . . ?.s.
Enough alcohol should be used just to dissolve
the acid. Shake thoroughly, and add:—
Silver nitrate . . . 16 g.
Hot water . . . .20 ccs.
This should be added ia small quantities at a
time, shaking thoroughly between each addition.
Allow the emulsion to stand for twenty-four
hours, then filter and use.
Hanneke's Formula
A. CeUoidin coUodion (4 %)
Ether
Absolute alcohol
To this add —
B. Silver nitrate
Distilled water .
Absolute alcohol
Then add in small quantities, shaking well after
each addition and observing the order given : —
C. Calcium chloride (crystal) . 4 g.
Distilled water .
Absolute alcohol
D. Citric acid .
DistiUed water .
Absolute alcohol
E. Castor oil .
Glycerine .
Absolute alcohol
For solutions B, C, and D, the salts or acid
should be dissolved in the water by the aid of
heat and then the alcohol added ; if this throws
down any crystals the solution should be gently
warmed, and as soon as clear added to the collo-
dion. In all cases the solutions should be added
in small quantities at a time with constant
shaking in between, so as to obtain as fine-
grained an emiUsion as possible.
Silver Bromide Printing-out Emulsion
This was suggested in 1906 by Valenta, and
gives an excellent printing-out paper.
620
ccs.
100
tt
30
>l
25
g-
25
ccs.
120
4
30
5
g.
5
CCS.
30
n
7-S
t>
7-5
tt
IS
tt
A.
CeUoidin collodion (3 %
1 . 1,000 ccs.
B.
Citric acid .
• . 20 g.
Absolute alcohol
. ■ 90 ccs.
Strontium bromide
3-2 g.
Glycerine .
4 ccs.
C.
SUver nitrate
20 g.
Hot distilled water
10 ccs.
Absolute alcohol
80 „
D.
Ether.
• 160 „
Mix A and B in daylight and add C in the dark-
room in smaU quantities with thorough agita-
tion ; add D, aUow the emulsion to stand fifteen
minutes, and then filter through wool and use
for coating. This gives an extremely rapid
Collodion Emulsion
119
Collodion Filter
printing paper with, a long scale of gradation,
and therrfore requires rathpr brilliant negatives.
An emulsion which is much more suitable for
the average negative can be prepared by adding
to the B solution : —
out no notice need be taken of it. To this silver
collodion add the following, whilst still warm : —
Calcitun chloride (anhydrous)
o-5g-
Greater contrasts still can be obtained by using
uranyl chloride or adding calcium chromate.
Collodio-chloride Emulsion for Development
This gives very slow plates, but the grain is
exceptionally fine and very warm tones are
obtainable.
Magnesium chloride (crystal)
Absolute alcohol .
4 g-
20 ccs.
Rub up in a mortar, and add —
Collodion (2 %) . . -So ccs.
As soon as the mixture becomes slimy, add —
Ether ..... 30 ccs.
And finally add —
Nitro-hydrochloric add . . o-6 ccs.
The silver collodion is prepared as follows : —
Silver nitrate . . . 4 g.
Hot distilled water . . 3 ccs.
When dissolved, add —
Hot alcohol . . . .20 ccs.
And then —
Raw collodion (2 %) . . 50 ccs.
The chloride collodion should be added to the
silver collodion in small quantities, well shaken,
and allowed to stand for twenty-four hours with
occasional agitation ; then it should be poured
in a fine stream into about sixteen times its
volume of warm water (100° P., or nearly 38° C.)
with constant stirring. The emulsion is pre-
cipitated in fine flocks, which should be collected
on a dean linen filter, gentiy squeezed, and then
weU stirred up with warm water two or three
times and finally well drained, rinsing once
or twice with alcohol. Five parts of the dried
emulsion shotild be dissolved in 100 parts of a
mixture of equal volumes of alcohol and ether,
shaken till dissolved, and then filtered.
Pure bromide and chloro-bromide collodion
emulsions were much used for transparency
making, but of recent years the gelatine lantern
plates have completely ousted them from prac-
tical use. They are, however, now employed for
negative work, and tiie most satisfactory formulae
are those given by Von Hiibl.
CoUodio-hromide Emulsion
Silver nitrate . . . 50 g.
Distilled water . . -5° ccs.
Dissolve, and add liq. ammoniEe (-880) in suffident
quantity to form a perfectly dear solution ;
^low to cool, and add the silver solution to —
Collodion {4 %) . . . 600 ccs.
This should be in a large bottle, preferably
one that will contain about three times the total
volume, and if any of the cotton or silver setties
Ammonium bromide
Hot distilled water
Alcohol
32 g.
35 ccs.
50 „
Shake the emulsion for about five minutes, and
then add in small quantities with vigorous agita-
tion about one-foirrth of its volume of dis-
tilled water. This causes the emulsion to pre-
dpitate. It should then be poured into about
ten times its bulk of water and well stirred, the
water drained off, and the washing repeated
three or four times. The shreds of emulsion are
finally collected on a linen filter, and gently
pressed ; then shaken up with alcohol, and again
pressed out. The emulsion shreds should now
be shaken up with 8|- oz. or 250 ccs. of absolute
alcohol, and allowed to stand for twenty-four
hours; at the end of this time 5J oz. or 150 ccs.
of the liquid should be poured off and replaced
by $\ oz or 1 50 ccs. of absolute alcohol in which
7% grs. or 0-5 g. of narcotine have been dis-
solved, and 8| oz. or 250 ccs. of ether added, well
shaken, and allowed to stand three days and
then —
Absolute alcohol . . . 250 ccs.
Ether 250 „
added and the emulsion filtered.
Chloro-bromide Emulsion
This can be made in predsdy the same way
as described above by reducing the ammonium
bromide to 416 grs. or 27 g. and adding 23 grs.
or 1-5 g. of pure anhydrous lithium chloride.
Both these emulsions are very suitable for posi-
tive work and also for sensitising with eosine
and other dyes for colour negatives.
Von Hiibl recommends a glydn developer, but
hydroquinone is the general favourite. Collodion
positives and negatives can be intensified, re-
duced, or toned Uke any other silver images.
In process work, collodion emulsion has been
revived of late years because of its suitability
for colour work, owing to the emulsion being
susceptible to colour sensitising with aniline
dyes. A chloro-bromide emulsion is used for
this purpose, and it is always exposed in the
moist state. The sensitising dyes are sometimes
added to the emulsion, and in other cases flowed
over. Excellent emulsions are on the market.
COLLODION, ENAMEL
A mixture used for giving to prints the
highest possible gloss, the process being called
enamelling, an expression sometimes incor-
rectiy applied to burnishing and rubbing with
encaustic paste. Enamel collodion may be
purchased ready for use, or may be made accord-
ing to the following formula : —
Pyroxyline . . . -4 grs.
Methylated alcohol . . | oz.
Methylated ether . • \ ,
Castor oil . . . -4 drops
(For methods of using, see " Enamelling Prints.")
COLLODION FILTER (Er., Filtre A collo-
dion : Ger., KoUodiumfiltrierflasche)
An arrangement for filtering the collodion
used in the wet-plate process. As here shown,
Collodion Pellicle
Collodion Process (Wet)
a tuft of cotton is adjusted loosely in the lower
part of the bulb-shaped receptacle at the top,
the collodion being poured into this and filter-
ing into the bottle beneath. A glass tube runs
Collodion Filter
from top to bottom to allow of the escape of air
as the filtered collodion ascends ; this tube should
be kept above the surface of the solution as the
filtering proceeds. {See also " Collodion Bottle.")
COLLODION PELLICLE
A preparation, advertised and described by
W. B. Bolton in 1876, for making sensitive
plates which could be used in a dry or wet state.
COLLODION POSITIVE
A collodion negative image taken on thin,
black-surfaced metal or on glass backed with
velvet or black varnish. By reflected Hght the
image appears as a positive. Collodion positives
are usually made by the wet-plate process {see
" CoUodion Process (Wet) "). A thin image being
necessary, the collodion should be diluted and
development stopped directly the details are out.
An iron developer gives the whitest deposit, and
allows a shorter exposure to be given. Except
when taken with a reversing mirror or prism in
front of the lens, the ferrotype image is laterally
reversed — that is, the left hand of the sitter
appears as the right hand in the picture. The
following developer gives an exceptionally white
deposit suitable for ferrotypes, etc. : —
Potassium nitrate . 200 grs. 22-8 g.
Ferric protosulphate . 300 „ 34-2 „
Acetic acid (glacial) . ij oz. 75 ccs.
Nitric acid (pure) , 30 mins. 3 „
Water . . .20 oz. 1,000 „
Collodion positives must be varnished or
glazed, as otherwise the film is abraded by hand-
ling.
COLLODION PROCESS (DRY)
In this process plates and papers coated with
a collodion emulsion {which see) are employed,
thus obviating the great disadvantage of the older
wet process in which the plates had to be exposed
immediately they came from the sensitiser. Full
information on preparing the emulsion is given
under the heading to which allusion is made
above. Generally, collodion plates are of about
the same speed as lantern plates, and they can
be developed with any standard solutions used
for gelatine dry plates. Glycine is particularly
recommended owmg to its freedom from fog.
COLLODION PROCESS (WET). OR WET-
PLATE PROCESS (Fr., Procidi d. la col-
lodion humide, CoUodion mouilli; Ger.,
Kollodiumverfahren, Masses hoUodionver-
fahren)
CoUodion was introduced into England in
1847 ; immediately afterwards R. J. Bingham
(one of Faraday's assistants) suggested its use
for photography. Gustave Le Gray, a noted
French worker, also suggested that collodion
might prove useful. The actual invention of the
first workable process is due, however, to F.
Scott Archer, who made the first collodion nega-
tives in the autumn of 1848, and who published
his perfected process in the Chemist for March,
1851. So popular did Archer's process become
that it practically displaced daguerreotype and
calotype, and it was almost exclusively used
between 1855 to 1881. It is largely used to-day
by process workers and by itinerant photo-
graphers ; while for certain other branches of
photography — lantern slides, for example — it is
considered by many to be unsurpassed. Its
chief advantages are a structureless film, an ex-
tremely fine grain, and clear whites. The fixing
agent is easily washed out of the film, and the
negative can be dried by heat. Wet-plate nega-
tives can also be easily reduced and intensified.
Wet plates are of low sensitiveness, their speed
being about the same as that of lantern plates.
The photographer must prepare his own plates.
A deep porcelain dish for the silver bath, a
size larger than the plate to be sensitised, is
required ; it must be scrupulously clean, and if it
has previously contained other chemicals it must
be very thoroughly Washed. Place 480 grs. of
silver nitrate in a dean pint bottle, and add 15 oz.
of distilled water (rain or tap Water will not do).
Shake until dissolved, and add 3 drops of piire
nitric acid. Keep a day or two before using.
Each ounce of the silver bath contains 32 grs.
of silver nitrate, and the strength should be
kept as near this as possible, using, if necessary,
an argentometer for testing the density. The
silver bath is filtered, poured into the porcelain
dish, covered with a piece of cardboard, and
placed in the comer of the dark-room that is
farthest from the developing sink. Adjust the
dark-room lamp so that a good Ught is thrown
on the dish. Wet plates wiU stand far more red
or yellow light than dry plates.
For coating the glass the following are neces-
sary : — (a) A 4-0Z. bottle of Mawson's collodion,
with iodiser in a separate bottle. Before use the
iodiser is poured into the collodion, and this
iodised collodion wiU keep in good condition for
several months, becoming deep red in colour, the
plates then requiring a much longer exposure.
Iodised coUodion can be purchased ready for
use, but the plan here described is preferable.
(6) Rubber solution for edging the plate.
For developing, fixing, etc., obtain : —
Pyrogallic acid
Glacial acetic acid
Ferric protosulphate
Mercuric bichloride
Liquor ammonise .
Lead nitrate
Potassium ferricyanide
Sodium hyposulphite or potas-
sium cyanide
. I
oz.
• 4
,,
lb.
oz.
>i
»>
11
I lb.
Collodion Process (Wet)
Collodion Process (Wet)
Before coating with collodion, the plate is
" edged " to prevent the film from leaving the
glass. A drop of rubber solution is taken up
on a piece of cotton-wool and run round the edge
of the glass, and the plate is then ready for
coating.
Take the glass at one comer between the finger
and thumb, and pour a small pool of collodion
upon it. Carefully tilt the glass so that the
collodion flows to the comer farthest from the
fingers, tilt again into the other top comer,
next bring the collodion to the comer nearest
the thumb, and then pour the surplus back into
the bottle via the remaining comer. While
the collodion is being poured into the bottle the
plate must be kept moving to and fro laterally,
or the collodion will set in ribs. This movement
of the plate must be continued for several seconds,
till the collodion is set. Replace the stopper
in the collodion bottle, close the door of the
dark-room, and immerse the plate in the sensitis-
ing solution.
When placing the plate in the silver bath, the
dish should be tilted, so that the solution flows
to one end. Place the plate in the other end of
the dish, and immediately lower the dish to let
the bath flow in an even wave over the plate. If
the flow is checked, a streak across the image
will result on development. The cover of the
dish is now replaced, and the door of the dark-
room can be opened for a minute or so.
Sensitising begins directly the plate is inserted
in the bath, and is complete in about two and a
half miuutes. The plate is ready to be removed
from the bath when the film presents a creamy
appearance ; but, as a rule, leaving the plate in
the bath for two or three minutes will suffice.
Of course, if it is desired to look at the plate
while in the bath the door of the dark-room must
be closed.
If ordinary dry-plate slides are to be used the
rebates for the glass must first be covered with
strips of blotting-paper. If the Wet plate
touches the woodwork of the slide, scum will
form over the plate and the picture will be
spoilt. If the strips of blotting-paper are damped
before use they can easily be flxed in the rebate.
Wet-plate slides are provided With silver wires
with the object of supporting the plate, but even
these slides require blotting-paper at the bottom
and top of the plate. After remaining in the bath
for two or three minutes the plate is removed by
being raised with the handle of a silver spoon,
or with a lifter made of horn or vulcanite. The
fingers must not be dipped into the silver bath,
and neither wood nor metal, other than silver,
must be used. The collodion of the sensitised
plate has a creamy, opalescent appearance,
owing to the formation of silver iodide in the
film.
The plate is allowed to drain for a few seconds
over the bath, and the moisture is then removed
from the back with a piece of blotting-paper,
the plate meanwhUe resting on its edge upon a
sheet of clean paper.
Next, the plate is inserted in the dark-slide,
care being t^en that the collodion film is not
in contact with either wood or metal. The expo-
sure for wet plates is from ten to twenty times
longer than is required for an ordinary dry plate ;
fresh collodion requites less exposure than stale,
and in cold weather the sensitiveness of the film
is considerably diminished. In a weak light or
in a slightly yellow one a wet collodion plate
is far less efiective than a gelatine film.
An acid, instead of an alkaline, developer
is necessary for wet collodion plates. The fol-
lowing is a formula for a pyro developer stock
solution : —
Pjrrogallic acid
Glacial acetic acid
24 grs.
2 oz.
This solution keeps well. For use, add 6 parts
of water to i part of the stock solution.
The above is quite reliable, but some workers
prefer ferric sulphate, as in the following : —
Ferric protosulphate . . i oz.
Glacial acetic acid . . i „
Water . . . • iS „
Methylated spirit should be added to the
developer after the bath has been in use some
time, to ensure even flowing of the solution over
the plate. A shorter exposure is required for iron
development. Developing and fixing dishes are
not required. The plate is removed from the
dark-slide, and the developer is poured quickly
and evenly over the film. The plate is kept mov-
ing during development, in order to keep the
film covered with solution. Fresh developer
must be used for each plate. The image develops
steadily, and usually begins to appear in about
ten seconds ; but in cold weather the time may
be considerably longer. Development is stopped
when all the details are visible. The plate is
washed for a few seconds under the tap and is
then fixed with potassium cyanide, which should
be kept in a saturated solution, and for use diluted
with double its volume of water.
" Hypo " can be used instead of cyanide ; but
it does not work so quickly, and takes longer to
wash out of the film. After flying with potassiTim
cyanide, the plate is washed for a minute or so
under the tap ; if " hypo " is the fixing agent,
five minutes' washing is necessary. If the pic-
ture is satisfactory, the plate can be dried in
front of the fire. The collodion image, when
flxed, should be bright and clear, without a trace
of fog or stain. The best reducer, should one be
found necessary, is cyanide and iodine, made by
dissolving a few crystals of iodine in methylated
spirit and adding a saturated solution of potas-
sium cyanide until the red colour of the iodine
has disappeared.
If intensification is required, a solution of
mercuric bichloride, followed by ammonia, can
be used as in dry plate operations. If the image
is very flat, or when black-and-white work is re-
quired, intensification with lead nitrate can be
adopted, using : —
Lead nitrate . . .1 drm.
Potassium ferricyanide . • li „
Wat^ 10 oz.
The plate is immersed in the above solution
tiU sufficient density is reached, then washed
under the tap till all yellowness has disappeared.
The picture, m most cases, need not be blackened
when intensified by lead, as sufficient density
is obtained without the use of an alkali. When
absolute opacity is required, ammonium hydro-
sulphuret can be used, after all the yellow stain
Collodion Transfers
Colloids
has been waslied from the film, It must be
noted that the lead intensifier has a drastic
action and must be used only for flat pictures
or for the reproduction of black-and-white draw-
ings.
Another method of intensification, known as
re-development, is perhaps the best for beginners.
When the image, after fixing, seems to be lack-
ing in contrast, the plate is rinsed and fresh
developer, mixed with a few drops of a lO per
cent, solution of silver nitrate, is flowed over the
film. The addition of the silver to the developer
gives vigour to the image. After fixing the plate,
mercuric intensification will give further con-
trast, if necessary. When dry, the plate should
be varnished, as the collodion film is easily torn.
For ferrotype plates, a thinner film is neces-
sary, and the iodised collodion should be further
diluted with sulphuric ether. A developer giving
a white deposit (see "Collodion Positive")
should be used. The general procedure of sen-
sitising, developing, and fixing ferrotypes is the
same as for wet-plate negatives.
In process work, a very clean working collodion
is required, and at the same time one that gives
great density. Further, the film must be tough
to ■withstand intensification and reduction.
Celloidin collodion of not more than 2 per cent,
strength is usually employed. Pure solvents
have to be used in order to avoid fog and scum.
Ammonium and cadmium iodide and cadmiimi
bromide with cadmium chloride are the general
ingredients of the iodiser. A typical formula
for coUodion suitable for process work is —
Celloidin . . . i oz. 31 g.
Alcohol (-805) . . 40 „ 1,136 CCS.
Ether (720) . . 60 „ 1,704 „
The following is the iodiser : —
Alcohol (-820)
Cadmium iodide
Ammonium iodide
Cadmium bromide
Cadmium chloride
Iodine
10 oz. 284 CCS.
i „ 15-5 g-
180 grs. 1 1 -6 „
IS „ I »
30 „ 2 „
10 „ -6 „
Take one part iodiser to nine parts collodion,
and allow to stand for ten to foiirteen days.
The silver bath is usually 35 to 40 grs. per oz.
Development is with the iron developer ; fixing
with potassium cyanide ; intensification with
either lead nitrate (for line negatives), or with
copper bromide (for half-tone), followed with
ammonium or sodiiun sulphide. " Cutting " or
reducing to sharpen up the dots or lines is gener-
ally resorted to, the solutions employed being
iodine and cyanide. For stripping, the negatives
are coated with rubber solution and then with
collodion to which a small proportion of castor
oil has been added to make it flexible. The glass
plates are, as a rule, edged with rubber solution
before coating with coUodion, to make the latter
hold.
COLLODION TRANSFERS
Collodion positives transferred from the ori-
ginal glass to other supports, usually paper.
Special collodions and papers for transfer work
are now commercial articles, and the process is
quite easy nowadays, compared with what it was
in 1857, when it was first practised no special
collodions for the purpose being then obtain-
able. A suitable transfer paper is made by evenly
coating smooth-surfaced cream-wove foolscap
with a solution of gelatine made by dissolving
i oz. of gelatine in from 20 to 30 oz. of water,
and then drying. After the collodion picture is
fixed and washed in the usual way, the transfer
paper is soaked and carefully squeegeed into con-
tact with the picture, film to film, and allowed
to dry. When dry, one comer of the paper may
be lifted with a penknife, when it will strip
from the glass and bring the picture with it. fi
the pictures to be transferred are large, the
glass should be coated with a substratum of wax
before the usual collodion is applied. Five grains
of pure sun-bleached white wax in i oz. of ether
forms the waxing solution ; this is spread evenly
and rapidly over the glass, and, when dry, polished
until no trace of the wax apparently remains,
although enough will be left to assist the picture
to leave the glass easily. In some cases, negative
films, too much under-exposed to print from,
were bleached by means of mercury and trans-
ferred to black paper, on which they appeared to
be positive and finished pictures.
COLLODIONISED PAPER
A term somewhat loosely applied to collodio-
chloride paper.
COLLODIOTYPE
An early name for any kind of photograph
produced by the collodion process.
COLLOGRAPHIC PROCESSES
A general term applied to collotype methods,
all based on the principle of the action of light
on a bichromated colloid, the latter being
usually gelatine.
COLLOGRAPHY
A process said to have been invented by
Pumphrey, of Birmingham, in 1880, and similar
to that formerly well known under such terms
as " Autocopyist," etc., in which a film of
gelatine on glass or on some flexible support,
such as parchment, was bichromatised and
dried. Writing or drawing is done on a suit-
able paper with solutions of iron salts, nutgalls,
or similar substances having a tanning action
on the gelatine surface, to which the design is
next transferred. By keeping the gelatine pad
moist and applying an ink roller, the Unes will
take the greasy ink, but the white parts wiU
repel it. Paper is then brought into contact
with the pad, and an impression taken by
rubbing or squeegeeing.
COLLOGRAVURE
A kind of collotype invented by Balagny, of
Paris, in 1893-4, ^ which gelatiuo -bromide of
silver films were converted into coUotype printing
surfaces, the prints being made with fatty ink.
COLLOIDS
A name derived from Greek kolla (glue) and
eidos (appearance), and given by Graham to
those non-crystalline substances which do not
diffuse through porous membranes. The chief
organic colloids are cellulose, starch, dextrine,
tannin, gelatine, caramel, and albumen. The
Colloids
123
Colloids
inorganic colloids are hydrated oxides of iron,
hydrated silica, alumina, etc.
Graham, in 1861, discovered that many sub-
stances, particularly those which readily crystal-
lise, diffuse through animal membranes, whilst
other substances, such as gelatine, which do not
crystallise, do not so diffuse. (Modem researches
have shown that Graham's conclusions must be
modified somewhat.) The latter class of bodies
he called " colloids." The diffusion of the crystal-
line salts through a membrane he termed
" dialysis," and t£e vessel in which the solution
was placed a " dialyser." There are a great
m.any natural or organic substances, such as
starch, dextrine, gums, albumen, caramel, rubber,
resin, etc., which are colloids and behave pre-
cisely in the same way as the first-mentioned
gelatine ; but there are also many inorganic
chemicals, such as ferric hydrate, silicic acid,
etc., which act similarly. Apparently these
dissolve in water, but when submitted to the
test of dialysis prove themselves to be true
coUoids. The apparent solutions of such sub-
stances are called " pseudo-solutions," to differ-
entiate them from the so-called true solutions.
Graham also discovered that water was not
unique in forming colloidal solutions, but that
alcohol, benzole, glycerine, and sulphuric add,
as well as other solvents, were capable of acting
in the same way ; and the term " sol " is used to
designate these. Thus, hydrosol indicates a
water sol, alkosol an alcoholic sol, and glycerosol
a glycerine colloidal sol. Generally, when the
solution is of an organic nature, it is termed an
" organosol."
The scientific student may here be told that,
practically, a sol or colloidal solution consists
of two ingredients, a Uquid and a solid, the latter
being in an extremely finely divided state, dis-
tributed or suspended in the Uquid. The
sharply separated parts of the sol are said to
be its phases, and in colloidal solutions there are
several multiple-phase or heterogeneous forma-
tions, and the one phase, being in an extremely
finely divided state, naturally presents to the
second phase a very large surface, and with
normal examination the sol appear perfectly
homogeneous. This" is called microhetero-
geneity." Many substances, particularly those
which form jelUes or " gels," do not, however,
show this particular form of heterogeneity, par-
ticidarly when coagulation is eiiected, and then
it is termed " macroheterogeneity." In con-
tinental Hterature, the term " disperse-hetero-
gene " is used for the former, and a generic term
of " dispersoids " is used for all microhetero-
geneous systems. Oth^r coUoid solutions take
another form, and this has been likened to a
sponge, that is, they practically form a network
distributed throughout the dispersion medium.
The density of colloidal solutions cannot be
calculated from the densities of the disperse
phase and the dispersion medium, or the sub-
stance and solvent; for instance, a solution of a
given quantity of gelatine in a given quantity of
water is not the sum of their respective volumes,
but less, a small but marked contraction taking
place. Their osmotic pressure is very low, and
in many cases not to be detected, and their
boiling and freezing points vary but very slightly
from those of the liquid, water, alcohol, etc.
It has been already stated that colloids would
not diffuse through an animal membrane, but
recent researches have shown that this is only
partially true, and that some colloids will diffuse
as well as crystalloids, but at a much slower
rate, so that the fundamental difference is in
their rate of diffusion.
Provided that the size of the particles of the
disperse phase are sufficiently small, they exhibit
imder a powerful microscope peculiar vibratory
motions, which were first discovered by Brown
in 1827, and are therefore called " Erownian
movements." This motion is approximately a
zig-zag or to-and-fro motion, and has been
ascribed to the contrary pull of gravity and the
viscosity or thickness of the liquid. Particles
which are larger than 3 to 5 /* (i /t = -001 milli-
metre = i-^ioTs "!•) do not show this movement.
Many hydrosols appear perfectly dear and homo-
geneous, but others e:!diibit the phenomena of
fluorescence or opalescence when illuminated by
suitable light, and Tyndall's phenomenon is often
apparent witii light of very small wave length,
that is to say, the partides are suffidently large
to reflect violet or ultra-violet light of extremely
short wave length, and polarise it. This is the
foundation of ultramicroscopy.
The disperse phase carries a positive or nega-
tive electric charge, which is dependent to some
extent on the dispersion medium — that is, the
water or other liquid — and sometimes on its
alkalinity or acidity. Colloidal solutions can
exhibit a change of condition under mechanical
action, or the application of heat, and the dis-
solved substance may separate in an insoluble
form or be converted into jdlies by the addition
or certain substances, such as electrolytes. When
the substance separates out in an insoluble form
it is known as a " gel," and if formed from an
aqueous solution it is known as a " hydrogel,"
an " alkogel " from alcohol, and a " sulfogel "
from sulphuric add, etc. The process of the
formation of the gel is called pectinisatiou or
coagulation. When the residue left after coagu-
lation is soluble in water, the process is said to
be reversible ; if insoluble, it is irreversible.
Frequently an insoluble and otherwise irrevers-
ible coUoid is predpitated in the presence of a
reversible colloid; it also becomes reversible;
and the coUoid that produces this state is known
as a protective colloid, or, to use the German
word, a "schutz-koUoide." Lottermoser has also
pointed out that by certain predpitating agents
a colloid may be precipitated from the hydrosol
in such a condition that it will again form a
hydrosol, and therefore suggests the terms
" solid " and " liquid " hydrosol, and confines
the term hydrogel to the insoluble amorphous
substance. The law is that sols with opposite
electric charge precipitate one another, but
those of like charge do not.
Gels or jellies may be considered as coUoid
solutions in which the disperse phase is in a
higher concentration, and molecular and col-
loidal solutions can diffuse through a gel more
or less rapidly, according to the concentration
of the disperse phase of the gel.
CoUoid al solutions differ from true solutions
in that the latter are perfectly homogeneous
under the most critical visual examination that
can be applied, whilst the former show the
Collotype
124
Colour
particles under sufficiently high power as already
pointed out. They differ also from suspension
liquids or mixtures in that in the latter the
particles or disperse phase are sufficiently large
to be seen with the naked eye or a weak power.
There is, however, some evidence to prove that
these divisions are but arbitrary, and that so-
called true solutions may be of a colloid nature.
P. Weimam and Wolfgang Ostwald ("Grun-
driss der KoUoidchemie" ) considering that, as sus-
pensions, colloidal and true solutions are merely
varying degrees of dispersion, have proposed
the name of " dispersoids," and the latter
divides them into (i) coarse dispersions, such as
suspensions and emulsions; (2) colloidal solu-
tions ; (3) molecular dispersoids ; and (4) ion-
dispersoids, assuming that free ions exist. The
crystalloid solutions belong to classes (3) and (4).
The above classes merge one into the other, and
colloidal solutions are divided into suspension
colloids and emulsion colloids, which are also
termed suspensoids and emulsoids. The occur-
rence of colloidal silver and gold is assumed
in many photographic processes, and many
reactions can only be satisfactorily explained on
this assumption. There is, however, an increas-
ing tendency to drag the phenomena of colloids
into every obscure photographic process, and
there is the grave danger that it may be used
merely to cloak our ignorance of the true state
of affairs.
COLLOTYPE (Fr., Phototypie ; Ger., Licht-
druck)
A process known also as " phototype," and,
in slight variations, as " Albertype," " Arto-
type," etc. It is based on the principle that
if a film of bichromated gelatine is exposed
to light under a negative, and the unaltered
bichromate is washed out, the fihn will have a
similar property to that possessed by a Utho-
graphic stone of attracting ink in some parts
and absorbing water in others, the water repelling
the ink. It differs essentially, however, from
lithographic work in the fact iiat the attraction
for ink and water in the different parts is pro-
portionate to the action of the Hght, so that
the strength of the ink image varies in proportion
to the light and shade of the picture. The dis-
covery of this property was made by Fox
Talbot in 1853, and his researches were followed
up by A. Poitevin, of Paris, from 1856 onward.
The first practical collotype process was intro-
duced by Tessi^ du Motay and Ch. R.
Marechal, of Metz, in 1865 ; and the perfection
of the present-day process of collotype is due
to the labours of Josef Albert, Husuik, and
Obemetter. Although the process is still largely
worked, its commercial success has been much
retarded of late years by the progress of half-
tone, photogravure, and other etching methods,
and it has to a considerable extent fallen into
disfavour, especially in England and America.
The general method of working the process
is as foUows : — A thick glass plate is ground on
one side with fine emery powder, and is then
placed on a levelling stand or levelling screws,
and having first been coated with a suitable
substratum and dried, is flowed over with a
measured quantity of bichromated gelatine.
When the film is set the plate is placed in a dry-
ing oven, which is brought up to a temperature
not higher than 1 30° F. (54° C), at which the dry-
ing takes about two hours. When cool, the plate
is placed with the negative in a special printing
frame, pressure being applied by wedges. The
plate is next washed to remove the unaltered
bichromate, and allowed to dry. To prepare the
image for printing, the surface is flooded with a
mixture of glycerine, water, and sometimes other
ingredients, allowing it to stand for thirty minutes.
Then the excess is removed and the plate is
rolled up with a lithographic roller charged
with a special collotype ink, which is similar
to lithographic ink, but stifier. When com-
pletely inked, paper is laid on the plate and
pressure applied in a press. An ink image re-
producing the tones of the original is thus
obtained. Success depends on the proper form-
ation of a grain caused by reticulation of the
gelatine during the drying, and the grain is
modified by exposure according to the action of
the light passing through different parts of the
negative.
Many modifications of detail have been made
by different workers, but the above general out-
line applies to all the methods, except that in
some cases attempts have been made to form
the image on aluminium, copper, lead, and other
plates instead of glass.
Collotype in colours has been worked with
success for some years in Germany, and to some
extent in England. The number of negatives
made varies with the number of different colours
required. A collotype plate is made from each
negative, and all its parts are blocked out except
those required for that particular colour. The
printing is then done as in chromo-hthography,
the impressions of each colour being super-
imposed in exact register.
COLOPHONY (Fr., Colophane ; Ger., Colo-
phonium)
Another name for resin, more used on the
Continent than in England. Properly it is
applied to a black resin, the solid residuum of
the distillation of turpentine after the oil has
been worked off. (Particulars of resins are given
under the heading " Gums and Resins.")
COLORIMETER (Fr., Colorimitre ; Ger., Far-
benmesser)
An instrument for ascertaining the strength
or purity of a substance by comparing its colour
with a given standard. There are several forms,
as, for example, Mill's, in which the colour is
varied by altering the depth of a tinted solution
until a match is obtained ; I<ovibond's, in which
a number of coloured glasses are adjusted ; and
so on. A colorimeter is occasionally useful in
photography, as, for instance, in the volu-
metric estimation of silver nitrate solution with
potassium chromate, in which it is often difficult
to recognise the red reaction that ensues owing
to the original yellow colour of the test solution
itself. A properly adjusted colorimeter renders
the change of tint at once manifest.
COLOUR (Fr., Couleur ; Ger., Farbe)
A person sitting in a perfectiy dark room can
see neither the form nor colour of the objects
around him ; but the moment light is admitted
Colour '25 Colour
TABLE OF SUBTRACTIVE COLOUR MIXTURES OR SUBTRACTIVE ANALYSIS (STOLZE)
Orange
Yellow
Yellow
green
Green
Blue green
Cyan,
blue
Indigo
blue
Violet
Bluish
Indigo blue
violet
Blue
Blue
violet
Cyan, blue
Greenish
Greenish
Bluish
Blue green
blue
blue
grey
Bluish
Blue
Blue
Grey
Green
green
green
green
Yellowish
Green
Bluish
Green
Violet
YeUow
green
green
grey
green
Greenish
Yellow-
YeUow
Green
Yellowish
Dirty red
YeUow
yellow
green
green
olive
brown
Gold
Olive
Yellowish
Yellowish
OUve
Olive
Red-
Orange
yellow
grey
grey
grey
brown
Deep red
YeUowish
Grejdsh
Yellowish
Grey
Grey
Greyish
Dirty red
Deep red
red
yellow
grey
violet
brown
violet
Deep red
Scarlet
Yellowish
grey
Grey
Bluish
grey
Bluish
violet
Violet
Red
violet
Purple
he at once sees the shape of objects and also
their colours. It is obvious then that to have
colour there must be light. Colour is due to
the suppression or absorption of some of the
constituent rays of white light {see " Spec-
trum"). A sheet of red glass looks red because
it has suppressed or absorbed that particular
region of the spectrum or those colours to which
red is complementary {see " Colour, Comple-
mentary "), and it is the residuary colours that
give the observer the impression of red. Pre-
cisely the same thing happens with any substance
whidi is not transparent, as, for instance, a
sheet of red paper or a green leaf ; the light
incident on its surface penetrates to a slight
depth into the substance of the paper or leaf,
and there meets with a material or surface which
reflects the Hght back to the eye, but in its
passage into and out of the paper or leaf the
light undergoes selective absorption, and the
residuum of the incident light now appears
either red or green.
White, grey, and black are not colours ; the
first is the sum of all the spectral rays ; grey is
all the rays reduced in intensity ; whilst black
is the suppression of all light, and therefore of
all colour. This can be strikingly illustrated by
projecting a spectrum or a series of coloured
gla.sses or filters on to a white, a grey, and a black
surface. In the first case, all the colours are
seen in their original purity and strength, whereas
in the case of the grey surface, the colours are
still there, but they are reduced in luminosity,
that is, they appear less brilliant. With a black
surface, such as good black velvet, the colours
are absorbed entirely.
Colour may also be formed by the interfer-
ence of the light rays with one another, but this
is also a suppression of some of the spectral
rays. {See "Interference of Light.")
It is usual, therefore, to designate colours as
" body colours " and " surface or interference
colours." To the former class belong aU coloured
pigments, and to the latter those colours seen
on a diffraction grating, a thin soap bubble or a
peacock's tail feathers.
It is important to differentiate between the
action of mixed pigments and mixed lights, as
the results are not comparable. In the former
case, mixing increases in each case the suppres-
sion or absorption of light with each pigment
used, whereas the mixing of coloured lights adds
light to light. To illustrate the first point, take
three printing inks, red, yellow, and blue, such
as are used in trichromatic printing, and examine
the absorption spectrum of each. The letters
at the top of the diagram refer to the Fraunhof er
lines, the colours being placed underneath ; the
black portions show the assumed absorptions
of the inks, whilst the white portions show the
TABLE
OF ADDITIVE COLOUR MIXTURES OR OPTICAL SYNTHESIS (HELMHOLTZ)
Violet
Indigo blue
Cyan, blue
Blue green
Green
Greenish
yellow
Yellow
Red
Purple
Dark
Whitish
White
Whitish
Golden
Orange
Orange
Dark
crimson
Whitish
crimson
White
Whitish
yellow
YeUow
yellow
Yellow
Yellow
crunson
Whitish
crunson
White
Whitish
yellow
Whitish
Greenish
Greenish
crunson
White
Whitish
green
Whitish
green
Green
yellow
yellow
Green
Blue green
Cyan, blue
Whitish
blue
Water blue
Indigo blue
green
Water
blue
Water blue
green
Blue green
Colour Absorption
126
Colour, Complementary
light reflected, the sum of which is severally
red, yellow, and blue. Now, it is obvious that
by superimposing these three spectra there is
no part which is transmitted by all three, and
the result is total absorption of light, or black.
Taking the case of three-coloured Ughts, by
mixing them on a screen by means of a triple
lantern, just the reverse of the above eifect is
obtained ; for convenience, let there be taken
red, yellow, and blue glasses, matching approxi-
mately the inks referred to above. Then, con-
sidering not the absorptions or black portions,
but the white or transmitted portions in the
figure, it will be imderstood that the whole
spectrum is transmitted and the result is white
Hght.
The former is called subtractive colour mixing
or analysis, whilst the latter is termed additive
colour synthesis. It must not be overlooked
that whilst pigmentary colours have been
dealt with, in the case of subtractive colour
analysis, the argument applies also to super-
imposed transparent colour filters.
The tables on the preceding page show the
difference between the two systems.
Red Int
YiUou Inn
BIm /a*
Red Orange Yetlow Bnei) Blue Violet
Diagram Indicating Absorption Spectra of Red,
Yellow and Blue Printing Inks
In these tables the colour resulting from a
mixture of any two colours is found where the
vertical and horizontal colouxs meet. Also, the
term " whitish " means that the colour appears
pale — that is, mixed with white light. It is
usual to designate the main or predominant
colour and precede it by the colour with which
it is mixed ; for instance, there may be a full
or pure green ; when mixed with blue, this
becomes bluish-green ; with still more blue, a
pure blue-green ; with increasing quantity of
blue, it becomes greenish-blue.
COLOUR ABSORPTION
Whilst colour itself is an absorption of light
{see "Colour"), it is extremely important in
some cases to know the colours absorbed by
certain materials, such as aniline dyes for filter
making. The only method of determining this
satisfactorily is by means of a spectroscope, or,
for accurate work, a spectro-photometer. It is
laborious work, as the absorption of a dye solu-
tion will alter with increased concentration or
depth of solution, and it is necessary, therefore,
to make very careful spectro-photometric obser-
vations at various dilutions. This, however, can
be performed much more readily by photography,
as has been done by Uhler and Wood, of the
Carnegie University, of Washington, U.S.A., and
more completely by Wratten and Wainwright in
their " Atlas of Absorption Spectra," which con-
tains the absorption spectra of 170 dyes. For
this work was used a small box spectrograph
fitted with a prism grating, and the dye solution
was contained in a wedge cell of rectangular form
of I cm. (-4 in.) internal length and 5 mm.
internal width, with a diagonal partition which
divided it into two wedge-shaped cells, the one
being filled with the dye solution and the other
with the solvent, so as to obviate the prismatic
effect of the cell. The thickness of the dye
solution thus varied considerably, the actual
thickness from end to end of the slit being about
I to 15. The spectrograph was provided with a
wave length scale and an ultra-violet filter. Pre-
cisely the same results can be obtained by using
a parallel-sided cell of fixed width and varying
the strength of the solution, or keeping the dye
strength constant and varying the cell width,
but fiese plans are laborious and do not give
the required information in such compact form.
COLOUR, COMPLEMENTARY (Pr., Couleur
compUmentaire ; Ger., Komplementdr-
farben)
For every saturated and unsaturated colour
there exists another colour which, when suitably
mixed with it, forms white ; such pairs are called
complementary colours. It is important to
know— roughly, at any rate — the complementary
colours, because one can at once determine the
colour of the filter required to absorb one or
the other. For instance, supposing one had to
photograph a photomicrographic object which
was stained green and blue in parts, and it was
desired clearly to differentiate the green ; then
all one would require to know would be the com-
plementary colour to green, and a filter of that
colour would absorb Qie green and show it as
black. On the other hand, if one wanted to
show the green and suppress the blue-stained
portions, then one would only require to know
the complementary colour to the blue to absorb
this and render the green clear.
The following table, compiled by Prof. Griin-
berg, of Vienna, contains the sum of the observa-
tions of the leading physicists of the day : —
Colour
Wave
length
in iJ-i^
Complementary
colour
Wave
length
in iJ-iJ.
Red
Orange
Gold yellow
Yellow
Greenish yellow
656
608
(585
1576
(571
1566
564
Greenish blue
Blue
Blue
Blue
Indigo blue
Indigo blue
Violet
492
489
483
472
462
447
433
He also gives the following very simple
formula for finding approximately the com-
plementary colour : —
in which h' = the complementary coloiu: and
Colour, Effect of
127
Colour Screen
L the given wave length. Ex. — What is the
complementary to wave length 589 ?
424
V = 49S —
= 498 —
589-
424
30
■559
498 — 14-13 = 483-87
There is no true spectral colour complementary
to the pure green spectrum region ; this is found
in the purples or crimsons made by a mixture
of violet and red. (See also " Zander's Comple-
mentary Colour Process.")
COLOUR, EFFECT OF
The effect of the various colours on the photo-
graphic emulsion is dependent chiefly on whether
the emulsion is colour-sensitised or not, on the
use of colour filters, and the length of the
exposure. The ordinary (non-colour-sensitised)
plate is sensitive to the ultra-violet, violet and
blue rays, the commercial iso- or orthochromatic
plate has an added sensitiveness to yellowish-
green and yellow, whilst the panchromatic plate
has red sensitiveness as well.
There is one effect of colour which is particu-
larly marked when using screenplates, and that
is the effect of reflections from surroundiup
coloured objects on a sitter or object. When
dealing with ordinary monochrome photography
this is entirely overlooked, but with colour repro-
ductions these coloured reflections obtrude them-
selves sometimes in the most imexpected manner.
COLOUR FILTER (See " Colour Screen or
Filter.")
COLOUR FOG (See "Fog, Colour.")
COLOUR, FUNDAMENTAL (See "Colour
Sensations.")
COLOUR PHOTOGRAPHY (See "Auto-
chrome Process," " Ives' Process,"
" Lippman's Process," " Screenplate
Colour Photography," etc.)
COLOUR, POSITIVES IN (See "Positives
in Colours.")
COLOUR SCREEN OR FILTER
A sheet of coloured glass, or glass coated with
dyed gelatine or collodion, or a cell containing
a coloured hquid, used to modify the action of
some particular region of the spectrum on the
sensitive plate. It is usual to divide colour
screens into two classes, (a) continuing and (6)
contrast screens, though the division is purely
arbitrary and the two insensibly merge one into
the other. The most used form of screen or
filter is the yeUow screen, which is employed
with iso- or orthochromatic plates to reduce
the excessive action of the ultra-violet, the
violet and blue rays, which it does by partially
or wholly absorbing them, and thus, by prolong-
ing the exposure, gives the green and yellow rays
more time to act so that the colours may be
reproduced more nearly in the order of their
respective visual luminosities (see " Colour
Sensations" and "Luminosity, Visual"). The
exact depth of the yellow screen is dependent
on the relative sensitiveness of the emulsion to
the yellow and blue, and also on the effect desired.
For instance, in photographing extremely faint
white cirrus clouds against a blue sky the differ-
ence in photo-chemical action of the sky and
clouds is so shght that a contrast or deep-coloured
screen is used abnormally to suppress the action
of the sky. On the other hand, when it comps
to a pictorial representation of a field of wheat
intermingled with poppies, the visual lumin-
osities of which may be approximately equal,
the operator's aesthetic feehng or education must
teach him to choose either to disregard the truth
and to accentuate the golden hue of the wheat at
the expense of the scarlet poppy, or else to obtain
a compromise between the two. In such a case
another factor, of the permissible exposure, comes
into play.
Numerous dyes have been used or suggested
for making the yellow screen, which has now
largely replaced the old form of pot glass orange-
colour screen, which contained also a consider-
able proportion of black that merely increased
the exposure by cutting down the available
hght. Aiu-antia, auramine, naphthol yellow,
methyl orange, tartrazine, and filter yellow K,
have all been used. Of these, the last is by
far the most effective, as it completely suppresses
the rdtra-violet rays, which are invisible to us,
and has a gradual absorption for the violet and
blue. It is a very soluble dye, and is stable to
light in the ordinary way.
The following instructions are modifications
of those issued by the Hoechst Dyeworks, the
makers of this dye, for the manufacture of yellow
screens, and they may be considered typical for
making all filters, the quantities and dyes merely
varying according to the particular requirements.
Stock Dye Solution
Filter yellow K -31 grs. 2 g.
Distilled water . 14 oz. 38 mins. 400 ccs.
Stock Gelatine Solution
Gelatine (hard emul-
sion) . . . 420 grs. 60 g.
DistiUed water to . 16 oz. 1,000 ccs.
Wash the gelatine by stirring two or three times
in distilled water, then drain and add to about
three-quarters of the total quantity of water,
dissolve in a water bath at 120° P., and if it is
to be kept, add a grain of thymol or a few drops
of carbolic acid, filter, and make the total bulk
up to 16 oz. or 1,000 ccs.
No. I Yellow Filter
Stock gelatine solution 2 oz. 1 20 ccs.
Stock dye solution . 24 mins. 3 „
Distilled water . . 168 ,, 21 „
No. 3 Yellow Filter
Stock gelatine solution 2 oz. 1 20 ccs.
Stock dye solution . 48 mins. 6 „
Distilled water . . 144 „ 18 ,,
No. 3 Yellow Filter
Stock gelatine solution 2 oz. 1 20 ccs.
Stock dye solution . 96 mins. I2 ,,
Distilled water . . 96 „ 12 „
No. 4 Yellow Filter
Stock gelatine solution 2 oz. 120 ccs.
Stock dye solution . 192 mins. 24 ,,
For every 16 sq. in. or 100 sq. cm. of glass
allow 122 minims or 7 ccs. of the dyed gelatine,
and two of each of iiie screens must be bound
Colour Screen
123
Colour Screen
together. The increase in the exposure with the
above filters for pinachrome or erythrosine bathed
plates is No. i 1-3, No. 2 i-y, No. 3 2-0, and
No. 4 3'0 times. For commercial iso- or ortho-
chromatic plates — that is, those sensitised in
the emulsion before coating — the exposure is
about half as much again.
The glass of which the screens are made should
be selected patent plate, about ^ in. thick, and
it should be as parcel as possible ; for the best-
quality screens optically worked glass should
alone be used. In order to test the glass for
parallelism of its sides, it should be placed on a
sheet of black velvet and held at an angle of
about 45° some distance from the cross-bars of
a window, so that the reflection of these can be
seen in the glass. On turning the glass round
on the velvet, the image of the cross-bars will
be seen to be double — that is, the reflection
from both the front and back of the glass will
be seen. These double images should, as far
as possible, be constant in position one to the
other, and not shift up and down or from side
to side. The glass must be thoroughly cleaned
and placed on a thick sheet of plate glass which
has been accurately levelled, and the necessary
quantity of dyed gelatine poured on to it,
coaxed out to the edges with a glass rod, and
allowed to set, when it can be put away to dry.
It may be pointed out here that the position
of the filter has some effect on the focal length
of the lens and also on the definition of the
image. When placed behind the lens it slightly
lengthens the focus, but its effect on definition
is a matter of actual test with every filter,
though the nearer the filter is to the plate the
less the effect ; therefore, obviously, if placed
in contact with the sensitive surface, the ques-
tion of the quality of the glass is not of so much
moment, and in this case even fixed-out and
washed dry plates may be used.
The cementing of colour screens is a messy
process, and requires considerable practice to
perform successfully. A fairly thick solution of
Canada balsam in xylol, such as is used by micro-
scopists, should be used, and the screens well
warmed for at least half an hour, so as to ensure
that they are thoroughly dry ; the balsam
should also be gently wanned. A pool of balsam,
about half the size of the plate, should be poured
on to one screen somewhat near one edge, and
the other screen lowered first on to this edge
and slowly allowed to fall down, when it will
squeeze the pool of balsam out so as to cover
the whole surface. Then a stout buUdog clip
should be fastened on each side, and the screens
put away in a warm place for the balsam to
dry out ; this will probably take four or five
days. At first it is better to use excess of
balsam, as this will be squeezed out and can be
easily cut off when dry ; but with experience the
quantity of balsam may be reduced.
The filters for three-colour work are innu-
merable, the following being satisfactory : —
Hoechst Dyeworks' subtractive filters for
three-colour printing of all kinds.
Blite-violet Stock SoluHSn
Crystal violet . .61-7 grs. 4 g.
Warm distilled water 120Z. 155 mins. 350 ccs.
Glacial acetic acid . 5-6 mins. 5-6 drops
Filter
Dye solution 338 mins. 20 ccs.
Gelatine solution (6 %) 3J oz. 100 „
or—
Stock Solution
Rapid filter blue . 15I grs. i g.
Hot distilled water 6 oz. i6o mins. 180 ccs.
Liquor ammonias . 8 mins. 8-10 drops
Filter
Dye solution . 338 mins. 20 ccs.
Gelatine solution . 3J oz. 100 „
This is faster to light than crystal violet.
Green Stock Solution
Rapid filter green I . 62 grs. 4 g.
Distilled water . 3J oz. 100 ccs.
Filter
Dye solution . .338 mins. 20 ccs.
Gelatine solution (6 %) 3^ oz. 100 „
This transmits a narrow band in the extreme
red ; the following does not, and should always
be used with panchromatic plates : —
Stock Solution
Filter blue green . 15^ grs. i g.
Rapid filter yellow ■ iSi „ i ..
Distilled water . 3^ oz. 100 ccs.
Filter
Dye solution . -338 mins. 20 ccs.
Gelatine solution (6 %) 3^ oz. 100 „
Red Stock Solution
Rapid filter red I . y^ grs. 5 g.
Distilled water . 7 oz. 200 ccs.
Filter
Dye solution . -338 mins. 20 ccs.
Gelatine solution (6 %) 3J oz. 100 „
Allow 118 minims to every 16 sq. in., or 7 ccs. to
every 100 qcm., and cement two glasses of each
colour together. The ratio of exposures for
pinachrome or pinacyanol bathed plates is, for
the blue screen (yellow printing) negative, 4 ;
for the green screen (red printing) negative,
8-12 ; for the red (blue printing) negative, 8-12.
For liquid filters the following, suggested by
Newton and Bull, for use with panchromatic
plates, with cells of i cm. internal thickness : —
Blue Filter
Victoria Blue B
(Bayer) (1% sol.) . 448 mins. 47 ccs.
Naphtholgreen(i%sol.) 174 ,, 18 „
Distilled water to . 20 oz. 1,000 „
This will not keep well when mixed.
Green Filter
Rapid filter green (1%
sol.) . . -87 mins. 9 ccs.
Naphthol green (1% sol.) 87 „ 9 „
Rapid filter yeUow K
(1% sol.) . . 87 „ 9 „
Distilled water to . 20 oz. 1,000 „
Red Filter
Rose Bengal (1% sol.) 442 mins. 84 ccs.
Rapid filter yellow K
(1% sol.) . . 442 „ 84 „
Distilled water to . 20 oz. 1,000 „
The above are to be used for the subtractive
Colour Sensations
129
Colour Sensitising
process or thtee-colour priiiting, whether on
paper or in the shape of superimposed stained
transparencies for projection. For the pro-
jection of transparencies by means of coloured
lights or the additive process, the following should
be used for obtaining the negatives : —
Violet-blue Stock Solution
Crystal violet . . 62 grs. 3 g.
Methylene blue . isi ,, i >,
Distilled water 8 oz. 384 mins. 250 ccs.
Glacial acetic acid . 5-6 mins. 5-6 drops
Filter
Dye solution . .338 mins. 20 ccs.
Gelatine solution (6 %) 3 J oz. 100 „
Green Stock Solution
Rapid filter green 2 . 62 grs. 4 g.
Distilled water 40Z. 107 mins. 120 ccs.
Filter
Dye solution . -338 mins. 20 ccs.
Gelatine solution . 3 J oz. 100 „
This transmits a narrow band in the red, but
the following does not : —
Stock Solution
Filter blue green . 18J grs. 1-2 g.
Rapid filter yellow . 38I ,, 2-5 ,,
Distilled water . 7 oz. 200 ccs.
Filter
Dye solution . .338 mins. 20 ccs.
Gelatine solution . Sj oz. 100 „
Stock Red Solution
Rapid filter red 2 . 77 grs. 5 g.
Distilled water . 7 oz. 200 ccs.
Filter
Dye solution . -338 mins. 20 ccs.
Gelatine solution (6 %) 3I oz. 100 „
The quantity of dyed gelatine per area is the
same as for the subtractive filters, and two filters
of like colour must be cemented together. The
ratio of exposures with pinachrome or pinacyauol
bathed plates is blue 4, green 12, red 12.
COLOUR SENSATIONS
Although there are considered to be but six
or seven spectrum colours — ^red, orange, yellow,
green, blue, indigo, and violet — they melt so
insensibly one into the other that there are an
Curves Representing Actions of Various
Spectrum Colours
infinite number of distinct colours ; again, in
natural objects there are innumerable colours.
It has been proved, however, that there are only
three fundamental colours, that give rise to all
the other colours by the excitation of three sets
9
of nerve fibrils in the retina. This theory was
enunciated first by Thos. Young (" Lectures on
Natural Philosophy," 1807), and further elabor-
ated by Clerk-Maxwell {Edinburgh Transactions,
21,27s, 185s), Von Helmholtz, Abney, Konig,
and otiiers. The curves representing the respec-
tive actions of the various spectrum colours,
according to Konig and Dieterici, are shown in
the accompanying diagram, and represent the
sensations excited in ttie retinal nerves by the
three fundamental colours. There is some
difference in opinion between physicists as to
the exact wave lengths of the fundamental
colours, but there is not much error in the assump-
tion that they are : —
Red — extreme end of the visible spectrum
about A. 665.
Green — a. 507.
Blue — \ 475.
The red sensation curve begins about \ 680,
reaches its maximum at x 575, drops strongly
at A. 490, with a slight rise again toward \ 450,
and ends at \ 390. The green sensation curve
begins at \ 680, rises to a maximum at A. 550,
and ends at h 440. The blue sensation curve
rises from A 580, rises sharply at a 480 with a
maximum at A 450, and ends at A. 390.
The above may be considered as the now
generally accepted theory of the colour sensations,
but Hering suggested six fundamental colours —
red, green, yellow, blue, white, and black. This
theory has not been accepted, but is interesting,
as on it has been based a four-colour printing
method (Zander).
COLOUR SENSITISING
It was very early recognised that certain
colours acted more strongly on the photographic
plate than others, and that the former were nearly
all those that reflected the violet and blue
spectral rays, which therefore were called the
chemically active " or " actinic," whilst green,
yellow, orange, and red hardly produced any
action at all. This view prevailed for many
years, though Herschel pointed out in 1842 that
it did not apply generally, as violet petals faded
most quickly in green light and the other blue
flowers faded most in yellow light. Draper
enunciated the law that only those rays acted
chemically on a substance which were absorbed
by it.
In 1873 H. W. Vogel was examining various
silver salts in the spectrograph and found that
some English colIo(Uon plates, which had been
stained with a yellow dye to prevent halation,
were distinctly sensitive to green. Led by this
fact, Vogel examined the absorptions of various
dyes and then added them to collodion emulsion,
and found that these also sensitised for the
colours they absorbed. This principle was con-
firmed by others, and soon after was successfully
applied to commercial gelatine plates by Attout
Tailfer, of Paris.
The action of a very large number of dyes has
been examined by various authorities, Eder,
Valenta, Von Hiibl, Eberhard, Hinterberger,
Ruh, etc., and the first-named, who has paid
special attention to this subject, has formulated
the following important conclusions: (i) The
absorption spectrum of neither an alcoholic nor
Cok>ar Sensitising
130
Colour Sensitisktg
of an aqueous solution of the dye coincides with
the position of maximum light action on the
dyed gelatino-bromide of silver. (2) The maxi-
mxan of sensitiveness of the dyed silver bromide
lies nearer the red than does the absorption
maximum of any solution. (3) The position of
the maximum of absorption of the dye in gelatine
and that of the maximum of sensitiveness of the
dyed silver bromide differ generally by about
thirty wave lengths ; that is to say, those rays
of light that are most active photographically
on the dyed silver bromide possess a mean greater
wave length of about thirty wave lengths than
those that are absorbed by the dyed gelatine
(without the silver bromide). (4) The absorp-
tion maximum of silver bromide dyed with
eosine coincides exactiy with the maximum of
light sensitiveness on silver bromide dyed with
eosine ; that is to say, those light rays which are
absorbed by eosine-dyed silver bromide have the
same wave length as those for which the dyed
silver bromide shows the increased sensitiveness.
(5) The dyes must stain the silver bromide grain ;
the dyes that act vigorously are all " substan-
tive " dyes. (6) They must show in the dry
state — on dyed gelatine, or more correctiy, on
dyed silver bromide — even in considerable
dilution, an intense absorption band if they are
to produce an intense action on the silver
bromide. A narrow absorption band gives a
narrow sensitising band.
Although it has been established that a colour
sensitiser must dye the silver bromide grain, yet
all dyes that stain the silver bromide are not
sensitisers. Neither fluorescence nor fugitive-
ness to light plays any important part, as pure
erythrosiue is not fluorescent and yet is a power-
ful sensitiser, and is fairly stable to light, whilst
cyanine is very unstable and is a good sensitiser.
Apparently, there is no connection between the
chemical constitution of a dye and its sensitising
powers, thongh I<umidre and Seyewetz have
concluded that the sensitising action is con-
nected in some way with the chromophoric group
of elements. Joly has pointed out that all the
sensitisers are photo-electric, and assumes that
electrons are set free from the dye which act
on the silver halides.
Colour sensitive plates may be divided into
practically two main classes, the commercial
isochioma-tic or orthochromatic plate and the
panchromatic plate. The former are usually
prepared by adding erythrosine to the emulsion,
either at the time of mixing or just before coat-
ing, and are sensitive mainly to yellow-green and
yellow, there being a characteristic gap or lack
of sensitiveness in the blue-green. The pan-
chromatic plates are nearly all made by bathing
the finished and dried plates in a solution of the
erythrosine.
The method of introducing the dye into the
emulsion has considerable influence on the result-
ing colour sensitiveness. Those dyed in the
emulsion — that is, before coating — ^have usually
a lower x than plates bathed in a dye solution ;
that is, they are less colour sensitive, though the
leason for this is not apparent.
Although excellent commercial colour-sensi-
tive plates can be obtained, the following
information may be useful. To sensitise for
blue-green and green, up to about \ 5,500, fihe
best dye is acridine otange NO, of the I^eoshardt
Parbwerke, Miihlheim.
Stock SohtHon
Acridine otange NO . 9>6 grs. i g.
Alcohol . . . 200Z. 'ijOoo CCS.
Industrial alcohol may be used instead of th«
pure. The actual sensitising bath is : —
Stock dye solution . 4 oz. 200 ccs.
Distilled water to . 20 ;; 1,000 „
For greenish-yellow and yellow up to \ 5,900,
erythrosine should be used, and the most suit-
able dyes are bluish erythrosine of the Badische
Anihn and Soda Fabrik, that made by Schu-
chardt, of Gorlitz, or the pure dye of Meister,
Ivucius and Biiining, of Hoechst. A stock
solution is made of i : 1000 of alcohol, as with
acridine ; the sensitising bath is : —
Stock dye solution . 4 oz. 200 ccs.
I/iq. ammonise (-880) . 96 mins. 10 „
Distilled water to . 20 oz. 1,000 „
Erythrosine is an excellent sensitiser for the
above region, but it leaves a minimum or gap
in the bluish green, which, however, fills up with
a generous exposure, so that it can be used
instead of acridine orange for all but spectrum
work in the blue-green, and has the advantage
of being more readily washed out of the gelatine,
alcohol alone being able to remove the last traces
of acridine.
To sensitise for green, yellow,, and red up to
about A 6,200^\ 6,400, one of the following
should be used : orthochrome T, pinaverdol,
pinachrome, or homocol, the action as red sensi-
tisers being greater in the last two than the
first two. A I : 1000 alcoholic stock solution
should be made, which should be kept in the
dark ; the actuai sensitiser is —
Stock dye solution
Distilled water
2omms.
20 oz.
2 ccs.
1,000 „
For the extreme visible red pinacyanol should
be used in the same way.
For the infra-red, about wave length \ 7,180,
" littie a," as it is usually called, dicyanine
should be used as above, only the stock solution
must be added to the water at the very last
moment, when everything is quite ready, and
the plate immediately flowed with the dye, as
the weak solution loses its sensitising power very
quickly.
The most convenient method of sensitising is
by means of a grooved trough, into which, when
filled with dye solution, the plates can be dropped.
Or the worker may use a dish twice as large as
the plates to be sensitised at one time. These
are put at one end of the dish ; the dish is
tilted, and the dye solution poured into the
empty end ; then the dish is tilted back, so
that the dye solution runs in an even wave over
the plates. The dish should be gentiy rocked
for three minutes, then the plates removed and
washed in a good stream of running water for
three minutes, and set up to dry in a proper
drying cupboard, or in an air-tight box coirtain-
ing a saucerful of calcium chloride.
An alternative method of sensitising -Whidi
considerably hastens the drying, is to replace
two-fifths of the water in the above baths by
Colow S^sitiveness
131
Colour Sensitometry
acetone or methyl alcohol ; the plates then dry
in abont half an hour in a warm place.
The hest panchromatic sensitiser is that sug-
gested by R. J. Wallace.
Pinacyanol (1 : 1,000 sol.) i34nuns. 14 ccs.
Pinaverdol (i : 1,000 sol.) 106 „ 11 „
Homocol (i : 1,000 sol.) 106 „ u »
Liquor ammonise . . 318 „ 33 „
Alcohol ... 8 oz. 400 „
Distilled water to . 20 „ 1,000 „
The plate to be sensitised should be clean work-
ing and with a fine grain, and therefore not too
rapid. Care must be exercised as to the dark-
room illumination and no light should be used
for red sensitising. B. J. W.
COLOUR SENSITIVENESS
Silver bromide precipitated in the form of an
emulsion possesses great sensitiveness for the
ultra-violet, the viol^, and blue spectral regions.
With an adioixtiire of iodide of silver, precipitated
at the same time, the sensitiveness extends
beyond the bright blue slightly into the bluish
green, but there is no practical sensitiveness to
green, yellow, orange, or red. Sensitiveness to
these regions is ooaferred on the silver hsdides
by the addatitm of certain dyes to the emulsion
in the making, or preferafbty by bathang the dry
plates in aqueous solutiions of dyes. It will be
noted that the expression " no practical sensi-
tiveness " is used, and this is employed for the
specific reason that if the exposure is sufficiently
prolonged, all the spectral colours will affect the
silver haUdes, but the more actinic rays must be
screened off by suitable filters ; it is not practical
to give such prolonged exposures in the process.
COLOUR SENSITOMETER
A series of coloured glasses or dyed gelatines
having special spectral tcaiasmissions, used for
testing the colour sensitiveness of plates. Vidal
constructed one of the first c^ these instruments,
and the Chapman - Jones plate tester can also
be used for the same purpose. Abney has sug-
gested a somewhat similar instrument. They
have not found extended practical application.
{See " Colour Sensitometry.")
COLOUR SENSITOMETRY
Soon after the introduction of the colour
sensitive plate some method was found needful
for espressing the added colour sensitiveness, and
this was effected by exposing a plate in the
spectrograph and estimating Idle densities by
visual examination or merely drawing a grapliic
curve, a test of great unreliability, still further
com^oated by the fact that prismatic spectro-
graphs were used. Later, plates were exposed
to isolated patches of monochromatic light, a
curve being obtained from the resulting negatives.
This method was stiU further improved by using
a spBctrnm and varying intensities of white hght
and obtaining an interpolation curve.
The great disadvanltage -of the specfctographic
method is that it is not capable 6i brief and
eommoffily understood 'expressitm, and therefore
many attempts have been made to obtain sensito-
metric tests by means of dhaifts of coloured pig-
ments, which are open to the most serious
objection that the pigmentary cdlours reflect
an enormotts amotmt of white Ught, and whilst
there is no object in nature that does not reflect
white light, what the worker really desires to
measure is the true increase in sensitiveness to
a pure colour. Abney' s colour sensitometer and
the Chapman-Jones plate tester consist of
cOloTired glasses or gelatines of equal luminosity,
transmitttag either small or broad isolated
pat(ihes of the spectrum, and the densities obtain-
able can then be read and charted. Later, Bder
and others dividfed the spectrum into three
broad regions, the one including the bltte and
violet up to about \ 5,000, whici is practicjflfly
the sensitiveness of the ordinary emulsion ; a
second region extending from the blue through
the green to the yellow up to A 5,900 ; and a
third, used only for panchromai;ic plates, extend-
ing through the red. Eder utilised the Scheiner
sensitometer, and thus expressed numerically
the actual ratio of speeds of the non- colour-
sensitised emulsion and the added colour sensi-
tiveness.
This method has been still further exitendfed
by Mees and Sheppard to the Hurter and Driffield
system, and is the most practical. The following
are briefly the main features of it : the H. & D.
sector wheel and the screened acetylene light
{see " Plate Testing ") are used, and between
the light source and the sector wheel are insel'ted
absorbent solutions which limit the active Hght
to particular regions of the spectrum. For test-
ing commercial iso- or orthochromatic plates, a
yellow and a blue filter fEder) are used ; the ydlow
filter consists of a 4 per cent, solution of potas-
sium chromate (not bichromate) in a thidcness erf
I cm. The blue filter is a 2 per cent, solution of
ammonlo - sulphate tit copper, also in i cm.
thickness. The plate to be tested is exposed
behind ttiese two filters, and after develop-
ment the inertias are found in the usual waJy,
and the result or ratio termed x {chr6ina, a
colour), and is — ■
yellow inertia
■blue inertia
blue sensitiveness
yellow sensitiveness'
For instance, a commercial iso plate was foimd
to have an inertia of 0-34 behind the "blue screen
and an inertia of 4-8 behind the yellow screen ;
IShen—
yellow inertia 4-8 _ blue sensitiveness roo _
blneinertia 0-34 " jreUaw sensitiveness /-i ~
X 14-
For panchromatic plates, it is essential to know
also the increased sensitiveness to red ; and
Mees and Sheppard use three screens as fallows :
the blue screen is Eder's given above, which
passes the violet and blue up to \ 5,000 ; the
green screen, which passes from \ 5,900 to
\ 5,000, consists of Eder's chromate screen
given above plus a screen of i cm. thickness
of a -saturated solution of copper acetate ; the
red screen is made with rose Bengal and tar-
trazine : —
Rose Bengal . . 48 grs. 5 g.
Tartrazine . . 96 „ lo ,,
Distilled water to . 20 oz. 1,000 ccs.
Gelatine . . 728 grs. 73 g.
Allow 20 minims, or 1-25 ccs., to every square
inch of glass.
Colour Test for Plates
132
Colouring Photographs, etc
In all cases the screened acetylene light
has been used, and whilst this does not give
the absolute inertias of the plate, the ratios of
colour sensitiveness are preserved. For three-
colour work the actual filters to be employed
may be used in the same way, and if an exposure
be made without a filter the necessary increase
of exposure for the blue-violet filter over the
unscreened plate can readily be found. Con-
siderable influence is exercised naturally upon
the results obtained by the nature of the Ught
employed, and one can easily understand that
the Standard light should be, if possible, daylight
of constant spectral composition, or a secondary
standard with as near as possible the same spec-
tral composition ; for if the light be yellow, with
a decided paucity in violet and blue rays, and
corresponding richness in yellbw and orange, the
colour sensitive plate would show a much higher
colour sensitiveness, which would be totally
misleading. B. J. W.
COLOUR TEST FOR PLATES {See " Plate
Testing.")
COLOURING PHOTOGRAPHS, ETC.
The three popular processes for colouring
prints and sUdes are by means of aniUne dyes,
water colours, and oil colours. Colouring by
the crystoleum process {which see) is also widely
practised. Aniline dyes, although not so per-
manent as water colours, have largely super-
seded the latter, the dyes being so cheap and
easy to use ; they are also transparent, and allow
the details in the pictures to show through them,
whereas some water and oil colours are body
colours which hide aU detail.
Photographs to be coloured with dyes or
transparent pigments should not be deeply
printed or given too warm a tone ; but these
points are of no importance when body colours
are used. A desk of some kind, or an easel,
will be required for large prints, but small ones
may be laid flat upon a table or held in the
hand. I/antem slides and other transparencies
are best held in the hand over white paper, or
placed upon a retouching desk in sudi a way
that the light comes through the slide, using
preferably artificial Ught, as slides coloured in
dayUght are sometimes disappointing when
viewed on the screen ; transmitted light allows
the density of the colours to be better judged.
Sable brushes of the sizes known as No. o (very
small) to Nos. 5 or 6 wiU be found the most
servicealile for average work, but others, as
experience dictates, may be found useful.
Aniline Dyes.— These are the simplest of aU
colours in use, and may be used for sUdes and
all kinds of prints, although they appear to best
advantage on ortoiary P.O.P. (gelatine) prints.
Suitable dye solutions all ready for use may be
purchased, the colours being put up in cheap sets
and in very convenient form. Penny packets
of dyee, obtainable at oil shops, are good enough
for experimental work ; to prepare them for use
dissolve first ia J oz. of acetic acid or vinegar
and make up to 2 oz. with water. The raw dyes
may be dissolved and prepared in the same way,
but very little of the actual dye need be used,
as they are very strong, and a few grains will
make a large quantity of coloured solution. The
number of colours will depend upon the character
of the work ; clever colourists, it should be said,
can get aU the colours they want by using only
three — blue, yeUow, and red — as by mixing
these in suitable proportions any colour likely
to be needed can be produced ; blue and yeUow
make green ; red and yeUow, orange ; blue and
red, violet, etc. etc., the exact tints depending
upon the proportions of the two colours. The
average worker wiU prefer ready-made dye
solutions, and the foUbwing wiU be found the
most serviceable : Blue, yeUow, brown, oUve
green, scarlet, purple, orange, and pink. These
dyes may be combined if desired, green and
orange, for example, making citrine ; orange
and purple, russet ; etc. The secret of success
in using aniline dyes is to have them weak,
building up the colours required by repeated
washes of the dye rather than attempting to
obtain in one application a colour of fuU strength.
So important is this that the beginner is advised
to begin colouring with dyes near to a water
tap, so that as the colours are put on they may
be largely washed off under the tap, the opera
tions being repeated until the desired strength is
obtained. The process is reaUy that of staining
or dyeing the print rather than painting, as the
last-mentioned term is generally understood.
If the print is mounted and cannot be satis-
factorily rinsed in water, the colours should be
appUed to the print very dUute, and immediately
blotted with clean white blotting-paper. This
prevents the dyes acting too quickly, and
obUges the worker to proceed slowly and build
up the colour. Blotting-paper is not suitable
for use on sUdes, and the sUdes should be repeat-
edly rinsed instead, unless the dyes are appUed
sufficiently weak in the first instance. Prints
do not usuaUy require any preparation for
colouring, but if much blotting or rinsing is to
be done or the brush is at aU stiff, it is advisable
to harden gelatine films — P.O. P., bromide and
gasUght papers and lantern sUdes — with a solu-
tion of I oz. of formaline in 10 oz. of water ;
the fixed and washed sUde or print is immersed
in this for about ten minutes and then washed
weU. Alum should not be used for hardening
previous to colouring with dyes, as it is apt to
react chemicaUy wiUi some of the coloiurs.
Water Colours. — ^Water colours may be
employed for aU kinds of prints and sUdes. They
differ essentiaUy from dyes in that they do not
sink into and stain the film, and therefore the
surfaces need to be specially prepared so that
they do not repel the colours ; also, a medium
is necessary for the colours in order that they
may not dry duU and dead. A suitable appUca-
tion for prints is the foUowing oxgaU mixture : —
Purified oxgaU . .15 grs. 6 g.
Methylated spirit . . i oz. 250 ccs.
DistiUed water , . 4 „ 750 „
This should be weU mixed and appUed to the
surface with a broad, soft brush, and the print
when dry wiU be in a proper state to take both
water colours and even oil colours. This pre-
paration is essential for albumen prints and
others with a greasy surface, but may be omitted
in the case of freshly-made P.O.P. or other
gelatine prints.
A suitable medium to use in place of water
Colouring Photographs, etc. '33 Colouring Photographs, etc.
for the water colours is made by dissolving a
small quantity of the best gnm arable in sufficient
water to cover it, and ad^ng two or three drops
of glycerine. This is not necessary for matt
surface prints. An albumen solution must be
used as a medium when colouring albumen
prints, and some workers use it for all kinds of
glossy prints ; it takes the place of the gum
mixture, and is qmte as good. The albumen
mixture consists of the following : —
White of egg . . i oz. 30 ccs.
Glycerine . .15 drops 15 drops
Liquor ammonise .15 „ 15 „
Ammonium carbonate 20 grs. 13 g-
Water . . .2 drms. 7 ccs.
Whip the white of egg to a froth, allow to stand
until clear, add the other chemicals previously
dissolved in the water, and filter through muslin.
The choice of water colours is an important
item ; there is a feeling in favour of colours
in pans and not in tubes, but there is probably
not much in the preference. Some are trans-
parent, others semi-transparent, and others,
again, are opaque or body colours. An expe-
rienced worker may use any or all for print
colouring, but for lantern slides transparent
colours must be used. They are easily recognised
by painting a few dabs upon glass and examining
by transmitted light. Transparent colours are
I^ssian blue, crimson, alizarine yellow, Italian
pink (which is really a yellow), ohve green, sap
green, purple madder and lake, and burnt car-
mine. The opaque colours are light red, yellow
ochre, scarlet lake, ultramarine, Naples yellow,
burnt uniber, and Vandyke brown. The semi-
transparent colours are sepia, madder brown,
raw and burnt sienna, cobalt, and bistre. The
above list is not by any means complete, but
contains enough for average work. When white
is required, Chinese white and no other should
be used. For faces of portraits the colouring is
usually put on very weak in the form of cross
hatching, but for all other work colours are
brushed on in the usual way, using plenty of
the medium so as to weaken the colours.
Lantern slides can be coloured with trans-
parent water colours, but they need no special
preparation, although inany consider it advis-
able to harden them with formaline. Colours are
applied in broad, even sweeps, and but little
difficulty will be experienced except in skies,
which more often than not are plain glass.
When the Prussian blue — ^really thepnly pigment
available for the purpose — ^is put on the plain
film, brush marks are likely to show, but this
defect is remedied by dabbing the blue while
wet very gently with the finger-tip, or with a
piece of kid ^ove stretched over the finger.
The sky may be stained an even blue with dyes,
and then given character with water colours.
The slides also may be chemically toned to
various tints and then completed with water
colours. Considerable practice is necessary for
lantern-slide work, and no small artistic skill,
if it is wished to avoid the banal effects fre-
quently seen in commercial sUdes.
Oil Colours. — Painting in oils, particularly upon
enlargements, is chiefly a profession^ practice,
and the method of doing the work depends to
some extent upon the mlaterials used. Traas-
parent oil colours may be handled in a different
manner from that adopted when body (opaque)
pigments are used. The latter cover up the
miage, whereas the former, which give a rather
weak effect, permit the shades and details of
the picture to show through. For strength and
high colouring the opaque colours are necessary,
and for their use a knowledge of drawing and
painting in general is requisite, as the photo-
graphic image is simply used as a base. The
colours whidb will be found of the greatest ser-
vice are emerald green, Vandyke brown, indigo,
Indian red, burnt umber, pink madder, light
red, raw sienna, Naples yellow, yellow ochre,
burnt sienna, crimson lake, raw umber, ultra-
marine, flake white, and ivory black.
Any kind of print may be coloured in oils —
bromide paper being the most vyidely used —
but owing to the oily nature of the colours it
is necessary to size the print first in order to
prevent the colours sinking into the paper. To
make a suitable size, dissolve one pennyworth of
clear patent size (obtainable at an oil-shop)
in one pint of hot water, and when nearly cool
give the picture a coat, and set aside to dry in
a warm place. The coat of size must not be
too thick, or it may peel off at a later stage and
bring the colours with it. The brushes should
be varied both in kind and size, according to the
work. There should be provided stout hog-hair
brushes, some thin badger brushes, and a few
small sables ; a badger softener is also useful.
Megilp is used for thinning the colours, and a
plentiful supply of turpentine should be provided
for washing the brushes.
The meOiods of applying the actual colours
vary considerably. It is usual to apply a suit-
able tint to the deepest shadows, and to work
from this to the highest lights, using a more
solid colour as the work proceeds, the reverse
of water-colour painting. Brapery and costumes
in portrait work may first be covered with
transparent colour, working into it the various
tints for the shadows, halt-tones, and high lights.
After the first tints have been put in, it is usual
to let the canvas dry and to rub over with
poppy oil, removing the excess with chamois
leather ; the more delicate colouring is then
worked in. It is difficult to give precise in-
structions for colouring, and the worker must
to a large extent be guided by his own tastes.
When the painting is completed it should stand
on one side for a month before varnishing with
copal or mastic, and in no case must the varnish
be applied until the painting is dry. Copal is
a hard and durable varnish, but maiiic is widely
used because it dries quicker and, if necessary,
may be removed easily.
For lantern sUdes transparent oil colours must
be used. They are sometimes put on with a
brush in the same way as water colours, but it
is more general to dab on the colouring with the
finger-tip. The best way of obliterating the
grain of the finger-tip is to work upon the slide
placed at different angles so as to cross the
markings and break them up very lightly into
a series of small dots. The finer details are
best coloured by means of a fine sable brush,
but too much colour must not be put on, as it
is better to under-paint than over-paint, it
being easier to add the colour than it is to take
Coma
134
Combiaaiion Printing
it away. A useful dodge is to put the oil colours
at first on the plain glass side, from which they
may easily be removed if any error is made,
or the colouring may be put on the cover glass
of the slide. Parts of the slide may be coloured
with dyes and parts with oil and water colours
with good effect, but, no matter what process
of colouring is adopted, some practice is neces-
sary, particularly with oils, which are the most
difficult for a beginner to use satisfactorily. A
slide for colouring in oil or water colours must be
lighter and brighter than those for ordinary use,
and it is important that they be dried in a room
free from dust, as any specks or hairs upon the
sUda will show up very prominently when
magnified upon the screen. P. R. S.
COMA (Fr., Aberration zonale; Ger., Zonen
abirrung, Nebeliger saum)
Synonyms : oblique spherical aberration, zonal
aberration. A defect resulting from the unequal
magnification of the different zones of a lens,
these zones being defined as imaginary circles
dividing the surface of the lens into concentric
rings. As a result of coma the image of a bright
point of Ught towards the margin of the field of
view, produced by obUque rays, will be rendered
as a comma- or pear-shaped blur — whence the
name " Coma." Coma may occur in a lens other-
wise well corrected for chromatic and spherical
aberration, and is approximately removed by
careful design of the curves of the objective and
precise selection of the different kinds of glass.
COMBINATION PRINTING
The art of making a print by the use of two
or more negatives. The simplest form of com-
bination printing.is the printing of a cloud into
a landscape, but combmation printing proper
is the art of adding trees, figures, or other objects
to a picture, as practised by Rejlander, Robin-
son, and other past masters of the art. Com-
bination printing had its origin in 1855, when
Berwick and Annan, of Glcisgow, exhibited a
Arrangement for Combination Printing
picture printed from two different negatives — a
figure ia a landscape. In 1858 Sarony patented
an improved process which consisted of taking
up the different portions of the collodion film
from the glass of one or more negatives and
laying them down upon another glass in their
proper relative positions and printing from it.
Rejlander, however, was the first to draw
attention to the possibihties of combination
printing, and in 1857 he used thirty negatives
to produce a single picture (" The Two Ways o^
I,ife"), which he exhibited at the Manchester
Exhibition of that year; all except the part
required was blocked out on each negative, all
the negatives were then laid in turn upon sensi-
tive paper and printed; the remainder of the
paper being covered witii black velvet. In tiie
followuig year (1858) Robinson produced the
first of his famous series of combination prints,
" Fading Away," for which five negatives were
used, and in 1863 "Bringing Home the May"
(nine negatives) ; this type of combination
printing tiien became the craze.
The methods fully described under " Clouds,
Printing in," may be adopted in some forms of
combination printing ; but in others, such as the
addition of a figure to a landscape, or the sub-
stitution of a suitable background for an unsuit-
able in a figure subject, a different method will
be more fitting (see, for example, "Backgrounds,
Printing in "). In many cases, however, th&
pencil and brush marks described under the
heading first given above will be found useful
in securing registration.
For combining portions of two or more nega-
tives to form one print, whether the object is to
print a new background to a figure or to combine
in one picture selected parts of two or three
landscapes, etc., the method described under the
heading, "Backgrounds, Printing in," or some
modification of it, can be adopted. In some
respects the method about to be described has
points of advantage compared with that given at
the reference last mentioned. A silver print is
taken from the figure negative, and the figure
cut out very carefully with a sharp knife. Both
parts of the print must be kept to form masks.
First, the portion from which the figure was cut
should be attached to the glass side of the figure
negative, and then the two negatives should be
held together vertically with their edges resting
on the table and the comers accurately coincid-
ing, or preferably placed on a retouching desk
witii their comers together. The figure negative
must be underneath and the glass side of each
negative towards the worker. The figure that
was cut from the rough print must now be
attached to the glass side of the background nega-
tive in such a manner that it corresponds in
position accurately with the opening in the
mask on the figure negative, this opening being
easily seen for obtaining a correct adjustment by
this method of holding the two plates.
In printing, it is immaterial which negative
is used first. Either negative is placed in the
printing frame with one edge in close contact
with the woodwork of the frame — preferably the
edge that was resting on the table when the
masks were adjusted on the negatives. In the
diagram the edge a b is shown pressed closely
against the frame, the comer being pressed right
into that of the frame. The printing paper
need not be cut accurately to fit the negative,
but it must touch the same side and the same
corner of the frame as the negative. The paper
is indicated by dotted hnes. When this part of
the printing is finished, the print and the nega^
tive are removed from the frame, and the secoi^d
negative is placed in the frame with its corre-
sponding side and comer pressed, closely against
the side and comer a b. The print is again
Coailiiiied D«velopment
135
Comets, Photographing
pteced in position as before \rath the same side
and earner touckiag tlie same parts of the
frame, and the second part of the printing com-
pleted!
If the masks have both beea accura^^ely fitted
to their respective negatives, the two parts of
the print should join perfectly. Each print wiU
show a soft outline due to the fact that the block-
ing out is on the glass side of the negative, and
these two outlines will slightly overlap and soften
into each other in such a manner that, with
reasonable care in fitting the masks and in print-
ing, the junction will not show. When the block-
ing out is on the filtn of the negative it is ahnost
impossible to prevent the junction from show-
ing as a hard and crude line, white in some
places, dark in others. Masking on the glass side
possesses the great advantage that it does not
spoil the negative for other purposes. At any
tame the masking may be removed, leaving the
negative uninjured.
COMBINED DEVELOPMENT AND FIXING
{See "Development and Fixing Com-
bined.")
COMBINED LENSES
When two lenses, such as the Zeiss single
anastigmats, are combined to form a doublet,
there is a simple formula for finding the focal
let^tii of the combination. It is to divide the
piDdnct of the focal lengths of the two com-
ptarents by their s-orn. minus the distance by
wMoh tiieir optical centres or nodes of emission
are separated. Thus, in the case of two lenses
with focal lengths of 7 in. and 1 1 in. respectively,
with a separation of 2 in., the focal length is
arrived at as follows :
7 X II
7 + 11—2
77
16
4H in.
If a positive and negative lens are combined,
the focus of the negative lens is taken as a minus
quantity, the calculation being otherwise the
same.
It is often necessary to find the focal length of a
lens which when added to another of known
focus shall produce a given focal length. Thus,
a angle lens having a focal length of 18 in. is
to be used with another so that the focal length
is reduced to 12 in. The rule is to multiply the
focus of the lens of known f ocUs by the focus
desired, and to divide the product by the known
focus less the desired focus. Taking the above
example, the working is : —
18 X 12
18 — 12
216
= 36 in.
No account of the separation has here been taken,
but if absolute accuracy is desired witii, say,
a separation of 2 in., the formula is, : —
(18 X 12)-
• = 3Sf in
18 —12
(See also "Magnifier.")
214
T
COMBINED REDUCERS {See "Reducers,
Combined ")
COMBINED TONING AND FIXING {See
"Toning and Fixing, Combined.")
COMETS. PHOTOGRAPHING
The first attempt to portray the form of a
comet was in the case of Donati's comet of 1858,
but the results were very imperfect, owing to
the photographic processes bemg then in their
infancy. The first useful photographic cometary
records are of Tebbutt's comet of 1881. The
gelatine dry plate had been introduced, and
with its increased rapidity, compared with the
old collodion plates, the problem was much less
formidable. Further improvements were made
by the employment of large-aperture telescopes,
chiefly of the reflector class. Inasmuch as the
comet is generally moving very rapidly in a
special orbit of its own, irrespective of the earth's
direction of rotation, the usual equatorial tele-
scope is of little use unless special arrangements
are made. To obviate the difficulty various
schemes have been devised. The most success-
ful, and the only one we need mention in a prac-
tical treatise, is that employed by Prof. E. E.
Barnard, of the Yerkes Observatory, near
Chicago. He first makes a preliminary obser^
vation to determine the rate of motion of the
cometary nucleus, and its direction as pro-
jected on the sky. Then, attached to the eye-
piece of his telescope, with which he follows the
comet nucleus during exposure of the plate,
he provides a fine spider thread fixed on a mov-
able frame actuated by a delicate micrometer
screw. If, now, he knows how far the comet
will move on the ground gVass of his camera in,
say, a second, he has only to move this adjust-
able cross-wire, set in the direction of the comet's
motion, by the same amount, and then by
keeping the comet nucleus continually bisected
by the cross-wires, its image will of necessity
be kept exactly on the same portion of tie photo-
grapluc plate. It is a similar problem, but some-
what more delicate, to that of taking a series of
photographs of a. moving object with a kine-
matograph camera : tiie whole apparatus is
usually braversed by means of a screw-and-worm
gear.
For recording the whole phenomena attend-
ing the passage of a comet, probably the most
useful instrument is a wide-angle camera attached
to a perfectly rigid form of equatorial mounting.
Needless to say, the better the lens that is avail-
able the better will be the resulting photographs.
The modem wide-angle anastigmat is the ideal
instrument, and as in these cases it is an object
of definite area that has to be portrayed, the
greater the ratio of aperture to focal length the
shorter will be the time of exposure necessary to
obtain a satisfactory image, and in consequence
the risks of failure due to vibration or bad
weather will be minimised in proportion.
The plates used should certainly be backed and
panchromatic, as a considerable proportion of
the cometary light is green and yellowish-green,
and this is all ineffective if ordinary plates, sen-
sitive only to the blue and violet, are employed.
Development should be very carefully per-
formed, as in general the range of gradation
wfll be very great, varying from the intensely
brilHant nucleus to the fflmy streamers constitut-
ing the delicate tail. The developer may be
pyro soda, rodinal, metol, or metol-hydroquinone,
but the developers giving excessive density with-
out the full scale of detail should be avoided.
Compass, Photographer's
136
Composite Portraits
COMPASS, PHOTOGRAPHER'S (Pr., Bous-
sole horaire ; Get., Photographischer Kom-
pass)
A magnetic compass the dial of which is ar-
ranged to indicate the time of day when the
subject, in any given direction, will be most
favourably lighted for photography.
COMPENSATING EYEPIECE {See "Eye-
pieces.")
COMPENSATION FILTER
A screen (generally yellow) for cutting off
excess of ultra-violet, blue, and violet rays {see
also "Colour Screen or Filter"). In process
work it is used largely in colour work, especially
with collodion emulsion, it obviating excessive
staining of the emulsion in cases where the latter
is stained by the addition of a dye.
"COMPENSATOR" NEGATIVES
A system advocated by Newton Gibson and
published in April, 1905, for preventing hala-
tion without backing and controlling contrasts
when taking difficult subjects, particularly
interiors. The method is to place a dry plate,
glass side towards the lens, in the camera and
to give a very short exposure in order to secure
the high-lights and not the shadows ; the plate
is then developed, fixed, and dried. When
quite dry the under-exposed negative is placed
in the dark-slide in contact (film to film) with
another dry plate, and the same view taken
again through the compensator negative, taking
care to give a fuU exposure for the shadows. If
the first negative is of the right density, the
second wiU develop in good gradation, the win-
dows and other high-lights not being over-
exposed and too dense, because of their being
covered by the compensator through which the
light has to pass to act on the second plate.
Obviously the camera must not be moved in the
slightest degree between the two exposures, or
the picture will not be in register ; and the
system is therefore out of the question where the
camera cannot be left untouched for some time.
^Success depends mainly upon the accuracy of
register, and the relative amount of exposure
and development necessary for the compensator
negative and for the final negative. It is possible
to over-correct the highest lights by making them
so dense on the first negative that light wUl not
go through them.
The process can be adapted to existing faulty
negatives. A thin positive is made by contact
on celluloid film, and when developed and dry
it is bound or cemented to the negative in the
position occupied when printing. The thick-
ness of the celluloid film between the negative
image and the sensitive paper when printing
wiU cause no trouble if a fairly concentrated
light, entirely from the front and not from the
sides of the frame, is used for printing.
COMPOSITE, ANALYTICAL, OR
"AVERAGE" PORTRAITS
A style of picture made by taking several
portraits of the same size upon one plate, or
hj printing from several portrait negatives
Kpon one piece of paper, the result being sup-
posed to give a type of the whole. Sucii pic-
tures are claimed by some to be of scientific
value to students of anthropologjr, but they are
more generally looked upon as curiosities. About
the year 1887 they were popxdar in the United
States. Their origin is said to be due to a con-
versation between Herbert Spencer and Francis
Galton about the year 1876, and Darwin also
had some correspondence on the subject in 1877.
The original idea was to have heads of two
different people, one upon each half of a stereo-
scopic picture, and to combine the two in a
stereoscope, which method serves admirably;
but not more than two different heads can be
combined in this way, whereas by taking nega-
tives specially for the work any number of faint
images of several portraits in succession can be
obtained on one plate, finally developing the whole
as one portrait. If reasonable care is taken in the
making of such a composite negative there is
seldom anything about the composite picture
to indicate that it is not a mere portrait of an
individual, whereas, of course, it is a com-
bination of the portraits of several. Full or
three-quarter faces make the best composites,
and before beginning the work the focusing
screen should be marked where the eyes, nose,
and mouth are to be upon the screen, the mark-
ings being made when the first sitter is posed
and focused. The images of the sitters which
follow must be adjusted to those lines ; and as
there is a variation in the distances between
eyes, nose, and mouth, the camera has to be
adjusted after each partial exposure. The total
time of exposure must be divided up between
the number of sitters. If, for example, the time
required for an ordinary portrait is three seconds,
and it is required to make a composite portrait
of three sitters, the exposure in each case will
be one second. When the number of sitters is
relatively great, the lens must be stopped down
to allow of increased exposure being given.
For example, in making a composite portrait of
six sitters, it would be better to use such a
small stop that the exposure would be increased
to, say, twelve seconds, when each sitter would
be given two seconds. The lighting should be
the same throughout, and it is also advisable to
have a dark covering over the shoulders and
round the neck, instead of white collars, fancy
ties, blouses, etc., so as to obtain a uniform
eSect.
An inferior method is to copy a series of por-
trait prints upon one plate so as to get one
negative of the whole ; and another is to make
transparencies from several portrait negatives
(if they match properly) and make one negative
from them by contact or through the camera,,
printing or copying each in turn so as to get
a negative of the whole, by a series of partial
exposures.
Probably the most famous of all composite
portraits was that produced by Oliver Lip-
gincott, of New York ; it included portraits of
fty-one bank managers, and took from Decem-
ber 10, 1908, to July 27, 1909, to complete.
All were taken full face, and all eyes and pupils
were registered, irrespective of the size of the
head. Positives were made from the original
negatives — all of which were taken separately —
by means of prismatic reflectors and a twelve-
power magnifying glass, and registered accurately
Composition, Pictorial
137
Compressed Gas
upon the screen. Every fourth positive was
again converted into a negative, and every fourth
negative again into a positive, the process being
repeated until the finsJ negative was arrived at,
and the whole of the fifty-one individuals con-
verted into one portrait. Lippincott states
that it took 783 negatives and positives to
accomplish the work, and, deducting failures,
it took 553 positives and negatives to complete
the one picture, which was widely published
under the title of " The King of Pinance." '
Composite prints of a sort may be made from
existing portrait negatives if they happen to
match in posing, lighting, and size. P.O.P. is
used and the first negative partly printed, the
remaining negatives being then printed in turn
upon the one piece of paper, and the print iinished
in the usual way.
There is a kind of composite photography (not
portraiture) frequently employed in the pro-
duction of picture postcards. Figiures are cut
out from different prints, stuck upon the same
base, and copied, in this way obtaining many
curious but worthless, inartistic, and untruthful
effects.
COMPOSITION, PICTORIAL
Composition is the placing or arrangement of
the difierent component parts of a picture in
such a manner that the result is pleasing and
harmonious. Much has been said and written
about the so-called " laws " of composition. The
use of the term " laws " is hardly justifiable.
Even the most definite and emphatic rules may be
broken with impunity, frequently to the advan-
tage of the resiit. The most that can fairly be
said is that some arrangements are found to
be more pleasing than o&ers in the impression
they create. By studying the elements of these
more pleasing arrangements certain generalities
are deduced, but these should not be dignified
by the name of laws.
It is safe to say that the best pictorial Work is
not the result of a rigorous application of some
clearly defined code of " laws." It is rather the
outcome of a kind of instinct, a natural feeling
for what is harmonious, tasteful, and pleasing.
Whether that instinct can be created is very
doubtful ; but it can certainly be fostered and
cultivated by careful study of Nature, and of
graphic representations of Nature produced by
others who have themselves studied and ob-
served. Thus will be produced a perception or
sense that certain things are " right " and that
others are " wrong " ; and efforts can then be
made to secure the right and avoid the wrong.
The natural limitations of photography
impose severe restrictions on the worker in his
attempts to secure what he considers to be good
composition. Apart from combination printing
and certain limited means of modification, he is
almost confined to selection of subject and point
of view to secure the result he desires. He
should by all means famiharise himself with any
available expedients that may assist him to
reach the desired goal, but to a great extent he
will have to content himself with what is before
him rather than what he would wish.
Nevertheless, it may be helpful to give a few
examples of what is, in a general way, to be
Bought for or avoided. A picture should contain
one principal object, or group of objects, which
should not be placed too far from the middle of
the space. Everything else should be comple-
mentary and subordinate to this. Two or more
objects of equal importance will distract the
attention and produce a lack of unity. The eye
should be led or attracted to the principal
object — there should be nothing that forms a
kind of barrier. There should be no strong
patches of hght, or anything else that irresistibly
attracts the eye, at the edges of the picture.
Neither should lines lead out of the picture or
to the unimportant parts of it. Detached patches,
either of Ught or shade, should not be scattered
about over the space. The horizon line should
not bisect the picture, neither should the space
be divided into halves diagonally. One mass
may advantageously be repeated by another
similar but subordinate. Upright lines may be
contrasted with, and broken by, horizontal ones ;
and a line leading in one direction may be
balanced by one running in the opposite direc-
tion. Balance, however, should not be too sym-
metrical and formal. An arrangement of masses
that forms a rough triangle with the apex towards
the top of the picture is generally efiective ; as
is also one in which the main lines radiate from
the principal object.
Such general suggestions as these might be
extended to great length. But no multiplication
of them, or knowledge of them, will of itself
be sufScient to ensure the production of pictures
of satisfactory composition. Patient and care-
ful study and analysis of pictures of acknow-
ledged merit wiU be foimd interesting and help-
ful. It will aid in forming ideas as to the means
by which certain satisfactory results may be
obtained, and will strengthen those faculties of
judgment and good taste without which the most
elaborate series of rules of composition will be
of no avail. {See also " Lines in Composition.")
COMPOUND LENS
An almost obsolete term used to denote the
difference between the single or landscape lens
and the double or triple combinations composed
of more than one cemented element.
COMPRESSED CHEMICALS
For convenience of carriage when touring,
many photographic chemicals are now obtain-
able either compressed into small glass or card
packages or in the still more portable form of
tablets, " tabloids," " scaloids," etc. The advan-
tage of this method of packihg chemicals, besides
the small amount of room that they occupy, is
that the worker is quite certain of having pure
standard reagents, which only require dissolving
in water to form the usual photographic solu-
tions.
COMPRESSED GAS
For producing the oxy-hydrogen light (lime-
Ught), a hydrogen flame, supplied with oxygen
under pressure, plays upon a small cylinder of
lime, a spot on which is heated to incandescence.
Some years ago the lantemist had to manu-
facture one or both of the gases employed, but
the method is now obsolete, and it is usual to
obtain the gases, compressed into steel cylinders,
from one of the companies who make a specialty
Concave Lens
138
Condenser
of suppljdng them in this foim. Photographic
dealers and phatmaceutical chemists are gener-
ally prepared to obtain compressed gas to order,
the dtiarge being so much per cubic foot. Each
cylinder needs to be fitted either with an auto-
matic regulator, which will adjust the supply of
gas to requirements, or with a reducing valve
{see also " Cylinder, Gas "). To obtain the best
results with a mixed jet, both the oxygen and
the hydrogen should be under pressure, although
an experienced lantemist can get good results
with a mixed jet supplied from the gas main
and from a cylinder of compressed oxygen.
For ejector and blow-through jets, only the
oxygMi need be under pressure. For determining
the content of a cylinder, a pressure gauge is used.
Compressed acetylene (the gas is dissolved
under pressure in acetone) is. obtainable, and can
be used for lantern purposes.
CONCAVE LENS (Ft., Lentille concave; Get.,
Hohllinse)
A lens that is depressed or hollowed out ;
known also as a divergent lens. When two faces
are concave, as at A, it is described as " concavo-
A. Concavo- B. Concavo- C. Concavo-
concave Lens convex Lens plane Lens
concave " ; when one is concave and the other
convex, as at B, it is "concavo-convex"; Eind
when one of the faces of a concave lens is
plane, as at C, it is " concavo-plane." The
" biconcave lens " is the " concavo-concave."
The " concavo-convex " is also known as a
"meniscus" lens.
CONCENTRIC LENS
A lens patented in 1888 by Dr. Schroder and
introduced in 1892 by Ross, being perhaps the
earliest application of the new Jena glasses in
Great Britain to photographic work. It is com-
posed of two symmetrical combinations, each
consisting of a plano-convex of glass of high
refractive but low dispersive power, and a plano-
concave of low refraction but higher dispersion
than that used for the convex lens. The two
plane surfaces are cemented and the inner and
outer curves are concentric ; hence the name.
The lens has an excellent flat field over a wide
angle, and is still esteemed for copying.
CONCENTRATED SOLUTION
A solution made up very strong, chiefly in
the form of a stock developing solution, and
needing to be diluted with water before use ;
it may or may not be saturatedi It is not
synonymous with saturated solution (which see),
although sometimes thought to be so. Rodinal,
certinal, azol, and similar developers are con-
centrated solutions. The single-solution devel-
oper given under the heading " Adurol " is a
good example of a concentrated home-made
developer. Concentrated solutions are handy
for storing ; they do not take up so mudi room
and as a rule keep better. Almost any developer
with which the worker is instructed to take
equal parts of Nos. i and 2 (or A and B) may
be made in a more concentrated form by simply
using halt the water given in the formula, and
adding the other half at the time of using.
Hydroquinpne cannot in the ordinary way be
made up in a highly concentrated form, but for a
" ten per cent." formula see " Hydroquinone."
Toning baths are not, as a rule, made up in a
highly concentrated form, because of the danger
of the gold precipitating, particularly when sul-
phocyanide is used ; the following, however, has
been recommended for the use of wotikers whose
dark-room space is limited and who -vrash to
keep a highly concentrated bath : —
Gold •chloride . 8^ grs. 4-8 g.
Strontium chloride . 85 „ 48 „
Distilled water . i oz. 250 ccs.
Heat the water to 200° P. (93° C), add the gold,
and then the strontium. Next add 7 drms. of
water in which 25 grs. of potassium sulpho-
cyanide have been dissolved. Heat again to
the same temperature as before, filter, and
make up to 2J oz. with water. This is highly
concentrated, and keeps well ; when a toning
bath is to be made up for use, add J oz. of the
concentrated solution to 5 oz. of water.
CONDENSATION (See "Lenses, Condensa-
tion on.")
CONDENSER
In optical projection the condensing lenses
cause the rays of light emitted by the lamp or
jet to pierce the transparency from all points,
the rays being then transmitted to the objective
or focusing lens. Diagram A shows the general
optical system by which projection is accom-
plished, E being the illuminant, F condenser, G
transparency or sUde, and H objective or focus-
ing lens. The condenser shown is the one com-
monly used. Light rays, unless intercepted,
always travel in straight hues and, as indi-
cated at E, in straight lines from their source.
This holds good, no matter whether the illu-
minant be oil, limelight, acetylene, or electric
Ught. For the purposes of optical projection,
it is necessary to collect a large angle of these
rays, transmit them through the shde, and pass
them on to the projecting objective, by means of
which a large image is brought to a focus upon
the screen placed at some distance beyond.
A. Optical System of Optical Lantern
In cases where the illuminant may be regarded
as a point, such as with the Umeli^t or Sectric
arc, many experts consider that the Herschel
form of condenser B possesses advantages. Many
years ago two lenses of somewhat long focus and
shaped as at C, were employed, but this form has
Conjugate Foci
139
Continuing Action of Light
long bee» obsolete. XUe forms shown at A, B,
anAC are capable of cc^ctung a fairly large cone
of raya ; ths lens next tbe light serves as the
collecting lens atid, for transmitting the rays to
the second lens, wluch bends and converges,
them towards the objective, as^ at A. The dis-
tance of the iUiiminant from the condenser
governs the angle at which the rays are sent on
towards the objective. The triple form of con-
denser D possesses many advantages for micro-
scopic and other scientific work, inasmuch as it
cellefits a greater angle of light.
In the best condensers the lenses are ground
to a. sharp edge. The lens nent to the illuminant
unavaidaWy gpts very hot, and hence should be
mounted loosely in the cell, for if at all tight it
B. Herschel C. Condenser D. Triple-lens
Condenser witii Two Long- Condenser
focus Lenses
will, in expandtng. with the heat, . become cellr
bound, and; a crack will probably result. One
method of preventing tins is: to provide the
mounts with three or four: spring cUps or spring
rebates; which allow o£ the expansion of tie
glass and ^o erf ventjlation. The intense heat
arising ironi; poweriul arc lamps, such a& are
necessaiT^ in Jdnematograpli prpjection work,
tends to overheat the lenses in a very short time,
and the danger of breakage is therefore uicreased.
Several makers, recognising this fact, have pro-
vided means for the ready removal of the con-
densers from their, cells, so that fresh ones may
be substituted at intervals during a display, and
this without serious interruption. When using
all forms of: condensers, sudden cold draughts
must be guarded against, or cracking will almost
certainly occur.
The. bull's-eye condenser, as used, in photo-
micrography, is described under its own heading.
CONJUGATE FOCI (Pr., Foyers conjuguis;
Ger., Konjugierte Brennpunkte)
The distances between lens and object, and
lens and image ; known respectively as the major
and minor conjugate. They are always- pro-
portional to the ratio between the size of. the
object and Uiat of' the image. Thus, in enlarg-
ing: from quarter-plate to whole-plate — a ratio
of. 2 — the major conjugate, or distance between
lens and bromide paper, wiU, be twice the dis-
tance betweai lens and negative. If F = focal
length of lens and R = ratio, then^ whether
enlarging or reducing, F x (B + i) = the greater
distance, or major conjugate ; and the major
conjugate -5- r =; the lesser distance, or minor
conjugate. If, however, the image is full-size,
the conjugate ioei, are each, equal to twice the
focal length, of the lens.
CONTACT BREAKS
Meohanicali devices for automatically "mak-
ing" and. "breaking" the current flowing, through
the primary wiading of an ioduction coil {which
see). Several forms of contact breaks are in use, the
most popular, being the hammer, electrolytic, and
motorr-mercury breaks. The first-named con-
sists of a metal spring, carrying a soft iron head
and pressing agaiust a platinum point which
completes the circuit when no current is passing
through the coil; hut when ths current is
switched on the soft iron core becomes a magnet,
attracts the block of soft iron, and draws the
metal spring from the platinimi poiiit,, thus
" breaking " contact. The metal spring, or
" hammer " rapidly vibrates, " making " and
" breaking " contact while the coil is working.
In the electrolytic break, the current is com-
pleted by a platinum point projecting from a
porcelain cylmder immersed in an electrolyte.
When the current is turned on, electrolytic
bubbles immediately form round the metal point
and break the circuit ; the bubbles disperse, and
the contact of the platinum with the water again
completes the circuit The rapidity with which,
the bubbles form and disperse makes the electro-
lytic break a highly eB^ient one. The motor-
mercury break consists of a jet of mercury
rapidly revolving in a sealed chamber with two
or more strips of metal fixed in the sides. When
the jet strikes a metal strip the current flows
through the coil ; when the metal is passed the
contact is broken.
Contact breaks make and break the flAw of
electricity through the coU from a few hundred
to several thousand times a minute. In X-ray
work an efficient contact break is of the highest
importance.
CONTACT, OPTICAL (Pr., Contact optique ;
Ger., Optische Beriihrung)
When two substances are cemented so closely,
together that there is no air space between, and
the four surfaces have apparently been reduced
to two, they are said to be in optical contact.
A typical example is a pair of lenses cemeiited
with Canada bisam ; while the silver coating
on a mirror afiords another, instance. To mount
prints in optical contact is to cause them to
adhere to suitable glasses, usually bevelled, by
means of a warm solution of gelatine. Prints
mounted in this way are often known as opalines,
presumably because they sometimes have a
margin of white paper, winch, when seen through
the glass, resembles opal. {Seet also " Op^toes.")
CONTACT PRINTING AND CONTACT
PROCESSES
All printing papers and lantern slides may be
printed by contact, the term indicating the
placing of the sensitive surface of the paper or
plate to be printed upon in contact with the
film side of. the ne^tive. The alternative
method is that of printing by enlarging or
reduction thxougk a lantern or camera.
CONTINUING ACTION OF LIGHT
This action occurs only in the carbon and'
kindred processes of photographic printing;
that is, in those that depend on the fact ffiat
gelatine and other colloid substances become
insoluble when impregnated with an alkaline
bichromate and exposed to light. The process
of rendering insoluble, once begun by exposure
Contrast
140
Control in Printing
to light, continues after the print is taken from
the frame, even if stored in a perfectly dark
place, so that a partially exposed print may be
completed by this continuing action. It is,
however, very slow and uncertain. It depends
on the presence of dampness in the air ; and,
consequently, it is much more rapid in wet
weather than in dry. This continuing action
may be entirely prevented by storing tiie print
in an absolutety iy receptacle, such as a calcium
storage tube used for tiie platinotype process.
When prints can be developed within a few hours
from tile time that they are taken from the
frames, the keeping of them under moderate
pressure between dry blotting-paper is sufficient
to prevent any appreciable increase in depth.
CONTRAST
The range of tones in a negative or print,
from the highest light to the deepest shadow.
A print is said to be fiat or lacking in contrast
when the highest light is a pale grey, the deepest
shadow a medium grey only, and the gradation
between the various tones is very slight. A
print possesses good contrast when the highest
light is either pure white or a very pale tone,
the deepest shadow a rich black, and well-marked
gradations separate the various details and tones.
In nature the range of contrast may be from
one to several hundreds ; in a print on matt-
paper the range from pure white to deep black
is about one to twenty-five. In a highly glazed
print the range may extend from one to fifty.
CONTRAST, EXCESSIVE
This may exist in a negative or print when
the scale of tones is too long for the sensitised
film to record satisfactorily. The darker tones
wUl be a mass of black, since the deepest have
gone beyond the deepest tone of the paper, while
the lighter tones will be a mass of plain white
without detaU. A familiar example is the blank
white sky that is frequently seen in a print when
the sky portion of the negative is over-dense.
Reduction is the proper treatment for an over-
dense negative. {See other headings, in par-
ticular " Bennett's Reducer.")
CONTRETYPE NEGATIVE
A negative produced by sensitising a gelatine
plate with potassium bichromate, drying, expos-
ing under an ordinary negative, and soaking
in water containing Indian ink or any coloured
dye. The colour is absorbed by those parts of
the gelatine not afiected by light; and in this
way, after fixation, is obt^ed a duplicate of
the original negative, but reversed.
CONTROL IN PRINTING
Methods of treating negatives, or methods of
treatment adopted while printing, may be
summarised under the above heading. The
object in all cases is the same ; namely, to pro-
duce a better, a more harmonious, or a more
satisfactory print than that which the negative
would give if the ordinary course were pursued.
It is quite incorrect to assume that it is only
inferior or imperfect negatives that require
such assistance. The more critical the worker
becomes with regard to his results, the more
will he adopt methods of control. In a large
proportion of subjects, the lighting or other
conditions may render the resultant negative
inharmonious — ^not necessarily harsh or imper-
fect technically, but inharmonious in the sense
of there being strong lights, or emphasis, in parts
where such strength is detrimental to the general
effect. It is control for securing true balance
of light and shade, and for obtaining the most
artistic result, that is the object of the treatment
described.
The most simple method of control consists in
shielding those parts of a negative which tend
to become too dark, while the remainder of the
print attains its full strength. In some cases
this may be a simple shielding of a small comer
or one end, while in others it may be necessary
to shield almost the entire plate while a sm^
part prints out fully. In printing by diffused
daylight, a piece of thin wood or c^d may be
supported at about -J in. or i in. above the sur-
face of the negative, and covering those parts
that attain their full depth too soon. The light
diffuses gradually under the edge of the shiud,
grading softiy from full action through the un-
shielded portions to practically no action at all
under the greater part of the shield. The manner
in which the change is effected, the sudden or
the gradual transition from fuU printing to no
action at all, will be determined by the distance
of the shield from the negative. Even if as
close as J in., no line or sudden mark will show.
In the case of a bright window in an interior
photograph, a hole may be cut in a sheet of card,
and the card supported above the negative so
that the hole is exactiy over the window, allow-
ing its details to print out fully while the other
parts are restrained. The effects of slight hala-
tion may be entirely removed in this manner
without any work on the negative.
In printing by artificial light, the same results
may be obtained by]keeping the shields in motion
while they are in use. By that movement, the
risk of a sharp line showing is entirely obviated.
The greater the extent of the movement of the
shield, the softer the transition of its effect.
A second method, which is very useful in those
cases in which there is a well-marked line in
the subject at which the change in strength of
printing should be made, consists in covering
the glass side of the negative with very tViin
tracing paper or ground-glass varnish. The
paper or varnish is cut away from those parts
that print too slowly. The tradng paper to
employ is that sold by artists' colourmen under
the name of papier vigital, or vegetable tracing
paper. It is very thin and translucent. It
should be slightiy damped and attached to the
glass at the margins by a httie gum. When dry,
parts may be cut away as desired, the edges of
the cut parts being sectired by a touch of gum.
Matt varnish is finer in character, but more
difficult to apply. The degree of restraint pos-
sible may be increased by using a yellow-tinted
varnish. The extent to which parts of a negative
are held back in printing by this method is not
great, but still sufficient for all ordinary nega-
tives. A negative that has been prepared in
this manner can be printed quite sttccessfully by
artificial light by the simple expedient of xeeping
the frame moving slightly during the exposure.
In diffused dayli^t, no movement of the frame
Convention, The Photographic i4>
Copper
is necessary, the thickness of the glass plate being
sufficient to diffuse the light and prevent hard
lines showing at the edges.
A third method of controlling results consists
in cutting out a mask that will fit exactly those
parts which require holding back. The most
satisfactory way of making the mask is to take
a silver print from the negative, and, having
cut out the parts that print too quickly, to fix
them to a piece of plain glass the same size as
the negative. They should be put on in such a
manner that when the glass is laid exactly over
the negative the cut pieces wiU be in the pre-
cise position necessary. The printing is com-
menced in the usual manner, and as soon as
the parts that correspond with the mask are
sufficiently dark, the glass that bears the cut-out
pieces is placed in position, care being taken that
the comers coincide with the comers of the nega-
tive, thus ensuring that the mask is exactly in
position. Although it involves more trouble
in printing than does the use of tracing paper
or matt varnish, this method possesses the
advantage of allowing any degree of restraint
to be exercised.
CONVENTION, THE PHOTOGRAPHIC
The Photographic Convention of the United
Kingdom was founded in the summer of 1886.
Its object was to afford facilities to photo-
graphers, professional and amateur, for an
annual gatiering at some suitable town pre-
viously agreed upon, for the purpose of hearing
and discussing papers of photographic interest,
of holding exhibitions, social outings, etc. The
founders were the late J. Traill Taylor and
J. J. Briginshaw.
Conventions carried out on this model, but on
a much larger scale, have long been popular
amongst photographers in the United States.
CONVERGENT DISTORTION {See "Distor-
tion.")
CONVERGING LENS
A positive lens, or one capable of bringing
rays to a focus ; a convex lens. In practice aU
convergent lenses are convex, or thidker at the
-centre than at the edges.
CONVERTIBLE LENSES
The single components of a doublet lens cap-
able of being used alone or in combination with
other lenses, as in the casket lenses {which see).
CONVEX LENS
A lens that is raised in the middle ; the oppo-
site to concave. The "convexo-convex" has
^
A. Convexo-
convex Lens
B, Convexo-
concave Lens
C. Convexo-
plane Lens
(identical with the " concavo - convex " and
"meniscus"); and the " convexo-plane," one
convex and one plane surface, as at C. Th«
"biconvex" lens is the convexo-convex.
COOLING CHAMBER (Pr., Chambre rifrigir-
ante ; Ger., Kiihlzimmer)
An arrangement employed in dry-plate manu-
factories for cooling the emulsion on the plates
and causing it to set as quickly as possible. It
may consist of a tunnd-shaped compartment
about 15 ft. long, open only at each end, and
furnished with an ice tank at the top, while
below is a cold slab resting on a metal tray
filled with ice water. The plates on coming
from the coating machine are received on an
endless travelling band of woven wire, by
which they are carried along the cold slab and
through the cooling chamber, emerging with the
emulsion sufficiently set to allow them to be
removed.
COOPER-HEWITT LAMP (See "Mercury
Vapour Lamp.")
COOPER'S PROCESS
A plain, salted paper printing process now
practically obsolete. The paper was sized
with an alcohoUc solution of resin, the silver
sensitising solution being afterwards applied.
More simple sizing solutions are now used, as
described under the heading, " Plain Paper
Printing."
COPAL VARNISH (Pr., Vernis copal ; Ger.,
Kopalfirnis)
Gum copal is a natural product, which is
described under the heading " Gums and
Resins." Copal varnish is sometimes employed
for photographic purposes, a good formula
being : —
Copal .
Oil of turpentine
Linseed oil
2 oz. no g.
7i „ 375 CCS.
S ,, 250 „
two convex surfaces, as at A ; the " convexo-
concave," one surface of each kind, as at B
But as such a varnish cannot properly be
made by the cold process, and as the heating
of oil and turpentine is attended by grave risk
of fire, it is better to buy the varnish ready
made, advice which applies to all oil varnishes.
COPPER (Pr., Cuivre; Ger., Kupfer)
Copper has become a most important and
almost universally used metal for photo-engrav-
ing. It began to supersede zinc, which was
formerly used, as soon as the fish-glue enamel
process came into vogue, it having been found
that zinc deteriorated in the " buming-in " pro-
cess to which the enamel was subjected. The
copper used is mainly of American origin, and
this kind is considered the best for the purpose ;
a considerable amount also comes from the Con-
tinent, but this is generally harder, more brittle,
and more difficult to etch. The copper comes
on to the market in well-rolled and finely-
pohshed sheets of eitier 16 or 18 B.W. gauge
(•065 in. or -049 in. ; the higher the gauge
number the thinner the metal). Copper is
invariably etched with ferric chloride solution
of a strength of 35° to 40° Beaum6 (sp. g. up
to 1-36).
Copper Acetate
'43 Copper, Intensification with
COPPER ACETATE (Fr., AcState de euivre ;
Ger., Kupferaceteti)
Synonyms, copper subacetate, verdigris.
CntCaHjOj), HjO. Molecular weight, 199-5.
Solubilities, i in 14 water, soluble in alcohol. It
should be kept well stoppered. It is a poison,
the antidotes being emetics and the use of a
stomach pump, then white of egg, charcoal, iron
filings, magnesia, or pure potassium f errocyanide ;
avoid milk and fatty acids. It takes the form
of bluish-green crystals, obtained by dissolving
copper carbonate in acetic acid. It is used as a
colour screen in sensitometry. (See " Colour
Sensitometry." )
COFPER AND AMMONIUM SULPHATE
(Pr., Ammomio'Sulfate de cmvre ; Ger.,
Kupjerammoniumsuljat')
Synonyms, ammonio-cupric sulphate, ammo-
nio-sulphate of copper. CuSO^ 4NH, H,0.
Molecular weight, 245-5. Soluble in water.
It is a poison ; for the antidotes, see under
the heading " Copper Acetate." It is in
the form of a dark-blue crystalline powder,
and is obtained by dissolving copper sulphate
in a solution of ammonia and precipitating "by
alcohol. It is used as a light filter in sensito-
metry, and is then prepared in solution as
follows : —
Copper sulphate . .175 grs. 20 g.
Distilled water . . 15 oz. 750 ccs.
Dissolve, and add enough liquor ammoniee (-880)
to redissolve the precipitate first formed and
give a deep blue clear solution. Filter, and
add—
Distilled water to . .20 oz. 1,000 ccs.
COPPER BROMIDE (Pr., Bromure de euivre ;
Ger., Kupferbromid)
Synonym, cupric bromide. CuBr,. Molecular
weight, 223-5. Solubilities, very soluble in water,
less so in alcohol. It occurs as a greyish black
crystalline powder, but it is most easily made by
double decomposition, as follows : —
A. Copper sulphate . 250 grs. 29 g.
Hot water . . 10 oz. 500 ccs.
B. Potassium bromide. 238 grs 27-6 g.
Distilled water . 10 oz. 500 ccs.
Mix the solutions and allow to cool. It has been
suggested for use in the intensification of nega-
tives and for bleaching bromide prints for subse-
quent sulphide toning.
In process work, the copper bromide intensifier
is employed for intensifjring half-tone negatives,
chiefly for the reason that it is more amenable to
the " cutting " or reduction which every nega-
tive has to undergo in order to sharpen up Qie
dots.
The following is the formula generally em-
ployed for making up the copper bromide
solution : —
No. 1—
A. Potassium bromide
Water .
B. Copper sulphate .
Water .
500 grs. 52 g.
10 oz. 500 ccs.
500 grs. 52 g.
10 oz. 500 ccs.
The negative is bleached in this solution, rinsed
well, and placed until blackened in solution
No. 2 —
Silver nitrate . . i oz. 55 g-
Nitric acid . . 40 mins. 4 ccs.
Distilled water to . 20 oz. 1,000 „
GTeater density is given by flowing over a solu-
tion of either ammonium or sodium sulphide.
The copper bromide intensifier is usually em-
ployed in conjunction with the cutting or -reduc-
ing solutions of iodine and cyanide.
COPPER CHLORIDE (Fr., Chlorure de euivre;
Ger., Kupferchlorid)
Synonyms, cupric chloride, copper bi- or di-
chloride. CuCl, 2H,0. Molecular weight, 170-5.
Solubilities, i in -83 water, very soluble in alcohol
and ether. It is deliquescent, and must be kept
in well-stoppered bottles. It is a poison ; for
antidotes, see " Copper Acetate." It takes the
form of a greenish crystalline mass, obtained by
dissolving copper carbonate in hydrochloric
acid, or in a similar manner to the bromide,
using 117 grs. of common salt in B solution.
It is occasionally used as a reducer, SpiUer's for-
mula being: — (i) Alum, 2 oz. ; copper sulphate,
2 oz. ; salt, 4 oz. ; and water, 20 oz. (2) Saturated
solution of common salt. Mix equal parts of i
and 2, immerse negative, and wash.
Also, it has been suggested as an addition to
printing out emulsions to increase contrast, and
was used in Obemetter's process [which see).
COPPER. INTENSIFICATION WITH
A process for intensifying gelatine negatives.
A solution of bromo-iodide of copper is prepared
as follows : —
Copper sulphate
Water
100 grs. 76 g.
3 oz. 1,000 ccs.
Dissolve A and B separately and mix together,
allowing to stand twelve hours before using.
When dissolved, add with constant stirring the
following, which must also be dissolved : —
Potassium iodide . 8 grs. i8-2 g.
Potassium bromide . 20 „ 45-6 „
Water . . . i oz. 1,000 ccs.
A slight precipitate of iodide of copper of a
deep yeUow colour forms ; this is allowed to
settie and the clear part poured off for use. The
fixed and washed negative is placed in the above
until bleached and of a canary-yellow colour,
from five to fifteen minutes being usually
required. The solution may be used repeatedly
if strengthened occasionally with a few drops Of
a mixture made by dissolving 12 grs. of iodide
and 36 grs. of bromide in 2^ oz. of water. After
bleaching, the negative is washed well, and dark-
ened by placing in a strong solution of sodium
sulphite to which a few grains of silver nitrate
are added. Good results may also be obtained
by darkening with a hydroquinone developer.
The colour of the resulting negative is strongly
affected by the solution used for darkening
after bleaching. The above usually gives a
reddish deposit which is very non-actinic ;
rodinal a brown image, and the sulphite-silver a
darker one. Variations in colour when hydro-
quinone is used may also be obtained by altering
the proportions of sulphite and hydroquinone
C^per Ferricyamide
143
Copperas
Soth the blBactdag and, the darkening must be
done in dajiUghit ; &e -stronger the light the better
and quicker the results. After darkening, the
intensified negative is well washed in water and
finally dried. The process may also be used for
slides and bromide paper. When ijsed for prints,
the paper turns blue when bleaching, owing to
the formation of iodide of starch, but the colour
disappears when the hydroquinone is applied,
and the colour of the print is usually a good
brown.
COPPER AND POTASSIUM FERRI-
CYANIDE (Fr., Ferricyanure de cuivre ei
de potassium ; Ger., Kupfer-Bluilaugensalz)
KCuPe(CN),. Molecular weight, 334'5-
Soluble in water. It is poisonous ; for antidotes,
see "'Copper Acetate." This salt is always
prepared in solution by double decomposition,
generally in the presence of an alkaline citrate.
It is used for toning bromide prints and trans-
parencies {see "Copper Toning"), and is then
Teduced to tiie double ferrocyanide, KjCuPe
(CN), (a brownish-»red powder insoluble in
water), by the metallic silver ; white silver ferro-
cyanide is also formed.
COPPER PRINTING PROCESS
A priniting process introduced by Obemetter,
based on Hat fact that copper forms with, chlorine
a green salt (copper chloride) soluble in water.
Tins salt is sensitive to light, which reduces it to
hypochlonide of copper. Paper is saturated
with a mixture of copper chloride and iron
chloride, and when dry is exposed to light under
a negative. Afterwards it is immersed in a
solution of jiotassium sulphocyanide, and ulti-
mately treated with red prussiate of potash, a
brown picture being tiie result.
COPPER REDUCER FOR BROMIDES
A process of locally reducing over-dense
bromide prints, introduced by Fourtier in 1905.
A 5 per cent, solution of copper sulphate is mixed
with enough solution of potassium carbonate
until no further precipitate is formed. The pre-
cipitate is collected on a filter paper and wa^ed
with several changes of water, and then dissolved
in water to whidh a few drops of hydrochloric
acid have been added. To tins clear solution a
strong soluticm of ammonia is added until
the precipitate first formed is re-dissolved, the
resulting rich-blue liquid being a solution of
ammonio-chloride of copper. The actual re-
ducer is : —
Copper solution (as
above)
i oz.
25 CCB.
" Hypo " solution (S %) .
i ,,
25 .,
Water
20 „
1,000 „
The prints should be well soaked in water,
laid face upwards on a sheet of glass or the
bottom of a dean porcelain dish, and the reducer
applied with a tuft of eotton-wool. The action
of the reducer is stopped by washing the print
in water, and the reducer made to work more or
less rapidly by varying the quantity of water.
The above is really a roundabout method of
making copper diloride, and the same purpose
is served by mixing solutions of copper sulphate
and common salt.
COPPER SULPHATE (Pr., Sulfate de cuivre ;
Ger., Kupfersulfat)
Synonyms, cupric sulphate, blue vitriol.
CuSO« sHjO. Molecular weight, i249-5. Solu-
bilities, I in 2-5 water, i in 400 alcohol. It is
efflorescent, and should be kept well stoppered.
It is a poison ; for antidotes, see " Copper
Acetate." I/arge deep blue crystals, obtained by
dissolving copper carbonate in sulphuric acid.
It was occasionally used in the developer for
wet collodion, and is now used chiefly for making
the bromide, chloride, and ferricyanide salts.
It forms a rich blue solution with excess of liquor
ammoniae, and is a useful filter for col6ur sensito-
metry and three-colour work.
In process work, copper sulphate is used as
an addition to the wet-plate developer. Its
action is said to be merely that of retarding the
oxidation of the ferrous sulphate. Copper sul-
phate is also employed by process workers in
the copper bromide intensifier. In electro typing
it is the salt used with sulphuric acid to form the
depositing solution.
COPPER TONING
A process for toning bromide prints, originally
introduced by Eder and Toth in 1876, and
modified by Namias and others. The following
method, introduced by W. B. Ferguson in 1900, is
the most satisfactory. The colours obtained
range from warm black, reddish sepia, brown,
purple brown, purple crimson, reddish purple,
through many shades of red to the so-called red
chalk, according to the quality of the print and
duration of toning. The Ferguson formula has
appeared in many forms, a popular one being : —
A. Copper sulphate . 60 grs. 6 g.
Potassium citrate 240 „ 24 ,,
Water to . .20 oz. 1,000 ccs.
B. Potassium ferri-
cyanide . . 50 grs. S g.
Potassium citrate 240 „ 24 „
Water to . .20 oz. 1,000 ccs.
Use equal parts of eadi and immerse the print
until tiie desired shade is obtained. The toning
is made more rapid by adding 5 grs. of citric
acid per ounce of toner. Used in its normal
state the bath produces the first tones very
rapidly, while the final colour (red) requires from
twenty to forty minutes, according to the quality
of the print. Washing for ten minutes only is
necessary to stop the action of the toner at any
desired stage. The colours are produced by
the fommtion of copper and silver ferrocyanides.
The following copper bath has also been
recommended for ridi red tones : —
Ammonium carbonate
(saturated solution)
Copper sulphate
Potassium ferricyanide
ro grs.
25 .,
1,000 ccs.
2 g-
5 ,.
Owing to the alkaline condition of this bath it
produces red tones more quickly than does
the Ferguson formula.
COPPERAS
A common name for various sulphates. Thus,
copper sulphate = blue copperas ; iron sulphate
= green copperas; zinc sulphate = wiiite
copperas.
Coppering Solution
144
Copying Illustrations
COPPERING SOLUTION
A superficial coating of copper may be applied
to etched zinc plates by neutralising copper
sulphate with a strong alkali, such as ammonia
or cyanide. Previously, the plate is well washed
and scrubbed with caustic potash and whiting,
and is then immersed in the solution for a few
minutes, when it will be found coated with a
sufficient covering of copper.
COPYING
Copying should present no serious difficulty
provided suitable precautions are taken, and
correct exposures given. It is essential that
the print to be copied should be held perfectly
flat on a board which is parallel with the sensi-
tive plate. If this condition is not observed, a dis-
torted image will result. The arrangement shown
at A (p. 145) is simple, inexpensive, and answers
well for copying and also for other photographic
work. The direction of lighting is important.
A direct front light minimises the effect of the
grain of the paper, while a strong side light
accentuates it. On the other hand, a direct
front lighting cannot be adopted for glossy
surfaced prints on account of the reflections.
To avoid the sheen of the glossy surface,
lighting from one side, slightly in front, is
necessary.
For copying pictures under glass, the camera
front should be covered with a black cloth, and
a black or dark cloth should be hung up close
behind the camera to avoid reflections. A side
lighting is desirable for the same reason ; but
where the original is liable to show a grain, the
lighting should be from two sides. (For copying
oil paintings or water-colour drawings, see
" Paintings, Photographing.")
For copying an ordinary silver print, or any
strong photographic print with a glossy svirface,
a rapid plate will give the most truthful rendering
of the gradation. If the print is faded or yellow
an isochromatic plate should be used. For
copying a line engraving or drawing, or a wash
drawing, or a photographic print with very little
contrast on matt-surfaced paper, a slow plate
specially made for copying, such as a " process "
plate or a. fine grain ordinary plate, will give
the most satisfactory negative. In aU cases the
plates should be backed. Correct exposure is
most important, and the best method of deter-
mining this is by using a meter, which should be
placed flat against the picture that is being
copied and the time that is required for matching
the standard tint noted. Using a plate of which
the speed is 200 H. & D., the exposure for copying
a glossy silver print the full size of the original,
and using the aperture marked //16 on the
diaphragm scale, will be from one-fourth to one-
half the meter tint if a Wynne meter is used,
and from one-eighth to one-fourth with a Watkins
meter. A dark or red-toned photograph will
require longer exposure than a light or cold-
toned print. For copying a line drawing, one-
half the meter tint for a W3rune meter, and one-
fourth for a Watkins will be the correct exposure
for a slow plate, 40 H. & D. For a black-and-
white drawing in wash, these exposures should
be doubled.
The above exposures are for making a copy the
same size as the original. For other proportions.
the following will be the relative exposures, the
lens apertnte being the same throughout : —
Times the
Enlarged to
)) j»
Copying same
Reduced to
scale of the
original
2
I
f
i
i
i
Relative
exposure
I
A
IT
In process work, the art of copying has been
brought to great perfection for photo-mechanical
processes, where the reproduction has generally
to be made from a print or drawing. The essen-
tials that are carefully studied are : The light-
ing of the subject ; the parallelism of the origmal
to the sensitive surface ; the sharpness in defini-
tion of the image ; and the opacity and clearness
of the respective parts of the negative. The
first condition is generally secured by electric
arc illumination. The second is secured by the
use of stands on which are rails, the camera and
copyboard running on these rails to and from each
other ; also by rigid and accurate construction
of the camera. The third is secured by the
choice of suitable lenses such as are specially
made for process reproduction. The fourth is
secured by the adoption of suitable plates or
processes, the wet collodion process being gener-
ally considered the best for such work. Further,
it is very important to avoid vibration {see
"Copying Stand").
COPYING ILLUSTRATIONS FOR TRANS-
LATION INTO LINE DRAWINGS
A modification of the arrangement that is
illustrated and described under the heading
" Camera, Vertical " may be used for project-
Arrangement for Projecting lUusfrations for
Translation into Line Drawings
ing book or newspaper illustrations, when
such illustrations are taken from photographs
and have to be translated into line. The
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Copying Stand
I4S
Copying Stand
glass platform a {see the illustration to the
present artide) is covered with a drawing-board,
and upon this is placed the paper, etc., upon
which the sketch is to be made. A trans-
parency made from the illustration to be copied
IS placed in the lantern b, and by means of a
sloping mirror c attached to the lantern lens
hood an image of the illustration ia projected
upon A, where it can be drawn on the paper
provided.
COPYING STAND (Pr., Pied-table, Chevalet de
reproduction ; Ger., Reproduciren-Stativ ,
Kopier-Stativ)
An arrangement for keeping the camera and
copy parallel when reproducing plans, drawings,
photographic prints, etc. It usually consists of
an upright copyboard or easel running on
parallel rails, and capable of being clamped in
any position. The camera may also be mounted
to run on the rails, but is often stationary. Illus-
tration A shows an ordinary copying stand.
In process work, the copying stands used are
the products of considerable ingenuity, the
occasion for which was the necessity of avoiding
any want of sharpness through vibration. One
ation, tilting stands are sometimes employed
in order to get the best light possible on the
original.
A curious form of copying apparatus used for
A. Ordinziry Copying Stand
of the earliest and most usual methods for attain-
ing this object was to suspend the copying base
on ropes which depend from the ceiling ; but
the ropes get hardened by constant tension and
in time fail to neutralise the vibration. One
way of overcoming this drawback was to insert
spiral springs between the ends of the ropes and
the suspension hooks ; and another was to
suspend the base from a beam swinging like a
scale beam.
The above methods are now considered clumsy
and obsolete, and the usual form of apparatus
now employed is the spring stand B. The base
is swung on spiral springs F attached to a rigid,
stand. Where no vibration is anticipated, rails
may be laid on the floor and the camera and
copyboard placed on separate stands, with
wheels running directly on the rails, or the copy-
board may be fixed to the wall whilst the camera
is on a running carriage. This system is largely
used in Government offices for map reproduction.
Another plan often employed for large work
is to have rails laid both inside and outside the
dark-room, the copyboard being on ,a carriage
outside, and a plate-holder being mounted on a
carriage inside, whilst the lens is fixed in an
opening made in the wall of the dark-room;
in this way the dark-room itself becomes the
camera. Where daylight is used for illumin-
10
B. Spring Copying Stand
copying large paintings in the open air is the
revolving camera stand, which can be turned
according to the direction of the sun's rays.
The vertical copying stand C is often used for
copying from books, or from small natural objects
which can be best arranged on a horizontal
board. I/evy's copying stand D and E combines
not only the vertical, but also the tilting and
horizontal forms. With these vertical stands a
prism or mirror box must be used in conjunction
with the lens.
G. Vertical Copying Stand
For producing reversed negatives, which!
invariably have to be made for photo-mechanical
processes, the camera stands must be provided
with a turntable so as to place the camera side-
Copyright
146
Copyright
•ways to the copyboard, the image being then
Teflected by mirror or prism, as shown in the
vertical stand C. On the Continent, cop3?ing
stands have been made for such reversal work
with the copyboard and the camera carriage both
placed across the stand at an angle of 45 degrees,
but, of course, still parallel to one another and
■provided with reversing prism as before. In
this way some floor space is saved with large
cameras.
For copying transparencies a " transparency
attachment " is usually connected up to the
camera and stand ; it is a simple light-tight
conical bellows with provision for inserting the
transparency. Rotary copyboards and rotary
transparency holders are often employed in
copjring, especially in colour work, to place the
negative at different angles from the vertical or
the term " colourable imitation." In other
words, a copy need not be an exact copy. It is
sufficient to be able to show in the case of the
infringement of a copyright that the original
photograph has been copied by a mechanical
or hand method.
The period of protection granted by the Act
is for the term of the natural life of the author
and seven years after his death. It has no
relation to the life of the owner of the copyright
except in the case where he is also the author.
Usually, there is no room for doubt as to who
is actually the author, but in the case of a photo-
graphic firm, where the finished photograph
passes through a number of hands, it has been
held that the author is the person who effectively
is as near as he can be the cause of the picture
which is produced — that is, the person who
D and E. Combination Copying Stand
horizontal line. For correcting distortion a
transparency holder with universal movement
may be employed.
COPYRIGHT (Fr., Droit d'auteur : Ger.,
Verlagsrecht, Urheberrecht)
Protection against copying and other forms
of reproduction is granted to photographs
equally with paintings and drawings. The Act
by which this protection is afforded is the Copy-
right Works of Art Act of 1862, the clauses of
which Act, taken in conjunction with the Judg-
ments of the courts during the years that have
intervened since then, cover the many incidents
which may arise in the creation of copyright, in
its assignment, and in the infringement of copy-
right works. The Act defines copyright as " the
sole and exclusive right of copying, engraving,
reproducing, and multiplying any photograph
and the negative thereof by any means and of
any size " — that is to say, the reproduction of a
photograph by another graphic method, such as
drawing or painting, may yet be an infringement
of the copyright. The Act in another place uses
superintended the arrangements by putting the
people into position. It has also been held that
an absentee principal cannot be the author, even
though, by the creation of system in his business,
he may be actually just as responsible for the
result as though he had been present.
The most important clause in the Copyright
Act is that which describes the conditions as to
payment when a photograph is taken, because
upon these conditions the ownership of the
copyright depends. The Act expressly states
that when the negative of any photograph is
made for or on behalf of any other person " for
a good and valuable consideration," the copy-
right belongs to the person for or on whose
behalf the work is done. Thus, in the case of
an ordinary sitter in a studio, the copyright is
his ; in the case of a landscape photographer
working for an employer, all copyrights in the
views taken are the employer's. The question
of what is " good and valuable consideration "
has involved some nice points of law. Articles
of value, or board and lodging, may be agreed
upon as " valuable consideration," and there
Copyright
147
Copjrright
is, in fact, one case in which the granting of
permission to photograph certain premises was
judged to be valuable consideration " to the
photographer because it gave him the oppor-
tunity to sell numerous copies of the photographs
Jie had taken.
It should be noted that the Act does not say
■on payment of the consideration, and, so far as
the ownership of copyright is concerned, non-
payment to the photographer by his customer,
or employer, does not give the first-named any
rights in the photographs ; the copyright remains
with the customer or employer, whilst the photo-
grapher must sue in the usual course for payment
or wages. In cases of doubt as to the owner-
ship of a copyright this forms a useful test. If
one is in a position to sue for payment one
cannot then have any ownership in the copy-
light.
The portrait photographer should also note
that in the case of negatives taken at the same
■time as others at the sitting, but not ordered
Tjy the customer, the copyright is neverthe-
less the property of the customer. In cases
where this point has arisen it has been held that
payment was for the labour of the artist as a
whole, and, therefore, covered all the exposures
made at the sitting. Any use made of such
extra negatives will thus be an infringement of
the sitter's rights.
Again, when, as sometimes happens, the por-
trait of a person is taken by the order and at
the expense of a second person, the copyright
naturally becomes the property of the person
paying, or suable for payment. And, in the
absence of any agreement that the photo-
grapher should make some negatives for himself
at such a sitting, the whole of the portraits
taken are the property of the person ordering
the work.
Though the Copyright Act does not say any-
•thing about the ownership of the negative, it is
perfectly dear on one point — ^namely, that the
sale or disposal of the negative by the owner of
the copyright to another person without the
formal assignment of the copyright in writing to
■either buyer or seller causes tiie copyright to be
destroyed. This fact should be borne in mind
when purchasing negatives or acquiring them
.along with the purchase of a business. It is
necessary to draw up an itemised list of the
subjects, sufficient for separate identification,
and to have the whole document signed by the
vendor transferring the copyright to the pur-
■chaser, or by the purchaser reserving the copy-
right to the vendor, according as the copyrights
are, or are not, to change hands.
Before referring to the assignment and regis-
'tration of copyright, one minor clause of the Act
must be noted — namely, that which enacts
that any person may copy any work in which
there is no copyright, and may represent any
scene or object, notwithstanding that there
may be copyright in other representations of
such scene or object. This clause has a very
practical application in the reproduction of the
works of Old Masters, in which, of course, there
is no copyright, but any number of photographers
may make copies of such works and severally
acquire rights in their copies, even though these
latter are practically identical. Similarly, there
is nothing to prevent several photographers from
photographing a landscape from a particular
point of view ; even though the negatives are
almost identical, copyright may be obtained by
each separate author.
Assignment of the copyright in a photograph
may be whole or partial. The sole rights to
reproduce in any form or place whatever may
be sold with, or without, the negative, though
there can be no object in the photographer retain-
ing the negative, since his rights to make a
single print from it have been disposed of. It
is more usual, however, to assign specifically
limited rights to reproduce, such as in a given
issue of a journal or newspaper, as a calendar
or window-bill, as a postcard, or as an advertise-
ment for a particular class of goods. The nature
of the assignment being clearly defined, the
photographer is left free to dispose of other
limited assignments in other ways, but a form
of assignment loosely worded (for instance, the
following : " Received of A. B. los. 6d. for the
right to reproduce my photograph of Trafalgar
Square. — C. D.") might be taken to mean the
sole rights of reproduction. An assignment or
licence to reproduce should clearly state the
particular purpose for which the photograph is
to be used. In the case of reproduction in news-
papers, it is usually understood that the photo-
grapher's name should be acknowledged imder
the photograph, or on the same page, and that
no use be made of the photograph without extra
payment in extra issues of the paper, or any
other publication of the same proprietorship.
Although anyone purchasing the sole copy-
right in a photograph or other work is thereby
at liberty to reproduce it in any form, the Act
forbids the alteration of such photograph, or
the reproduction thereof in an altered form,
during the life of the author and without his
consent — that is to say, that such altered version
must not be represented as the unmodified work
of the originator.
The registration of a copyright is important
to those who have business in seUing rights of
reproduction, inasmuch as the Act provides that
" no proprietor of any such copyright shall be
entitled to the benefit of the Act until such
registration, and no action shall be sustainable,
nor any penalty recoverable, in respect of any-
thing done before registration." In other words,
registration is a formal claim to rights in the
photograph. It is made at Stationers' Hall, on
forms provided for the purpose. On this form
five columns are provided, but it is only neces-
sary, when registering a copyright, to make
entries in Nos. i, 4, and 5 ; Nos. 2 and 3 are
required only when a copyright is assigned by
one person to another. In column i a Short
description identifying the photograph is given,
in No. 4 the name and address of the proprietor
of the copyright, and in No. 5 the name and
address of the author. The author, as already
pointed out, may or may not be the same person
as the proprietor. This form, filled up on these
lines, is deposited at Stationers' Hall, together
with a copy of the photograph, the fee for
registration being one shilling. The precise form
of the photograph is immaterial ; a straight print
from the negative suffices to protect the photo-
grapher's rights regarding the issue of enlarge-
Copyright
148
Corona Photography
ments or even of worked-up reproductions in
colour by hand or by three-colour printing. It
is simply necessary that the photograph regis-
tered should plainly identify the original work
of the author.
Infringement of copjrright may take a number
of forms. The Act specifically forbids any person
to " repeat, copy, colourably imitate, or other-
wise miUtiply for sale, hire, or distribution,"
or to cause or procure these acts to be done.
The phrase " colourably imitate " protects the
photographer against piracy of his work by
draughtsmen or artists, who might use the
photograph as a basis for drawings ; it is not
necessary, to prove infringement, that the illegal
copy should be identical with the original from
which it was made.
The Act distinguishes between two classes of
infringer : (i) those who in knowledge or ignor-
ance commit one of the acts mentioned above,
and (2) those who, with knowledge of the
unlawful character of the copies, import or
distribute the latter in the United Kingdom.
The copyist, or person who employs a copyist,
is regarded as liable whether he act in knowledge
or ignorance of the copyright, whereas an
importer is liable only when he acts with know-
ledge of the unlawful nature of the copies. It
will thus be seen that a photographic enlarger,
who prepares an enlargement of a photograph
sent to him, is equally liable with the person
who gave him the order, and this even though
both may be in ignorance of the existence of
any copyright. Under the Copyright Act there
is no need that a photograph which has been
registered at Stationers' Hall should be marked
" copyright," but it is a natural assumption that
any recent photograph is copyright, even though
formal claim (registration) has not been made.
The remedies for unlawful copying granted
by the Act are of two kinds : (a) penalties and
(6) damages. As already stated, no penalty
can be recovered for any such infringement
committed before the copyright has been regis-
tered, but damages may be obtained in the case
of copies which are made before registration and
sold afterwards. The maximum penalty which
can be obtained under the Act is £10 for each
unlawful copy, together with the forfeiture by
the infringing party to the proprietor of the
copyright of sil such copies. Formerly, this
provision of the Act was interpreted to mean a
payment of a coin of the realm for each unlawful
copy, and on this basis large sums were form-
erly obtained in the case of unlawful reproduction
in a newspaper of large edition. But a later
judgment of the Court of Appeal has held that
it is not necessary to fix the total penalty at a
sum which, when divided by the number of
copies, works out to a coin of the realm. When
taking action for penalties it is only necessary
to prove the infringement. The photographer
must show that the copyright is his property by
virtue of the fact that he took the photograph
without payment in the original instance, or
that it was assigned to him in writing at the
time of taking, or that he had subsequently
purchased it. In action for recovery of damages
he must prove not only his ownership of the
copyright, but the damage sustained by the
infringement.
Where a registered photograph has been
reproduced without permission, it is an easy
matter to obtain satisfaction from the offending
party, but when the photograph has not been
registered the owner of the copyright needs to
proceed with some care. He should first register
the photograph immediately, and he is then in
a position to take such action against the parties
stiU producing, or those selling, the copies as
will induce the infringer to settle the matter
privately. Very frequently the infringement is
the resiUt of ignorance or carelessness, and it is
usually good practice to assume that it is so,
and to write pointing out the infringement and
to ask what the party in question is prepared
to do. In this letter it is not wise to name any
specific sum which would be acceptable to the
photographer. Where the infringement is
clearly unintentional, many photographers are
prepared to accept twice (or even the same) the fee
payable had application for the use of the photo-
graph been made by the pubUsher.
Copyright, created and registered in England,
is secured ipso facto in the other countries sub-
scribing to the Berne Convention of International
Copyright. These countries are as follow :
Algiers, Belgium, Denmark and the Faroe
Islands, Prance and its colonies, German
Empire, Hayti, Italy, Japan, I/iberia, Luxem-
burg, Monaco, Norway, Spain, Switzerland,
Tunis. Under this Convention the photo-
grapher in each country must comply with the
formalities of his country (the country of origin),
and he obtains in the other countries the degree
of protection which is granted to natives in
these countries. The degree of protection varies
within wide limits among civilised countries.
In France, for example, protection is granted
only to such photographs which are adjudicated
to be works of art, and it would appear that
judgment in this respect must be given in regard
to each particular photograph, apart from the
reputation of the photographer as an artist.
In some countries — Germany and Belgium, for
example — ^it is not necessary to register, and
therefore it is difficult to discover whether the
formalities in the country of origin have been
compUed with in these cases. In Great Britain
— and, indeed, whenever there is any doubt
- — the safest course is to assume that copy-
right exists in any photograph, painting, or
drawing. G. E. B.
CORALLIN (Fr., Coralline ; Ger., Corallin)
Synonyms, pseonine, aurin. A mixture of
several complex aniline dyes, which is interest-
ing as being the first dye used to colour-sensitise
collodion films. It is not used now, having aa
extremely weak action on gelatine plates.
CORONA PHOTOGRAPHY
The corona is the brilliant pearly-white lumin-
escence observed roimd the eclipsed sun during
a total solar eclipse, when the ordinary brilliant
simlight is obscured by the intervention of the
dark moon. Many attempts have been made by
astronomers to observe it visually or to photo-
graph it in ordinary sunlight, but all these have
hitherto been unsuccessful, and it is only during
an ecUpse that it can be examined. There is no
limit, either of size or quality, to the apparatus'
Corona Photography
149
Cosmical Photography
which can be usefully employed to photograph
this wonderful solar appendage, and as indicat-
ing what are perhaps extremes, excellent pic-
tures of the coronal streamers have been made
with ordinary camera lenses of about 5 in. focal
length, and also with large mirror telescopes of
more than 70 ft. focal length. Each variety,
however, has its special advantages, and the
general apparatus may be divided into two divi-
sions according to the scale on which the pic-
tures are primarily photographed. With the
smaU scale cameras, lenses of very great angular
aperture can be employed, with all the advan-
tages of extensive flat field and light intensity.
These will be most useful for recording the
extreme limits of the coronal streamers or rays,
which are found to be very different from eclipse
to eclipse, so that as complete a record as pos-
sible is desirable.
With the large scale apparatus the programme
is best confined to obtaining detailed pictures of
the brighter regions of the corona near to the
sun's disk, and as the light gradations in this
region are very great, it is generally found neces-
sary to take exposures of different lengths for
the different zones, and develop accordingly,
so that the intense portions are not rendered
unprintable.
If possible, the most rapid panchromatic
plates should be employed for photographing the
corona, as the principal part of the corona
radiations is in the green near wave length 5,303.
The exposures possible will, of course, depend
on whether the observer has the use of an equa-
torial mounting and driving mechanism or not.
If he has not, probably half a second will be the
maximum exposure possible with a camera of
about 7 in. to 9 in. focal length. When the
more elaborate mounting is available, exposures
of from ten seconds to four or five minutes
are given so as to record the farthest outlying
streamers.
Very interesting series of experiments have
been tried at several eclipses. For comparison
purposes two exactly similar photographic
cameras have been used side by side, clamped
firmly together so as to move as one. In front
of one of these cameras, between the lens and the
corona, there has been placed a special piece of
apparatus for detecting polarised Hght, so that
if any of the light coming from the solar corona
is polarised in any particular direction, the dififer-
ence will be clearly shown on the photograph
by the presence of a series of bands as compared
with the image taken with the other camera
having the lens alone. By such means it has been
satisfactorily proved that a large proportion of
the light from the corona is polarised, and it is
thought that this may be owing to its being
light from the sun reflected from the minute
particles of which the corona is assumed to be
composed.
By obtaining comparable photographs with the
same instruments at intervals during a long
period of years it has been noticed that the form
of the corona decidedly changes ; and these
changes are found to be in accord with the
changes on the sun's surface as evidenced by
the presence or absence of the dark irregular
markings called sunspots. When these are very
numerous, showing the sun to be very active.
then the corona is found to be very extensive
in all directions round the sun, long streamers
passing off practically in all directions. When,
oil the contrary, the sun's activity is at a
minimum, and there are few sunspots, then
the coronal streamers are chiefly confined
to the regions on either side of the sun's
equator ; the regions near the sun's poles
are at these times occupied by very beau-
tiful plumes or aigrettes, which have all the
appearance of the stream lines shown by a series
of filings congregating about the poles of a
magnet. This fact has given considerable prob-
ability to the suggestion that the solar corona
is due to some electro-magnetic discharge from
the Sim's surface.
CORRECTED LENS
A lens having the chemical and visual foci
coincident. A properly achromatised lens is
said to be MMde»--corrected when, in spite of the
addition of a second glass, the blue rays still
come to a focus nearer the lens than the yellow,
and ot)«>'-corrected when the blue rays come to
a focus behind the yellow ones.
CORRECTION COLLAR
A rotating collar sometimes fitted to high-class
microscopic objectives. The varying thi(±uesses
of the cover glasses placed over microscopic
objects affect the value of the corrections of
high-power objectives. The correction collar
overcomes this difficulty by varying the separa-
tion of the combinations of the objective.
CORROSIVE SUBLIMATE (See "Mercuric
Chloride.")
COSMICAL PHOTOGRAPHY
So many different subjects requiring special
treatment are included in the general class of
celestial or cosmical objects that for the majority
of them it will be more satisfactory to describe
the methods of photographing them under their
respective special headings (which see below).
As regards the actual photographic details of
procedure, however, much that is common to
all celestial photography may most conveniently
be detailed here.
Apparatus. — ^This will vary from the hand
camera to the powerful and specially adapted
mechanical camera of the astronomer ; they will
all, however, have in common the feature of
being focused for parallel rays, or, as it is
usu^y termed, set for infinity. The reason
for this is that for all practical purposes all celes-
tial objects are so far distant from the earth
that any differences between their respective
distances are inappreciable. This fact wfll to
many constitute a considerable simplification,
as undoubtedly the use of a " fixed focus "
camera admits of apparatus being efiSciently
used in a condition which would be much too
rough for photographing objects whose distances
were different. In photographic language there
is no " depth of focus " difficulty in celestial
photography, and the flatter the field of defini-
tion given by the lens the more satisfactory will
its performance be. This leads at once to the
fact that for photographing large areas of sky
the modem anastigmat type of lens, giving
Cosmorama
150
Covering Power
critical defiaition over a large angle, is the
most efficient instrument.
In many cases the question of cost may serve
to prohibit the employment of a sufficiently
large lens camera — or refractor, as it is usually
termed — and work of the highest type of accuracy
has been done with concave mirror cameras.
These involve only the optical working of one sur-
face, and thus for a given sum the instrument
may be of a much greater power. Two kinds of
reiiector have been principally used : speculum
metal and silvered glass. The former were excel-
lent, but when they tarnished it was exceedingly
difficult to re-polish them without altering the
shape of the reflecting surface and thus destroy-
ing the definition of the image. Most of the
reflecting telescope cameras now in use consist
of a surface of glass accurately ground to a
parabolic form and then coated over with an
exceedingly thin film of pure silver. This offers
the important advantage that when it becomes
tarnished it can be dissolved away in a few
minutes and replaced very quickly with a new
film without in any way interfering with the
shape of the glass surface.
Plates. — For most kinds of celestial photo-
graphy, excepting that of the sun and moon,
it is advisable to employ the fastest plate obtain-
able, provided that the grain is not noticeably
prominent. On account of the subjects being
generally of special coloration, the isochromatic
or panchromatic plates now so easily obtainable
should be preferred to the non-colour sensitive
brands, as without them it may be found im-
possible to render differences which are quite
easily noticeable to the eye.
Development. — This will, in general, be
exactly the same process as would be used for
ordinary terrestrial photography. Again except-
ing photographs of the sun and moon, the
general tendency will be for under-exposure to
be experienced, so that the treatment recom-
mended for this should be the normal procedure
for astronomical work if harshness in the results
is to be avoided. Any of the standard developers
may be employed with practically equally good
result. Pyro soda, metolquinol, and rodinal
are all used by some of the best workers, and
there is little to choose between them. In general,
no bromide or other restrainer should be used ;
the negative should be thin and full of detail
rather than dense and contrasty. To further this,
development should never be over-done, as it is
practically impossible to remedy it by subse-
quent reduction, whereas a thin negative, with
detail, may be gradually intensified and re-
intensified, by means of mercuric chloride and
ferrous oxalate, imtil the requisite density is
obtained.
For copies all the usual media are available.
Lantern slides of good astronomical subjects
make beautiful and interesting records.
(For details of various subjects see " Comets,
Photographing," " Corona Photography,"
"Eclipses," "Lightning," "Moon," "Nebulee,"
"Rainbow," "Stars," "Sun," etc.) C. P. B.
COSMORAMA (Pr., Cosmorama: Ger., Kos-
morama)
An early arrangement for the inspection of
photographs or pictures. These were laid
horizontally on a semicircular table or platform,
each picture having an inclined mirror to reilect
it to a viewing lens, at which the spectator's
eye was placed. The pictures were illuminated
by concealed lamps and were inspected in
turn.
COSMORAMA STEREOSCOPE (Fr., Stirio-
scope cosmorama : Ger., Kosmorama
Siereoskop)
An early form of stereoscope made by Messrs.
Knight, in which two large lenses were used
having a segment cut off, so that they could be
placed with their centres 3 in. apart.
COTTON-WOOL
Prepared from the hairs of the seed of gos-
sypium Barhadense and other species of gos-
sypium. It has many uses in photography, and
the variety known as absorbent cotton and sold
in rolls, wrapped in blue paper usually, is the
best to use. The very common and coarse
variety used for packing should not be used for
wiping wet negatives, as it contains grit and
other coarse foreign matter, which is apt to
scratch gelatine. All negatives should be wiped
after the final washing with a wet pad of cotton-
wool.
This material also makes a serviceable filter
for liquids, a tuft being lightly placed in the
neck of a fimuel and the liquid filtered through
it. It does not filter as thoroughly as filter
papers, but it will serve for some liquids, par-
ticularly varnishes.
In process work, cotton-wool has numerous-
uses, and the " absorbent " wool is commonly
preferred. A wad of it is generally foimd the
handiest means for cleaning zinc or copper with
pumice powder or whiting to remove grease.
The absorbent cotton is also used for filtering the
albumen-bichromate or fish-glue solutions. The
development of albumen-bichromate inked prints
is effected with the help of a tuit of cotton. By
its means, too, the scum which sometimes forms
on wet-plate negatives can often be effectually
removed without damaging the negative.
COVER GLASS
A plain glass bound up with a transparency
(lantern slide) to protect the film. Also a plain
glass used as a cover for the object on a micro-
scopic slide.
COVERING POWER (Pr., Pouvoir d couvrir :
Ger., Deckkraft)
The extent, or boundary, to which a lens will
produce a well-defined and properly illuminated
image. The circle of illumination produced by
a lens is practically the measure of its covering
power ; but definition must also be considered,
for this may not be equally good all over the
circle. It is desirable to have a lens which will
cover a slightly larger circle than is sufficient
to include the size of plate used ; otherwise
there will be a falling-off of definition and of
light when using the rising front. The better
the lens the more satisfactory should be its
covering power ; a good modem anastigmat
will readily cover, when stopped down, a plate
at least a size larger than that for which it ia
intended.
Cow2ui's Developer
151
Cracked Negatives
COWAN'S DEVELOPER
A formula advocated many years ago by
A. Cowan for use with negatives.
No. I. — Pyrogallic acid 20 grs. 4 g.
Nitric acid . 2 drops 'S cos.
Water to . .10 oz. 1,000 „
No. 2. — Strong liquor
ammoniae . i oz. 25 ccs.
Potassium bro-
mide . . 37| grs. 8 g.
Water to . .10 oz. 1,000 ccs.
In cases of ordinary exposure mix in equal parts.
For under-exposure add more of No. 2, and for
over-exposure more of No. i and bromide.
A. Cowan also prepared a solution of pyro-
gallic acid which is always ready for use.
PyrogaUic acid . , i oz. 18.3 g.
Citric acid . , .60 grs. 2-25 „
Water to . . . 54J oz. 1,000 ccs.
Dissolve the citric acid in water and add the
pyrogallic. The solution will contain 8 grains
of pyro to the oimce of water, and will keep good
for many months. In using it dilute according
to formula employed.
Another developer known as " Cowan's " is
the following (known also as a citrate of iron
developer), recommended for chloride lantern
plates : —
No. I. For cold tones —
Potassium citrate . 100 grs. 200 g.
Potassium oxalate . 30 ,, 60 ,,
Hot distilled water to . i oz. 1,000 ccs.
No. 2. For warm tones-
Citric acid . . 90 grs. 180 g.
Ammonium carbonate 60 ,, 120 ,,
Cold" distilled water to . i oz. 1,000 ccs.
No. 3. For extra warm tones —
Citric acid . .130 grs. 260 g.
Ammonium carbonate 40 ,, 80 ,,
Cold distilled water to . i oz. 1,000 ccs.
In mixing solutions Nos. 2 and 3 it is better
to put the crystals into a deep vessel, and, after
adding the water, leave alone until all efferves-
cence ceases. It is advisable to make it over-
night. To 3 parts of any of the above solutions
add I part of the following at the time of using : —
Ferric sulphate .
Sulphuric acid .
Distilled water to
120 grs. 240 g.
I drop 2 ccs.
1 oz. 1,000 „
COXIN
A solution of crocein scarlet 3 B and a yeUow
dye, in which exposed plates were bathed, or
which was added to the developer so that they
could be developed in daylight ; the subject of
a German patent in 1902.
C.P.
The initial letters of the words " Candle-
power " (which see). Also an American term
placed after the name of a chemical to indicate
that it is chemically pure.
CRACKED NEGATIVES
Negatives are easily cracked if cheap frames
with, uneven beds and imperfect springs are
used. The crack may at first appear slight and
unimportant, but in time it invariably extends
across the plate. With care the film on a cracked
negative need not be broken ; merely bind the
negative to a piece of glass of the same size by
means of gummed strips of paper, or cement it
bodily to the glass by means of a mixture of
Canada balsam and benzole or xylol, the crack
being first of aU filled in with the mixture.
Many workers duplicate cracked negatives in
the following manner. First paint on the glass
side and along the crack a fine line of Brunswick
black or other opaque varnish, and then make
a positive transparency, on which, of course, the
crack will be represented by a thin white line.
Then, by means of a retouching pencil or a
camel-hair pencil and suitable medium, retouch
the white Une, and make a negative from the
transparency. Much depends upon the position
of the line and the degree of skill exercised.
There are two systems of taking a print from
a cracked negative without the crack showing,
A, Printing from
Cracked Negative
on Revolving Frame
B. Cracked Negative
at Bottom of Deep
Box
but the work must be done in daylight. One
is to place the frame on a board attached to
strings A, and to keep the board swinging or
rotating in the shade while the picture is being
printed. Another is to place the frame at the
bottom of a deep box B, also in the shade. These
methods are rather slow, but they give the best
results possible with cracked negatives.
It is, of course, possible to remove an unbroken
gelatine film from a cracked glass, and one of
the best methods of doing so is the following :
Carefully clean a sheet of glass one size larger
than the negative to be treated, place the cracked
negative, film side upwards, upon it, and coat
evenly with enamel collodion.
Put on as much as the film will hold without its
running over, allow to set thoroughly, and wash
till the water runs freely off it ; drain, and coat
with a solution of 20 grs. of gelatine in i oz.
of warm water, and allow to set thoroughly.
Then immerse the cracked negative with its
prepared film in this mixture : —
Hydrofluoric acid . 60 drops 6 ccs.
Glycerine . . i oz. 5° ..
Alcohol . . I ,, 5° ..
Water to , . 20 „ 1,000 „
Cracks in Varnish
IS2
Cristoid Film
In a few minutes the film will be free at the edges,
and it should then be carefully coaxed off the
glass by means of a camel-hair brush and trans-
ferred to a dish of cold water. Slip under the
released film a sheet of glass coated with gela-
tine solution made as already stated ; or use
an unexposed dry plate that has been fixed and
washed. Coax out any wrinkles with the camel-
hair brush or by blowing, and allow to dry in a
horizontal position. If the cracked negative has
been varnished, all traces of the varnish must be
removed before any attempt is made to remove
the film. (See " Varnish, Removal of.")
It is possible to do without the collodion, and
so simplify the work of transferring the film,
but greater care will be necessary. Immerse the
negative in 12 oz. of water to which 60 drops of
hydrofluoric acid have been added, and after
the film becomes loose at the edges, coax it off
very gently in the manner already described.
Wash for about ten minutes, at the end of which
time the film will be enlarged considerably ; if
required it can be left in the enlarged state, but
otherwise it must be immersed in a solution of
equal parts of water and methylated spirit until
it has contracted to its original size. Then
float it upon a gelatine plate as above described.
In the case of a cracked new negative the
film may be removed by soaking for about thirty-
six hours in a cold saturated solution of common
washing soda ; all the after operations are as
described in the preceding paragraph.
Cracked negatives other than gelatine are best
treated as broken negatives (which see).
CRACKS IN VARNISH
Cracks upon varnished collodion plates are
more common than upon gelatine plates. Nega-
tive varnish is essentially a gum or resin dis-
solved in a volatile solvent. When the varnish is
spread over the surface of the film, the solvent
evaporates and leaves a coating of the gum
resin on the film ; as the resin dries it contracts
and sometimes cracks. Circumstances that lead
to cracking are (i) making the varnished negative
too hot (either by heating for the purpose of
hurr3mig the evaporation or by printing in a
hot sun) ; (2) insufficiently waslung after fixing ;
(3) storing in a damp place ; and (4) using an
imsuitable varnish.
Cracked varnish on a collodion negative may
be remedied to an extent by rubbing finely-
powdered lampblack, or soot, into the cracks
by means of the dry finger-tip or a piece of
chamois leather, and then revamishing.
Cracked varnish on modem gelatine negatives
may be treated in the same way, but it is better
to remove the varnish entirely and then revar-
nish. To remove varnish, soak i)i the solvent
which was used for the varnish ; if this is not
known, methylated spirit may be tried, as most
of the resins, etc., used for varnishes are soluble
in spirit. After a good soaking rub with cotton-
wool and give the negative one or two more
soakings in spirit, so as to get rid of the last
traces of the varnish. A little ammonia may be
added to the second spirit bath with good effect.
CRAPE MARKINGS
A defect met with in wet collodion work, and
taking the form of markings having the appear-
ance of crape or fine net work. They are due
to the use of too gelatinous collodion or a strong
cadmium bromo-iodiser. Solvents too much
diluted with water may also cause the defect.
CRAWLING
A developer is said to " crawl " when it does
not flow evenly over the film, being prevented
from doing so by the greasy surface caused by
the faulty condition of the collodion bath ;
crawling may also be due to an excess of alcohol
in the developer. Printing paper is said to
" crawl " when it expands or contracts during
the progress of printing, as some papers are
prone to do. If, for example, a bone-dry paper
is put into a frame and placed out of doors in
damp weather, the paper may expand during
printing and cause blurred outlines of the image
to appear. Damp paper put out to print under
a negative on a hot day wiU sometimes show
the same effect, through contracting while
printing. The defect is more common with
albumen paper than any other.
CRAYON ENLARGEMENT (Pr., Agrandisse-
ment au crayon ; Ger., Stift- Vergrosserung)
An enlargement usually on rough-surfaced
bromide paper, worked up with crayons. The
proportion of hand-work may vary greatly,
from the mere removal of spots and blemishes
to an elaborate amount. Much of the black-
and-white work now seen on bromide enlarge-
ments is, however, done with the aerograph.
CRAYONS (Pr., Crayons: Ger., Stifle)
Small pencils of pipeclay, kaoUn, or chalk,
incorporated with various mineral or metallic
pigments, and used for drawing, working-up
enlargements, prints, etc. They are obtainable
in the form of chalks, as loose points for adjust-
able holders, or enclosed in cedar pencils. Those
employed on enlargements are known as bromide
pencils (which see). Coloured crayons are used
for introducing backgrounds into carbon prints.
In process work, lithographic crayons, consist-
ing of a mixture of wax, shellac, soap, and lamp-
black, are largely used. A wet-plate haU-toue
negative can be locally intensified by rubbing a
crayon gently over the part where strength is
desired. Half-tones can be stopped out for
fine etching and vignetting by the use of the
crayon wherever required. I,ithographic crayons
are preferred to black chtdks for drawing on
grained papers and scraper boards for reproduc-
tion, because the work is fixed, owing to its
waxy or greasy nature, without further treat-
ment.
CREAM OF TARTAR
A common name for acid potassium tartrate.
(See "Potassium Bitartrate.")
CRESCO-FYLMA
A name given to a film-stripping and enlarging
solution introduced in 1891, the patent on which
has now, of course, expired. (For similar
solutions, see " Film Stripping.")
CRISTOID FILM
A gelatine film introduced as a substitute for
glass plates or celluloid, and consisting of two
Critical Angle
153
Crystal Varnish
coatings, the lower one being a slow emulsion
and the upper one a. fast emulsion. The chief
advantage claimed was that errors in exposure
were eliminated, because if the upper film was
over-exposed a good negative would be obtained
on the lower film ; also halation was entirely
obviated. The film before development was
treated with formaline, and, after the usual
operations, squeegeed down to plate glass, a.
bath of alcohol and formaline being used to cause
the film to contract to its original size. If this
bath was omitted, the expansion of the gelatine
due to the. absorption of water during the opera-
tions of developing, fixing, and washing gave
enlarged negatives.
CRITICAL! ANGLE
The angle at which a ray passing through a
transparent substance is totally reflected. If a
thick plate of glass be held between the eye and
a light the critical angle will be reached when the
inner surface of the glass, either upper or lower,
according to position, reflects as from a silvered
surface.
CRITICAL ILLUMINATION
In microscopy, critical illumination is obtained
by arranging tie illuminant, mirror, and substage
condenser in such a manner that the image of
the lamp flame is seen in the centre of the field
when looking through the microscope. Critical
illumination is not practicable with low powers,
but it is essential when obtaining the finest
definition a lens which wiU give with high powers,
and more especially when using the immersion
lenses. Recent experiments have shown that
critical illumination has been obtained when the
back lens, on looking down the tube without an
eyepiece, is just filled with light. Daylight can-
not be used for critical work. The Nemst lamp
is a convenient Ught for photo-micrography, but
for visual purposes an oU-lamp with f-in. wick
gives excellent results. The lamp, with the
flame edgeways to the microscope, should be
placed with the wick about 9 in. in front of the
mirror, which must have the plane side turned
to the light. The mirror is placed so that the
hght is reflected in a direct line through the
substage condenser and objective. A diatom
slide is placed on the stage and the substage
condenser racked up and down till the image
of the flame is seen in the centre of the field.
If the eyepiece is now removed, the back lens
should (providing the substage condenser is of
Bufficientiy high aperture) be filled, or nearly
filled, with light. That portion of the field of
view only which contains the image of the lamp
flame gives critical definition.
If the flame image is a disturbing factor to
the work in hand, it can be removed by slightly
lowering the condenser, but the definition sulfers.
Critical illumination is necessary only for powers
of J in. and upwards. I<ow powers should be
worked without the substage condenser, and
with the concave surface of the mirror turned
to the light.
CROOKES' TUBE
The high-vacuum tube (named after the in-
ventor) which produces the X-rays. In an
X-ray tube the vacuum is brought to less than
one-millionth of the density of the atmosphere.
In the original Crookes' tube the cathodal rays
were allowed to fall on the glass ; this was
improved by Prof. Jackson, who caused the
cathodal rays to fall on a metal plate connected
with the anode (anti-cathode). Another improve-
ment was the cupping of the cathode to allow
all the cathode rays to fall on one spot on the
anti-cathode, this arrangement constituting the
" focus tube." (See also imder the heading
" X-ray Photography.")
CROSS FRONT CBi., Dicentrement horizontal ;
Ger., Kreuz-Obj'ektivbrett)
A provision for moving the lens of the camera
sideways, so that a littie more of the subject
may be included at one side or the other, without
having to shift the apparatus. It generally
consists of a panel sliding in grooved rails, with
a clamping screw to maintain its position when
adjusted.
CROSSED LENS
A crossed lens is one having its two sides of
a similar nature, either concave or convex, but
A. Concave
Crossed Lens
B. Convex
Crossed Lens
of different curvatures, as illustrated at A and B.
CROWN GLASS (See " Glass.")
CRYSTAL CUBE (Pr., Cube de cristal : Ger.,
Kry stall Kubus)
A stereoscopic device, invented by Henry
Swan, depending on an application of the angle
of total reflection of glass surfaces. Two
rectangular glass prisms are ground to an angle
of 39° or 40°, and are placed with their widest
sides in contact, or nearly so. One of a pair of
stereoscopic photographs is attached to one side
of the prism combination, and the other behind.
On inspection, the rays from the picture at the
back of the glass are transmitted direct to one
eye, while ti&ose from the second picture are
reflected from the surface of the prisms where
they touch to the other eye, and appear as if
also coming from the back. The two pictures
therefore coalesce, giving stereoscopic relief,
the effect being as if a solid object were imbedded
in the glass.
CRYSTAL MARKINGS (Fr., Marques
cristalUnes ; Ger., Krystall Bezeichnen)
Crystalline or tree-like markings on or under
the film of a collodion or gelatine negative.
They are usually due to insufiScient washing
after fixing, and sometimes they do not appear
till many days have elapsed.
CRYSTAL VARNISH
A particularly clear varnish, used mostly for
lantern shdes, autochromes, and other trans-
Crystallisation
IS4
Crystoleums
parencies. There are many different formulae,
and for lantern slides the following is one of
the many suitable : —
Gum dammar
Benzole
125 grs.
5 oz.
52 g.
1,000 CCS.
Apply this cold. For autochromes a stronger
solution should be used, namely, i oz. of dammar
in 5 oz. of benzole, and the plate should be
warmed slightly before the varnish is poured on
{but see "Autochrome Process," where a further
formula will be found).
Equal parts of pale Canada balsam and rectified
oil of turpentine make a good crystal varnish
for maps and engravings, but for fixing pencil
drawings i oz. of mastic dissolved in 6i oz. of
rectified spirit is recommended. It is not
advisable to use crystal varnish for negatives,
shellac varnish being better. Another crystal
varnish is that known as celluloid varnish,
which is largely used for lantern slides. It is a
solution of celluloid in acetone or other solvent.
CRYSTALLISATION (Fr., CristaUisation ;
Ger., Krystallisation)
A substance or salt when dissolved in water
to featuration will gradually deposit crystals,
or crystallise out if the water be evaporated.
This is called " wet crystallisation." Some-
times a dry salt is fused and allowed to cool,
when crystals will also form ; this is called
" crystallisation by fusion." Again, a volatile
salt maybe heated, when it will go off in the form
of vapour and crystallise on a cool surface ;
this is " crystallisation by sublimation."
CRYSTALOTYPE
An old name for photographic transparencies
upon glass, either in the form of lantern slides
or larger plates for window decoration. It ivas
the original Enghsh name, "hyalotype" being
the American.
CRYSTOLEUMS
Photographs coloured to give the appearance
of direct paintings upon glass ; known also as
chromo-photographs. The system of colouring
is about two centuries old, and, before the days
of photography, engravings and prints were
used as a base, the process being known generally
as mezzotinto painting. The advent of photo-
graphic prints on paper did much to revive the
interest in colouring processes. A modem
crystoleum print properly finished looks, as is
intended, like a painting upon glass, bu,t actually
a transparent photograph comes between the
colouring and the glass. The diagram shows
the construction of a crystoleum photograph. A
is the front glass, on which a photograph B is
pasted face downwards. When dry the photo-
graph is made transparent, and delicate details
coloured with ordinary oil colours, but the
broad masses of colour are not put on. Another
glass D, of the same size and shape as A, is put
at the back, but is prevented from touching the
photograph by means of strips of paper H,
which leave a small space at c. On the back E
of the second glass are painted the broad masses
of colour. The whole is backed up with a piece
of flat cardboard or other backing G, leaving a.
space p. When viewed from the front the colours
are seen through the transparent photograph,
and the whole has the appearance of a deUcately
painted picture upon glass.
The working details are as follow : A suitable;
print is made upon albumen paper, which is the
only photographic paper suitable, it being thin
and tough. The print is placed in hot water
until it becomes quite flaccid, and is then made
surface dry by pressure between clean white
blotting-paper. A piece of convexo-concave
glass (flat glasses are not so suitable), sold
specially for the purpose, is then made quite
clean, and its concave side coated with clear
starch paste or warm gelatine. The damp
print is laid paper side downwards upon a flat
piece of glass, and its face is coated with the
adhesive selected. The print is then placed face
downwards in contact with the inner (concave)
and prepared surface of the glass, and pressed
into close contact. The surplus paste must be
removed from between the print and the glass,
this being accomplished best by laying a piece
of wet parchment over the back of the damp
print, pressing out the ad-
hesive with a knife handle
or toothbrush handle. The
paste must be expelled, also-
all air-bubbles, by a not too
firm pressure, which must be
worked always from the centre
of the print to the extreme
margin. When in perfect con-
tact the parchment is taken
away, the back of the print
wiped free from any super-
fluous adhesive, and the whole
put aside to dry thoroughly.
The correct mounting of the
picture is most important, as
any errors will spoil the effect.
When dry the print must be
made transparent, and this is
accomplished in one of two
ways — ^namely: (i) Rub the
back of the print with glass-
paper in order to remove as much of the
paper as possible (the actual picture being, of
course, underneath, next to the glass) ; a medium
glasspaper is used at first, followed with a very
fine one in order to remove aU scratches, and to
lessen the possibility of suddenly penetrating,
the actual picture on the albumen. When the
bulk of the paper has been evenly rubbed away,
the glass side of the picture is warmed before
a fire, or over a gas-stove, and at the same time
a piece of paraffin wax is rubbed on the paper
side of the print, the object being to saturate
the picture with warm wax. When the print
appears equally transparent all over, all super-
fluous wax is removed with a piece of flannel
and the picture allowed to cool. When cold
the wax may be further polished, and if not
evenly transparent it must again te glass-
papered on the dense parts and waxed again.
(2) The alternative process consists in leaving
the paper print of its original thickness and
making it transparent by rubbing into it a
solution of \ oz. of Canada balsam in 3 oz. of
either benzene or chloroform, the former being
the cheaper. Another solution for the purpose
is Canada balsam 2^ oz., paraffin wax i oz.,
i-G
Section of
Crystoleum
Cupric
1 55
Curvilinear Distortion
and -white wax i oz., heated together and used
in the same way as the wax in. the first
method.
Upon the print prepared as described all
the fine details are now coloured, these includ-
ing the lips, eyes, jewellery, etc. A finely-
pointed sable brush is used, and ordinary oil
colours slightly diluted with megilp. After the
colouring, the second glass is put on at the back
and bound by the edges to the first one to keep
it in position. It must be as close as possible
to the first glass, but not touching, and it may
be kept from contact by sticking two or three
thicknesses of stamp edging along the edges
of the front of the second glass ; or a narrow
strip of thin cardboard may be used in the same
way. The colouring on the second glass may be
very crude, the masses of colour being put on
the back and care being taken not to overlap
the outlines. No details or hghts and shades
are wanted, as they appear in the picture itself,
but body colours only are wanted, these being
mixed with a proportion of flake white. The
colour already in the print must be considered ;
consequently, to picture fair hair in a portrait,
white tinted with yellow will serve. Upon view-
ing the picture from the front (holding it over
white paper), one can easily judge whether the
colouring is correct or not. If not, it may be
corrected or removed with a rag and turpentine.
The iinal operation consists in attaching a piece
of white cardboard to the back of the second
glass and binding the whole together by means
of narrow paper strips, and then framing. Fancy
gilt frames are the most suitable, but obviously
any may be used. Special solutions for mount-
ing the pictures, making them transparent, and
for preserving the transparency and colouring,
are articles of commerce. P. R. S.
CUPRIC
An adjective derived from cuprum, the Latin
word for copper. (See "Copper.")
CUPROTYPE
A printing process invented in 1857 by
C. J. Burnett, of JBdinburgh. It was on the lines
of the ink process (which see), copper chromate
(cM^ric chj-omate) being used.
CURVATURE OF FIELD (Pr., Courbure du
champ ; Ger., Bildwolbung)
Synonym, aberration of form. A defect in a
lens whereby the image of a flat object does not
Curvature of Field
lie on a plane surface, but on a curved or saucer-
shaped one. Thus, as shown in the diagram,
the rays forming the image of the arrow trv
render it in space at y x as curved instead of
straight, the result being that if the centre of
the image is focused the margins will be out of
focus, and vice versa. Curvature of field must
not, however, be confused with curvilinear dis-
tortion (which see) — a not uncommon mistake —
for the arrow will be shown as straight on the
focusing screen, although of unequal definition
along its length. When a lens is subject to
curvature of field the best result is obtained by
focusing for a point midway between the centre
and the margins of the picture, as shown by
the dotted line, and using a small stop. Curva-
ture of field may be reduced in compound lenses
by increasing the separation, but only at the
expense of astigmatism. The introduction of
the new Jena glasses has rendered it possible
to obtain lenses at once free from astigmatism
and possessing a flat field.
CURVILINEAR DISTORTION (Fr., Distor-
sion ; Ger., Verzeichnung, Distorsion)
An aberration occurring in a single lens,
whether consisting of only one glass or of several
cemented together, which- causes straight lines
at the margins of the picture to appear curved.
If the diaphragm c is in front of the lens, as in A,
the image of the squareD shows " barrel-shaped "
distortion ; while when it is behind the lens,
" pincushion " distortion is present, as in B.
The barrel distortion is usually considered less
objectionable, and all single lenses are now fitted
with the diaphragm in front. Distortion de-
creases as the focal length of the lens becomes
Barrel-shaped Distortion
B. Pincushion Distortion
greater, being most apparent in short-focus
objectives. It is obviously objectionable for
architectural work, or anything requiring accur-
ate reproduction of straight lines. The position
of the stop has an important influence ; if it is
brought nearer to the lens distortion is reduced,
but, unfortunately, at the expense of definition.
Curvilinear distortion is completely cured in
doublet or " rectilinear " lenses by placing the
stop in the centre between the two combinations,
when one kind of distortion neutralises the
other. It is owing to this fact that distortion
in a negative may be corrected in enlarging, if
the same lens is used as the negative was taken
with ; for in the enlarging lantern the previous
position of the stop is reversed, coming between
lens and image (enlargement), instead of between
lens and object, which in this case is the
negative.
Cutch
156
Cycle, Camera on
CUTCH {See " Catechu.")
CUT-OUT MOUNT
A sheet of cardboard in which an opening —
rectangular, circular, oval, etc. — has been cut,
generally with a bevelled edge. The print is
moiinted on a second board, which is placed
behind the other. This method of moiyxting is
more generally employed for drawings and
sketches than for photographs.
CUTTING
A term used in connection with the sharpen-
ing up of the dots in making half-tone negatives,
as referred to under many separate headings.
(See, for example, " Clearing Solutions.")
CUTTING SHAPE, OR MOULD (Pr.,
Calibre; Get., Beschneideglaser)
A template used to guide the cutting knife
in trimming prints. It is commonly made of
plate glass, though zinc and other metals are
occasionally employed. Cutting shapes are
obtainable in all sizes, and may be square, oblong,
circular, oval, etc. Curiously enough, it is
difficult to get a rectangular glass cutting shape
with absolutely true and parallel sides. This,
combined with the unfortunate ease with which
the shapes sUp, even in practised hands, together
with their liabiUty to get broken or chipped, no
doubt explains the growing popularity of guillo-
tine cutters and print trimmers. Cutting shapes
with the lower side ground are less slippery
than those of plain glass.
CYANIDES
Salts formed by the combination of a metal
with the radicle CN. An example is potassium
cyanide, KCN.
CYANINE (Fr., Cyanine ; Ger., Cyanin)
Synonyms, cyanine iodide, quinoline or chino-
line blue, diamylcyanine. CjjHssN,!. Molecular
weight, 544. An aniline dye obtained by the
action of caustic potash on an alcoholic solution
of lepidine-iodo-amylate and chinoline-iodo-
amylate. It was for some years the only practical
red sensitiser known, but its action was extremely
uncertain and its sensitising power weak, and it
has been entirely superseded by the newer iso-
cyanines. It occurs in monoclinic crystals having
a green metaUic lustre, and gives a rich blue
solution in water and a more reddish one in
alcohol. The aqueous solution is extremely
sensitive to light. Cyanine bromide, chloride,
sulphate, and nitrate can be prepared by treat-
ing the iodide with the respective silver salts
but they act in the same way as the iodide.
CYANOFER AND CYANOGRAPHIC
PROCESS
Names sometimes given to the PeUet process
(which see).
CYANOGRAPH
A photographic device for recording the blue
light in the atmosphere ; invented in 1903 by
MaiUard and Reiss, of Belgium. The apparatus
consists of a driving clock which, at regular
intervals, unrolls a short length of a band of
sensitive paper, on which is made an exposure,
a suitable blue filter being interposed. It has
been used chiefly for attaching to captive
balloons for the purpose of testing light in high
altitudes. In X-ray photography a piece of
card is used as a filter, and the rest of the
apparatus enclosed in a lead casing.
CYANOTYPE PROCESS. NEGATIVE {See
" Blue-print Process.")
CYANOTYPE PROCESS. POSITIVE {See
" Pellet Process.")
CYCLOGRAPH (Pr., Cychgraphe ; Ger.,
Cyklograph)
A panoramic camera designed by A. H.
Sxuith, by which the whole outer circumference,
or any portion, of a cylindrical object — such as
a vase — may be photographed on a single flat
plate. The object is supported on a circular
platform, which is made to roU along a straight
guiding surface at a right angle to the axis of
the lens, so that as it moves forward it also
revolves, like a carriage wheel advancing. This
is, in fact, making use of the principle of a
cydoidal rotation. At the same time, an
opaque screen having a narrow vertical slit is
made to travel on a parallel path at a speed
proportionate to that of the object, in such a
manner that each successive portion of the
object is exposed to the lens when nearest to
the straight surface — or, in other words, when
it is at the cusp of a cycloid, and its movement
is consequently infinitesimal.
The name cyclograph is also given to a
panoramic camera invented by Mons. Damoizeau,
which turns in a complete circle, so that the
entire horizon, or the inside of a circular build-
ing, may be photographed. A band of film is
employed, and several circles may be taken in
succession on the same band if required.
CYCLE. CAMERA ON
There are many opinions as to which is the
best plan of carrying a camera on a cycle, much
depending upon the size of camera and amount
of apparatus it is desired to carry. Many of
the pocket and folding cameras need not be
considered, as they go into the pocket and do
not inconvenience the rider in any way ; but
it is advisable to carry them in an inner pocket
rather than an outside one, chiefly to protect
them from road dust. A favourite method of
carrying larger and unpocketable cameras is to
strap them firmly to the middle of the back of
the rider ; very broad shoulder-straps will be
found less tiring than narrow ones. If the
camera is not held firmly it may work round
under the arm, and cause considerable incon-
venience when riding, and possibly an accident
when dismoimting or turning a comer. Com-
mercial carriers are made to fix either in front
of the handle bars or behind the saddle. Front
carriers are to be preferred, as the camera is
then always in sight ; if placed behind the rider,
it is apt to be forgotten when dismoimting, and
the rider may be thrown. Cameras when carried
on a cycle should always be wrapped in a water-
proof focusing cloth or other covering, or be
enclosed in a proper bag or case, in order to
protect them from road dust, which otherwise
Cyclol
157
Cylindroscope
will cause pinholes on the negative, and possibly
interfere with the working of the shutter and
plate - changing mechanism. Tripods may be
strapped to the handle-bar, on the fork of the
machine, etc. ; some individuals prefer to strap
them, under the flap of the case, which rests
on the front carrier, and attach the projectinj
ends to the handle-bars.
CYCLOL
A one-solution developing mixture introduced
in 1892, and consisting of rodinal, eikonogen, and
hydroquinone. (See "Developers, Mixed.")
CYLINDERS. GAS
Annealed steel cylinders, tested hydraulically
to withstand a pressure of 3,000 lb. per square
inch, and charged with compressed gas — oxygen,
hydrogen (generally, coal-gas), dissolved acety-
lene, etc. Periodical re-annealing is necessary,
and the gas compressing companies will not take
the risk of filling cylinders unless their regula-
tions in this connection are comphed with. The
construction of the valve is such that all dust
and grit should be prevented from entering it ;
and therefore before connecting the fittings the
valve should be opened for an instant so that
the rush of gas may dislodge anything in the
way. Cylinders of compressed gas are used by
the lantemist, who must become familiar with
Section of Cylinder Valve and of the Stem
and Adapter of Fitting
the working of the valve, a cross section of which
is shown in the illustration. The valve is
screwed into the cylinder, the gas from which
leaves by the narrow passage A when the spindle
B is sUghtly withdrawn by turning its squared
portion C by means of a key ; the gas passes
to the lantern fittings through the inverted
cone D. The gas-tight joint with the automatic
regulator or reducing valve (one of these is
necessary to reduce toe pressure of the gas and
provide a convenient means of attaching the
rubber tubing), is made entirely by mechanical
means, and all daubing of the screw threads
with soap, grease, red-lead, etc., must be strictly
avoided ; accidents have been caused in this
way. The stem E of the regulator or reducing
valve is itself threaded, and has an adapter F
upon it. Screw this adapter close to the
shoulder G of the fitting; without any rela-
tive movement between stem and adapter,
screw the latter into the cylinder valve ; in
this way the cone on the end of the stem will go
home into the inverted cone D of the valve. When
it can go no further, it may be found necessary
to undo the fitting by, say, the third of a turn,
and then screw the adapter in as far as it will
go. Cylinders and fittings for oxygen are
frequently painted black, and for hydrogen red ;
on the former the screw threads are right-
handed, and on the latter left-handed. {See also
. " Limelight.")
CYLINDERS. LIME
Cylindrical pieces of Ume, small portions of
the surface of which are heated to briUiant in-
candescence by a flame supplied with oxygen
under pressure. Linies are sold packed in tins,
but those put up singly in sealed glass tubes
are the most generally convenient. They
rapidly disintegrate when exposed to air. The
chief point in their use is to turn them frequently
to prevent deep pitting. (See also " Limeught.")
CYLINDRICAL PERSPECTIVE
Photographs taken with cylindrograph or
other panoramic cameras of the half circle form
are said to be in cylindrical perspective. {Seg
"Cylindrograph" and "Cylindroscope.")
CYLINDROGRAPH (Fr., Cylindrographe ;
Ger., Cylindrograph)
A panoramic camera invented by Captain
P. Moessard, in 1889, with which photographs
embracing an angle of 170* may be taken on
a ce^uloid film bent to a semicircle. The film
holder or dark-sUde is flexible, so that it adapts
itself to the required form when inserted in the
camera. The lens is made to rotate on a vertical
axis passing practically through its optical
centre ; while a tube terminating in an upright
slit near the surface of the film is rigidly attached
to the lens setting. When a lens is swung on
its optical centre tiie image remains stationary ;
the various portions of the semicircular film
therefore receive the parts of a continuous
picture, while the moving sUt ensures that only
that part directiy opposite the lens is exposed
as the latter moves. This form of camera has
been of much value in photographic surveying,
for vertical lines may be ruled at regular dis-
tances apart on the photograph, to indicate the
relative angular positions of the different objects
on a horizontal plane ; or a glass ruled with
similar lines can be laid on the photograph for
the same purpose. To inspect the views in
correct perspective, an instrument known as
the cylindroscope {which see) is employed.
A panoramic camera on much the same
principle was designed by Marten, of Paris,
in 1845, for use with curved daguerreotypes.
CYLINDROSCOPE (Ft., Cylindroscope: Get.,
Cylindroskop)
An instrument designed by Captain P. Moes-
sard for the inspection or exhibition of panoramic
views obtained with his cylindrograph camera
{which see). The print is curved to a radius
agreeing with that occupied by the film in the
camera, and the point of view is in the centre,-
a suitable eye-lens being used if necessary.
D
DAGUERRE, LOUIS JACQUES MAND^
Bom at Cormeilles, a village near Paris,
November i8, 1789; died July 10, 1851.
Inventor of the diorama (1822) and of daguerreo-
typy (1838). He began his photographic experi-
ments about 1824 by unsuccessful attempts to
fix the im^ages in the camera obscura ; his
neglect of his diorama and scene-painting busi-
ness caused his wife to seek advice with regard
to his sanity. In December, 1829, he entered
into partnership with Niepce, who for fifteen
years had been working on the same subject,
and who had made some important discoveries
which he now shared with Daguerre. The two
worked together up to the time of Niepce's
death (1833), when Isidore Niepce took the place
of his father. Five years after the death of the
elder Niepce, Daguerre accidentally discovered
the process which bears his name, and in the
same year (1838) made an unsuccessful attempt
to form a company to work the process. In
July, 1839, Daguerre divulged his secret and
published the process at the request and expense
of the French Government, who awarded him a.
life pension of six thousand francs on the con-
dition that the process should not be patented ;
notwithstanding this condition, a patent was
taken out in England in 1839. Daguerre wrote
Historique et Description des ProcSdls du
Daguerreotype et du Diorama (1839), and Nouveau
Moyen de Preparer la Couche Sensible des Plaques
Destinies d Recevoir les Images Photographiques
<i844).
PAGUERREOTYPE PROCESS
The earliest commercial photographic process,
the invention of Ivouis Jacques Mand6 Daguerre.
By its means a photographic positive image is
produced on a polished silver surface. It was
published in France, in July, 1839, and during
the next twelve years attained great popularity,
but the introduction of Frederic Scott Archer's
wet collodion process, in 1848, soon had the
effect of rendering the older process obsolete,
and it is now not practised except experi-
mentally. Being the first in the field, extreme
interest naturally attaches to it, and it has been
thought desirable to explain its working in
detail.
Daguerre's process, as slightly modified in
details by the inventor in the course of its com-
mercial practice, is the one here described, it
being impossible in the space at command to
discuss the many modifications introduced by
other experimenters during the ten or twelve
years following 1839. Briefly, a daguerreotype
photograph is an image formed by mercury
vapour upon a silver-coated copper plate. The
process comprises five operations, namely, clean-
ing and polishing the silvered plate, sensitising, ex-
posing in the camera, developing, fixing and finish-
ing. The sheet copper was silvered either elec-
trically or mechanically. In England, as a rule,
SheflSeld plate was employed, this being made by
soldering silver to copper to form an ingot and
then rolling to the reqiiired thickness. The most
perfect polish upon the silvered surface was
necessary, and to obtain this it was cleaned with
weak niteic acid and pohshed with pumice
powder, tripoli, and ohve oil, the final polish
being apphed with buffs made of velvet, the
plate having been previously heated to drive
off the oil. For the purpose of heating during
polishing, the plate was supported upon an iron
wire frame A, and heated with a spirit lamp.
It was essential to obtain a high polish, and
dozens of methods of securing this were sug-
gested.
The second operation, sensitising, was modified
quite a number of times. In Daguerre's original
plan the plate was subjected to fumes of iodine,
until it assumed a definite golden yellow. If the
action of the iodine was prolonged, a violet
A. Wire Frame used by Daguerre for Sup-
porting Silvered Plate WMIe Polishing
colour was produced, and this was much less
sensitive to light. Daguerre's iodising box B
had double walls. The vessel of iodine H
had over it a ring supporting a piece of wire
gauze. The small Kd j was in position only
when the box was not in use. The plate to be
iodised was attached to the imderside of the
proper lid K ; the lid z, enclosed the whole. The
sensitising took a long time, as the crystals of
iodine had to remain in their natural state, and
must not be heated because of the possibility
of moisture condensing upon the plate. The
vapour caused silver iodide to be formed on the
silver plate, which was then sensitive to Ught.
Although Daguerre appeared to be satisfied with
plates prepared in this way, many other photo-
graphers tried to increase the sensitiveness. God-
dard, for example, in 1840 exposed the iodised
plate to the action of bromine vapour, thereby
forming silver bromide upon the plate in addition
to the iodide ; and in 1841 Claudet used chlorine
vapour in the same way ; either of these modi-
fications reduced the exposure by about four-
fifths. Bingham followed vnth. bromide of lime,
which for a time was widely used. These
accelerators caused the yellow film to assume
58
Daguerreotype Process
1 59
Daguerreotype Process
other hues, and in each case the plate was put
back again to the iodine fumes until it assumed
a rosy hue.
The third operation was that of exposing the
plate in a camera (for Daguerre's instrument, see
Camera"), and, as in ttie case of modem dry
plates, the time of exposure depended upon the
actinic value of the light, etc. Daguerre's times
of exposure in Paris, and with plates prepared
simply with iodine, are said to have been from
five to thirty minutes ; objects in shadow, even
in the brightest weather, required twenty min-
utes at least. The daguerreotype plate, how-
ever, in its modified form needed only from five
to thirty seconds, according to subject, light, etc.
It was not an jincommon practice, when
Daguerre's original process was used, to whiten
the face of the sitter by means of powder in
order to shorten the exposure for the face ;
then, in order to bring out the details of the
dark objects, such as the dress, a piece of black
cloth attached to a long stick was held in front
of the sitter's face during the time the extra
exposure was given to the dress.
An obvious defect in a daguerreotype picture
B. Daguerre's Iodising Box
taken in an ordinary camera was that the image
was reversed, exactly as in a ferrotype (or tin-
type) portrait. To obviate this, it was neces-
sary to reverse the image by means of a mirror
attached to the lens, thus increasing the already
lengthy exposure by about one-third.
The fourth process was that of development,
or " mercuriaUsation " of the image on the
exposed plate. The latter was taken into the
dark-room and placed in a dark box C in such a
way that the surface was suspended over a
saucer of mercury heated to a temperature of
about 140° P. (60° C). The box had under
its bottom a lamp M, which heated a dish of
mercury in which was a thermometer N. The
plate P, as removed from the camera, was held in
a grooved blackboard q, where it could be
viewed through the glass panel R. The lid of
the box is shown by S. The fumes of the mer-
cury " developed " the image in the course of
about twenty minutes. The final operation
consisted in removing the unused iodine from
the plate of silver in order to prevent the further
action of light. A saturated solution of common
salt was first used, and later a weak solution of
godium hyposulphite. The developed plate was
placed in filtered rain-water for a second only,
and then immersed in one of the fixers just
named until the yellow colour had quite dis-
appeared ; warm distilled, boiled, or filtered
rain-water was then allowed to run in a stream
over the plate in order to wash it. The shadows
were represented by the polished surface of the
silver, and the lights by the adhering and very
delicate film of mercury, which, if fingered in
any way, would be wiped off. Therefore, in
order to preserve the pictures, they were placed
under glass and the air excluded. In some cases
the picture was treated with a solution of gold
and sodium hyposulphite, which brought out the
details with greater force and brilliancy. This
idea was originated in 1840 by Fizeau, of Paris,
who used a solution of 7 grs. of gold chloride in
10 oz. of distilled water, this being mixed with
a solution of 30 grs. of sodium hyposulphite in
4 oz. of water.
The expense of the silvered plates was a
C. Daguerre's Developing or Mercurialising
Box
great drawback to the daguerreotype process.
As late as 1853, the price charged for a
quarter-plate daguerreotype portrait was fifty
shillings, and for a half -plate eighty shillings. It
was the custom to " improve " daguerreotype
pictures by colouring them. Colours groimd
extremely fine were used and dusted on dry
with a fine camel-hair brush, the process needing
great care, as it was almost impossible to
remove any of the colour apphed. When the
colours were on they were breathed upon to
make them adhere. Claudet's method was to
mix the colours with alcohol, and apply cautiously
with a soft brush, and to dust on dry colours if
the liquid colours were not dark enough. The
colours chiefly used were gold, carmine, chrome
yellow, and ultramarine, by combining which
any desired tint could be obtained.
Major-General Waterhouse has found that
daguerreotype plates can be developed with a
wet collocLon (physical) developer to give a
Daguerreotypes, Cleaning
i6o Daguerreolsrpes, Electrotsrping
positive image as usual, or with an alkaline
developer, or with ferrous oxalate, to give a
negative image. If before exposure the plates
are treated with an alcoholic solution of
erythrosine, they show sensitiveness to the less
refrangible end of the spectrum. Copper plates
sensitised with iodine and bromine yidd images
if exposed and developed with ferrous oxalate
or an alkaline developer, and the results are
fairly certain.
DAGUERREOTYPES, CLEANING AND
RESTORING
Cleaning and restoring a daguerreotype picture
is at all times a risky process, and should not
be attempted unless the worker is particularly
careful and patient. Many methods have been
advocated, but they all need care and thought,
and rather than run the risk of ruining a picture
it is better for the uninitiated to leave the work
alone. It must be remembered that daguerreo-
types are valuable relics, and that comparatively
few modem photographers know how they were
made. The pictures become indistinct and dull,
not by fading, as the modem photographer under-
stands it, but as a result of the oxidising influence
of the atmosphere, which has been unwittingly
allowed to act upon them, either because the
hermetic sealing was imperfectly executed, or
because it has become broken away. In this
article is described the method of deaning and
restoring that is considered to be the most
reliable, but before any attempt is made to
improve the picture the processes by which it
was produced should be thoroughly under-
stood {see "Daguerreotype Process"), the res-
torer will then know the composition of the
photograph. This photograph consists of a most
delicate film, on the sujface of a silvered plate,
not varnished or protected in any way, and
susceptible of injury from any rubbing or
abrasion. Flicking off the dust with a silk
handkerchief, or lightly touching the surface
with the finger or a camel-hair brush, may min
the picture. The operator must first try to
ascertain whether the picture is in its original
state, and whether there has been an earlier
attempt to clean or restore it, because shoidd
certain chemicals have been left in the film
the picture may be ruined when others are
applied.
The usual and best method of restoring a faded
or discolouied daguerreotype is as follows :
Take out the plate from the frame and immerse
the discoloured pictiire in a i per cent, solution
of potassium ||cyanide in distiUed water, care-
fully rocking the dish until the milky or smoky
appearance caused by oxidation disappears. If
the cyanide solution is not strong enough it
may be strengthened, but particular care must
be taken to use the purest of distilled water,
and not to touch the picture with any solid
substance, even with cotton-wool. As soon as
the discoloration (oxidation) has vanished, the
plate must be gently but thoroughly washed in
several changes of distilled water, avoiding
ordinary water. Finally, it is dried by gentle
heat in an atinosphere as free from dust as
possible, and in nine cases out of ten the simple
treatment will have restored the picture and
made it almost, if not quite, as good as new.
If, however, the restored picture lacks brillianca
and detail, it may be redeveloped, but as the
latter process is particularly risky it should be
attempted only in extreme and very bad cases.
Redevelopment is done by exposure to the
fumes of mercury, and not by the application of
any liquid. Procure an air-tight box about
3 ft. high ; at the bottom place a small spirit
lamp, and over it a saucer of pure metallic
mercury. Carefully fix the plate to be redevel-
oped to the lid of tie box in such a way that the
picture is face downwards when the box is closed.
Close the box so that the picture may be exposed
to the fumes of the mercury, and examine every
minute to see how development progresses.
When all detaU is restored, remove the plate.
Care must be taken during this process not to
inhale the fumes, £is they are poisonous. Lay
the redeveloped plate on a piece of clean, clear
glass, and bind the edges with silk strips, using
Canada balsam as an adhesive ; this binding
mu^t be done thoroughly in order to exclude
the air. Redevelopment is rarely necessary, and
is to be avoided on account of the risk to both
plate and operator.
DAGUERREOTYPES, COPYING
Daguerreotypes are difficult to copy satis-
factorily because of the character of tiie image
and the presence of the silvered plate. They
must be illuminated by a strong sidelight, all
other light being cut off, and the surroundings
should be dead black, in order to prevent reflec-
Method of Copying Daguerreotype
tions. Professional copyists place the daguerreo-
type picture inside a deep box lined with velvet,
black doth, or painted a dead black, with a hole
cut in one end, through which the camera lens
peeps. At the end nearest the picture, part of
the side of the box is cut away in order to admit
the sidelight, which light should preferably be
strong sunlight. As a general rule, the picture
should lie on its side, with its top edge facing
the direction of the light, because the marks of
the buffer sometimes show upon the original
picture, and as these lines run from top to bottom
they would be accentuated by a light striking
them at right angles. Focusing, stop, expo-
sure, plate, etc., are the same as for ordinary
copying, the whole secret of daguerreotype
copying being in the arrangement of lighting.
DAGUERREOTYPES. ELECTROTYPING
(Fr., Electroiypage des dagiierriotypes ;
Ger., Galvanoplastik der Dagtierreotypen)
The daguerreotype plate to be electrotyped is
immersed in an acidified copper sulphate solu-
tion, as employed by electrotypers, and is con-
nected by means of copper wires to an electric
battery or other source of current. A sheet of
soft copper is placed in the solution to form
the anode, this being also cotmected to the
By a. H. Blake, M.A.
NIGHT PHOTOGRAPHY
Daguerreotypes, Etching
l6l
Damp, Precautions Against
battery. A fine coating of copper is thus gradu-
ally deposited on the daguerreotype, but the
relief obtained is naturally very ^ght.
DAGUERREOTYPES. ETCHING (Pr.,
Gravure des daguerreotypes d I'acide
chlorhydrique ; Ger., Aetzen der Daguerreo-
typen)
A process for obtaining intaglio plates from
daguerreotypes, suitable for photogravure print
ing, was introduced in 1840 by Sir W. R. Grove
the inventor of the Grove cell. The daguerreo
type was immersed in a solution of one part of
hydrochloric acid to two parts of water, and
attached to a wire from the battery, which
consisted of a pair of Grove cells. Opposite the
daguerreotype, and about 2 in. away from it,
was placed a platiniyn plate connected with the
other pole of the battery. On the passage of
the current, an oxychloride of silver was formed,
and at the expiration of about thirty seconds
the etching was complete. The oxychloride
having been removed, the plate was ready for
printing from in an ordinary press. The results
obtained were, however, too shallow for anything
but very deUcate work, and proved unsuitable
for commercial use. In 1843 A. J. F. Claudet
patented a method of etching the daguerreotype
plate with acid, but the specification is by no
means clear.
DALLAS RUBBER-TYPE
An invention of Duncan C. Dallas, comprising
the making of a swelled gelatine relief, and from
it a plaster cast, the cast forming the mould for
a vulcanised indiarubber cast to be used as a
stamp, or in a press.
DALLASTINT. DALLASTYPE, ETC.
Duncan C. Dallas was the inventor of a num-
ber of processes based on the swelling of gela-
tine, when sensitised with bichromate and
exposed to light. Dallastint was a process in
which the half-tones of a photograph were repro-
duced by cau'sing the gelatine to reticulate into
a grain resembling that produced in the collo-
type plate. The effect was similar to that of
aquatint, and it was capable of rendering fine
detail and delicate gradation of tone. However,
the process never came into practical use, and
the details were kept secret The inventor
claimed that the process could also be used for
decorative purposes by transfer to pottery,
stone, wood, etc., and for printing on calico,
linen, and other textile fabrics.
Chromo-Dallastint was an adaptation of the
Dallastint process to colour printing by making
blocks for each colour.
DaUastype was a process proposed for making
relief blocks for typographic printing. The
inventor made half-tone blocks, and used a ruled
screen instead of, or sometimes in combination
with, his reticulated grain. The blocks were
made of type metal, evidently cast in plaster
moulds taken from the gelatine relief.
DALLMEYER. JOHN HENRY
J. H. Dallmeyer (bom 1830, at I,oxten, near
Versmold, Prussia ; died oS the coast of New
Zealand, 1883) came to England in 1851 and
entered the workshop of W. Hewitt, optician,
11
afterwards working for Andrew Ross. He
started in business for himself in 1859, and ia
1862 came to the front as a manufacturer of
photographic lenses. He made many improve-
ments in telescopes, and patented a single wide-
angle lens {1864) and a lantern condenser. He
married Hannah, daughter of Andrew Ross,
was elected F.R.A.S. in 1861, and retired from
active work in i88o.
DALLMEYER, THOMAS ROSS
T. R. Dallmeyer, son of J. H. Dalmeyer, bom.
1859; died December 25, 1906. Designed
many important optical instruments, lenses for
telephotography being perhaps the most import-
ant. Among his inventions are a rapid triple
cemented landscape lens and a. rapid rectilinear
landscape lens. He was a prominent member of
the Royal Photographic Society, and President
of that body from igoo to 1903.
DALLMEYER ■ BERGHEIM LENS (See
" Bergheim I<ens.")
DAMMAR {See "Gums and Resins.")
DAMMAR VARNISH
Gum dammar dissolved in benzole, chloro-
form or turpentine makes a clear varnish, which
may be used cold and applied, if necessary, with
a brush. It is particularly suitable for film
negatives, transparencies, etc. (Por formula, see
"Crystal Varnish.")
DAMP. PRECAUTIONS AGAINST
Damp plays havoc with apparatus and sen-
sitive material, which should always be stored
in a dry, airy place. Camera bellows become
mouldy in a damp place, lenses spotty, cameras
may come to pieces, and dark-slides refuse to fit
or draw out, and shutters to work. Preventives
are obvious. Where possible, it is advisable
to use, for home-made articles, a glue that has
been damp-proofed by mixing with it while hot
one-quarter its bulk of linseed oil, stirring
rapi(Uy during the addition. The addition of
I part of potassium bichromate dissolved in
the least quantity of water to 6 parts of
melted glue, made with as little water as possible,
makes a waterproof cement, which must be
stored in the dark until required for use. A
precaution against damp is to have cameras and
dark-slides brass-bound. Dampness in a dark-
room may cause the detachment of labels from
the bottles of chemicals, unless these labels are
protected by a coat of waterproof varnish
extending over their edges upon the glass.
Plates and papers deteriorate quickly if not
kept dry ; and if damp is suspected they should
be kept in a cupboard or in drawers, with some
calcium chloride in a tin, either without a lid
or with a perforated one ; the chemical absorbs
moisture, and when it becomes wet it may be
dried on a. hot shovel or in an oven and used
over and over again.
Damp must Slso be guarded against while
printing, as damp paper will probably spoil any
negative with which it is placed in contact {see
" Silver Stains "). When printing is carried out
in wet weather, and there is a likelihood of the
paper absorbing moisture, it is advisable to use
Dansac-Chassagne Process
162
Dark-room
a pad of waterproof sheeting between the back
of the paper and the frame back, or pads of
blotting-paper may be used if dried before a
fire after taking each print. Such a precaution
is particvdarly necessary when P.O.P or platinum
paper is used ; and in very wet weather such
papers may with advantage be dried before a
fire previous to printing.
Carbon paper (tissue) is insensitive when wet
and sensitive when dry ; but it is not generally
known that the film is insensitive when in a
state of absolute dryness amounting to complete
desiccation.
The walls — plain or papered — of dark-rooms
or work-rooms where photographic material is
stored may with advantage be covered with a
waterproof varnish formed of naphtha and
shellac, in the proportion of J lb. of the former
to I quart of the latter. The smell of the
mixture is unpleasant, but soon wears off, and
the wan is covered with a hard coating utterly
impervious to damp, and to which wall-paper
may, if desired, be attached.
A wooden erection used as a studio, dark-
room, or store-room, can be given a waterproof
coating with tar, which is as effective as, and
cheaper than, anything else. The following is
also suitable, and can be applied with a brush :
«qual parts of pitch and resin melted together in
a bucket over a stove, and then, after removal,
thinned with petroleum ether or paraflSn oil.
The fire risk in preparing this stuff is considerable,
and the job should be done in the open air.
DANSAC-CHASSAGNE COLOUR PRO-
CESS
A process of obtaining prints in natural
colours, which was introduced in 1897, and
originally said to be based on the selective
absorption of the silver image for the colours
used. On critical examination it proved to be
nothing more than local painting with solutions
of aniUne dyes in albumen.
DARK-ROOM, OR DEVELOPING CHAM-
BER (Fr., Laboratoire ; Ger., Dunkel-
zimmer, Dunkelkammer)
A room or cupboard devoted principally to
the operation of development, and from which
aU white or actinic light is excluded. Until
A. J. F. Claudet patented, in the 'forties, the
use of coloured media, preferably red, the devel-
oping chamber was really in total darkness ; but
since then the name of " dark-room " has been
somewhat of a misnomer.
The old idea that space is unimportant in the
room used for developing is quite erroneous,
particularly with respect to efficient ventilation,
so necessary to the health and comfort of the
operator. It is obvious, also, that greater con-
venience is secured when there is plenty of room
for shelves and benches, and for moving about.
DayUght, owing to its constant fluctuation, is
not recommended, and does not add to the
safety of the developing chamber, since sunshine
or bright light tends in time to bleach non-
actinic fabrics and materials, and mischief may
be done before this is noticed. It is preferable
to block out all daylight and to rely entirely
on artificial illumination. It is now realised
that, provided the colour of the light is carefully
chosen to match that region of the spectrum to
which the particular plate employed is least
sensitive, a much better iUumlnation is per-
missible with safety than was at one time
imagined, so long as the plate is not unneces-
sarily exposed to the direct rays from the lamp.
The old-style dark-room, where the operator
fumbled uncertainly in a dim, ruby glimmer,
knocking over bottles and breaking glass
measures in his inability to see a foot before him,
is rapidly giving way to saner arrangements.
In a properly designed developing chamber
some means should be adopted for preventing
the admission of light when the door is opened.
One way of doing this is to have a double door,
as indicated in the illustration which shows
how a room 12 ft. by 8 ft. may be fitted up
as a dark-room. Another way is to curtain off
a kind of alcove in front of the door, using a
heavy opaque material.
An abundant and pure water supply is an
important consideration if much work is to be
done. Iron pipes should be avoided, as rust is
objectionable in dealing with some sensitive
surfaces. If a constant supply cannot be had,
a portable tank with a tap or siphon, or even a
couple of large pails, may be used. Swing rose
Plan of Fitted Dark-room
taps should be fitted if possible ; ordinary taps
are more troublesome, giving too forcible a jet
and having a marked tendency to splash. But
if an ordinary tap is provided as well, for use
in filling bottles only, added efficiency is gained.
The more shelves that can be fitted the better.
Those which wiU hold the bottles or articles
most frequently in use should be low down and
well within reach. A small cupboard, with
drawers to hold unexposed plates and papers,
will be found extremely useful.
When a room cannot be kept permanently
for developing, a bathroom, or even a cupboard,
may be adapted temporarily for the purpose.
If the work is done at night, and no outside
lamps are near, there will be no need to obscure
any windows that may be present ; otherwise
a wooden frame may be made to fit closely in
the opening, and covered with any opaque or
non-actinic fabric. This is readily removable
when not in use, and may be replaced in a few
seconds. Portable dark-rooms of various kinds
are obtainable, and some of these fold into a very
small space. {See also " Dark-room Illumina-
tion," "Dark-room Lamp," " Dark-room Ven-
tilation," " Developing Bench," etc.)
Dark-room Clock
163
Dark-room Lamp
DARK-ROOM CLOCK (See " Qock, Dark-
room.")
DARK-ROOM ILLUMINATION
The colour of the light used for dark-room illu-
mination is important, both as regards its purity
and its general character. For ordinary negative
■work a pure red, that does not allow any blue
rays to pass, is^best, and for bf omide printing a
golden yellow or orange will give sufficient
safety with comfort in working. For most
colour-sensitive plates a pure deep red is best ;
but for some that are very sensitive to red a
special screen for the dark-room lamp is sold by
the makers of the plates. For all ortoiary plates
and papers theibest method for working satis-
factorily is to light the dark-room brilliailtly,
sufficiently well for seeing all bottles, measures,
plate boxes, etc., clearly and distinctly. Unless
there is sufficient light for working in comfort,
inferior results are inevitable. The room should
be lighted well, but the plate should be shielded
or protected from the ^rect rays of the lamp,
both in filling the slides and during develop-
ment. The plate may be brought near the lamp
the insertion of glasses or fabrics of different
colours according to the work in hand. With
transparent glass a good deal of light is often
wasted ; lamps with fabrics capable of diffusing
the light, or fitted with sheets of ground glass
or opal in addition, for the same purpose are
to be preferred, as the room is then more com-
fortably and uniformly lighted, and the bench,
shelves, etc., are more readily perceived. For
temporary use, as when travefiing, a folding
lamp A burning a candle or night-light is con-
vement ; but for constant work candles are
troublesome and uncertain. Oil lamps are
fairly satisfactory, if fitted with the wick adjust-
ment outside, as in B, and kept scrupulously
clean ; but gas and electricity are the o'nly forms
of illumination that can really be recommended.
From the facility with which it may be raised
or lowered, gas is perhaps the best of all, if
perfect ventilation is secured ; and a good pattern
of gas lamp is shown at C. A lamp for use with
electricity is illustrated at D ; hanging electric
lamps are also obtainable. The worker should
be warned that many of the red incandescent
electric bulbs in the market are unsuitable for
A. Folding
Candle-lamp
B. Oil-lamp with
Outside 'Wick Adjustment
C. Gas-lamp
D. Electric -lamp
for a few seconds, when necessary, for examin-
ation, but otherwise should be shielded as much
as possible. It is not necessary to cover the
dish, as the light reflected from the walls has
very little power ; but the dish should be 2 ft.
or 3 ft. from the lamp and shielded from the
direct rays. Artificial light is very much safer
for dark-room iUumination than daylight, and
should always be used when convenient.
DARK-ROOM LAMP (Fr., Lampe de labor-
atoire ; Ger., Dunkelzimmerlampe)
On the satisfactory working of the dark-room
lamp depends much of the operator's comfort
when developing, while the " safety '' of the
light emitted is an important consideration.
This is qualified to a great extent by the kind
of plate or paper that is being used, and its
particular region of colour sensitiveness. Thus,
for wet collodion plates an amber-coloured
glass may be used ; for bromide paper, one or
two thicknesses of yellow fabric ; for ordinary
plates, one thickness of orange fabric and two
or three thicknesses of yellow, or an amber and
a ruby glass together ; while for orthochromatic
plates a very deep ruby or a special shade of
green may be employed. Obviously, therefore,
the ideal dark-room lamp is one that will permit
photographic employment, unless masked with
non-actinic fabric.
With regard to the " safe light " used in the
lamp, care must be taken that it is suited to
the plate. A good way of ascertaining this is
to place an unexposed plate in the dark-slide,
with the shutter half-drawn, and to expose it
close to the lamp for about four minutes. It
shotdd then be developed, when, if the light is
unsafe, the exposed half wiU be fogged, and a
clear line of demarcation wiU be evident between
it and the unexposed portion. The exact
matching of the light to the plate can only be
done by photographing the solar spectrum on
the latter, and noticing the region of the spec-
trum which has no photographic effect. It is
then possible to obtaia a dark-room light of
the particular colour, or mixture of colours, to
which the plate is insensitive, by bringing the
spectroscope into service. Gelatine films, stained
with aniline dyes, are much used as safe lights,
as their colour may be nicely adjusted when
staining. These require to be kept between
two plain glass plates in the lamp. Since heat
is detrimental to the stained gelatine films,
lamps of special construction are made for use
with them. Other lamps have glass cells in
front, which may be filled with potassium
Dark-room Ventilation
164
Dark-slide
bichromate solution, or a solution of any
selected aniline dye. {See also " Bichromate
Lamp.")
DARK-ROOM VENTILATION (Fr., Ven-
tilation du laboratoire ; Ger., Dunkel-
zimmer-ventilation)
Adequate ventilation of the developing
chamber is essential to health. Perhaps the
simplest means of securing it is by the pro-
vision of hght- traps {which see) at the top and
bottom of the door, or in any other suitable
places. Unless, however, these communicate
with the outer air, the ventilation obtained will
scarcely suffice. It is as important to secure
egress for the foul air as to admit fresh, a fact
which is often overlooked, and outlets should
invariably be placed at the top. It is not at
all uncommon to find small dark-rooms merely
provided with ventilation aperhires near the
floor, in which case it is next to impossible for
the vitiated and heated air in the upper part
of the room to escape. A light-trapped cowl in
the roof forms a very efficient outlet, but proper
attention then requires to be paid to the pro-
vision of openings for the admission of fresh air
at or near the bottom of the room ; or the cowl
will merely serve to direct a stream of fresh
air downwards, and will cause an unpleasant
draught. It is often found necessary to use an
external electric fan, either to drive in the fresh
air or to draw out the fotU, but care must be
taken not to raise dust. Whenever dust is
found to enter by ventilation openings, muslin
stretched over a light frame should be inter-
posed before the aperture.
DARK-SLIDE, PLATE-HOLDER, OR
BACK (Pr., Chdssis, Chdssis nigatif;
Ger., Kassette)
A Ught-tight case to hold the sensitive plate
or film, always furnished with a shutter or
shutters, and made to fit closely at the back of
the camera, from which it may be withdrawn
at will. There are several kinds of dark-slides.
That commonly used with studio cameras has
a hinged door at the back for the insertion of
the plate, and some of the larger and better-
class studio sUdes have roller shutters instead
of those that draw out. Field camera dark-
slides are generally hinged in the middle, and
open like a book, taking two plates with an
opaque cardboard or metal separator between
A. Double Book-form Dark-slide
them. These A are known as " double book-
form " dark-shdes. The shutters are usually
cut across and hinged, so that they will fold over
the back of the sUde. whe|i drawn, and be out
of the way. Many hand cameras have solid
double slides, known as the American pattern,
with pull-out shutters of ebonite or aluminium.
These are not always perfectly light-tight,
especially when they get worn. An improved
pattern is shown at B. The shutters do not pull
right out, and particulars of the exposure may
B, Improved SoUd Dark-slide with
Pull-out Shutters
be written on them. To insert a plate, a. lever
at the bottom is pressed downward (see illiis-
tration B), and the plate then drops into position,
the lever returning and securing it. Metal and
cardboard dark-slides are also made. There
are many special kinds of sUdes or adapters,
to take film-packs, plates in daylight-loading
envelopes, etc. Roller sUdes {which see) are
intended for use with roll-films, and are furnished
with a winding key and spools.
In process work, the dark-sHdes are essentially
different from those used in ordinary photography.
The plate is generally held by means of adjust-
able bars, the bottom one being placed in a notch
corresponding to the size of the plate, and the
top one sUding down to rest on top of the plate
(see illustration C). The metal catches to pre-
vent the plate from falling outwards are of
silver when the sHde is used for wet-plate work.
Sometimes the bottom bar is formed into a
trough, to catch the silver drainings, and in an
American dark-slide known as the Benster
plate-holder a glass trough was let into the
wooden bar. For half-tone work the dark-
slides are provided with an additional pair of
C. Wet-plate Holder for Process Work
bars to hold the ruled screen, and in some forma
of holder these bars are adjustable so as to give
more or less separation of the screen from the
plate. Most of these process dark-slides have
roller shutters.
Dark-tent
i6s
Definition
DARK-TENT
Used for changing and developing plates. (See
" Developing Tent.")
DARLOT
A noted French optician and lens maker,
who made a speciality of casket lenses, under
which heading they will be found fully
described.
DAVIS FOCUSING SCREEN
A screen used for high-power work in photo-
micrography, invented by George E. Davis. It
is used in place of a glass screen for final focus-
ing, and consists of a piece of wood, preferably
mahogany, containing seven holes, any one of
which can take an " A " photomicrographic eye-
piece.
DAVY, SIR HUMPHRY
Bom at Penzance, December 17, 1778 ; died
jat Geneva, May 29, 1829. President of the
Royal Society, 1820; made many important
chemical discoveries and first decomposed
chemical compounds by means of electric cur-
rents, preparing in this way sodium, potassium,
etc. Assisted Thomas Wedgwood in his experi-
ments with light upon silver and described them
in the Journal of the Royal Institution (1802) ;
in the same year he discovered that silver cihloride
gave better results than silver nitrate in the pre-
paration of a sensitive surface. He made a
number of photomicrographs, or macrographs,
by throwing enlarged images of small objects
through a solar microscope upon sensitised paper
and white leather, but he failed to fix them.
DAYLIGHT CARTRIDGES
This term is applied to spools of flexible film
used in cameras specially adapted for them.
The strip of film is attached to a considerably
longer strip of black paper. The spool is placed
in position in the camera, and one end of the black
paper is put through a slot in an empty spool
and wound taut. The camera is then closed.
By continuing the winding, the first section of
the film is brought into position for exposure,
and the successive sections are in turn wound
along. A number on the black paper behind
each section can be observed through an open-
ing in the back of the camera, thus regulating
the winding and indicating the number of the
€xposure. When the last section has been
exposed, the rest of the black paper is wound
on to the spool to protect the film, and the
camera can then be opened, the exposed spool
removed, and a fresh one inserted. The film
thus exposed may be cut up into sections, or
developed in the strip either by hand or by
means of developing machines made specially
for the pivrpose. The device is an exceedingly
convenient and popular one. The smaUness and
lightness of the cartridges as compared with
plates, and the ease with which successive
spools may be used are strong points in their
favour, especially with travellers.
One precaution in the use of film cartridges
may be mentioned : care should be taken not
to allow the black paper to run loose on the
spool, as this will allow light to creep in at the
edges. Also, in folding cameras, avoid winding
the film while the camera is closed, as some part
of the bellows or lens may touch the film and
cause scratches upon it.
DAYLIGHT CHANGING
There are several methods by which plates or
films may be changed in daylight without the
necessity of resorting to a dark-room. Some
that come more or less in this category are
referred to under the headings " Changing
Bags," "Fihn Pack," and "Daylight Car-
tridges." In addition to these, there are special
slides made into which plates or fihns may be
inserted singly. A popufer form is one in which
each plate or film is enclosed separately in a
light-tight envelope. The drawing of the
shutter of the slide opens the envelope, which is
again closed as the Gutter is pushed in. The
exposed plate in its envelope may then be
removed and a fresh one substituted. The
number of exposures is thus only limited by the
number of envelopes employed. This permits
of the provision of plates and films of different
character, which may be selected as required.
DAYLIGHT DEVELOPMENT (Pr., D£-
veloppement en plein air ; Ger., TagesHcht-
entwickelung)
At various times many methods have been
suggested for doing away with the dark-room
for development, and they may be divided into
two main types : (i) those depending on the
use of a light-tight tank with ruby glass sides
into which the plate and developer are intro-
duced either in a dark-room or tent, the progress
of development being observed through the red
windows ; and (2) those in which red or non-
actinic dye solutions were added to the developer
so as to protect the plate from daylight. {See
"Developing Machine," "Developing Tank," etc.)
DAYLIGHT ENLARGING
The oldest method of enlarging, details being
published in the Athenaum dated July 9,
1853. A solar camera (which see) was used by
the early workers, and enlargements were made
upon albumen or other sensitive " contact " paper.
Bromide paper, as used to-day for enlarging, was
not commonly obtainable commercially until
1879 or 1880, although introduced five years
earlier. (For modem methods of daylight en-
larging, see "Enlarging by Daylight.")
DEAD BLACK
Recipes for dead blacks are given under the
heading " Blackening Apparatus."
DECIGRAMME, DECILITRE, DECIMETRE,
ETC. (See "Weights and Measures.")
DECOMPOSITION OF LIGHT (See "Light.")
DEFINITION (Vt., Definition; Get., Definition)
The degree of sharpness with which objects
are rendered by the lens. As a rough standard
for purposes of comparison, it is generally
assumed that the allowable " circle of confusion "
shaji be one-hundredth of an inch in diameter
— that is to say, a circle of that size shall be
accepted as a satisfactory rendering of what
should be a point. This only holds good for
Dekagramme
1 66
Density Curve
contact prints from the negative, as it is obviotis
that any enlargement would increase the error
proportionately and so bring it above the
standard limit. Some forms of lenses give a
curved or saucer-shaped field, so that when the
centre is sharp the definition falls away towards
the edges. This defect may be coimteracted by
using a smaller stop. Variation in definition also
arises from the inability of a lens to bring to a
focus objects on all planes at the same time.
Improvement in this direction also is brought
about by the use of a small stop. It is not always
necessary or even advisable to have equally
sharp definition in all parts of the subject, and
judicious selective focusing is frequently of
great advantage. Some lenses are specially con-
structed to enable the operator to introduce at
will any required degree of softness or diffusion
over the entire area. Such softness of definition
is often most effective in portraiture and in some
classes of outdoor work. It is generally out of
place in architecture, copying, and the rendering
of subjects for scientific purposes. In such cases
the standard of critical definition should be one
two-himdredth of an inch or less, and this stand-
ard is easily attained by good-class lenses. This
matter is pursued further in the article appearing
under the heading " Depth of Definition," which
should be read in conjunction with the above.
When spherical aberration is entirely absent
the centre of the field will be so sharply defined
that the most delicate sensitive film is too coarse
to register the smallest details. The structure
of the sensitive film varies from that of the
daguerreotype, which is practically grainless,
through albumen on glass, collodion, and slow
gelatine emulsions, until the rapid gelatine
emulsions which show a granular structure even
when magnified only a few diameters. (For the
extent of definition which may be reasonably
expected from a given type of lens at fuU aper-
ture, see " Field of I,ens.")
DEKAGRAMME {See "Weights and Meas-
ures.")
DELIQUESCENCE (Pr., DiUquesoence ; Get.,
Zerfliessung)
A property by which certain chemical saltS)
etc., absorb moisture and become " watery " on
exposure to the air. Ammonium sulphocyanide
and potassium carbonate are examples of
deliquescent bodies. Such chemicals should be
stored in a bottle tightly corked, or made up
in solution. (For Ust of deliquescent substances,
see " Chemicals, Storing.^)
DEMENEY CHRONOPHOTOGRAPHE
(Pr., Chronophotographe Demeney ; Ger.,
Demeney Kronophotograph)
A kinematograph machine introduced in
October, 1893, by Demeney, and improved
two months later by the addition of the " dog "
or cam motion, which may be described as an
eccentric roller that pulls down one picture-
length of film each time it comes round. This
is the first recorded instance of the employment
of that now well-known movement in the
kinematograph. Since then, the chronophoto-
graphe has been added to and elaborated. (See
also " Kinematograph.")
DENSITOMETER (Pr., OpaoitSmitre ; Ger.,
Dichtigkeitsmesser)
An apparatus for testing the density of a
given negative as compared with an average
or standard negative, and estimating the time
that wiU be required for printing. In Daw-
son's densitometer, a dense part of the negative
to be examined is held in front of a suitable
source of light, and a screen illuminated by the
light that is transmitted is compared with a
similar screen receiving light from the same
source through a diaphragm, the aperture of
which may be varied.
DENSITY (Pr., DensiU : Ger., Schwarzung)
The relative weight of silver deposited per
umt area and expressed mathematically as = —
log. e T or log. J O, T = transparency and O =
opacity, or, for convenience in working, it is
usually taken as = — log. m T. As defined by
Hurter and Driffield, the law which woidd pro-
duce absolutely true tones would be expressed
by saying that the quantity of silver reduced on
the negative is proportional to the logarithm of
the light intensity. Unfortunately, great con-
fusion exists generally in the use of the terms
" density " and " opacity," and the very common
expression, " a very dense negative," is a typical
example, inasmuch as what is really meant is
a negative with great opacities — that is to say,
the " opacity " of the silver deposited is so great
that there is very little transparency. By the
application of a simple factor, densities can be
at once converted into the weight of silver per
unit area.
DENSITY CALCULATIONS
In photo-chemical investigations it has been
foimd that, assuming that the times of exposure
can be divided into the four periods of under-,
correct, over-exposure and reversal, the ratio
of two densities in the period of under-ex-
posure are exactly equivalent to the ratios
of the two exposures, or that the amount of
silver reduced per unit area is directly propor-
tionate to the exposure. In the period of
correct exposure the densities are exactly pro-
portional to the logarithms of the exposures,
and this is expressed by the formula —
D = 7 (log. It ± C)
in which D = the density, y = a. constant
depending on the duration of development.
It = the product of the intensity of the light
and time, and C = a constant dependent upon
the speed of the plate.
The law connecting density with exposure
may be calculated by means of the following
formula — •
D =7log. ,[^0— (O — 1)0 "]
in which D = density, O = the opacity of the
plate to the chemically active rays, ;8 = a fraction
the hyperbolic logarithm of which is — — , it
= the exposure, and i = the inertia of the
plate.
DENSITY CURVE (See "Plates, Testing.")
Density Measurements
167
Depth of Tone
DENSITY MEASUREMENTS
The measurements of densities are always
effected with some form of photometer.
DENSITY, OR SPECIFIC GRAVITY (See
"Specific Gravity.")
DENSOGRAPH
A photometric instrument designed by Dr.
Goldberg, based on the use of neutral tint
■wedges, for obtaining automatically the charac-
teristic curve of a plate — that is to say, for
expressing the relations between the densities
and their corresponding exposures.
DEPOSITS ON NEGATIVES AND PRINTS
Pine granular or chalky deposits, usually
caused by lime in the tap water used for wash-
ing. Films allowed to dry with deposit adhering
will feel rough to the touch, but the printing
qualities of a negative are but seldom affected.
Such deposits are best removed by gently wiping
the surface of the negative, straight from the
washing water, with a pad of wet cotton-wool.
Methylated spirit or Baskett's reducer may be
lightly applied to remove dried-on deposit.
The peculiar form of deposit that sometimes
results from the use of an alum bath is due to
insufficient washing, either before or after using
the alum solution, a combination of chemicals
forming with the alum deposits on, in, or under
the film. Alum, is very dangerous to the life of
a gelatine film when it becomes mixed with
certain other chemicals. Fixing baths contain-
ing alum may be decomposed by the alum and
form deposits. There is no known method of
removing deposits caused by alum. If a harden-
ing bath is necessary, formaUue should be used,
as it does not form a deposit. (See also " Black
Spots " for a pecuhar form of deposit on prints.)
DEPTH OF DEFINITION, DEPTH OF
FIELD, AND DEPTH OF FOCUS
"Depth of field" is sometimes used as synony-
mous with " depth of focus " and " depth of
definition," the third expression more correctly
indicating what is meant. Theoretically, objects
on different planes, however small their separa-
tion, are brought to a focus by the lens at different
points. In practice, however, it is found that there
IS a certain range within which objects are ren-
dered with a satisfactory degree of sharpness. The
distance between the nearest and the farthest
sharp object is the depth of definition. The
two chief factors regulating this are the focal
length of the lens, and the size of the stop
employed ; the shorter the first and the smaller
the second, the greater is the depth of definition ;
the longer the focal length and the larger the
aperture, the smaller is the depth of definition.
If a lens is focused on a very distant object, and
then slightly racked away from the screen until
the limit of critical definition in the distance is
reached, it will then be in the position which
giyes the greatest depth of definition. The
nearest point showing satisfactory definition
wiU vary according to the focal length and the
stop, as already stated. The rule for finding the
exact distance (known as the hyperfocal dis-
tance) on which to focus to secure this greatest
depth, is as follows : Square the focal length
of the lens (in inches), multiply by 100, and
divide by the / number. The answer gives the
hyperfocal distance (in inches). Halving this,
distance gives the nearest point of critical
definition.
When a nearer object is focused upon there-
is a certain distance both before and behind it
within which the definition is also up to the
standard laid down. The amount of this depth
for any distance, lens, and stop, may also be
calculated. Let H be the hyperfocal distance
(inches) for the given lens and stop, D the dis-
tance (inches) focused for. The nearest point
of critical definition is then (H x D) -r (H -t- D) ;
the farthest point is (H x D) -r (H — D). The
range of good definition is always greater beyond
than before the actual point focused upon. It
follows that in estimating a distance to which
the focusing scale is to be adjusted (as in hand-
camera work) it is better to under-estimate it
than otherwise.
A lens is sometimes said to have a deep focus
when it renders both near and distant objects
sharply at one time ; but as the focus of a
pencil of rays should be a point, it is evident that
Diagram Showing, in Exaggerated Form, the
Effect of Diameter of Aperture on Disc of
Confusion
depth of focus is, strictly speaking, non-existent.
In practice it is convenient to assume that an
image composed of discs of confusion not more
than -01 in. in diameter is " sharp " ; so that in
this case the depth of definition is the distance
before or behind the true focal plane between
which the plate intercepts a cone of rays (of
which the lens diaphragm is the base) at less
than the diameter above named (-oi in.). It
thus follows that the larger the working aper-
ture the less the depth of definition, as indicated
in the diagram, in which A is the cone of rays
from a small aperture, B the cone from a larger
one, and C and d the diameters of the discs of
confusion respectively formed ; the more acute
the angle, the smaller is the disc. The surface
of the sensitive film is indicated by the line B.
By halving the diameter of the aperture the
depth of definition is doubled, and so on in the
same proportion. It also varies inversely as
the square of the focal length of the lens for
the same intensity, or inversely as the focal
length for the same aperture. (See also " Hyper-
focal Distance.")
DEPTH OF TONE
A term used, somewhat loosely, in pictorial
photography to describe the lowness of the tone
Derepas Mounting
168
Detective Camera
values, and in technical photography to describe
the extent to which a picture has been toned or
developed. A print is said to be deep or low
in tone when, generally intentionally, it has no
brilliant high lights, and the appearance is dark
or gloomy. Black or cold tones appear deeper
than warmer ones ; in other words, assuming
a black-and-white bromide print to be cut into
two, and one half toned to a brown, the brown,
as a rule, does not appear so deep in tone as the
black part. The depth to which a picture is
toned or developed influences considerably the
final result. As a consequence of toning gelatino-
chloride (P.O.P) and other print-out papers, the
tone becomes less deep, due to (a) the negative
being flat, foggy, or otherwise unsuitable, (6)
quick (or surface) toning, in which case the tone
is on the top and easily taken off by the fixing
bath, and (c) the use of a " hypo " bath in an
add condition. A black-and-white bromide
print that is not fully developed will lose much
of its depth of tone in a sulphide toning bath.
DEREPAS MOUNTING (See " Dry Mount-
ing.")
DEROGY
A French optician of the 'fifties and early
'sixties. In 1859, he made public a half-plate
convertible lens, with combinations fitting
together by bayonet joints instead of the usual
screws. Six changes were possible.
DESICCATED DRY PLATES
Dried, or heated, dry plates. It is well known
that dry plates, as ordinarily used, retain a con-
siderable percentage of water, mainly in mole-
cular combination with the gelatine. Howard
Parmer, to whom the idea of desiccated
plates is due, found that the water has a
large influence on the image at the time of
exposure, definition, detail, density, speed, etc.,
being aiiected. He found, moreover, that very
small diiierences in the percentages materially
afiect the result, so that negatives vary with
the atmospheric conditions, as to temperature
and humi(£ty, at the time of exposure. Accord-
ing to Parmer, " The drier the film, the
better the definition, and the greater the power
of rendering fine detail ; in lesser degree, the
greater the speed and facility of developing
density. This property of the film can be
utilised by desiccating dry plates for work where
definition, detail, brilliancy, or maximum speed
are desired, and in exposing plates wet where
softness of image or Uie destruction of small
textures and details are sought for. Extra
rapid and orthochromatic plates, in which the
former of these qualities is usually foimd
lacking, gain them when desiccated to an extent
hitherto only found in wet collodion or other
specially prepared films."
A perfectly flat-topped kettle containing boil-
ing water is a convenient appliance for desiccating
plates ; these are simply laid film side upwards
on the kettle top with a piece of bibulous paper
between to equalise the heating, and kept there
for a few minutes at a temperature of 200° P.
(about 93° C.) before being placed in the dark-
slides. Or a thick copper slab with an asbestos
cover can be used. Too great or too prolonged
beating will crack the dry plate or induce fog.
Desiccation must be carried out in a dark-room,
and the plates should be exposed while hot
or as soon after the treatment as possible.
In process work, desiecated dry plates have
been recommended for direct colour work.
DETACHABLE FRONT (Pr., Planchette se
dHachant ; Ger., Objehtivbrett)
A panel holding the lens and made to slip
into a rebated opening in the camera front, in
which it is secured by turn-buttons. It may
be either square or circular. Any number of
lenses, of different sizes, can thus be used on
Square Detachable Front
the same camera, a separate front being provided
for each lens. Por temporary use with a strange
lens, when a panel is not forthcoming, a piece of
stout cardboard may be cut to fit the opening
in the camera front, a circular aperture being
made in this to fit tightly on the lens. The
inner side of the cardboard should be blackened.
DETAIL (Pr., DUail ; Ger., Einzelheit)
The dear rendering of detail is largely depend-
ent on focusing, and the defining power of the
lens. A tree may be so rendered as to appear
as a more or less homogeneous mass, or so as
to indicate its leafy detail. The degree to which
detail should be shown depends upon circum-
stances ; in some cases the most minute details
require to be dearly shown, and in others such
a rendering is far from satisfactory. Suppres-
sion of detail results in the quality known as
" breadth," but over-suppression leads to a loss
of " texture." Por example, a wicker-work bas-
ket showing every detail dearly would probably
look -hard and "fidgety"; on the other hand,
the detail might be so suppressed as to make
it di£B.cult to recognise that the basket was of
wicker-work at all. The direction and strength
of the light and the state of the atmosphere
are important considerations.
DETECTIVE CAMERA (Fr., Chambre ditec-
tive : Ger., Detectiv-Kamera)
A term that appears to have been invented
by T. Bolas, who in 1881 described a twin-lens
magazine hand camera with focusing adjust-
ment and pneumatic release, and having a
reversing prism placed before the lens, so fiiat
the apparatus need not be directed at the
person to be taken, who woujd remain quite
unsuspicious of being photographed. I,ater, the
name was applied loosely and inappropriately
Deterioration
169
Developer
to all box-fonn magazine hand cameras, which
are still so designated in Prance. Practically
the only cameras likely to be of real service in
the detection of crime are those which are either
entirely disguised, or are worked from a dis-
tance by the aid of a telephotographic lens.
(See also " Disguising the Camera.")
DETERIORATION
I<enses, chemicals, and sensitive plates and
papers all deteriorate more or less according to
the length of time and manner in which they
are kept. The commonest form of lens deterior-
ation IS due to the gradual depoUshing of the
glass surface by dust, the action being assisted
by the careless or rough use of the dusting cloth.
It is better to remove dust by blowing it off, bul)
if wiping is necessary it must be done carefully
{see "Lenses, Cleaning"). Sometimes when a
lens is put on one side for a time an iridescence
spreads over its surface, due to dampness.
Lenses stored in a strong light often become
slower in action, because of the yellowing action
of light upon the balsam with which the lens
glasses are cemented together.
Dry plates and sensitive papers deteriorate
very quickly if not properly stored in a dry,
fliry place, the worst place being a high shelf
where gas fumes can get to them. The effect
of age on a plate much resembles that of a very
slight exposure to light ; but dry plates keep
remarkably well if stored carefully, and skilled
workers can frequently get good results on
plates as old as twenty years.
J. B. B. Wellington in 1905 pointed out
that the popular sulphide toning bath has a
deteriorating effect upon plates and papers ;
everyone knows that the minute quantities of
siilphur contained in a London fog wiU tarnish
silver articles, producing upon them a thin film
of silver sulphide, and that the sulphur in
coal gas has the same effect when the gas is
burnt. It is thus easy to understand how much
more deleterious must be the large quantities of
sulphur given off from the sulphurising bath of
sodium sulphide on the still more delicate silver
bromide and silver chloride which go to make
np the emulsions coated upon plates, films,
papers, etc. When these are kept in a room in
which sodium sulphide is employed, they will
become unusable in the course of a few weeks.
Plates affected by sulphur will develop with an
iridescent stain, with general deterioration and
fog. Bromide and gaslight papers are affected
in practically the same way, producing a flat
and dirty print. With P.O.P. the surface will
assume a metallic lustre, and when printed will
be difficult to tone. Self-toning papers appear
to discolour more quickly than other papers,
but frequently this defect disappears in fixing.
DEVELOPER (Fr., RMlateur ; Ger., Ent-
wickler)
Any agent used to render visible the latent
image, or, in other words, to reduce to silver or
other metal the latent image produced by the
action of light upon any sensitive salt. In
ordinary photographic phraseology the term is
applied to the solutions generally; whereas
strictly speaking it should be appUed only to
that chemical or agent which actually reduces
the exposed silver salt.
The composition of the developing solutions
varies considerably not only with eadi make of
plates, but frequentiy with each worker; but
there is a definite quantity of developing agent
which should at least be used, and this is un-
doubtedly largely dependent on the number of
molecules in the active group, and the amido
groups are more active than the hydroxyl
groups. Von Hiibl has given the following table
based on this fact, which shows the best con-
centration of the actual developing agent and
also the strength usually employed, assuming
that a 5 per cent, solution of potassium carbon-
ate is used as the alkali.
Weight in every 100 parts of
developer
Calculated Generally used
Metol .
0-6
0-6
Pyrocatechin
0-6
0-6
Hydroquinone
. 0-6
. o-5^i-o
Amidol
. 0-4
. 0-4 — 0-8
Paramidophenol
■ 0-5
. 0-4— 0-7
Pyrogallol
• o-s
. 0-3— 0-6
Eikonogen
0-9
. 0-8 — 1-5
Adurol .
I-O
i-o
Diogen .
I -2
1-2
Glycine . 0-5-
-17
.. . :ii ...
I-O
i.1-_ _ ;-
rapidity of development.
I
II
III
IV
V
VI
VII
VIII
Pyrocatechin -f- caustic soda
15
100
0-6
5
10
20
sUght
0-3
Metol -t- potassium carbonate .
20
75
0-8
5
10
0
very slight
0-5
Hydroquinone + caustic potash.
25
60
I-O
no
105
70
slight
0-4
Amidol ......
30
50
0-4
50
60
5
considerable
Adurol + potassium carbonate .
30
50
0-6
30
45
25
considerable
0-6
Paramidophenol + potassium carbonate
40
38
0-5
70
30
30
considerable
0-5
Rodinal ....
40
38
0-5
45
40
30
slight
o-g
Pyro + potassium carbonate
40
38
0-5
35
55
40
considerable
0-3
Glycine + caustic soda
45
33
0-6
90
70
125
slight
0-8
Eikonogen + potassium carbonate
50
30
0-5
85
55
80
slight
0-6
Pyrocatechin + potassium carbonate .
60
25
0-5
140
60
70
very considerable
0-6
Hydroquinone -|- potassium carbonate
70
21
0-7
95
80
120
slight
0-4
Diphenal ......
75
20
0-8
30
80
25
slight
0-7
Glycine + potassium carbonate .
75
20
0-5
210
130
115
very considerable
I-O
Ferrous oxalate ....
75
20
05
280
go
80
slight
0-8
Piogen -t- potassium carbonate .
1-
95
16
0-4
115
120
80
considerable
0-7
Developer, Viscous
170
Developers, Mixed
A second table, also due to Voa Hiibl, is that at
the foot of the preceding page. In column I. is
given the duration of development to yield a cer-
tain density, in column II. the relative rapidity of
development, in column III. the relative density-
giving power, in column IV. the slowing of
development in seconds by the addition of
2 per cent, of potassium bromide, in column V.
the retardation in seconds due to cooling the
developer to 50° P., in column VI. the retarda-
tion in seconds by diluting with an equal volume
of water, ia column VII. the action of broirdde
on the density, and in column VIII. the keeping
power of the mixed developer, i being taken as
that which keeps longest.
A developing solution should contain a certain
quantity of alkali to form the actual developing
salt or to increase the reducing power of the
developer proper ; and for this reason it is called
the accelerator. A preservative is required to
prevent too rapid oxidation or the deposition
of an organic stain due to the oxidation of the
developing agent.
The alkalis generally used are sodium car-
bonate, potassium carbonate, and caustic soda
and caustic potash. Some alkalis act better
than others with given agents, and on the Euro-
pean Continent potassium carbonate is generally
used, whilst in England the corresponding
sodium salt is used. The preservative is usually
sodium sulphite, whilst potassium metabisulphite
is occasionally used also. Only a few years ago
an alkaline bromide was recommended in almost
all cases, but this was partly due to the fact that
the plates then did not work quite free from fog.
Of late years the use of bromide has become much
less general. Formulae for the various developing
agents are given under the respective chemicals.
DEVELOPER, VISCOUS (See "Viscous
Developer.")
DEVELOPERS, COMPARATIVE COST OF
The prices given below are approximate for
each working quart (40 oz.) of developer at
normal strength as prepared for pouring upon
the exposed plate. The chemicals are taken at
British retail prices.
Adurol (one solution) .
Adnrol (two solutions) .
Amidol
Edinol
Eikonogen (one solution)
Eikonogen (two solutions)
Ferrous oxalate .
Glycine (one solution) .
Glycine (two solutions).
Hydroquinone
Hydroquinone-metol
Imogen sulphite .
Kachin (one solution) .
Kachin (two solutions)
Metol
Ortol ....
Pjrro-soda .
Pyro-metol .
P3rrocatechin (one solution)
Pyrocatechia (two solutions)
Rodinal
Metol-hydroquinone, according to one maker's
s.
d.
I
0
I
3
0
6i
I
8
0
9
t
3
0
S
0
7
0
10
0
51
0
7i
0
5f
0
II
I
0
0
10
t
I
0
5
0
6
0
4
0
9
0
7
formula, costs rod. per quart, and according
to another maker's only 5jd. In actual prac-
tice, and on the basis of developing a fixed num-
ber of plates, there is not much difference,
as many of the more expensive solutions are
capable of treating a far greater number of
plates than the cheaper ones, bulk for bulk.
DEVELOPERS, MIXED OR COMBINED
Mixed developers — as, for example, hydro-
quinone and metol — ^have become popular.
Developers are of two distinct kinds : (i) those
that give detail quickly and density afterwards ;
these include metol, rodinal, etc ; (2) those that
give density first and detail gradually — ^for
example, hydroquinone and pyro. Taking one
of each class and blending, it is possible to obtain
a combination of characteristics ; thus metol
with hydroquinone gives detail without excessive
thinness of the image or duration of development.
The most is obtained with a combined developer
by compounding it from one having a. low
factor number (see " Development, Factorial ")
with one of a high factor ; and while most
developers may be mixed together, there is no
advantage in combining two developers of
practically the same factor numbers, as, for
instance, pyro and hydroquinone, both of which
may be said to have, roughly, the factor of 6.
A better combination is hydroquinone (factor 6)
and metol (factor 30).
The best known and most widely used com-
binations are hydroquinone and metol, and pyra
and metol, but the foUowitig have also their
advocates : Metol-adurol, hydroquinone-eikono-
gen, hydroquinone-pyrocatechin, hydroquinone-
rodinal, hydroquinoue-amidol, metol-glycin, and
others. Formulae for some of the best knowa
mixtures are : —
Hydroquinone-Metol
Metol . . .33 grs. 3-4 g.
Soditmi sulphite . 99 „ 10-2 „
Hydroquinone . . 40 ,, 4 ,,
Potassiiuu carbonate . 198 ,, 20
Water to . . . 20 oz. 1,000 ccs.
The above is a one-solution developer, ready
for use. (See also " Metol-Hydroquinone." )
Pyro-Meiol
A. PyrogaUic acid . 55 grs.
Metol . . . 45 „
Potassium metabi-
sulphite . . 120 „
Potassium bromide 20 ,,
Water (boiled) to 20 oz.
B. Sodium carbonate
(crystals) . 4 oz. 200 g.
Water (boiled) to 20 „ 1,000 ccs.
Use equal parts of A and B.
Eikonogen-Hydroquinone
A. Hydroquinone . 40 grs. 4 g.
Eikonogen . . 120 „ 12 „'
Sodium sulphite . i oz. 50
Citric acid . . 20 grs. 2 "
Water to . .20 oz. 1,000 ccs,
B. Sodium carbonate 60 grs. 6 g.
Sodium hydrate . 32 , 3-2
Potassium bromide 6 ,', -6 ,',
Water to . .20 oz. 1,000 ccs»
Mix A and B in equal parts.
5-5 g-
4-5 „
12 „
2 „
1,000 ccs.
Developers, Mixed
171
Developing
Metol-Glycine
Glycine . . .50 grs.
Metol . . . 10 „
Sodium sulphite . 21 oz.
Potassium carbonate . 2I „
Water to . . . 20 „
One solution, ready for use.
Edinol-Hydroquinone
20 oz.
5 g-
125 „
125 „
1,000 CCS.
Water to
Acetone stdphite
Sodium sulphite
Edinol
Hydroquinone
Potassiimi carbonate
Dissolve in the order
75 grs.
I oz.
30 grs.
IS „
2 oz.
named, and
1,000 CCS.
7-5 g.
SO „
3 „
i-S „
100 ,,
for over-
exposure add one drop of a 10 per cent, solution
of potassium bromide to each ounce of devdoper
used. The above is a one-solution, ready for use.
A.
B.
Hydroguinone-Rodinal
Hydroquinone . 120 grs.
Sodium sulphite . i oz.
Citric add . . 5 grs.
Potassium bromide 60 ,,
Water to . .20 oz.
Potassium carbonate 2 „
Rodinal . . i „
Water to . 20 „
136 g.
S4-5 „
•s „
6-8 „
1,000 CCS.
100 g.
so „
1,000 CCS.
For soft negatives use equal parts of A and B
and water. For brilliant and harder negatives
use equal parts of A and B without water. For
detail increase the proportion of B, and for
density increase that of A.
Pyro-Amidol
Sodium sulphite . 198 grs. 20 g.
Sodium carbonate . 66 „ 6-6 „
PyrogaUic add . 20 „ 2 „
Amidol . . . 10 „ I ,,
Water to . . . 20 oz. i ,000 ccs.
Add the amidol just before developer is required,
and it will be ready for use. It will not keep.
Metol
Adurol
Sodium sulphite
Potassima carbonate
Potassium bromide
Water to .
Adurol'Metol
118 grs.
410 „
7 oz.
4-7 ,.
21 grs.
20 oz.
13-5 g-
47 „
383 „
256 „
2-4 „
1,000 CCS.
Dissolve the chemicals in the water in the order
named. To develop plates add 1 part of the
above to 2 parts of water.
Pyro-Hydroquinone
This is a mixed developer sometimes advo-
cated, but both agents being slow-acting and
somewhat aUke, it is not particularly advan-
tageous. It is induded here chiefly because
of the boric add in the formula : —
Hydroquinone
Pyrogalhc add
Potassium metabi-
8 grs.
80 „
•8 g.
8 „
sulphite .
Boric acid (crystals)
Water .
Sodium sulphite .
Sodium carbonate
80 „
10 „
20 oz.
I „
1 »
8 „
I „
1,000 CCS.
so g.
SO „
Water .
20 „
1,000 CCS.
The boric add is used as a restrainer because of
its remarkable corrective power in cases of over-
exposure.
A mixture of hydroquinone and eikonogen was
introduced ia 1892 under the name of " Mixtol."
The formula is : —
Sodium sulphite
Hydroquinone
Eikonogen .
Potass, ferricyanide
Potassium carbonate
Caustic potash .
Potassium bromide
Boiling water
Glycerine to
924 grs.
115 .,
77 „
154 „
577 „
"5 „
8 „
18 oz.
5 mins.
92 g.
II-5 „
77 „
I5-S „
57-7 „
II-5 „
•8 „
1,000 CCS.
5 ,,
Mix in the order named, allowing each to dis-
solve before adding the next. The solution is
of a. yellowish colour, and keeps well. For
" instantaneous " work, add one-half water ;
for time exposures, two-thirds, or omit the
caustic potash and increase the carbonate to
700 grs., and add more bromide if necessary.
It may be used over and over again, and it is
daimed not to stain or friU.
A mixture of rodinal, hydroquinone, and
eikonogen, known as " Cydol," was at one time
popular. The formula is : —
Eikonogen
Hydroquinone
Rodinal
Sodium sulphite
Potassium carbonate
Water to
100 grs.
30 .,
9 drms.
2^ oz.
2i „
20 „
10 g.
3 „
■9 „
125 „
125 „
1,000 ccs.
The above is a stock solution. For use in
warm weather, i part is mixed with 7 parts of
water ; iu cold weather, less water is used ;
and in very cold weather, only 3 parts of
water.
Two developers are sometimes used separatdy
instead of mixing, but they have no advantages
over the combined developers given above.
Detail is first secured with a quick-working
developer and density afterwards obtained with
a slower-working one. The following is an
example : Develop with rodinal of ordinary
devdoping strengtii untU all detail has been
brought out ; then finish with ordinary pyro-
soda devdoper, or preferably with the following
one-solution mixture of hydroquinone : —
120 grs. 12 g.
I oz. 50 „
If,, 88 „
20 „ 1,000 ccs.
Hydroquinone
Sodium sulphite
Potassium carbonate
Water to .
DEVELOPING
This artide will be devoted to a simple ex-
planation of the ordinary method and practice
of developing a dry plate. The exposure having
been made, the closed dark-sUde is removed to
the darjc-room, and the plate devdoped either
at once or at any convenient time afterwards.
The work must be done in a safe light. In
front of the lamp place a cleaned earQienware
developing dish of the required size, and near
it a glass measure containing about 2 oz. of the
developer. Into another dish pour some fixing
solution, made by dissolving 4 oz. of sodium
hyposulphite ("hypo") in 20 oz. of water.
Developing
172
Developing Bench
As all photographic solutions work more
elowly when cold, it is advisable to mix up all
solutions some time before they are needed, as
when freshly mixed they are very cold, particu-
larly the " hypo " solution, whidi drops almost
to freezing point when newly mixed. By stand-
ing some time, the solutions become of lie same
temperature as the room. Anything between
6s° and 70° P. (18° and 21° C.) is the best for
developing and fixing solutions.
The beginner is recommended to use the hydro-
quinone-metol developer {see " Developers,
Mixed "), and he should be informed that each
chemical in the formula plays its own part.
Hydroquinone and metol are the developers
proper ; but they need the help of the other
ingredients. Hydroquinone gives density, and
metol detail ; so by combining the two, density
and detail are obtained at the same time. The
sodium sulphite is included to preserve the solu-
tion, and is called the preservative. The sodium
carbonate or potassium carbonate quickens the
developing action, and is called the accelerator.
Potassium bromide is frequentiy added, and
this controls the action, and keeps the negative
clear. As each has its own characteristic action,
it will be obvious that were the chemicals in
separate solutions, they could be so adapted, if
necessary, to suit under- or over-exposure ; but
there is no need to trouble with separate solu-
tions. A good mixture is given below :
Hydroquinone .
. 30 grs.
7 g.
Metol
• 10 „
2-3 „
Sodium sulphite
■ 350 „
80 „
Sodium carbonate
• 350 „
80 „
Potassium bromide
5 ,.
I-I5 .,
Water to .
. 10 oz.
1,000 CCS.
Take particular care that no stray light enters
the room, and that the only illumination comes
from the red lamp. Remove the exposed plate
from the slide and look at it, but not too near
the lamp. Nothing on it will be seen ; it wiU
appear exactly as it did before the exposure. The
image is latent (that is, concealed or hidden),
and it needs to be brought out by the developer.
Put the plate in the developing dish, the
sensitive or creamy side of the plate being
upwards and the glass side resting on the
bottom of the dish. Then pour the developer
over the plate in one quick sweep, so that the
plate is completely covered in one sharp even flow,
preferably from one comer. If the developer is
properly applied, no air bubbles will form ; but
should any appear, break them quickly by touch-
ing them gentiy with the finger-tip, or, prefer-
ably, with a clean camel-hair brush. Then rock
the dish from side to side and end to end, so that
the developer flows evenly over the entire plate,
taking care to expose it to the red light as littie
as possible. The brightest parts of the resultant
picture, such as the sky, wlute collars, and white
dresses, etc., will appear first of all. If the expo-
sure is a landscape the sky wiU be the first to
appear ; but it will be black, as all lights and
shades are reversed in a negative, the black or
very dark parts of the actual scene appearing as
almost clear glass and the whites almost or quite
opaque. After the sky, the half-tones of the
pictures will appear, and finally the details in
the shadows. The developing dish must be
gentiy rocked all the time. When the image has
appeared, the plate must not be removed, but
development continued for some little time
longer, so as to add density to the negative.
Continue for about a minute or so after the
density appears to be correct, as this will be
considerably reduced in the fixing bath.
It is important to know how long to continue
development, and some experiments at the cost of
a few plates will teach more than will many-
pages of printed matter. A negative that is
taken out of the developer too soon is very thin,
and will not give a good, clear picture ; whereas a
negative that has been left in the developer too
long will be dense or harsh. As a general rule,
when the negative is suflScientiy developed, the
dark parts in the negative, such as the sky, will
show through the negative, and can be seen when
the plate is examined from the glass side. The
plate may also be taken out of the developer once
or twice, and examined by holding it up to the
red lamp, and its density judged by looking
through it.
In cases of under-exposure, the image comes
up very slowly, or only the high lights appear
and not the half-tones and shadows. Devdop-
meut should be complete in ten minutes or even
less. If after, say, fifteen minutes nothing, or
very little, appears on the plate, try breathing
on it, or warm the developer, but only very Uttle,
or the film will melt. If after a long time nothing
appears, the plate may be destroyed as being
useless. On lie other hand, if the image appears
extremely quickly, and the plate goes black all
over in a minute or two, the plate has been over-
exposed, or fogged by light other than that
through the lens. A little extra potassium
bromide added to the developer wiU sometimes
save over-exposed plates if it is known that they
are over-exposed before the developer is poured
on ; but after development has started it is a
waste of time to add the bromide.
Subsequent processes, assuming that aU has
gone well, include a minute's rinsing in cold water,
and transference, film uppermost, to the fixing
bath, in which the plate remains for a period
twice as long as that occupied by the whiteness
in disappearing. Thus, if the whiteness disap-
pears in ten minutes, allow the negative to
remain for a further ten minutes. {See also
" Fixing.") Finally, the negative, which may
now be brought out into the daylight, is washed
for at least tiiirty minutes in running water {see
also " Washing "), while it stands on edge.
The beginner is recommended to adopt the
factorial system of development. {See " De-
velopment, Factorial.")
DEVELOPING AFTER FIXING {See " Fix-
ing before Development.")
DEVELOPING BENCH OR SINK (Pr.,
Etabli de dSveloppement ; Ger., Entwick-
lungsbanh)
A bench or table specially designed for develop-
ing, and usually provided with a stoneware or
leaden sink. The top, if of wood, should be
coated with shellac or other waterproof varnish.
The height should be such that the operator
can work at it without either stooping or strain-
ing, and there is no reason why it should not
Developing Dish
173
Developing Machine
be low enough for the worker to sit at, if this is
desired. The contitmous standing customary is
merely fatiguing, and in no sense necessary. A
very sHght slope to the sides of the bench, so
that spSt solutions may run into the sink, is
useful ; but this is often much overdone, so
that bottles are liable to be upset, and the
contents of full dishes to escape over one side.
The developing bench may be either fixed or
portable, but the essential features are practically
Developing Bench
the same in each case. A typical portable bench
is illustrated. The sides are grooved so as to
drain into the sink, which is of vitrified stone-
ware. The water is supplied by a swing-arm
rose tap, under which may be placed a loose grid
to hold dishes, etc. Convenient shelves for
bottles, and racks for dishes, are fitted.
DEVELOPING DISH {See " Baths.")
DEVELOPING FILMS (See "Beveloping
Machine," "Pihn Developing, etc.")
DEVELOPING AND FIXING COMBINED
A system of developing in which a sufficient
amount of " hypo " is mixed with the developer
in order that developing and fixing may be per-
formed at the same time, a method thought
much of at one time but little used nowadays.
The secret of successful work is in the use of the
correct amount of " hypo " to balance the
developer. The " hypo " may be mixed separ-
ately and added to a developer, or made up in
the developer itself. For the latter method
edinol is perhaps the most snitable : —
Sodium hyposulphite 150 grs. 26 g.
Sodium carbonate . J oz. 62-5 „
Sodium sulphite . 300 grs. 52 „
Edinol . . . J oz. 21 „
Dissolve the first three in 12 oz. of water, add
the edinol, and use at once. The former method
is to make up the "hypo" and developer proper
separately and mix before use, as follows : —
Ordinary developer . 5 oz. 150 ccs.
Sodium hyposulphite sol. (20 %) 2 or 3 drops^
The following developer is one that is popular
upon the Continent, and works well with
"hypo" :—
g-
Hydroquinone .
. 60 grs.
8-5
Metol
Sodium sulphite
Sodium carbonate
• 30 „
■ 450 „
■ 600 „
4-3
64-5
8=;
Water to .
. 16 oz.
1,000
The " hypo " solution is added in the proportions
stated above immediately before use.
If properly mixed, development is completed
at the time the plate is fixed, and the negative
simply requires the usual washing. The method
forms an interesting experiment, but is not recom-
mended for valuable exposures, as with some
plates it does not always work so well as could
be wished. " Hypo " also acts as an acceler-
ator with some developers. (See " Hypo in
Developer.")
Kachin is one of the most suitable developers-
for combination with " hypo." J. Mcintosh
advocates the following : —
A.
B.
C.
For use take of A 160 minims, B 240 minims,.
C 20 minims, and water to make i oz.
DEVELOPING MACHINE (Fr., Machine de
diveloppement ; Ger., Entwicklungsma-
schine)
Various machines have been devised from-
time to time for the semi-automatic develop-
ment of plates or films. One of the most suc-
cessfiil for films was introduced in 1903 by'
Kodak, Ltd., and may be worked in fuU daylight.
The spool of film having been inserted in the
machine and the lid closed, a handle is turned
which winds the film face outwards against a^
coiled " apron " of celluloid, with ribbed rubber
edges acting as separators between the layers-
Kachin
60 grs.
15-5 g-
Sodium sulphite .
600 ,,
155 ,.
Water to .
8 oz.
1,000 ccs.
Caustic soda
40 grs.
18 g.
Water to .
5 oz.
1,000 CCS.
Sodium hyposul-
phite
I oz.
500 g.
Water to .
2 ,.
1,000 CCS.
Kodak Developing Machine
of film. The developer is then introduced and
the film slowly rotated for a given time. It
may next be washed and fixed in the same way
and removed from the machine. Development
takes from four to eight minutes, according to-
the temperature. In a later pattern of the
machine {see illustration), the film having beea-
woimd into the red ceUuloid apron, is placed
Developing Tank
174
Development, Factorial
in an npright cylindrical tank, and left for a
epecified time in a dilute developer. A water-
proof lid to the tank allows it to be reversed at
intervals during development.
DEVELOPING TANK (Fr., Riservoir de
divelopp&ment. Cuvette hermitique ; Get.,
EniwicMungsbehalter)
A metal or stoneware tank intended for stand
or time development. There are many different
patterns for both plates and films. In the
Watkins developing tank a metal rack, holding
one dozen plates, is attached to the lid in such
a way that when inserted in the tank the plates
are horizontal ; the advantage is that one or
two plates only can be developed if desired,
with bu,t a small quantity of solution. The
plates having been inserted in the dark-room,
and the closely-fitting lid adjusted in position,
the developer is pouied in at a light-trapped
delivery piece projecting at one end of the tank.
This delivery piece serves not only for the
admission and dUscharge of the various solutions,
which may be done in daylight, but can be used
to hold a thermometer to give the temperature
of the developer and the consequent time of
development. Another typical developing tank
is Griffin's, in which the solutions are poured
through a light-trapped funnel and run off by
a tap at the side. A chain is attached to the
tank by which it may be hung under a tap
for waslung the negatives after development.
Tanks for " stand " development, in which
the negatives are left for a long time in a dilute
developer, consist usually of a grooved stone-
ware trough with a lid ; these require a dark-
room for the different operations. (See also
■" Developing Machine.")
DEVELOPING TENT (Pr., Tente de dSveloppe-
ment ; Ger., Entwicklungszelt)
A portable folding tent for development out-
doors, or in any place where no dark-room is
available. In the wet-plate period every photo-
grapher was obliged to carry a dark-tent with
him, as the plate had to be sensitised directly
before use and developed immediately after
exposure. The few peripatetic ferrotype workers
still remaining use a similar contrivance. Small
portable developing or changing tents are often
a great convenience to travellers and tourists.
DEVELOPMENT, CONFINED
A system of development advocated in 1898
by Colson, a Frenchman, but now rarely used.
The principle was to restrict the amount of
developer in contact with the plate. The
latter was placed in the developer in the usual
way; but suspended over it and nearly, if not
quite, touching it was a sheet of plain glass ;
or the exposed plate was soaked in water, and
the plain glass in the developer, and the two
placed in contact, repeating the process as often
as necessary. Colson claimed that less fog and
dearer negatives were produced in this way. The
process was recommended for over-exposed
plates, the first of the methods above noted
ibeing employed.
JDEVELOPMENT, DAYLIGHT {See " Day-
light Development.")
DEVELOPMENT, FACTORIAL
A system of determining the duration of
development by noting the time of appearance
of the first trace of an image on the plate and
multiplying this time by a factor, ttie result
being the total duration of development required
to produce a negative of given density. This
method was suggested by Alfred Watkins in
1893, and has been found in practice to be very
reUable except in a few cases of exceptionally
low temperatures and very dilute developers.
It may be looked upon as one of the first prac-
tical steps to reduce development from mere
happy-go-lucky guesswork to a definite and
exact method. Like all methods based on laws
it is elastic and capable of adjustment to the
individual worker's ideas of what is a correct
negative ; or, in other words, by reducing or
increasing the factor a thinner or denser nega-
tive may be obtained suited to the particular
printing process employed. It is an ingenious
appUcation of Hurter and Driffield's law of con-
stant density ratios, and is based on the fact
that with correct exposure the total duration
of development for a given density bears a fixed
ratio to the time of appearance of the image,
assuming that the developing power of tiie
solution remains constant, and tiiis rule holds
good for variations in strength of the developing
agent, in the amount of the alkah, bromide, and
temperature.
The following factors are those generally used
for the principal developers : —
Adurol . . . 5
Azol . . . . 30
Certinal . . . .30
Cristoid pyrocatecliin . . 30
Diogen . . . 12
Edinol . . . .20
Eikonogen .... 9
Glydne-potash . . .12
Glycine-soda . . . . 8
Hydroquinone + bromide . 5
Imogen sulphite . . . 6
Kachin . . . .10
Kodak powder . . .18
Mequin . . . .12
Metol . . . . -30
Metol-hydroquinone . . 14
Ortol 10
Paramidophenol . . .16
Pyrocatechin . . .10
Pyro-metol (Imperial Standard) 9
Pyro-soda . . . -4-15
Quinomet . . . -30
Rodinal . . . -30
Synthol . . . -30
PVRO-SODA AND PYRO-POTASH FACTORS
Pyro
Grs. per oz.
I
2
3
4
8
I
2
3
4
5
Bromide
Grs. per oz.
.1
4
i
I
2
o
o
o
o
o
Factor
9
5
4J
4
3i
18
12
10
8
6i
Development, Factors for
I7S
Development, Stand
Factors for soft, nonnal, and strong contrasts
with " tabloid " formulae (Burroughs and Well-
come) : —
Soft Normal Strong
Amidol .
7
10
12
Edinol .
14
20
24
Eikonogen
8
12
15
Glycine .
9
13
16
Hydroquinoue.
3
4l
S
Metol .
20
30
35
Metol-hydroquinone
10
14
16
Paramidophenol
12
16
18
Pyxo
4
6
7
Pyro-metol
6
9
II
The factor for a combined developer with the
developing agents in equal quantities is the
mean of the two, for example : —
Pyro 6 Metol 30
(6 + 30) -=- 2 = 18
If the agents are not in equal proportions the
factor for each is multiplied by the number of
parts and the results added together and divided
by the total number of parts of both agents;
thus, supposing that the proportions were pyro
4 parts and metol 2 parts, it would be —
6x4 = 24
30 X 2 = 60
60 + 24 = 84 -=- 6 = 14, the factor
required.
The above factors are given merely as guides,
and those that have been found to give a nega-
tive of normal contrasts, that is, one with a
7 = 1, but should the worker think that such
a negative is too soft or too hard, he has merely
to increase or decrease the factor to obtain
greater or less contrasts. Supposing one were
using a metol-hydroquinone developer with a
factor of 15, and the time of appearance were
9 seconds, the total duration of development
would be 15 X 9 = 135 seconds.
The great advantage of the factorial system
is that it gives the beginner an excellent idea of
how long to develop and enables even the
advanced worker always to obtain negatives of
similar character.
DEVELOPMENT, FACTORS FOR {See
" Development, Factorial.")
DEVELOPMENT. FORCING
When a plate is under-exposed, many workers
add more of the alkaline solution to the developer,
and continue the development until the plate
begins to fog, or until it is considered impossible
to secure more detail. Although by this method
of forcing development the utmost shadow
detail is secured, it has the disadvantage of
making the light tones much too strong and
dense ; and Qie result is a harsh negative,
excepting in the case of subjects deficient in
contrast, for which subjects this method is
satisfactory. For all others, a better plan is
to take the negative from the developer, let it
rest in plain water for about five minutes, and
then continue development in a considerably
diluted solution containing a large proportion
of alkali. The dilute solution is thought to
yield much softer contrasts.
DEVELOPMENT PAPERS
The opposite to print-out papers; they are
papers on which the image is brought out by
development after exposure. The principal and
most widely used development papers are those
known as bromide and g^light papers, described
fuUy under separate headings. Phosphate paper
is also a devdopmeut paper, and in some cases
this is sold under fancy names. The above are
development papers proper. Carbon is in a
sense a development paper as the image cannot
be seen until the exposed tissue has been washed
in hot water. Platinum, ferro-prussiate, and
the ferric papers are usually referred to as
partial dev^opment papers, because the image
shows very faintly after exposure, and needs
development in order to bring it to its full
strength.
In the United States, the term " development
paper " is applied exclusively to gaslight paper.
DEVELOPMENT. STAND (Pr.
dans Us cuvettes verticales ; Ger., Stand-
entwickelung)
This term was applied by Meydenbauer in
1892 to a system of developing plates in upright
grooved tanks in extrem^y dilute developers,
though the system was first described by
Wratten and Wainwright in 1882. It is claimed
for this process that the grain of the silver
image is much finer than by any other method,
that the gradations are truer and the results
more uniform ; in addition to which no visual
examination is required, and therefore the plates
are freer from fog. On the other hand, unless
the developer be occasionally agitated there is
considerable risk of peculiar local markings and
stains. For many years after its reintroduction
by Meydenbauer, extremely dilute solutions
were recommended so that the duration of de-
velopment was prolonged even up to twenty-four
hours. Recentiy, however, a more sane view
of the matter has been accepted, and time has
been so considerably reduced that it has now
practically been merged into " time develop-
ment." (See "Development, Time.")
It is often considered that the necessary in-
crease in the duration of development is calcu-
lable from the dilution — that is to say, if a
normal developer takes three minutes to obtain
a certain density, it will, when diluted ten times,
require 3 x 10 = 30 minutes ; this statement
is not borne out by carefui photometric measive-
ments, and Wratten and Wainwright have
published certain researches on the subject
based on such measurements which disprove
this assumption. They point out that stand
development cannot be considered economical,
as most of the commercial tanks require far
too much developer ; with 29 oz. for six half-
plates, after half an hour's development the
solution is so oxidized as to be useless. The
idea that a plate may be left in a stand developer
for an indefinite time is also wrong ; as is also
the theory that a plate which should require only
thirty minutes will be as much spoilt in an hour
as the same plate developed for six minutes
instead of three. It is as important, therefore,
to know the correct duration of stand develop-
ment as that of ordinary development. They
further point out that the increase of time
Development, Theory of
176
Development, Theory of
required with rodinal is largely dependent
upon the amoimt of air dissolved in the water
to make the developer. For instance, a plate
that required three minutes' development with
I : 20 rodinal required forty-two minutes when
developed with i: 200 rodinal diluted with air-
free distilled water, and not thirty minutes ;
forty-six minutes with ordinary distilled water,
and fifty-two minutes with ordinary tap water.
Pyro-soda and glycine are not dependent on the
amoimt of air in the developer, but a ten times
diluted pyro developer requires fifteen times
the length of development with the strong
developer.
Edge markings are very liable to occur, due
to the plates being too near to the edges and the
bottom of the tank, and thus being starved of
developer. Plates are also as liable to chemical
fog in stand development as in any other kind,
and therefore too prolonged development should
be avoided or bromide should be added to the
developer, in which case the exposure must be
increased, and not the duration of development.
Zinc tanks should be avoided, as they are very
Uable to be attacked by alkahs.
DEVELOPMENT, THEORY OF
The old theory of development was that the
reducing agent or developer reduced the exposed
silver bromide or latent image to metaUic silver,
and that the bromine combined with the alkali
to form an alkaline bromide, and this is usually
expressed by the following equation : —
AgBr + DNa = Ag + Na Br -1- D
in which D merely stands for the developing
agent. This was satisfactory as far as it went,
but it really explains very httle. The later
theories, which involve a consideration of the
ionic theory, assume that when a salt is dis-
solved in water it is split up into so-called ions,
which are consia»red to be atoms of the elements
carrying an electric charge. Metallic or basic
ions are usually termed kations, and the acid ions
are termed anions, the former carrying a positive
and the latter a negative charge. Chemical
reactions are now considered to take place
between ions, and only when the substance goes
into solution, and ttius becomes dissociated
or ionised. According to this we might represent
the formation of silver bromide by the following
equation : —
+ -+- + - + —
K + Br -(- Ag + NOj = Ag Br + K -f NO,
which roughly shows the dissociation of
potassium bromide into the potassion K carrying
a + or positive charge, and bromion carrying a
- or negative charge, silver nitrate being dis-
sociated into positive Ag + and negative
nitrion NO, — then the final result would
be:—
+ ~ + - + - + -
KBr + AgNOj = AgBr -|- KNO,
and as a positive and negative charge meet in
AgBr this becomes unionised, and is precipi-
tated as an insoluble precipitate.
If now we apply this to development, and we
assume the formation of an alkaline phenolate,
as in the case of pyrogallol with only sufficient
caustic soda to form this, we might represent the
action as follows : —
- +
CONa
Hc/^\cOH +
I + Ag -I- Br =
Hcl JcOH
HC
CO
Br
HC/>jCOH _^.
Ag + + N^ +
HCl JcOH
HC
That is to say, the pyrogallol loses a negative
charge which neutralises the charge on the silver
ion. No account is here taken of any change
in the pyro, though such must take place, but
the oxidation products are not well known.
In the case of hydroquinone, however, where
we know that the product formed from it in
development is quinone, we can simply write
the equation as follows : —
COH
CH / \ CH
oc
'A'
which is I I
ChL JCH *°"^^'^^°*°ChI JcH
COH CO
hydroquinone ionised hydroquinone
-I- +
+ H,
then
CH
CH
OC
0
CH
CH
CO
ionised
hydroquinone
CO
0
CO
, ionised silver silver
+ bromide " metal + Qumone
+ +
-I- 2 Ag = 2 Ag +
CH CH
ca
CH
and the ionised hydroquinone has merely lost
two negative charges which neutralise the
positive charges of the silver in the ionised silver
bromide, and the two oxygen ions combine to
form quinone.
Obviously there are certain physical pheno-
mena which one must take into consideration,
and an emulsion consists of a number of particles
of silver bromide embedded in a jelly. The
modem theory of a jelly is that it consists of a
number of minute cells with passages in between
ramifying in all directions, and the cells and
passages contain a weak solution of gelatine,
whilst the ceU walls are formed of a very strong
solution. In each cell we may imagine a grain
or particle of sUver bromide, and for the developer
to reach this it is obvious that it must first
Development, Theory of
177
Development, Theory of
traverse the passages, and then difinse through
the cell walls. The first is termed macro-diffusion,
which takes place at a rapid rate, and the later
action, which is comparatively slow, is known as
micro-diffusion. It has already been pointed
out that a chemical reaction can only occur when
the silver bromide goes into solution and is
ionised into + Ag and — Br. The instant
the developer reaches the dissolved silver it is
reduced to the metaUic state and deposited,
provided there be some nucleus or germ on which
it can deposit. This nucleus is the latent image
{which see). Were there no nucleus, then the
silver would accumulate in solution till super-
saturation occurred, and then the chemical
action would cease. As soon as the dissolved
silver is deposited, fresh silver takes its place,
and so the process proceeds till the whole of
the silver available is reduced.
In the above rough sketch of what is supposed
to take place, we must not lose sight of the
important fact that, as pointed out in the note
on the latent image {which see), Scheffer has
proved that the action of light is to cause
the protrusion of filaments or threads from the
sensitive salt grain, and therefore these would
rapture the cdl walls, and so render the access
of the developing agent much easier.
Now, if we consider what happens when a plate
is devdoped, we shaU at once see that at first
we shall have some silver halide grains, which
are so affected by light as to be readily reduced
by the developer, and some which are not affected.
As development proceeds we shall have {a)
some grains already reduced to metallic silver,
(6) others not yet completely reduced, and (c)
others which are not light- ajOBected and there-
fore not attackable by the developer. Natur-
ally, at first the progress of development will be
rapid, as the whole of the light- affected grains
will be capable of development, but as it pro-
ceeds there will be fewer and fewer of the (6)
grains, so that development gradually gets
slower and slower, and we may es5)ress this
by saying that: the rate of increase of density
= constant (maximum density attainable —
density obtained).
Here the constant or velocity constant is
usually termed K.
If die temperature of the developer be raised
then the velocity constant, or K, increases, and
this is termed the temperature coefficient, which
is generally defined as the ratio for correct
development at 10° C. (50° P.) difference of
temperature.
The efficiency of a developer E is the velocity
of development compared with ferrous oxalate
at 20° C, divided by R, which is the reducing
power, or the number of grain-molecules of
AgBr reduced by one grain-molecule of the
developing agent. The energy P is the con-
centration of bromide producing the same
retardation of development as with ferrous
oxalate for o-oi n potassium bromide. For
a complete mathematical treatment of the
subject, the reader is referred to " Theory of
the Photographic Process," by Sheppard and
Mees.
Before leaving this subject it would be as well
to consider the question of the chemical constitu-
tion of the actual developers or reducing agents.
12
Of late years the number of developers has been
largely increased, and a glance at their true
chemical names will at once prove that they are
highly complex organic suhstances belonging
to the benzole or naphthalene series.
Benzene or benzole has the formula CjH„ but
in 1865 Kekul6, from a long series of experiments,
came to the conclusion tiiat the six atoms of
carbon in benzene form a closed-chain or nucleus,
and that the molecule of benzene is symmetrical,
and that each carbon atom is directly united
with one, and only one, atom of hydrogen. The
graphic formula usually adopted is as follows : —
Now, in the above formula it is obvious that
if two of the six hydrogen atoms were replaced
by two other atoms or groups they might be
arranged in one of five different ways, as shown
in the accompanying diagrams, in which, for
the sake of clearness, the C atoms are omitted
and the added group or atom expressed by x.
Then, if one x group occupies any given position,
that numbered i, for instance, tihe other may
occupy 2, 3, 4, 5, or 6. But these five formulae
only represent three isomeric compounds, that
is, compounds of the same composition CgH^;*;,
and not five, because it is obvious that IV. and
V. are practically identical with I. and II., which
may be at once seen by writing them on thin paper
and looking at them first in the normal way and
then through the paper. In order to distinguish
these three compounds, they are said to be in the
ortho, meta, and para positions : —
X
0
Ortho
Meta
Now, obviously in the ortho position the two-
X groups are joined to carbon atoms which are
directly united or are next to one another, so-
Development, Theory of
178
Development, Theory of
that we could actually represent an ortho
compound as
X X
X X
^-2 ortho 2-3 ortho 3-4 ortho 4-5orth9 5-6 ortho 6-1 ortho
Exactly in the same way, the meta compounds
could be represented by placing a; ;i; at i — 3,
2 — 4. 3—5, 4 — 6, 5 — I and the para at i — 4,
2 — 5, or 3 — 6 positions.
Now, it has been proved by Lumi^re and
Seyewetz and by Andresen that a developer must
have two hydroxyl OH groups or two amido
NHj groups joined to the benzol* ring, and
that tiese groups must be either in the ortho
or para positions to be developers. The latter
compoimds are the stronger developers, the
ortho compounds the weaker, whilst the meta
compoimds are not developers at all. If one of
the hydrogen atoms of a hydroxyl group be
replaced by an alkyl radicle — that is, an alcohol
radicle, such as ethyl C2H5 — or by another
radicle, then the developing power is destroyed,
as, for instance, in phenetroia
CC,H,
NH,
If, on the other hand, one of the hydrogen atoms
of an amido group be replaced by an alkyl
radicle, then the developing power is increased,
as in the case of
OH OH
and
halide atoms CI or Br, then the developing power
is increased, as in the case of
OH OH
;a or Br
OH
Para-dihydroxybenzole
or hydroquinone
O H
Monobrom or monochlor -para-
dihydroxybenzole or adurol
If three hydrogen atoms in the benzole ring
are replaced by tiiree NHj or OH groups, then
the developing power is increased, and here,
as in the case of the di-substitution products,
the ortho-, meta-, or para position plays an
important part, thus
OH
OH
, OH
is weaker than
Ortho-dihydroxybenzole
or pyrocatechin
Ortho-trihydroxybenzole
or pyrogallol
because in the former there are only two OH
groups in the ortho position, whilst in the latter
there are three OH groups all in the ortho
position. Again, if one OH and one NHg group
be added to the ring, then we have a still more
energetic developer, as in the case of
OH
NH,
para-amidophenol, the
base of rodinal;
whilst the addition of another NHj group in-
creases the action still further, as in the case of
OH
iNH,
NH,
Para-amidophenol
NHCH3
Monomethyl - para-
amidophenol or metol
Besides the OH and NHj groups, the hydrogen
atoms of the benzole ring may be replaced by
other radicles, such as carboxyl COOH, and
the sulpho group SO3H, but these reduce the
developing power, and in this case the position
of the added or substituted radicle plays an
important part, as in the instance of
OH OH
CO.H
and
'COjH
NHj
Para-amidophenol —
ortho-carbonic acid
the former being but a very weak developer,
whilst the latter is a vigorous one.
If a hydrogen atom be replaced by one of the
NHa
Para-amidophenol —
meta-carbonic acid
1-2-4 diamidophenol
or amidol.
which is at once an ortho- and a para-amido-
phenol, and diamidoresorcin
OH
NH
-4-6 diamidoresorcin
a double para-amidophenol, in which tiie OH
and NHj groups, as shown by the lines, are in
two para positions; this is still more energetic.
There are two developing agents which belong
to the naphthalene Cjo Hs series, and naphthalene
may be considered as two benzene rings joined
together, and which at the points of jimction
Development, Thermo
179
Development, Thermo
have lost their hydrogen atoms, so that we may
write naphthalene graphically as
CH CH
C
CH r^"*V" »> CH
CH
CH CH
Here, too, the hydrogen atoms may be replaced
by other atoms or groups, and we have
NHj
mathematical expression for the temperature
coefficient is —
SO.H
and
SOjNa
OH
oi amido-, /Sj naph-
thol-, 3j sulphonic add
or eikonogen.
OH
SOsH
oi amido-, 0^ naph-
thol-, j3, 183 acid sul-
phonate of soda or
diogen.
It win be easily seen that the Greek letters
and the numbers refer to the positions of linking
of the substituted atoms. In the above sketch
the developing bases only have been considered,
for many of the actual developers are salts, such
as chlorides, sulphates, oxalates, etc., of these
bases.
DEVELOPMENT. THERMO
A name invented by Alfred Watkins for a
system of developing in which the duration of
development is varied as the temperature of the
developer varies, to distinguish it from " time
development " pure and simple. Although it
had been known for a long time that develop-
ment was prolonged in cold solutions, Houdaille
in 1903 was one of the first to suggest a definite
rule, in conjunction with hydroquinone, to the
effect that a variation in temperature of the
developing solutions of 1° C. caused a variation
of 5 per cent, in the time of appearance of the
image and the duration of development. In
1905 Ferguson and Howard pubKshed a method
of obtaining a given gainma or degree of contrast
with a developer of constant composition at
varying temperatures by developing strips of a
plate exposed behind a sector wheel for different
times, measuring the gammas obtained and plot-
ting them on a chart. Later, Ferguson sug-
gested a simpler method, in which only two strips
were developed for given times and the tempera-
ture coefficient of the developer found by a very
simple logarithmic calculation. The objection
to both these methods is that a sector wheel
and photometer are required. As, however,
Ferguson's method is simple, and the basis of
that to be described later, it is briefly given here.
The first thing to determine is what is known
as the temperature coefficient of the developer
used, or the increase in velocity of development
for a rise of 10° in temperature, from which the
increase in rapidity of development for 1° can
be found by dividing the logarithm of the
temperature coefficient by 10. The usual
velocity at {t + 10°) C.
= 6";
velocity at t' C.
therefore 6, or the increase for 1°, is—
log, of temperature coefficient
log. 6.
Ferguson has suggested that two strips of a
plate should be exposed to the same graduated
series of hght and one developed at f C. and the
other at t° + x° C. ; then the times required
to obtain the same gamma or degree of contrast
on each plate will be M and m, and as the times
are inversely proportional to the velocities
log b = log- M-log.m
°' X
in which 6 = tihe temperature coefficient for 1° C,
and 10 log. b will be the temperature coefficient
for lo" C.
To make this quite clear two strips of a plate
should be developed so as to show the same
degree of contrast, one at a given temperature
and the other at this temperature plus a certain
number of degrees. Two strips A and B of a
plate were exposed to the same graded series of
light, and A took 3^ minutes to obtaiu a gamma
= I at 10' C. and B took 2^ minutes at 18° C,
then —
log. 3-5 = -5441
log. 2-s = -3979
■1462
Now the difference of temperature (^ as it is
usually written) was 18 — 10 = 8°
. • . -1462 -^ 8 = -0182 = log. 6
. • . 10 log. 6 = -0182 X 10 = '182 = the temper-
ature coefficient for the plate and developer used.
Having found the above, to find the necessary
duration of development at 14° C. to obtain the
same gamma the formula is —
log. M — X log. b = log. m
or, in words, from the logarithm of the time
required at 10° C. subtract 14 — 10 = 4 times
log. 6, and the result will be the logarithm of
the time required ; assuming that log. 6 = ■0182
as above, then —
log. 3-5 =
4 log. 6= '0182 X 4 =
•5441
•0728
•4713 = log. of 2-96
minutes, the time required.
Watkins has done away with the sector wheel
or graded series of lights and the finding of
the gammas ; he merdy exposes a plate on a
landscape including some sky and cuts it in
two, or makes two exposures. It is essential to
have some means for warming up the developer,
dish, and measure, and also to have a thermome-
ter. When the developer, dish and measure are
warmed up, say to 75° P. (about 24° C.) the
plate is placed in the dish and flooded with the
developer, the time accurately noted, and the
first appearance of any image also noted ; the
plate being now of no further use it may be
thrown away. The second half of the plate is
now developed in a developer of exactly similar
composition, only colder, the time of appearance
Development, Time
1 80
Dialyser
noted, and we have all the factors necessary for
finding the time of development for any tempera-
ture with that particular plate and developer
if we know also the factorial number {see " Devel-
opment, Factorial ") of that developer. Sup-
pose, for example, that a metol-hydroquinone
developer with a factor of 15 is being used,
and it is found that at 50° P. (10° C.) the first
appearance of the image takes place in 40
seconds and at 66° P. (i8-8° C), the first appear-
ance takes place in 28 seconds ; then turning
to a table of logarithms we find that log. 40 =
I -602060 and log. 28 = 1-447158, then —
1-602060 — 1-447I58 = 0-154902.
Now the difference in temperature is 66 — 50
= 16, then 0-154902 -i- i6 = -009681 = log. of
28-3 seconds, and as the factor for this developer
was 15, then 28-3 x 15 = 424 seconds =
7 minutes practically, which is the time required
to develop the plate at 57° P. (14° C).
It is obvious from this that we can calculate
a table for every degree (or two degrees will be
enough) rise or fall in temperature of the
developer, by multiplying the log. factor by 2
and adding for every two degrees drop or sub-
tracting in the case of a rise, and then multiply-
ing the number by the factorial number. This
may seem somewhat compUcated, but the
logarithms have merely to be read from a mathe-
matical table-book and simple division, multi-
plication, and subtraction performed.
DEVELOPMENT, TIME
Practically, this method of development was
estabhshed upon a sound basis by the researches
of Hurter and Driffield, who proved that it was
only necessary to reduce or increase the duration
or time of development in order to obtain nega-
tives of any desired degree of contrast, and that
it was not necessary to tinker with the con-
stituents of the developer. The outcome of this
work was the slow recognition of the fact that
it was advisable to use a given developer at a
given temperature for a given time to obtain
a particular class of negative. This method is
particularly valuable in the case of colour-
sensitive plates, which may be immersed in the
developer completely protected from light, and
at the end of the stated time washed and fixed.
(See also "Development, Thermo.")
DEVIATION (Pr., Deviation; Get., Abweichung)
An optical term denoting the alteration in the
course of a ray of light when bent from its
original path by refraction or reflection. The
length of a prismatic spectrum alters according
which happens when the mean emerging rays'
(say the green, at the e Praunhofer line) and the
incident rays make the same angle with the
prism, as shown in the illustration, the latter
is said to be in the position of " minimum
deviation."
DEXTRINE (Fr., Dextrine; Ger., Dextrin)
Known also as British gum. This white or
yellowish-white powder, soluble in water, in
which it forms a viscous and gummy solution,
insoluble in alcohol and ether, has the formula
(CoHioOs)^. The pure substance is made by
submitting starch paste to the action of malt
extract ; after filtering, maltose is precipitated
by repeated treatment with alcohol, and finally
the dextrine is thrown out by adding sufficient
absolute alcohol. It is also made by the action
of heat or of nitric acid on potato starch. It
has the same chemical composition as starch,
but its properties are different. The principal
use of dextrine is in the making of mountants
{which see). There is a further variety, of a
brown colour, but this is not used as a mountant.
In process work, dextrine has been advocated
as an addition to the etching bath, the addition
of gummy matter to the bath being claimed to
facilitate etching and keep the etched surface
bright. Dr. Albert has recommended a powder,
which is believed to be a mixture of dextrine and
powdered alum, for use with the nitric acid
solution, to cause a frothing of the bath ; the
theory is that the solution is oxygenated and the
hydrogen gas given off is absorbed.
DEXTROSE
Known also as glucose and grape sugar ; a white
crystalline solid, formula CgHuiOa, readily soluble
in water. It has been recommended as an
addition to mountants and as a preservative
for plates, but is now rarely used. It is employed
in some processes of silvering glass.
DIACTINIC (Fr., Actinique ; Ger., Aktinisch)
Capable of passing actinic or photographically
active light ; the opposite of non-actinic.
DIAGONALS OF PLATES {See "Sizes.")
DIAGRAMS AS LANTERN SLIDES. {See
" I<antem Slides, Diagrammatic")
DIALYSER
A parchment, skin, or paper stretched over
the open end of a glass or wooden vessel, which
Deviation of Rays Passing Through Prism
to the position of the prism with reference to the
rays of white light falling upon it (" incident
rays"). When tiie prism is so placed that the
spectrum is practically at its shortest length.
Dialyser
is then placed in an outer container of water
{see illustration). Into the dialyser are poured
liquids such as thin solutions of gelatine or
other colloid containing salts, the latter diffusing.
Diamidophenol
i8i
Diaphragms
-through the septum into the water, and leaving
the gelatine or other coUoid in the dialyser. In
the illustration, a is the dialyser, b the outer
vessel of water, and c the septum or skin.
DIAMIDOPHENOL (See " Amidol.")
DIAMIDOPHENOL HYDROCHLORIDE (See
" Amidol.")
DIAMIDORESORCIN (Fr. and Ger., Diamido-
resorcin)
C, H, OH OH NH, Ha NH, HQ. Molecular
weight, 153. Solubilities, soluble in water, more
soluble in sodium sulphite solution. It is a com-
plex organic salt, very similar in its action to
amidol, and, Uke that, developing in the presence
of sodium sulphite only. (See also " Diamine.")
DIAMINE
A form of diamidoresorcin {which see) intro-
duced by Lumi ^e as a developer. A formula is :—
Sodium sulphite (anhy-
drous) . . .250 grs. 30 g.
Diamidoresorcin . 85 ,, 10 „
Water to . .20 oz. i.ocxj ccs.
DIAMOND LENS
In the early days of photographic optics
experiments were made with every kind of
transparent body which could be formed into a
lens. Claudet had a small lens fashioned from a
diamond, expecting much from the high refrac-
tion of this substance. However, it was not
found to be of any practical value. It was
destroyed in a fire at Claudet's Regent Street
studio, London.
DIANOL
Lumi^e's preparation of oxalate of diamido-
phenol or amidol {which see), which is claimed
to be rather more soluble than the hydrochloride,
the usual salt employed.
DIAPHAN. AND DIAPHANOTYPE
An obsolete process used for obtaining trans-
parent pictures for viewing in a diaphanoscope.
Diaphan pictures were upon paper, and diaphano-
types upon glass, but the terms were often
reversed, and in the end all the pictures were
known as diaphanotypes. The process as
advocated by Thomas Sutton (published Decem-
ber 15, 1856) was as follows: "Thin photo-
graphic paper must be employed. Immerse for
half an hour in a solution of 20 grs. ammonium
chloride ; hang up and dry. Sensitise by float-
ing on a bath of nitrate of silver, containing
50 grs. of nitrate to i oz. of water ; hang up in
the dark to dry. In printing, apply the back
of the paper to the negative and print through
the paper very deeply. In this way the silver
in the heart of the paper becomes reduced.
Wash well, and tone in a wtak gold bath made
by adding 15 grs. of gold chloride in 20 oz. of
water to a solution of 50 grs. of hyposulphite
of soda in another pint of water. Leave the
print immersed till it is thoroughly toned, then
fix it in one part hypo to ten parts of water.
The hypo reddens it slightly, but it becomes
perfectiy black on drying. Wash as usual, dry,
and wax." Sutton also advocated a develop-
ment process for producing the pictures. Other
workers made an ordinary paper print trans-
parent with wax or Canada balsam, backing it
up with a duplicate print, while others coloured
their pictures. At the end of the diaphanotype
" craze," the pictures resembled crystoleum
pictures.
The terms were also applied at one time to
lantern slides and window transparencies, both
plain and coloured.
DIAPHANOSCOPE (Fr., Diaphanoscope ;
Ger., Diaphanoskop)
A contrivance, much resembling the aletho-
scope, pantoscope, or lantemoscope, intended
for the exhibition of transparent positive photo-
graphs. It consists of an enclosed box, which
may or may not be furnished with a lens, the
pictures being placed inside at a distance from
the eye preferably equal to the focal length of
the lens with which the negative was obtained.
DIAPHRAGM SHUTTER (Fr., Obturateur d.
diaphragms ; Ger., Blende-verschluss)
A shutter made to work between the two com-
binations of a compound lens — that is, against
the Ci^vihiagai, and opening from and closing
to the Centre. It is obvious that the shutter
itself acts as an expanding and contracting
diaphragm, though not necessarily circular, and
that consequently a large part of the exposure
is practically given with a smaller aperture than
that of the fixed diaphragm. The definition of
the lens is thus improved, but the efficiency of
the shutter (the relative proportion of the expo-
sure during which it is fiyly open) is rather low.
When of good quality, diaphragm shutters give
excellent results. They are much used on the
better-class hand cameras, and are usually so
fitted as to form part of the lens mount. The
exposures marked on cheap diaphragm shutters
are seldom reliable.
DIAPHRAGMS (Fr., Diaphragmes ; Ger., Blen-
den)
A diaphragm is the aperture, fixed or remov-
able, used in front of a single lens and between
the combinations of a double lens, generally
referred to as the " stop." The various forms
of diaphragms, systems of marking, values, etc.,
are as follow : —
Various Forms. — The three patterns in general
use are known as " rotating," " Waterhouse,"
and " iris." Very cheap lenses, and those of
obsolete patterns, are usually fitted with fixed
stops, or pierced circles of metal which are let
into the lens tube. Rotating stops are mostly
fitted to wide-angle and landscape (single) lenses,
and are employed in many hand cameras ; a
series of circular holes of various sizes are
pierced round the margin of a revolving disc
fitted to the lens mount. Waterhouse dia-
phragms were invented by John Waterhouse,
of Halifax, in 1858, a circular aperture being
cut in a thin piece of sheet metal and inserted
into a slot in the lens mount, a separate piece —
called a stop — being required for each opening.
The " iris," the most modem form of diaphragm,
consists of a series of curved plates of metal,
vulcanite, or other material, fitted inside the
lens tube and attached to a ring on the outside
Diaphragms
1S2
Diaphraigtns
of the lens mount ; by revolving the ring the
plates are made to open and dose, thus form-
ing apertures of various sizes. Some Continental
lenses have other forms of stops, but they are
rapidly falling into disuse. The form in which
the diaphragm is made does not affect its action
on the lens in the least, and optically one stop
is as good as another ; it is in the matter of
convenience where one pattern has any advan-
tage over another. The iris pattern — so named,
by the way, because it opens and closes like the
iris of the eye — is undoubtedly the most con-
venient and popular pattern.
Systems of Marking. — ^There are at least half a
dozen systams of marking. Stops are marked
with numbers, such numbers, as a rule, appear-
ing upon the iris ring or lens mount when the
iris system is used, upon the top or handle of a
Waterhouse diaphragm, and upon the circular
revolving disc in the case of rotating diaphragms ;
in the last-mentioned case the number appears
opposite to the aperture which it indicates, so
that when the stop is in use in the lens itself its
number is visible outside the lens tubes. In-
cluded in the stop-marking systems in vogue
are the " f," " U.S.," " Dallmeyer," " Goerz,"
" Zeiss," and " Voigtlander," besides many
others. The " f " and " U.S." systems are
adopted for all but i per cent, of the lenses in
general use, and of these the former is the more
popular, especially in England, it being in
a sense self-explanatory. The " f " number
simply means tie proportion of the diameter
of tiie stop to the focal length of the lens. For
example, //8 is of a diameter one-eighth the
" focus " of the lens. The " f " value of an
unnumbered stop can be ascertained by dividing
the focal length of the lens by the diameter of
the stop. For example, a i-in. stop with a lens
of 8-in. focal length is known as //8 ; a -J-in.
stop with the same lens, f/16 ; a J-in. stop with
the same lens, f/32, and so on. Thus the " f "
number is not a fixed dimension, but always a
relative one, varying with the lens employed ;
obviously //8 with a i6-in. lens would mean a
diameter of 2 in., whereas with an 8-in. lens it
would mean a diameter of i in. Strictly, the
" f " numbers should be i, ^V. A> ^tc, but the
fractional form is ignored, and the numbers
spoken of as 8, 11, i5, etc. Stops of definite
f " values may easily be cut to the required
size. Suppose, for example, that with a lens of
6-in. focal length, an f/16 stop is required,
then, 6 divided by 16 = ^ = | ; therefore,
the stop must be f in. in diameter.
While, in the above rough-and-ready system
of measuring, the " f " value of a stop may be
accurate enough in the cases of ordinary rapid
rectilinear and single lenses, extreme accuracy
is essential in the case of modem and improved
anastigmat lenses ; for while a slight error may
be of Httle moment with a small stop, the same
amount of error — ^which error is, of course,
proportional to the aperture — ^becomes serious
with large stops, which are a feature of anas-
tigmat lenses. It is necessary in such cases
to consider the effective apertiire. The stops on
a modem lens by a good maker are always
correctly numbered, and it is only when a worker
attempts to check the optician's calculations by
dividing the focal length by the aperture that
he finds an imaginary error. The division
system described above leads to false conclu-
sions when some modem anastigmat lenses are
measured by it, because of the great condensing
power of the lens in front of the stop, from which
lens measurements are taken. To quote an
example ; one of the most expensive of anastigmat
lenses has a stop the value of, and marked, //8 ;
but the aperture of the stop is one-ninth the focal
length, and, according to the rough and ready
rule given above, woiUd be f/9 ; while the stop
marked//;, although accurate, is/// according
to the division method. The following method
of finding the effective aperture of a stop is more
reliable with all kinds of lenses. The camera is
set at " infinity," or a distant object is focused
upon the ground glass. A piece of card is then
put in the place of the ground glass, or pasted
thereon, so as to entirely cover it. In the
centre of the card, and on the spot exactly
opposite the lens, is made a hole the size of a
pin's head. The camera is then taken into the
dark-room, and by the assistance of a ruby or
orange light a disc of bromide paper is cut to
fit the inside of the lens cap. The cap, with the
sensitive paper inside it, is then placed on the
lens in the usual way, the sensitive side towards
the stop. A lighted candle is then held against
the hole in the cardboard for about half a
minute, so that the light may travel through
the camera, lens and stop to the bromide paper.
The latter, after exposure, is taken out and
developed, when a circular black spot will
be found thereon, and the diameter of this
spot win be the effective diameter of the stop
used. If the exposure is made with the largest
stop, the developed spot gives the effective
aperture at which the lens will work, and the
focal length of the lens divided by this, the true
aperture, gives the "f " number.
Opticians have adopted standard " f " numbers,
namely, yiS, 5-66, 8, 11 '3, 16, 22-6, 32, 45, and
64, but stops may be "in between" any of
those named, or larger or smaller than 3" 16 and
64 respectively. As a general rule, 11-3 is
spoken of as 11 and 22-6 as 22, but in the case
of larger stops the decimal point, when it occurs,
is always mentioned, as, for example, 4-5, 5'8,
68, etc.
The " U.S." system (now practically obsolete
in England) has long been popular in the United
States, for which reason tiie initials are looked
upon as indicating that country. Such, how-
ever, is not the case. " U.S." stands for
" uniform system," as an attempt was made,
first of all in 1881, by the Royal Photographic
Society to induce all lens makers to adopt a
uniform system of marking diaphragms.
The Royal Photographic. Society's standards
and recommendations (dated 1901) are as
follow : — (i) That intensity ratio be defined as
dependent upon the effective aperture (and not
upon the diameter of the diaphragm) in relation
to the focal length of the lens. (2) That effec-
tive aperture be determined in the following
manner: The lens shall be focused for parallel
rays; an opaque screen shall be placed in the
principal focal plane, the screen being provided
in its centre (in the axis of the lens) with a
pinhole ; an iUuminant shall be placed imme-
diately behind the pinhole and the diameter of
Diaphragms
183
Diazotype
the beam of light emerging from the front sur-
face of the lens shall be the measure of the
effective aperture. Note. — It will be found,
except when the diaphragm is situated in front
of the lens, that the diameter of the diaphragm
itself is seldom identical with the effective
aperture. (3) That every diaphragm be marked
with its true intensity ratio, as above defined,
in the following order of sequence : //4,
//5-6, //8, //1 1-3, //16, //22-6, //32, //45-2,
//64, etc., each diaphragm requiring double
the exposure required by the preceding dia-
phragm. Should the greatest effective aperture
of a lens not conform exactly to one of the
intensities set forth above, this aperture should
be marked in accordance with the definition of
effective aperture, but all succeeding smaller
apertures should be marked in uniformity with
the above sequence.
Stops marked by the Uniform System are
commonly known as Nos. i, 2, 4, 8, 16, 32, 64,
128, and 256; the respective "f" values are
4, 5-6, 8, II, 16, 22, 32, 45, and 64.
Most of the lenses produced in France are
marked according to the method advocated by
the Paris Congress of 1889. //lo is taken as
the unit aperture, the series advancing as the
" Uniform " system ; No. i is //lo, No. 2 //14,
No. 4 //20, and so on.
Influence of Diaphragms on " Rapidity." — The
"rapidity" of a lens depends upon the stop
used. The " U.S." numbers indicate relative
exposures, but the "i" numbers do not, although
the relative exposures are easily calculated from
them. To find out the relative values of the
" f " stops, first square them, and the exposure is
then as one product is to the other. Thus,
fli6, for example, requires four times the
exposure necessary with //8, because 16 x 16
= 256, which is four times 8 -t- 8 = 64. When
makers mark their stops as foUows, //8, 11, 16,
22, 32, 45, and 64, each stop requires double
the exposure of the preceding one and half that
of the succeeding one.
The Use of Diaphragms. — ^The main functions
performed by stops are as foUow : — (i) They
govern the definition. A large stop, such as that
generally used for focusing, may produce an
indistinct image upon the focusing screen or
sensitive plate, and it may be necessary to insert
smaller stops into the lens in order to secure
better definition. If, say, an object a few feet
from the camera is sharply focused with a large
stop, the background and surroundings may not
appear sharply defined. The insertion of a
smaller stop serves to cut down the area of the
base of the cone of light formed by the lens,
and the result is increased definition (see " Depth
of Definition "). (2) To correct functional errors
(as covering power) in a lens. Lenses not of the
modem and improved anastigmat pattern have
certain optical errors which show themselves
when very large stops are used, and many of
the older and even modem common lenses do
not yield a sharp image all over the plate,
a defect that is corrected by the use of a small
stop and consequent increase in exposure. (3)
To add to, or subtract from, the number of
planes in a picture. AH views are composed of
various planes, or distances. When a large stop
is used, only one plane is in focus, and - the
smaller the stop the greater the number of planes
made clear and sharp.
In process work, various forms of diaphragm
apertures are used, with the object of promoting
the dot formation. The principle is that the
apertures in the ruled screen act as pinhole
lenses and form an image of the diaphragm, so
that in this way the shape of the dot image is
controlled. The square diaphragm is most
ID
A. Penrose Diaphragm
System
B. Adjustable
Diaphragm
commonly used, but squares with extended
comers are also employed to promote the
joining up of the dots in the high lights.
The Penrose diaphragm system A standardises
the use of such stops, the apertures being
arranged on the basis that each smaller stop
requires an exposure of half as much again
compared with the next larger size. The
adjustable diaphragm B enables any size of
square opening to be formed.
DIAPOSITIVE
An old name for a lantern slide or similar
transparency made to be viewed by transmitted
light. The name differentiated transparencies
from positives upon opaque supports as, for
example, daguerreotypes, ferrotypes, and wet
collo(fion pictures backed up with black material.
DIATOMS, PHOTOGRAPHING (See
" Photomicrography.")
DIAZOTYPE
There are several printing processes based
on the light-sensitiveness of the diazo compounds,
which, although not much used, are of con-
siderable interest, as they give a great range of
colours. The diazo compounds are extremely
rich in oxygen, and are formed by the action
of nitrous acid on the aromatic amines, amido-,
sulphonic acids, amidocarbonic acids, etc., and
readily combine with certain phenols and
amines to form azo dyes. If a paper or material
impregnated with a diazo compound is exposed
under a negative, the diazo compound is decom-
posed by (ie action of light, and on immersion
in a solution which forms a dye with the diazo
compound a negative image is obtained.
The primuline process invented by Green,
Cross and Bevan in 1890 is based on the light-
sensitiveness of the diazo compound of primuline,
a yellow water-soluble dye which dyes material
or paper without a mordant. Paper or material
is immersed in a solution of : —
Primuline
Hot water to
320 grs.
20 oz.
33 g-
1,000 CCS.
Diazotype
184
Dichromatic Photography
and then washed and inunersed in —
Sodium nitrite . . 64 grs. 6'6 g.
Hydrochloric acid . 1 50 mins. 1 5 ccs.
Water to .
1,000
It should then be dried in the dark and exposed
under a vigorous positive till those parts under
the bare glass are colourless. Then wash
thoroughly with water, and treat with one of
the following solutions : —
For Red
;8-Naphthol . . 9-6 grs. 10 g.
Sodium hydrate . 128 ,, 13-3 ,,
Water to . . .20 oz. 1,000 ccs.
For Orange
Resorcin . . .64 grs. 6-6 g.
Sodium hydrate . 106 ,, n ,,
Water to . . .20 oz. 1,000 ccs.
For Purple
o-Naphthylamine . 190 grs. 20 g.
Hydrochloric acid . i oz. 50 ccs.
Water to . . . 20 ,, 1,000 ,,
Eikonogen
Water to .
Pyrogallol
Water to .
For Black
. I2S grs.
20 oz.
For Brown
■ 113 g".
13 g-
1,000 ccs.
12 g.
1,000 CCS.
Wash well after development. Various col-
oured images can be obtained on the same print
by local application of the above solutions with
a brush. This process does not give pure whites.
Andresen suggested the following modifica-
tion : —
Pyridine base (pure) . 1 10 grs. 23 g.
Boiling water . . 10 oz. 500 ccs.
then add —
Sulphuric add (pure) . 180 mms. 37-5 ccs.
Distilled water . 180 „ - 37-5 ,,
Benzidine sulphate is formed, and partially
separates out. Cool the solution down to
100° to 120° P. (38° to 49° C), and add—
Sodium nitrite
Water
86 grs.
I oz.
18 g.
50 ccs.
in small quantities with continuous stirring.
The benzitoie sulphate is diazotised and dis-
solves. FUter the solution and pour into five
times its volume of alcohol, which precipitates
the diazo compound; filter out the precipitate,
and dissolve (without drying, as it explodes when
dry) in —
Distilled water to . 20 oz. 1,000 ccs.
The paper or material is sensitised in this cold
solution by floating or immersion for two min-
utes, dried in the dark, and exposed under a
positive, and then developed in a 2 per cent,
solution of amidonaphthol sulphonic acid — S,
or amidonaphtholsulphonic acid — 9, containing
2 per cent, of sodium hydrate. Deep blue images
with pure whites are thus obtained.
Peer's process uses aniline diazosulphouate,
amidobenzols, etc., with ■» phenolic alkalis.
amines, and phenylamines, the following being
typical sensitisers : —
1. Sodium toluoldiazo-
sulphonate . 240 grs. 25 g.
(8-Naphthol . . 240 ,, 25 „
Sodium hydrate . 76 ,, 8 „
Distilled water to 20 oz. 1,000 ccs.
2. Sodium ditolyltetrazo-
sulphonate . 240 grs. 25 g.
/i-Phenylendiamin 190 „ 20 „
Distilled water to . 20 oz. 1,000 oca.
3. Sodium ditolyltetrazo-
sulphonate . 240 grs. 25 g.
Resorcin . . 211 „ 22 „
Sodium hydrate .154 ,, 16 „
Distilled water to . 20 oz. 1,000 ccs.
The paper is immersed in these solutions, and
after drying exposed for about five minutes to
sunlight or electric light. On the exposed parts
the insoluble azo dye is formed, whilst in the
unexposed part the sensitiser remains colourless
and washes out. The print should be fixed in
hydrochloric acid.
Andresen discovered in 1894 another diazo
printing process. The sensitiser is the diazo
compound of o-uaphthylamine or /8-naphthyla-
mine, the former giving brownish grey images
and the latter brown-red. If the exposed paper
is washed amd treated with tetrazo-diphenyl
ether, violet images are obtained.
5 oz.
150 ccs.
Distilled water .
heat to boiling, and add —
o- or /3-Naphthyla-
mine . . . 220 grs. I4'3 g.
then add —
Hydrochloric acid
(sp. g. I-I9) . . 152 grs. 10 g.
and as soon as the salt has dissolved add —
Hydrochloric acid . 617 grs. 40 g.
with constant stirring, and cool the paste down
to 40° P. An evolution of gas takes place, and
a yellowish solution is formed which must be
filtered into an ice-cold dish. Ploat paper on
this for fifteen seconds and dry in tiie dark.
Expose for two or three minutes under a nega-
tive in the sun and develop in a 10 to 20 per
cent, solution of twice fused acetate of soda,
and wash well.
These processes give rather pleasing effects
when appHed to silks and other materials.
DI-CARBOXYLIC ACIDS (See
Acids.")
DICHROIC FOG
' Carboxylic
(See "Pog.")
DICHROMATIC PHOTOGRAPHY
A process of colour photography invented by
Gurtner, in which only two constituent colours,
blue and orange-red, are used. Two plates are
placed film to film, the nearest to the lens being
coated with a transparent emuteion stained
yellow ; on this only the blue rays act, and on
the rear plate, which must be panchromatic,
the yellow, orange, and red rays act. Prom theM
Dicyanine
185
Diffraction Grating
two negatives are made prints, in orange-red
for the front plate and blue for the rear one,
and superimposed. Obviously it cannot give
pure reds or pure yellows, but merely for land-
scape work some pleasing results have been
obtained.
The same principle is used by Smith and
Urban in kinematography and with far greater
success, because as the pictures are now pro-
jected very r^dly, and the observer sits in a
darkened room, one is not sensible of the absence
of any colour or the failure to make pure white.
DICYANINE (Fr. and Ger., Dicyanin)
Solubilities, soluble in water and alcohol. This
is a complex aniline dye prepared by the action
of an alcohoUc solution of caustic potash on
o- 7-dimethylchinoline salts with the aid of
atmospheric oxygen. It forms greenish glitter-
ing crystals which dissolve in alcohol with a
greenish-blue coloiir, and in water with a more
reddish tinge, both solutions being decolorised
by acids. It is one of the best sensitisers known
for the extreme red, partieularly for the region
about X 7,200, the range extending through
the orange and yellow, but it gives a deep
minimum or lack of sensitiveness between B
and P in the green and green-blue, and is not
therefore so much in use as some of the other
dyes. It is very easily decomposed in weak
solution, and therefore should only be added to
the sensitising bath immediately before use.
{See also " Colour Sensitising.")
DIETZLER
An optician of Vienna, chiefly noted for his
manufacture of the orthoscopic lens designed
by Prof. J. Petzval, which was first issued
in 1858, although calculated as early as 1841.
{See "tenses, Orthoscopic")
DIFFRACTION (Pt., Diffraction : Get.,Diffrak-
tion, Ablenkung, Beugung)
When light passes through a very narrow
slit it apparency bends roimd the edges and
spreads out on both sides. The subject is fully
gone into under the heading " Diffraction
Grating."
In process work, a theory advanced in regard to
the action of the ruled screen used for the half-
tone process is that diffraction plays an import-
ant part, espedaUy with the finer screens, and
some authorities claim that advantage can be
taken of this action to promote the better forma-
tion of the half-tone dot. DifEraction is said to
produce the effect of larger or smaller dot images
instead of only stronger or weaker ones, as would
be the case if there were no action of deflected
light.
DIFFRACTION GRATING (Fr., Roseau de
diffraction ; Ger., Diffraktions-Gitter)
An opai^ue screen containing a large number
of fine silts, or a transparent screen having
opaque lines engraved upon it very close together.
A pencil of light is formed of a wave front or a
series of overlapping waves which may be repre-
sented by the diagram A, in which I, is the light
source and a b the main wave front in which
every particle excites fresh secondary waves, as
shown by the curve c d. Neariy all these
secondary circles mutually interfere one with
the other, except in the main wave front c d.
This interference cannot be seen, but its exist-
ence can be proved by limiting the size of the
main wave front by an opaque screen S S, which
stops out some of the secondary waves but not
all, and the latter are seen as delicate fringes
B F on each side of the main wave front. This
can be experimentally proved in a very simple
way. Take a black opaque card about 6 in. or
8 in. square, and cut in the centre a slit about
I in. long and about ^ in. wide. Take also a piece
of glass about 3 in. square and either smoke it
or cover it with black varnish, and with a fine
A. Diagram showing Principle of
Diffraction Grating
needle-point scratch a thin, clear line about
f in. long. On holding the card at arm's length
close to a brilliant light, and examining it through
the scratch on the glass, held close to the eye,
there will be seen a bright central image of the
sUt, and on each side of it faint black lines, which
are the diffraction fringes. If in front of the
light source a violet glass is placed and then a
deep red one, there will be obtained images, as
shown in the diagram B, in which o is the central
image, v the violet bands or fringes, and R the
red ones, the violet being nearer together than
the red. If a green glass is used the green fringes
would fall midway between the red and violet.
The explanation of this phenomenon is as
follows : In diagram C let A B represent an
opaque screen with an aperture c D, and I, the
beam of light, which, proceeding in a straight
line, forms a bright central image at E F. Now
diffraction, or the bending of the light waves
round the edge of the opaque screen, will cause
secondary waves to proceed in all directions from
every particle of ether lying between c d. For
the sake of clearness, let us consider only the
waves in one direction, and represent these as
straight lines c G D H. Let us further assume
that between c and d there are eight ether
particles acting as sources of secondary waves.
If we now draw c w at right angles to the path
of the rays, it will be at once seen that the
waves from d have further to travel than those
from c by the distance d w. Let d w be a wave-
length, tiien obviously |- D w is exactly half a
wave length ; drawing a perpendicular from
f w to the ether partides we at once see that
the wave from 4 is exactiy half a wave length
from c, and the same distance in front of that
from D. By the same reasoning it will be found
Diffraction Grating
1 86 Diffraction Grating Replicas
that
half
I is half a wave-length in front of 5, 2
a wave-length in front of 6, and so on ;
so that every ray is in opposite phase with
another ray in the slit. Now two rays in oppo-
site phase {see " Interference of Light ") produce
interference or darkness, so that on the screen
G E H F there would be a dark band. By similar
them, the rulings acting as opaque screens ;
those on metal are known as reflection gratings.
Diagram B represents practically the spectra
which are obtained with any diffraction grating.
They are arranged on each side of the central
white image o. The spectra nearest o are called
the spectra of the first order, then there is a
B. Diagram of Diffraction Bands or Fringes
reasoning we could find beyond this particular
angle a bright band where the secondary waves
would be in the same phase.
It is obvious that the greater the number of
apertures in an opaque screen the greater the
number of secondary waves formed, and there-
fore the greater the chance of interference.
Further than that, the narrower the slit the
greater must be the obliquity or the angular
distance from the central image, for the greater
obliquity will be required to produce the neces
sary difference between the paths of the rays
from a narrower slit ; that is to say, the more
slits there are in a unit length the greater the
obUquity. Now we have already seen that the
violet bands are closer together than the red,
and that the green would lie in between, so that
if we illuminate a series of slits by hetereogeneous
white light the waves wiU be sifted out iuto
their respective positions, and we obtain a
spectrum in which the rays are arranged accord-
ing to their wave length.
Praimhofer was the first to utilise the pheno-
menon of diffraction, and he made his gratings
of silver wire wound round two iine threaded
gcrews placed some distance apart. The next
C. Diagram showing Cause of Diffraction
Bands
forward step was the ruling of a series of fine
lines with a diamond on glass, and later still
the glass was silvered. Then Rutherford, of
New York, ruled the lines on plane speculum
metal, and later on spherical mirrors of speculum
metal. Diffraction gratings on glass are called
transmission gratings, as the light passes through
dark space filled by the invisible infra red and
the invisible ultra violet ; then we have the
spectra of the second order overlapped even in
the visible spectrum by the violet of the third
order. Then follow the fourth and other order
spectra, the number being dependent on the
brilliancy of the light and the character of the
grating.
A moment's consideration will prove that the
spectra formed by a diffraction grating cannot
be as brilliant as a prismatic spectrum, for
although there is some loss of light with the
latter, through the reflection from the front
surface of the prism and by absorption in the
glass itself, yet in the case of the diffraction
grating not only does the bulk of the light pro-
ceed to the central image, which is useless, but
the rest is split up into the various spectra on
each side. Sometimes, too, in consequence of
some peculiarity in the ruling, one or other of
the spectra may be much more brilliant than
the others.
A grating spectroscope or spectrograph is,
however, much to be preferred to a prismatic,
as the rays are arranged exactly according to
their wave-length, whilst with the prismatic
spectrum the violet and blue are spread out at
the expense of the red and orange, which are
cramped together. {See also " Spectrum," " Dif-
fraction Grating Replicas," etc.)
DIFFRACTION GRATING REPLICAS (Fr.,
Replicas des rSseaux de diffraction; Get.,
Diffraktions-Gitter-Abklatsche)
Original gratings, whether on glass or metal,
are extremely expensive, and numerous attempts
have been made by Rayleigh, Abney, and others
to reproduce these by photographic means, but
the most successful way is that of taking casts
in celluloid. Thorpe, Ives, and Wallace produce
these, and the latter has given full working
instructions, of which the following is an
abstract : —
PyroxyUne
Pure amyl acetate
i8i grs.
I oz.
3-9 g-
1 00 CCS.
Add the pyroxyline in small quantities to the
amyl acetate, shake well till dissolved, and allow
to stand for twenty-four hours. At the end o£
that time the resultant collodion should be
poured from a height of at least 3 ft. or 4 ft.
in a very thin stream into a large tray filled
with water, the latter being constantly stirred
with a glass rod. In about twenty-four hours
Diffraction Grating Replicas 187
Diffusion of Focus
the whole of the pyroxyline is precipitated in
the form of white or light gjrey flocculait masses,
which should he collected and dried. The pur-
pose of this precipitation is probably to purify
the pyroxyline, as any collodion poured into
water gives up what Eder has called " pyroxyline
gum." The particular pyroxyline recommended
by Wallace is not obtainable in England,
but Hopkins and Williams's high temperature
pyroxylme gives excellent results, as does also
Mawson and Swan's collodion when precipitated
in this way. It is not necessary to use amyl
acetate before the precipitation, the ordinary
solvent of equal parts of alcohol and ether
proving quite satisfactory, and the precipitation
is instantaneous. When thoroughly dry the
precipitated pyroxyline is again dissolved in the
above proportions, and the collodion carefully
filtered tlbrough paper. This, which is trouble-
some unless pressure is used, may be avoided
by allowing the collodion to stand three or
four days, when the whole of the impurities
settle to the bottom of the bottle.
The grating should be carefidly levelled in a
drying cupboard, and this is absolutely essential
to prevent the occurrence of dust ; next, it is
carefully dusted with a soft camel-hair brush,
and the solution flowed over the surface. The
exact quantity is a matter of experiment, too
thin a filia being difficult to handle whilst too
thick a film gives a matt surface. About 1-5 ccs.
is the right quantity to use for a 2-in. grating.
The best method of applying the solution is
with a fine pipette, which will hold just the
necessary quantity. This enables one to distri-
bute the solution over the surface without
touching the grating itself, and the solution can
be easily led to any part, or an air bubble brought
to the edge and broken.
The coated grating should be left in the cup-
board for at least twelve hoiirs, and longer is
preferable, even for three or four days ; the
longer it is left the easier it is to handle. To
strip the cast, the grating should be placed in a
dish of distilled water, when the edges will soon
begin to show shadow bands. As soon as these
are observed the grating should be taken from
the dish, and any adierent water removed
with a soft rag. Slight pressure with the thumb
nail along one edge will cause the cast to spring
from the metal, and it should then be grasped by
a pair of wide- jawed forceps, as used in micro-
scopy, and pulled off with a firm but even
motion in a direction parallel to the lines of the
ruUng. The edges of the cast should be trimmed
off, and it should then be lowered on to a piece
of carefully cleaned and polished plate glass,
which should be immersed in distilled water
and lifted out with a small pool of water on its
surface. One edge of the cast should be lowered
on to the glass first, and then the rest gradually
lowered so that it pushes the water in front
of it without the occurrence of air bubbles. As
soon as it is in position one edge should be clipped
by a strong metal dip, and a piece of soft velvet
rubber passed across it in the direction of the
rulings ; when contact is obtained everywhere
the edges should be cemented down with some
of the collodion as used for the cast. This can
be applied with a very fine camel-hair brush.
The cast may be cemented face up or face down.
but with the latter there is less chance of the
rulings being damaged. When the cast has
been cemented it may be dried by heat, gentle
at first, but gradually increased to 167° P.
(75' C). The chief cause of failure is dust
particles between the glass and the replica. If
the replica is mounted face down, another piece
of glass may be cemented to the back.
There is some contraction of the cast in drying,
but this is small. Wallace found that with a
grating of 28-857 loia. width and 16,397 lines
the shrinkage was 0-176 mm. on the entire width,
or about six lines more to every one thousand.
The shrinkage can, of course, be easily deter-
mined by accurate measurement of the original
grating and the cast ; thus, in the case referred
to above, the original width = 28-867 nim.,
width of replica = 28-691 mm. ; therefore with
a total of 16,397 lines in the original, 568 lines
= I mm. On the replica obviously 16,397 -r
28-691 = 572 per mm. This shrinkage simply
causes greater dispersion of the spectrum.
When examined in a quartz spectrograph these
replicas were found to transmit up to a. 2,613
in the ultra-violet, but obviously their glass
support absorbs up to about A 3,400. Prof.
R. W. Wood has suggested the use of thin
mica sheets, and naturally quartz could be used
for the support. This process of taking casts from
a grating in no way damages it, it being, in fact,
an excellent method of cleaning a grating.
DIFFUSED LIGHT (Pr., LumUre
Ger., Zerstreuies Licht)
Light that is spread and softened by the
interposition of any translucent medium, such
as douds, a misty atmosphere, a muslin screen,
ground glass, opal, etc. ; the opposite to direct
Ught, coming imobstructed from the source of
illumination. Printing in diffused light means
printing in daylight other than direct sunshine.
Diffused Kght in the camera, tending to cause
fog, is Kght that is reflected or scattered by the
sides of the camera, etc.
DIFFUSING SCREEN (Pr., tcran de diffu-
sion ; Ger., Verbreitungschirm)
Synonyms, diffusion screen, diffuser. Any
translucent material or fabric used to spread and
soften light. Thus, a frame covered with tracing
cloth, white muslin, or thin calico is employed in
the studio to obtain a soft, roimd lighting. A
circular diffusing screen is advisable in conjunc-
tion with the dectric light for portraiture, as
illustrated under the heading " Arc Lamp." A
sheet of ground glass or opal is often used in
enlarging by artifidal light without a condenser,
to distribute the iUumination equally over the
whole of the negative. The same method is
frequently adopted in daylight enlarging, though
an inclined white reflector is perhaps more usual.
White tissue paper is sometimes pasted over the
printing frame when a thin negative is required
to print slowly. A piece of groimd glass in the
dirk-room lamp, behind the ruby or orange glass,
gives a more even and better distributed light.
DIFFUSION OF FOCUS
The soft effect obtained by throwing the
image very slightiy out of focus on the screen
just before exposure, this produdng " f uzziness."
Dihydric Phenols '
DIHYDRIC PHENOLS
Derivatives of phenol or carbolic acid which
contain another hydroxyl group, thus phenol
or hydroxy-benzene is C0H5 OH, the dihydric
phenol CjHj (OH)j. Catechol, resorcinol, and
hydroquinone belong to this group, the last-
named being of much photographic interest.
DILUTE DEVELOPMENT
A method in which very dilute developers are
nsed, such as in stand development (which see
under the heading " Development, Stand ").
DIMINISHING GLASS
A double concave lens mounted in a holder
and used for examining drawings or photographs
which have to be reduced by photographic pro-
cesses. By its use it is possible to judge some-
what the effect of reduction.
DINITRO-NAPHTHOL
CioH5(N02)a OH. The sodium salt is known
as Martins yellow, which is sometimes used for
yellow filters. The sulphonic potassium salt is
known as naphthol yellow.
DIOGEN (Fr. and Ger., Diogen)
Solubilities, soluble in cold water, insoluble
in alcohol and ether. The acid sodium salt of
oi amido-, jSj naphthol-, |6j ^3 disulphonic add, in-
troduced in 1 897 as a developer. It freely dissolves
in alkaline sulphite and carbonate solutions,
giving a yellowish coloured developer, which is
readily amenable to the influence of a bromide.
DIOPTICHROME PROCESS {See " Duf ay
Dioptichrome Process")
DIOPTRICS
The department of optics referring to the laws
governing rays of Ught passing through trans-
parent media, as air, water, glass, crystal, etc.
DIPHENAL (Fr. and Ger., Diphenal)
CaHjOHNHjj CjH.NH,. Molecular weight,
2CO. Solubilities, almost insoluble in cold water,
very soluble in hot water ; soluble in alcohol and
glacial acetic acid. It must be kept in a well-
stoppered bottle. It is a highly concentrated
solution of the phenolate of diamido-oxydiphenyl
in caustic alkaline solution, and was introduced
in 1897 as a developer.
DIPPER (Fr., Crochet ; Ger., Kiivettenhaken,
Silberhaken, Plattenheher)
A kind of holder employed in the wet collo-
dion process, to inmierse the plate in the silver
bath. It may be of glass, porcelain, ebonite,
or silver wire, and is furnished with hooks or
A. Fluted Glass Dipper
projections at the bottom to hold the plate.
Those of fluted glass A, though somewhat liable
to breakage, are perhaps the cleanliest.
In process work, where the dipper is important
for the wet-plate process commonly worked,
various forms have been adopted. The usual
s Direct Finder
styles are the fluted glass A and ebonite B. The
forked dipper C is an American idea, the object
being to support large plates more firmly than
do the usual narrow dippers. Another kind of
dipper is made of hickory wood ; by pressing
the handle parts together the forks move apart
C. Forked Dipper
and allow the plate to be inserted. On releasing
the pressure the forks press the plate between
them, so that there is no chance of dropping
it. A coat of shellac varnish makes the wood
waterproof. A similar arrangement can be
used as a developing holder. Silver wire or
silver plate can be bent to the shape of a dipper,
but becomes expensive in large sizes.
DIPPING BATH (Pr., Cuvette verticale A bain
d' argent ; Ger., Kuvette)
The upright vessel of ebonite, glass, etc., for
containing the silver bath in the wet-plate pro-
cess. Those made of white glass are preferable.
DIPPING-BATH DEVELOPMENT
An early form of what is known as stand
development. It was advocated in 1892 by a
German, Dr. A. Meydenbauer, who described it
under the name of " Standentwickelung." Its
principle is found in the prolonged action of a
very diluted developer contained in a dipping-
bath. The early name " dipping-bath develop-
ment" has been superseded by " stand develop-
ment"; for fuU particulars, see "Developing
Tank" and "Development, Stand."
DIRECT FINDER, OR DIRECT-VISION
FINDER (Pr., Viseur direct; Ger.,
Direktsucher)
A finder in which the view or object to be
photographed is inspected direct, the camera
A.
FuU-sized Direci-rtsion Finder with
Wire Frame
being held up to the level of the eye. The full-
sized direct- vision finder A consists of a rectangu-
lar wire frame C the size of the plate used, and
Direct Positives
189
Dissolving Chemicals
having a small opening or sight b fixed at a
distance from it equal to the focal length of the
lens with which the camera is fitted. If the
sight is at the correct height, the eye placed
against it will see through the frame the exact
view included on the plate. The frame and
sight are either detachable or made to fold
down when not in use. When the camera is
not of fixed focus, the frame should be attached
B. Direct Vision Finder with Lens
above the lens, so that it may move with it,
to suit different extensions and to agree with any
rise or fall given to the front. Another form of
direct finder B consists of a concave lens, the
sides of which are trimmed to a rectangular
shape, with a small sight to indicate the dis-
tance at which it must be inspected. This
gives a small but brilliant image. Cross lines
are usually marked on the lens to assist in hold-
ing the camera level.
DIRECT POSITIVES {See " Positives, Direct")
DIRECTOSCOPE
A stereoscope for the direct observation of
colour (screen-plate) transparencies without
reversal ; invented and patented by M. G.
Balmitgere in 191 1.
DISGUISING THE CAMERA (Fr., Deguisement
de la chambre ; Ger., Camera verstellen)
In detective work it is frequently necessary
to conceal the presence of the camera. This
may sometimes be done by causing it to resem-
ble some other article, such as a brown-paper
parcel, a bivndle of books, a brief bag, an opera
glass, etc. A box-form magazine camera is
easily made to look like a parcel by wrapping
it somewhat carelessly in brown paper and tying
with string, to which a luggage label may be
attached. Holes should be torn for the lens
and finder, leaving, however, a flap of paper
hanging loosely over them to hide them until
actually wanted. Many special forms of cam-
eras have been made for purposes of disguise,
such as one to work behmd the waistcoat of
the operator, the small lens protruding through
a buttonhole ; an apparatus for concealment in
the hat ;- another resembling a lady's reticule,
and so on.
Sometimes, in natural history photography, it
is required to prevent animals, birds, etc., from
knowing of the camera's proximity, and there
are many ways in wHch ttiis may be done. It
may, for instance be hidden by an arrangement
of boughs and twigs, or a moss-covered heap of
stones, and possibly operated from a distance
by a pneumatic or electric release. The precise
method chosen depends on the nature of the
surroundings. Considerable patience is called
for, and it is not unusual for the operator as
well as the camera to be completely concealed.
DISHES (Fr., Cuvettes, Cuves ; Ger., Schalen,
Tassen)
Dishes are described under the heading
" Baths." {See also " Cleaning Dishes.")
DISINFECTANT
Any substance which kills bacteria and
microbes, such as carbolic acid, formaline, corro-
sive sublimate, etc. Rapid oxidisers, such as
potassium permanganate, also act as disinfectants.
DISPERSION (Fr., Dispersion; Ger., Zer-
streuitng)
The breaking up of white light into the
various colours forming the spectrum, as seen
when a prism is interposed in the path of a
beam of light proceeding from a narrow opening
or slit. Sir Isaac Newton was the first, in 1666,
to show that rays of various colours have differ-
ent refrangibility. The shorter the wave-length
of the light the greater is found to be its refrangi-
bility ; thus red rays, which have the longest
wave-length, are less refracted than the violet
rays, which have the shortest wave-leugth.
The same law applies to the non-visible infra-
red and ultra-violet rays, at opposite ends of
the visible spectrum. There are, however, a
few cases in which the law is departed from.
If, for instance, fuchsine is prepared in the form
of very thin prisms, it produces a spectrum in
which the red and yellow rays are more refracted
than the blue and violet. This phenomenon is
known as anomalous dispersion.
Newton predicted that dispersion could not
be eliminated without at the same time losing
the property of refraction. This is now known
to be erroneous, since different kinds of glass
may give practically the same amount of dis-
persion, yet have varying refractive properties.
It is thus possible, by combining lenses made of
dissimilar kinds of glass, practically to neutralise
the effects of dispersion, a lens in which this
is done being known as achromatic. {See
also " Lens.")
DISSOLVING CHEMICALS
There is a right and a wrong way of dissolving
and mixing most chemicals, and in some cases
the method of dissolving affects the working
powers of the solution. The slowest and possi-
bly the worst way of dissolving a chemical is to
place it in a bottle of liquid and let it stand.
The quickest way is to have the salt, particularly
soda, near the surface of the water and suspended
therein in a canvas bag. However, for most
solutions, the simple addition of chemicals, when
not in large quantities, and frequent shakings
will be sufficient. Chemicals usually dissolve
more quickly in hot water than in cold, though
there are some notable exceptions to this rule.
{See "Solubilities.")
The order in which chemicals are dissolved
or mixed has its influence on the working and
keeping qualities of the solution. As a general
rule, ingredients are added in the order given in
the formulae, otherwise special instructions are
given. The following general hints should be
noted : — Metol should be dissolved in the water
before any other chemicals are added. Hydro-
quinone should always be dissolved after sodium
sulphite. When pyrogallic acid is used, the
Dissolving- Views
190
Distance Meter
preservative — acid, metabisulphite, etc. — should
be dissolved ia the water before the pjnro. When
gold toning baths are made, the gold should
always be added last, dissolved in water. Sul-
phuric acid should always be added gradually to
the water and not water to the acid, otherwise
combination takes place so energetically as almost
to resemble an explosion, and some of the acid
may be driven ia the face or over the clothes.
The list of solubilities presented in the table
that is given under the heading "Solubilities"
will assist in deciding whether much advantage
will be gained by using hot or cold water.
In some cases the temperature of the water
is not of much importance. Developers such
as pyro, metol, adurol, etc., are best dissolved
in water that has been well boiled in order
to get rid of the air, and then allowed to cool
slowly.
DISSOLVING-VIEWS
These are obtained by the use of two lanterns,
one above the other, or placed side by side. The
discs of light projected by the two lanterns must
coincide. Whilst a picture is being shown in
the first lantern, the iUuminant is quite low in
the second one. A slide is placed in the second
lantern, and then the light of the first one is
gradually lowered whilst that of the second one
is gradually turned up ; the first picture dis-
solves away during the blending of the hghts,
and at the same time the second picture makes
its appearance on the screen, talung the place
of the first. To facilitate the operation (especi-
ally when Ume-Hght is in use) the rubber tubing
from the two jets is connected to a duplex gas-
cock having four ways or channels, through
which the gases may be made to pass. Thus,
the oxygen and hydrogen of one illuminant is
partially diverted or reduced, whilst the tap
allows a fuU supply to pass to the other jet.
Dissolving effects are sometimes produced
with bi-unial lanterns with their objectives
furnished with iris-diaphragms opened and
closed alternately. This metiiod is very efiec
live, and saves having to interfere with the
adjustment of the iUuminants.
Dissolving effects of a kind may be produced
by means of a single lantern. The special
carriers for obtaining such effects are divided
into two classes. In one, a translucent screen
gradually obscures the light, and just at the
moment when the obscurity is complete, the
slide is quickly changed by means of a carrier
of the " to and fro " type. In another class, a
second slide is pushed into a carrier which already
holds a shde that is being shown ; the second
eUde passes in front of the first, the latter is
withdrawn, and then, by means of a spring,
the out-of-focus slide is quickly pushed back
into the place previously occupied by the first
shde. This form of carrier was invented by
R. R. Beard, and still enjoys popularity.
Dissolving efiects in kinematograph pictures
may be produced in two ways. If it is desired
to make provision for such efiects at the time of
taking the original negative film, it is accom-
plished as follows : An iris-diaphragm, capable
of completely closing at the centre, is fitted to
the camera lens, and a short length of fihn is
run through at the commencement whilst the
iris is completely closed. Proceeding to wind
through the film, the iris is gradually dilated
and fcially brought to its fiUl aperture. The
efiect upon the sensitive emulsion is that the
image of the object to be photographed fails to
impress itself at first, and as the aperture enlarges
in the iris, the film is more and more impressed,
tin at full aperture a full exposure is secured.
The negative is then developed ia the usual way.
Such a negative will yield a positive in which
the image gradually grows in strength, and as,
at the commencement, no image will be seen,
on projection the subject upon the screen will
appear to develop out of thin air. If the image
is intended to dissolve away and thus give
place to a different subject, the iris on the
camera is closed gradually whilst continuing to
wind the film. Thus, a reverse effect will result
when the negative is printed. Any subject may
be treated in a similar way at the printing stage
by regulating the illuminant used whilst print-
ing. Thus, at the commencement, the light is
kept very low, and as the films pass through the
printer the illuminant is gradually turned full
on tin sufdcient Ught is produced to secure
normal exposure. Yet another method is to
keep the iUuminant at a uniform brilliancy and
to regxilate the exposure by modifying the
speed at which the films are wound through the
apparatus.
To make one kinematograph subject dissolve
gradually into another, double printing is
resorted to. At that point where the first print
commences to weaken, through reduced expo-
sure, a second negative (of the second subject)
is placed in contact and gradually printed up,
till it reaches full vigour. Hence, instead of one
subject dissolving away entirely before a second
begins to make its appearance, the image of the
second subject will make its appearance, weak at
first, but gradually growing in strength and
finally becoming of full vigour, and this whilst
the preceding image melts away.
DISTANCE
That part of a picture farthest from the
spectator, and generally quite subordinate to
the rest of the view, to which, however, it must
stand in proper relation. Occasionally it forms
the motif of the subject. When a bluish dis-
tance is desired stronger than it would appear in
the ordinary way, an orthochromatic plate with
a aeep yellow colour filter will be of great assist-
ance. In telephotographic work it is often
dif&cult, and sometimes impossible, to render
distant objects clearly even by such means, on
account of the interposition of large volumes
of air of varying density.
DISTANCE METER, OR TELEMETER (Fr.,
TiUmitre ; Ger., Entfernungsmesser, Dis-
tanzmesser)
An instrument for estimating the distance
of an object from the camera, so that it may be
accurately focused by means of the focusing
scale, without having to inspect the image on
the screen. In one form A the distance is
indicated on a scale by a small pendulum in the
shape of a pointer. The appKance is held up
to the eye, so that the latter looks along the
sights towards the base of the object to be
Distance Scale
191
Dolland's Process
photographed. The index then shows the angle
made by the line of sight with a perpendicular
drawn to the observer's feet, which angle varies
with the distance of the object. By pressing
slightly with the forefinger on the top of the
pendulum it is prevented from moving when the
telemeter is lowered for examination. Another
type of distance meter consists of a small tele-
scope which indicates the distances on which
it is focused. In the pattern illustrated at B,
A and B. Two Forms
of Distance Meter
the instrument has first to be fully extended
and the eyepiece focused correctly on the grain
of the ground glass inside the telescope. The
eyepiece tube is then scratched with a knife,
so that the observer may always in the future
be able to secure the focus suited to his particular
vision. This having been adjusted, the object
glass is revolved until the object to be photo-
graphed is seen sharply on the ground glass.
The arrow wiU then point to the correct distance
of the object on the engraved scale.
DISTANCE SCALE (See "Focusing Scale.")
DISTILLED WATER (Ft., Eau distilUe ; Ger.,
Destilliertes Wasser)
Pure water, obtained by vaporisation in a
still and subsequent condensation of the vapour.
Distilled water is advised for many chemicals,
and as it may be obtained so very cheaply from
a chemist, it should be used when recommended,
and most certainly for such chemicals as gold
chloride, silver nitrate, and uranium nitrate,
which are both expensive and prone to decom-
pose in water containing impurities. Whether
distilled water should be used for all developers,
toners, etc., depends upon the character of the
ordinary water available. With many of the
common chemicals used in photography — all
sodiums, potassiums, etc. — tap or other water
good enough to drink will serve quite well.
In process work, distilled water is used in
large quantities for making up the silver bath.
The use of tap water is possible, but it occasions
some amount of trouble.
DISTORTION (Pr., Distorsion; Ger., Verdre-
hung)
It is a common error to attribute every un-
pleasing effect in the " drawing " of a photo-
graph to distortion, but, as a matter of fact, true
distortion is very limited in photography. The
most common and the most serious form is
known as curvilinear distortion, and is con-
fined to single lenses and to certain forms of
compound ones. In the case of the single lens
this distortion is shown by a bending of the
lines, which becomes more pronounced towards
the edges of the field, the bending being out-
wards from the comers when the diaphragm is
used in front of the lens, and inwards when
the diaphragm is placed behind the lens. {See
" Curvilinear Distortion.") Distortion by con-
vergence of straight lines is treated under the
heading " Swing Back." Violent perspective,
which is sometimes wrongly called distortion, is
quite distinct from it. If a photograph taken
with a rectilinear lens, however wide its angle
may be, is tested by the inflexible rules of
plane perspective, it will be found to be correct,
no matter how ridiculous it may appear owing to
the choice of too near a standpoint.
DIVERGENT RAYS
Practically all the light which the eye sees
or which enters a lens is composed
of divergent rays. Every point in
an object emits rays which diverge
^^ in all directions from which it is
■°*J^i^=el*^P visible, and the lens of the eye or
of the camera causes them to con-
verge and form an image. When an object is
extremely remote the degree of divergence is
very small, and such rays are termed parallel.
DIVERGING LENS
A concave lens, or one which is not capable
of producing an actual image. It is often called
a " negative " leus. The magnifying element
of a telephoto lens belongs to this class.
DIVERSITY
In pictorial composition, the introduction of
many varied objects each claiming more or less
attention. Unless kept strictly within bounds
it results in confusion.
DIVIDING BACK (S«e " Repeating Back.")
DODGING NEGATIVES AND PRINTS (See
" Control in Printing.")
DOLLAND'S PROCESS
A method of toning and intensifjdng platino-
type prints, worked out by A. W. DoUand. Its
advantages are that it strengthens a weak
platinum print, and at the same time changes
it to a pure black or blue-black colour. The
weak black picture to be strengthened and
toned — the more recently made the better, as
prints more than about ten weeks old are diffi-
cult to treat — ^is soaked in warm water and then
laid face upwards on a sheet of warm glass. All
superfluous water is blotted off, and a thin
covering of glycerine is gentiy spread over the
surface by means of the finger-tip or a broad
camel-hair brush. A strong solution of gold
chloride (15 grs. to yi drms. of water) is then
made up, and a few drops of it brushed over the
glycerine-covered print as evenly as possible.
The print soon begins to gain strength, and at
the same time the colour of the print gradually
changes to a warm black, then cold black, and
finally blue-black. As soon as the desired effect
is attained the print is well washed in water
in order to remove the gold and glycerine, care
being taken during the treatment with gold
that the high lights remain unaffected. After
washing, and in order to ensiire the reduction
and elimination of any gold compounds which
Donisthorpe Process
192
Double Exposures
are liable to be formed with the sizing o£ the
paper, the toned print should be sponged back
and front with any clean-working alkaline
developer, the formula specially recommended
by Dolland being :
A. Metol. . . 100 grs. 10 g.
Sodium sulphite . 2 ,, 100 ,,
Water to . .20 oz. 1,000 ccs.
B. Potass, carbonate 240 grs. 24 g.
Water to . .20 oz. 1,000 ccs.
Use equal parts of A and B, and finally wash
for about a quarter of an hour. AU the above
operations are best carried out in the strongest
daylight possible.
DONISTHORPE PROCESS
A printing method, invented by Donisthorpe,
in 1908, a modification of the old hydrotype
process. A negative is taken in the ordinary
way and after developing, fixing, and washing
is immersed in a mixture of vanadium chloride,
potassium ferricyanide, ferric chloride, and
oxalate. The silver image is probably converted
into chloride and ferricyanide and dissolves,
whilst vanadous salts are precipitated in situ
which harden the gelatine. After washing, the
negative is immersed in aniline dye solutions
which are absorbed by the hardened gelatine,
and not by any unchanged gelatine ; the dye
is finally removed by absorption by a film of
damp gelatine, thus obtaining a print. After
one print has been made, the negative is aga^'"
dyed for a few minutes, rinsed, and another
impression is taken.
DOPPLER'S PRINCIPLE
A principle discovered by Doppler, by means
of which it is possible to tell with considerable
accuracy the rate of travel of a star to or from
the earth. It being assumed that a star at a
fixed distance emits light waves of a given
length at a uniform rate, it is obvious that the
number of ether waves striking the observer's
eye will be constant in a given time. If, on the
other hand, the star be travelling away, fewer
waves will meet the observer's eye in a given
time, as the waves have further to travel. The
converse naturally holds good with a Ught
source travelling towards the observer. Now,
if fewer waves strike the eye in a given time, the
wave-length must be increased, whereas if more
waves strike the eye the wave-length is decreased.
In the first case the monochromatic light would
incline towards the red, and in the latter case
more towards the violet end of the spectrum..
The displacement is naturally dependent on
the velocity of movement of the bght source,
and this is usually measured for the F or H (3 line,
and taking the velocity of light as 299,860 kilo-
metres per second, it is obvious that about
61 kilometres per second would result in an
increase or decrease of i Angstrom unit in the
wave-length of this line.
DOT FORMATION
An expression used in relation to the half-
tone process when describing the dot effect
produced by photographing through the ruled
screen. The ideal dot formation is such that
ia the deepest shadows of the negative (the
most transparent parts) the dots are reduced
to mere pin points, and as the tones deepen
towards the highest lights (the darkest parts of
the negative), the dots grow in size until they
join together and leave small transparent open-
♦♦♦♦♦♦♦♦♦♦
Gradation Showing Ideal Dot Formation
ings between. Above is shown a diagrammatic
representation of the ideal dot formation.
DOUBLE CONCAVE (See "Biconcave.")
DOUBLE CONVEX (See " Biconvex.")
DOUBLE DARK-SLIDE (See " Dark-sUde.")
DOUBLE EXPOSURES
Two exposures may be made on one plate —
each one filling half the plate — by having a shield
of metal or thin wood fitted to the camera back
close to the dark slide. The shield covers half
of the plate while the other half is exposed ;
then the position of the shield is changed so that
for the next exposure it covers the exposed
half while the second half is exposed. The
shutter of the slide may be drawn right out for
each exposure ; the shield forms a perfect pro-
tection for the part covered. By means of such
a fitting a half -plate may be used for two quarter-
plate exposures.
A few years ago this method of making two
exposures on one plate was very frequently used
by amateur photographers for producing a type
of portrait tiiat could not be attained by any
other method excepting combination printing.
(See " Doubles.") Another form of double
exposure is that which is frequently utilised for
obtaining " spirit " or " ghost " photographs.
A plate is exposed in the usual manner on the
subject in which it is intended that the " ghost "
should appear. The lens is capped while the
figure that is to form the ghost is introduced.
Then a short supplementary exposure is made,
care being taken to avoid moving any paft
of the subject between the two exposures. A
transparent shadowy image of the added figure
will appear, solid objects in the picture being
visible through it.
An annoying form of double exposure is that
obtained by exposing the same plate twice, by
accid^it. The best method of avoiding this is
to make it a rule to change the plate immediately
after exposure when using a magazine hand
I' J *"*
5*"
T- 1
rt^ %
YELLOW
11 ^
RED
YELLOW + RED
A FOUR-COLOUR PRINT
AND THE
CONSECUTIVE STEPS
IN ITS PRODUCTION
The original, of which this is a
small portion, is an Autochrcme
Photograph hy H. ESSENHIGH
CORKE, F.R.P.S.
J-s/',-cia//v taken f.n' " l)'i/J FlmMri
as 1 !uv Grr^uj "
YELLOW + RED r ULUt r GKEY
BLUE
YELLOW + RED + BLUE
GREY
Double Extension
193
Doubles
camera, and to expose all plates in rotation
according to the nujnber on the dark-slides
when these are employed.
DOUBLE EXTENSION (Fr., Double Hrage:
Ger., Doppel Ausdehnung)
A camera is said to be of double extension
when its construction allows the racking-out
of the bellows to about twice the focal length
of the lens that is fitted. The ustjal arrange-
ment consists of an " extension frame " sliding
in grooved rails on the baseboard, and worked
by a rack and pinion. When two extension
frames are provided, allowing the bellows to
be racked out to about three times the focal
length of the lens, the camera is said to be of
triple extension. The advantages of a long
extension are that near objects may be success-
fully photographed, copying done fuU size or even
larger, and telephotographic work undertaken.
DOUBLE IMAGES
A double image on a negative is the result
of one of two causes. Either the camera has
moved during the exposure, or else the subject
has moved. If the latter, any moving part of
the subject will show a double outline, while the
remainder of the subject will be sharp. If the
whole of the image is doubled, it indicates
raovement of the camera, laterally or vertically,
according to which outUnes show the movement.
A double image in a print, if the negative is
sharp, indicates that the paper has moved during
printing, due to want of care in examining.
DOUBLE PRINTING (See "Combination
Printing.")
DOUBLE REFRACTION
When a ray of light passes through certain
materials it is not only refracted but divided
into two parts, one of which, called the ordinary
ray, obeys the ordinary laws of refraction, while
the other, or extraordinary ray, does not. The
most usual method of exhibiting this phenomenon
is to place a cross or other figure behind a slab
of Iceland spar, when it is seen to be duplicated.
The polarisation of light depends upon double
refraction. {See " Polarised Light.")
DOUBLE TONES
In silver printing these are frequently a source
of trouble. Owing to the lighter portions of the
subject toning more rapidly than the darker
ones, the light parts wiU be quite cold in tone,
a blue-grey, while the shadows may still remain
a brick red ; for, as a general rule, when the
light parts liegin toning at a more rapid rate
than the shadows, they continue in the same way
throughout the operation, the shadows taking
comparatively little gold. This defect most
frequently arises from one of two causes. Either
the toning bath is too weak, or there is too small
a quantity of gold for the prints in hand. The
combined toning and fixing bath does not give
double tones.
DOUBLE TONING
This is a method frequently adopted in silver
printing for obtaining tones that cannot be
secured by a single bath. Almost any chloride
13
emulsion printing-out paper will give fine black
or brown-black tones by first toning with gold
and then with platinum. A simple and satis-
factory method of working is to use a self-toning
paper. The prints should be washed, toned with
platinum, and then fixed, preferably in a fixing
solution that has been rendered slightly alkaline
with ammonia. A good toning formula is : —
Potassium chloroplatinite 3 grs.
Sodium chloride . 30 „
Citric acid . . 30 ,,
Water to . . 20 oz.
• -3 g-
3 ,,
3 „
1,000 CCS.
An entirely different double toning is that of
toning bromides and lantern slides to two dis-
tinct colours. {See " Lantern Slides, Two-colour
Toning of.")
DOUBLE TRANSFER
A term used in the carbon process to describe
the method of working when the reversed print
given by the ordinary single transfer method
is inadmissible. The print is transferred first
to a temporary support on which it is held dur-
ing development. {See "Temporary Support")
After drying it is transferred to a paper which is
to be its final support, and it is the necessity for
this second transfer that gives it the title of
double transfer. {See also " Carbon Process.")
DOUBLES
A popular form of freak photograph, showing
two pictures of the same person on one plate,
as, for example, a man playing cards with himself,
etc. This kind of picture was at one time (1880)
somewhat popular among professional photo-
graphers, but the work is now almost exclu-
sively confined to amateurs. Each half of the
plate is exposed separately, thus allowing the
figure to be taken twice on the one plate. Many
methods of making such exposures have been
advocated and a few accessories placed on the
market, but excellent doubles may be made
with the simplest of fittings.
A B
Cardboard Cap to Lens, Used in Producing
Doubles
For the partial lens cap method a lens cap is
made of blackened cardboard, as A, the ring c
being made to fit easily the front of the lens,
and then covered on one side with blackened
cardboard b from which a segment is cut off as
shown at A ; exactly how much to be cut away
should be found by trial. Having cut away a
very small portion, the partial cap is placed on
the lens and the picture examined on the
ground glass. The cutting away must be con-
tinued until one half of the picture is dark and
the other half Ughted. The dividing line as
seen on the screen will not be cleanly cut, but
will have a diffused or vignetted effect. About
Doubles
194
Dram, or Drachm
the proportion shown on the right-hand side
will have to be cut away, certainly not one half
of the card, as might be supposed. During the
cutting, the cap is revolved on the lens mount
so that both halves of the view can be seen, and
D. Card in Reversing Back
when one half vignettes or merges into the other
a trial plate may be exposed. It requires accu-
rate cutting to allow of one exposure merging
into the other, and to prevent the join between
the two separate exposures being distinguished.
If, for example, a thin under-exposed band
shows down the centre of the plate the covering
part B is too large, and not enough has been cut
away ; if, on the other hand, there is a dense
over-exposed strip, the aperture A is too large,
thus causing the centre to receive a double
exposure. To use the cap, it is placed on the
front of the lens with the opening on the right-
hand side, as in B, and the sitter is then
posed and focused on the haU (left hand) of the
screen on which the picture is seen, exposure
shutter set, dark-slide put in, and the exposure
made in the usual way, the shutter of the dark-
slide being drawn out all the way. For the
second half, the camera must not be moved,
the slide is closed, taken out, and the partial
cap revolved to the opposite side — that is, to
the position shown at C. The sitter then
assumes a position that will be visible upon the
second half of the focusing screen, the partly
exposed plate is again inserted in the camera,
and the second exposure made on the unexposed
half of the plate. Obviously the two exposures
E. Box to Fit on Camera Front
must be of exactly the same duration. For this
method the camera must be provided with a
shutter working behind the lens.
If the camera has no shutter, and exposures
are made by removing the cap, a cut cap cannot
be used. The circular card from which the
segment has been cut off, and without a ring,
can be fitted into the lens hood itself, and of
course covered over with the ordinary cap with
which the exposures are made.
Another favourite plan of making doubles is
to fix a card in the reversing back of the camera
(see D), the card being blackened and of a size
to cover one half of the plate. The first exposure
is made with the card at b, so as to photograph
the half marked A ; the card is then removed
to A in order that the remaining half of the plate
B may be exposed. The card used at the back
needs to be cut even more accurately than that
used in the lens, because being so near the
plate the dividing line between the two expo-
sures is more clearly cut. It is desirable to
select a background with vertical lines which
wiU not clearly show the division — a bookcase
or a door, for example — and the inevitable line
between the two parts of the image is so arranged
that it coincides with a strongly-marked natural
line in the view.
Another accessory (somewhat analogous to
the first method described) is shown at E.
This is a box of very thin wood, blackened
inside, about 6 in. long, 3 in. deep, and 4 in.
high ; it has a round hole cut in the centre of
the back part so that it may be fitted on the
front of a lens and used as a kind of partial
lens cap. The front of the box is fitted with a
sliding panel or half Ud, which slides across the
front in grooves, allowing each half of the plate
to be exposed in succession. Over all there is
a proper lid which serves as a, cap. This box
front is used after the manner of the partial
cap, and the exact width of the sliding panel
can only be found by experiment as before,
one side of the shding panel being cut accord-
ingly. The latter may be worked by a knob
on the centre of the panel itself, or by means of
a wire.
In aU cases it is advisable to arrange the whole
scene first, and to allow the sitter to try both
positions, examining the ground glass carefully
to see that all is included, and that no part
of the sitter — feet and legs, for example — gets
beyond the centre, or the whole efiect may be
spoilt.
A style of " double " portrait (two or more
positions at one sitting and with one exposure)
is that known as a " polypose portrait."
DOUBLET
An old term used to denote a double com-
bination lens, and usually composed of two
cemented meniscus lenses. The ordinary por-
trait lens is classed as a doublet. The rapid
rectilinear may be considered the typical doublet.
DRAGON'S-BLOOD {See " Gums and Resins.")
DRAINING RACK (S«fi " Brying Rack.")
DRAM, OR DRACHM
In apothecaries' weight 60 grs., or one-eighth of
an ounce ; in avoirdupois weight 27^ grs., or
one-sixteenth of an ounce. In fluid measure
one dram is 60 minims, or one-eighth of an
ounce. The French equivalent to one dram
(fluid measure) is 3^ cubic centimetres, (See
" Weights and Measures.")
Draper, John William
DRAPER, JOHN WILLIAM
Bom at St Helens, Lanes, 1811 ; died on the
Hudson River, 1882. Anglo-American author
and scientist. Went to America in 1833 and
became professor of physical sciences in Hamp-
den Sidney College, Virginia (1837), and pro-
fessor of chemistry in the University of New
York (1839). He made researches into the
chemical action of Ught, radiant energy, spec-
trum analysis, and photography. In 1839
<details published March 31, 1840) he was the
first to make a portrait of a living person, the
subject being his sister Dorothy Catherine
Draper, whose face was made white by powder-
ing and given an exposure of about half an hour
in bright sunlight. Draper was also the first
to photograph the moon (March 23, 1840);
it was necessary to give an exposure of twenty
minutes, a daguerreotype plate being used.
DRAPERY FOR FIGURE SUBJECTS
Portraits of draped subjects are popular with
photographers chiefly because drapery ofiers so
many opportunities for artistic treatment, being
often more pleasing than everyday dress, which,
more particularly in the case of feminine gar-
ments, goes so quickly out of fashion. As
regards the material and colour of drapery,
opinions largely differ ; some photographers use
ordinary muslin, others a cheaper fabric called
tarlatan, while a few favour bunting and sUk
shawls. Cheese - cloth is probably the best
drapery for the figure, and musUn for the head.
The material used should not be quite new, and
should have been washed, wrung out and rough
dried ; new materials contain too much stiffen-
ing to allow of their following the lines of the
figure properly, and this is particularly the case
with tarlatan, which needs a thorough washing
in hot water to adapt it to the purpose. White
flimsy material photographs too white in ordinary
lighting', and it is therefore better to make it
slightly dingy or less actinic by dyeing a pale
yellow colour, by steeping it in coffee, or by
allowing it to become somewhat soiled with
usage.
Blue, yellow, and even black muslins are also
advocated by many workers, but strong blues
and yellows should be weakened by rinsing in
water and hanging in the sunshine to rough
dry. The lines of the figure show very well
indeed through thin dark muslins, and good
effects are obtainable by draping a thin white
material over a dark one; but in aU cases of
head and shoulder drapery more depends upon
the softness and the character of the lighting
than upon the actual composition of the material.
Upon the lighting, exposure, and development
depends whether the material will photograph
the same tone as the flesh.
Drapery for the fuU length figure need not
be so thin as that used for head and shoulder
studies. Muslin and tarlatan are available, but
cheese-cloth is much more amenable to the
production of artistic folds, the choice largely
depending upon whether the more or less dim
outlines of the figure are required to show or
not. No attempt should be made to reproduce
the lines of orthodox clothes with cheese-
cloth, the best effects being obtained by, as it
were, hanging the material upon the figure or
195
Drawings, Copying
by imitating the ancient Greek style. One of
the many ways in which the Greeks differed
from all other ancient peoples was in their
method of covering their bodies. They did not
make what may be rightly called clothes ;
apparently they cut the cloth to the proper
sizes, hemmed the ends, decorated the pieces
with lines of coloured embroidery, and sewed
on buttons. To make a serviceable cheese-
cloth garment in the Greek style, and suitable
for full-length female figures, the width of the
piece must be, for the long and flowing principal
garment, equal to the height of the model. If
seams are unavoidable, let them run vertically,
they can then be more or less hidden in
the folds. The width of the principal garment
must be equal to double the distance between
the extended finger-tips ; the width will thus
be found to be ordinarily a little more than
twice the person's height. Fold the piece ver-
tically. Next, on each side of the centre, and at
such a distance apart as to leave an opening
for the head, place a button and button-hole ;
this opening should be the width of the model
across the shoulders. Along the upper edge
other buttons or hooks and eyes may be placed
at about ij in. intervals extending to the ends.
This garment, put on over the head, has a closed
side at the left, leaving the right open. The
draping of this garment will alone give all the
vertical effects desired and can be made to
expose either of the arms, either of the shoulders,
or the whole of one side of the figure. Undoing
one or more of the buttons or hooks allows it to
slip from either of the shoulders, and with only
two buttons there is a sleeveless garment. If
aU the fastenings are done up and the others
are put dose to the neck, the whole figure can
be covered, and yet one side may be exposed at
will. By putting a girdle or sash around the
figure an entirely new set of folds is obtained ;
and pulling the garment up through the girdle
and allowing it to fall gives a characteristic and
Diana-Uke effect. With a crossed girdle or
cincture over the shoulders still another series
of folds is obtained which conflnes the garment
to the figure and shows its outlines, and one
has at the same time the alternative of bare or
covered arms, and one side open. Over this,
to add to the beauty and variety of the folds,
is sometimes put a kind of mantie, consisting of
a piece as long as the main garment, horizont-
ally, but only half its vertical depth. This the
ancient Greeks buttoned on the shoulders and
made into the same artistic folds as the under-
garment. When the ends are cut off diagonally
they look Very well, and may be made to form
a series of folds like pleats. Add to this a very
long strip or scarf, about 24 iu. wide and of
indefinite length, to throw over the shoulders,
to twist about the arms, or to festoon about the
figure, and the photographer has all the neces-
sary materials fot the ordinary drapery of the
full-length figure.
DRAWINGS, COPYING
For methods of copying drawings, see under
the headings, "Engravings, Copying," "Copy-
ing," ^ " Copying Illustrations for Translation
into Line Drawings," and " Copying Stand."
In process work, the copying of drawings is
Drawings from Photographs ^9^
Dress for Sitters
brought to a high, degree of perfection. Cameras,
lenses, prisms, copying stands, arc lamps, and
all oOier apparatus are specially designed for
obtaining the most perfect negatives. Parallel-
ism between the various parts of the camera
and the copyboard is carefully studied. All
possible means for overcoming vibration are
adopted. Lenses are chosen to give extreme
definition to the margins of the plate, as well
as uniform illumination ; and the prism or
mirror employed for reversing must not in any
way impair the definition of the lens. The arc
lamps, which are generally preferred to day-
light for commercial work, are very powerful,
and reflectors are employed to concentrate the
light ou the copy. Care is taken to avoid reflec-
tions from the surface. Where the copy is a
wash drawing or painting in colours, isochro-
matic plates and screens are employed. For
copying bluish wash drawings, or drawings in
which Chinese white has been used (tending to
reproduce darker than the original), ssculin or
quinine filters are used to correct the efiect of
ultra-violet light.
DRAWINGS MADE FROM PHOTO-
GRAPHS
There are many methods of making line
drawings from photographs, and most of them
involve the destruction of the originals. In
essence, the lines of the photograph are gone
over with waterproof ink and the photograph
then bleached. Matt prints on bromide, gas-
light, or P.O.P. paper may be used, the last-
mentioned being fixed and washed, but, if it
can be avoided, not toned. The ink used must
be waterproof, Indian or Chiuese, applied in any
convenient manner, as, for instance, with an
ordinary pen, a mapping pen, a camel-hair
pencil, etc. When sufficient work has been
put on the print, the photographic basis is
entirely destroyed with a powerful solvent of
the silver image. Tiny reducer or bleacher may
be used, but in practice one that acts quickly
and without stain has its advantages, and
therefore a, mixtture of iodine and potassium
cyanide, both of which are poisonous, is the best.
The formula is : —
lo % solution of iodine
in methylated spirit 60 drops 125 ccs.
10 % solution of potas-
sium cyanide in
water . . . 10 ,, 21 „
Water . . . I oz. 1,000 „
This may be used stronger if the action is not
quick enough. The solution should not be
allowed to touch the fingers any more than is
rmavoidable. The mixture ought to destroy
the photograph in half a minute ; the picture
is then washed for five minutes and afterwards
dried.
The following process is used by many trade
workers : Make ordinary prints on a smooth
surface bromide paper, exposing and developing
in the usual way; after developing, harden
in an alum bath, wash and dry, but do not fix.
Then draw over the picture with good water-
proof Indian ink, and when the latter is quite
dry bleach in a copper-bromide bath made
by dissolving 50 grs. of potassiiun bromide in
I oz. of water, 50 grs. of copper sulphate in
another oujice of water, and mixing the two
solutions together. If after bleaching the draw-
ing requires further working up, it may be well
washed and redeveloped with any weak dry-
plate developer, dried, worked on, and again
bleached. After a good rinse the bleached
image may be totally destroyed, and the lines
left permanently black upon a white ground by
passing the bleached print through a potassium
cyanide or "hypo" bath. A saturated solution
of mercuric bichloride may also be used for
bleaching out the silver image. 'WTien the
results are required for use as originals in hue
photo-engraving, the bleached prints should be
kept from the light as much as possible, or
they may turn yellow.
A simpler process of drawing on a photographic
base is that of using a blue (ferro-prussiate) print,
preferably one that has not been made too dark
by over-printing. As the light blue colour
will not photograph, the drawing may be repro-
duced by hne photo-engraving processes without
any bleaching, although the blue image can be
removed, if desired, by immersing in dilute
liquor ammoniae, by a prolonged washing in
hard water, or better and quicker still, by
immersing in a solution made by dissolving i
part of potassium oxalate in 6 parts of water.
Solutions of sodium carbonate and caustic
potash will also bleach blue prints.
In process work, various methods are adopted
for making drawings from photographs. If the
photograph is mounted, and must not be
removed from the mount, it is best to lay over
it a piece of tracing gelatine, scratch the out-
line with a sharp point, and then to rub black-
lead or red chalk into the lines. This draw-
ing is turned face down on to a sheet of Bristol
board, or other surface to be drawn upon, and
rubbed down with the handle of a tooth-brush,
or by other convenient means. The drawing
is in this case reversed. It may be obtained
the right way by re-scratching on the back of
the gelatine and filling in this side instead of
that originally traced, or it may be reversed
by means of prisms when making the block.
A better way is by the use of the " Norwich
Film," a gelatine with a matt surface which
can be drawn on with pencil, crayon, or ink. The
resulting drawing may be used as a photographic
positive, or may be converted into a negative
by flowing with a non-actinic varnish. When
dry, the greasy ink or crayon is removed with
benzole or other suitable solvent.
The bleaching-out process, already described,
is perhaps the best way of converting a photo-
graph into a drawing.
Unmounted prints may be traced down on
to Bristol board or drawing paper by rubbing
the back with blacklead or red chalk, or by
putting common transfer paper between the
print and the drawing surface. The outiines of
the photograph are then gone over with a hard
penal or stylus.
DRESS FOR SITTERS
The part played by dress in photography is
an important one ; and a question put frequently
to the photographer is : " What dress shall I
wear ? " As a general rule the more simple the
Dress for Sitters
197
Dropping Bottle
dress the better if the portrait is to be what
may be termed a lasting one. Feminine fashions
change rapidly, and a photograph taken of a
sitter dressed in the prevailing fashion soon
becomes " dated," as it were. Colour is not of
the imgortance it used to be, as, with the modem
isochromatic plates and screens, fairly correct
interpretation of tone has become possible, and
the rendering of a yellow dress as black, or a
blue one as white, ought now to be a thing of
the past. W. Ingles Rogers carried out, many
years ago, some important experiments, and the
saHent facts in his report may be summarised
as follow : A gentleman's ordinary dress is not
sufficiently artistic to warrant a full-length
presentment ; its colour is preferably black. In
the case of uniform and special dress, the full-
length is preferable. Ladies require more careful
treatment from the standpoint of dress. As a
rule, long dresses make the best pictures, both
because the length of drapery gives height and
dignity, and because graceful and flowing lines
are then more easily obtained. As a matter of
fact, the female figure has no waist. It is a
pure invention, and a conventionality of form.
If, however, such a thing has to be considered
and sustained, the best place for confining the
dress is just below the armpits. This disguises
any lack of length in the lower limbs, and grace
and dignity are gained without the usual in-
artistic curving of the hips.
Next to form comes colour, and in this con-
nection no rule can be laid down that will pro-
duce perfect results with tmvarying fidelity.
Much depends on style and complexion ; but, all
other things being equal, monochrome (black,
white, or grey) gives the most favoured results.
Gaudy tints are opposed to the principle on
which the " science " of photography is based,
and are only tolerated by the camera when
neutralising an otherwise monotonous effect.
In cases of necessity — ^for example, where the
sitter's wardrobe does not contain what the
perfection of photographic art requires — the
table of tints, with their relative photographic
Colour of
Tint in
Combines best
Dress
Photograph
with
White
White ..
Black, dark blue, red, or
brown
Yellow . .
Grey . .
Black or dark green
Salmon . .
,, . .
„ „ ,t
Pink
„
„ 0 >'
Fawn
,,
)> »> '»
Scarlet . .
Dark grey
White or dark blue
Dark red . .
Black . .
White, Ught green, light
blue or grey
Brown
Black . .
White, light green, light
blue or grey
Light green
Light . .
Dark green, dark red,
brown or black
Light blue
..
Dark blue, dark red.
or violet
brown or black
Dark green
Black ..
Light green, yellow, or
grey
Dark blue
Medium
Light blue, white, or
or mauve
grey
Grey
Grey . .
White or black
Black
Black . .
White, light blue, green, or
grey
qualities, given in the preceding column, will
repay a careful study.
As for materials, the following are the most
suited to photography, arranged in the order of
preference : —
Name of
Material
Velvet . .
Silk
Cloth
Serge
Cahco goods
Woollen goods
Fur
Combines best
with
Linen, lace, crape, and fur
Crape, velvet, and fur
Linen, lace, crape, and fur
Linen and silk
Linen and cloth
Linen and silk
Silk, lace, and fringes
Silver ornaments are preferable to gold, and
if diamonds are worn they shoidd be slightly
smeared with soap to deaden their reflection
during the brief period of exposure. Long,
drooping curls or waves are effective in semi-
profile, but give to the full-face sitter an effect
of sohdity. The arrangement of the hair gives
a man his individuaUty in appearance, and
therefore should not be interfered with.
DRIFFIELD (See " Hurter and Driffield.")
DROP SHUTTER (Pr., Obturateur d, guillo-
tine : Ger., Guillotine Verschluss, Fall-
verschluss)
A shutter in which a panel, having a central
opening and working in a pair of grooved upright
rails, is caused to fall by gravity in front of
the lens, uncovering and re-covering the latter
as the opening passes it. This kind of shutter
is simple and easily made, but is somewhat
cumbrous, and will not give very rapid expo-
sures. It has been quite superseded by the
roller-bhnd shutter.
DROPPING BOTTLE (Pr., Flacon compte-
gouttes ; Ger., Tropfglas)
A bottle for the deUvery of a liquid or solution
in small quantities, or in separate drops. There
A. Dropping Bottle
with Pipette
B. Dropping Bottle
with Slotted Stopper
are various patterns. In one, A, a pipette or
dropping tube is let into the stopper. Another,
B, allows the drops to pass to a suitable Up in
the neck by turning the stopper, in which a slot
is cut. When not in use, a second turn of the
stopper shuts off communication with the lip.
Schuster's dropping bottle resembles a flask
Dropping Tube
198
Dry Mounting
drawn out at the top to a fine curved point, and
having a stopper at one side for the introduction
of the solution
DROPPING TUBE (Ft., Pipette compte-
gouttes ; Ger., Tropfrohr)
A tube having one end drawn out to a fine
point, and provided at the opposite end with a
rubber bulb, as illustrated. The bulb is com-
pressed, and the tube dipped into the liquid or
solution to be used ; on removing the pressure
from the bulb the liquid rushes up the tube.
^
— -
Two Patterns of Dropping Tube
Having withdrawn the tube, the liquid may be
delivered in drops as required by a gentle pres-
sure on the bulb. Another form is without a
bulb. With this, the tube is dipped into the
solution, its upper end closed with the finger,
and the tube withdrawn. If the depth of solu-
tion does not allow of this, the liqivd must be
drawn up by suction with the mouth, and the
upper end of the tube closed with the finger
before withdrawing it from the solution, but
this is very inefficient. On removing the finger
the liquid is delivered in drops. It is risky to
use this kind with poisons, lest the solution
should reach the mouth. A fountain-pen filler
is an excellent dropping-tube for quite small
quantities.
DROPS (Pr., Gouttes ; Ger., Tropfen)
Drops and minims are supposed to be syno-
nymous, but such is not the case. A minim is
one-sixtieth part of a dram, but a drop may
measure more than a minim, or less, as shown
by the foUowing Hst, which gives the average
number of drops which go to make up one
dram: Water, 71; nitric acid, 96; hydro-
chloric acid, 70 ; sulphuric acid, 100 ; ether,
290; alcohol, 130; turpentine, 220; castor
oil, 157; oHve oil, 168. Drops also vary accord-
ing to the way they are dropped and the recep-
tacle they are dropped from, but happily in
most photographic operations extreme accuracy
as to tiie size of a drop does not matter. A useful
arrangement in the form of a squirt, and called
a minim -meter, is sold by most chemists for the
purpose of measuring drops, or, more correctly
speaking, minims.
DRUMMOND LIGHT
An early name for the limelight, which is
described under its own heading.
DRY COLLODION
This term is sometimes applied to collodion
ernulsion which has been precipitated and washed
with water, and occurs in the form of fine flocks
or granular masses, which only require solution
in alcohol and ether to form a normal coUodiou
emulsion. (See also " Collodion.")
DRY COLLODION PROCESS
An old process, not now used, in which plates
were coated with an iodised collodion, sensitised
in a silver bath, washed, and bathed in certain
so-called preservative solutions, such as albumen,
honey, beer, tannin, coffee, laudanum, etc.,
most of which were hygroscopic to some small
extent, and thus kept the filin shghtly damp.
The first of the dry collodion plate processes of
any real service was that pubUshed by Dr. J. M.
Taupenot, on September 8, 1855. The original
method was to pour over the coUodionised and
sensitised plate a solution of iodised albumen,
dry, and dip for a second time into a silver
nitrate bath, wash, and dry. Plates prepared in
this way kept good for six or eight weeks.
Mayall suggested a similar process in May of the
same year. The great drawback of the process
was its slowness, the plates needing about five
times the exposure of wet plates. On May 2 1 ,
1855, Dr. Hill Norris, of Birmingham, published
his famous process, FothergiU following with his
process in 1856. Dry coUodion plates then be-
came articles of commerce, the Hill Norris
coUodio-gelatine plate (patented September i,
1856) becoming the most popular.
DRY ENAMEL PROCESS
A method used in printing the half-tone image
on to zinc or copper for etching. The sensitive
solution consists of —
Ammonium bichromate 125 grs. 25 g.
Powdered white sugar 270 ,, 54 „
Chromic acid . . 80 ,, 16 „
Albumen, from 2 eggs 7 eggs
Liquor ammoniae . 120 mins. 24 ccs.
Water . . .10 oz. 1,000 ,,
An alternative formula is —
Grape sugar . . 232 grs. I13'6 g.
Albumen . . 338 mins. 1657 ,,
Ammonium bichromate 46 grs. 22-5 „
Chromic acid . . 36 ,, 17-6 ,,
I/iquor ammonise . 120 mins. 24 ccs.
Distilled water . . 4i oz. 1,000 ,,
After coating the plate with this solution and
printing, it is dusted with finely powdered
anhydrous sodium carbonate, or magnesium
carbonate, brushing with a soft flat brush until
the image is clearly visible. A small room, in
which the atmosphere can be kept moist by
standing a bowl of water on the floor, is neces-
sary, so that the plate can absorb the requisite
amount of moisture to attract the powder. The
plate is burnt in, as usual in the enamel process,
and then placed in water, when all the parts
which have absorbed the powder develop away
quite clean. If any scum remains, a little moist
salt or dilute caustic potash wiU remove it.
DRY MOUNTING
The Derepas is perhaps the most perfect
method known of mounting prints and of building
up multiple mounts. The surface of the print is
not affected ; there is nothing that will harm
the most delicate print by any process ; there
is no cockling, even when a stout print is mounted
on a thin paper ; and it is durable when properly
carried out. A sheet of thin tissue is prepared
with shellac, the prepared tissue being com-
mercially obtainable. A piece of the tissue is
Dry Plates
199
Drying Box or Cupboard
touched witli a hot iron, which will make it
adhere to the back of the print, and both print
and tissue are then trimmed together. They are
next placed in position on the mount, covered
with a sheet of paper, and subjected to heat.
This is accomplished either by going over it
with a hot flat-iron, or subjecting it to pressure
in a heated press made for the purpose. The
heat causes the shellac to melt and so secure
perfect adhesion between print and mount.
Everything being dry there is no expansion with
its subsequent contraction, and print and mount
remain smooth and flat. There are no special
difSculties attached to this method, and the
results are excellent.
DRY PLATES (Fr., Plaques siches ; Ger.,
Trockenplatten)
Sheets of glass of given sizes coated with gela-
tine emulsions. The term arose in the early
days to differentiate them from wet collodion
plates. The introduction of the gelatine dry
plate marked a new epoch in photography.
There is some difference of opinion as to who
was the actual inventor. Burgess, Maddox,
Kennett, Wratten, and others all working at the
same time in practically the same direction. It
was, however, on September 8, 1871, when
Br. Maddox published an account of his experi-
ments, that the first hint was given. On July
18, 1873, J. Burgess, of Peckham, advertised
and sold ready-made emulsion with which
photographers could coat glass and so make their
own dry plates ; Kennett followed, and on
November 20 of the same year took out a
patent for his " pellicle," with which photo-
graphers could make their own plates. Improve-
ments followed rapidly, Bolton, Sayce, Wratten,
Mawdsley, Berkeley, Abney, Bennett, and
others doing much to bring the dry plate to per-
fection and to make it an article of commerce.
As far as can be ascertained, the first ready-made
dry plates were advertised in April, 1878, by
Wratten and Wainwright and the Wverpool
Dry-plate Company (Peter Mawdsley), the plates
by the latter firm being called the " Bennett
Plates," and the price for quarter-plates being
3s. per dozen. It was not until 1880 that gela-
tine dry plates became really popular.
In process work, considerable progress has
been made of late years in the use of dry plates.
Excellent commercial dry plates, specially made
for line, half-tone, or colour work, are now
obtainable. The methods of handling are not
very different from those in ordinary photo-
graphic work, except that greater care has to
be taken to avoid over- or imder-exposure and
fog ; the lines must be kept perfectly clear and
sharp, and in half-tone work great care and skill
have to be exercised to obtain sharp dense dots
of the right size and quality. In this respect
dry plates are more difficult to handle than wet
collodion. Backing is found to be an advan-
tage ; the negatives usually have to be cleared
with ferricyanide and " hypo " (Howard Farmer's
reducer) ; and intensification, preferably with
silver cyanide, is generally necessary. For the
making of dry plates, see " Coating," " Emul-
sion," etc. For the various taanipulations, see
" Exposure," " Developing," " Fixing," " Ton-
ing," "Washing," etc.
DRYING BOX OR CUPBOARD (Pr., fyuve,
Armoire ; Ger., Trockenofen)
A light-tight box or cupboard used in drying
gelatine plates after coating, and for other photo-
graphic purposes. The chief requirement is the
circulation of a current of dry air, in order that
the internal air may be continuously drawn away,
carrying with it by degrees the moisture from the
plates. The temperature of the drying cupboard
requires to be raised, but perfect ventilation is
of greater importance. A pattern recommended
by W. K. Burton consists of a box with a closely-
fitting light-tight door, and having light-trapped
air openings at top and bottom. Beginning near
the bottom, a bent channel or flue runs up
against one side of the box, a gas burner being
inserted in it near the top. When the burner
is lit it draws a current of air through the flue
from below, and consequently ensures a con-
stant circulation of air in the box. Another
kind of drying cupboard is warmed from beneath
by a gas-ring or oil stove, a sheet-iron bottom
being fltted. lyight-trapped openings at the
lower portion of the sides and a cowled
ventilator at top furnish the necessary air
current.
In process work, the arrangement for drjring
collotype plates is usually in the form of a box
or trunk supported about 12 in. from the
floor on four legs. The bottom consists of an
inverted sheet-iron box, under which is placed
a gas-ring or pipes. Holes are punched in the
side of the box to prevent the gas becoming
choked. The wooden part of the box is about
18 in. deep. About 6 in. from the top are two
iron bars, resting on ledges at the sides of the
box. These bars are provided with screws
placed at suitable distances with their points
Upwards. The plates rest on these screws, and
by adjustment of the latter can be levelled up,
so that the gelatine solution on the plates will
not run off. The bottom of the box is usually
covered with sand to equalise the heat. The
lid of the box is covered with gauze or an open-
textured cloth, so that the moist air can pass
through. A thermometer is inserted into the
box through a hole in the Hd.
Process workers find a dr3ring cupboard
necessary for quite a number of purposes ; in one
convenient form the bottom takes the form of
an inverted sheet-iron box, and there are holes
in the sides to allow the gas fumes to escape, or
a flue pipe can be led out from the back. In
the sides of the wooden part, just above the
sheet-iron bottom, are holes for drawing in a
current of air ; these holes are covered with a
baffle-board sloping towards the bottom. Shelves
or racks can be placed in the cupboard. On
the top a metal cowl ventilator is placed. For
heating, an ordinary gas-ring burner is placed
tmdemeath the bottom. The cupboard can be
elaborated by placing an electric radiator inside
and an electric fan on top to draw out the air.
The incoming-air can also be made to pass
through an opening picked with damp cotton-
wool, so as to stop any dust entering. For
colour-sensitising dry plates the cupboard must,
of course, be made perfectly light-tight. Such
a cupboard is very convenient for drying photo-
lithographic paper and carbon tissue, and will
be found generally useful.
Drying Marks
200
Dufay DIoptichrome Process
DRYING MARKS
These in negatives are most frequently patches
or portions which are stronger or weaker than
the remainder of the image, such portions pro-
ducing corresponding defects in the print. These
markings may be dxle to defective working, or
to causes beyond the worker's control. With
regard to the first, a plate may be drying very
slowly, and when partly dry the conditions of
drying may be changed to accelerate the drying
of those parts that still remain wet. The part
accelerated will almost always show greater
density than the remainder, and at times a
well-defined mark may separate the two
parts.
The second cause is uneven drying of the
plate in the course of manufacture. When plates
are racked for drying, no matter how perfect the
ventilation of the drying-room may be, the
edges, where the emulsion always tends to thin-
ness of coating, will always dry more quickly
than the centre, the result being that a Hne
appears round the edges. The exact cause of
this is a Uttle obscure, but the most satisfactory
explanation is that given by Homolka, who
ascribes the foggy line — for this is what edge
drying marks actually are — to a diffusion of the
faint traces of soluble haloid left in the emulsion
from the thin dry edge to the thicker and moister
centre. Actual drying marks from uneven dry-
ing of plates during the manufacture are now
rarely met with, though in the early days of diy-
plate photography they were of frequent occur-
rence, and manifested themselves in precisely the
same manner as in the unequal drying of nega-
tives— that is, by central patches of greater or
less density due to this portion being more or
less sensitive than the margins.
DRYING NEGATIVES
Negatives should be dried as quickly as possi-
ble consistent with drying evenly^that is,
with uniformity in the rate of drying. A
current of dry air is best, but a drjring cupboard
is good. In any case, the air should have free
and uniform access to their surfaces ; they should
not be dried close together, as in a draining rack,
neither should they lean against a w^ face
downwards. The place chosen should be as free
from dust as possible, and not too warm, or the
gelatine may melt. In summer and autumn
particularly, it is necessary that the plates should
be dried in a place protected against flies and
other insects. Cockroaches are said to be fond
of eating wet gelatine.
DRYING PRINTS
Prints in all processes should be freely exposed
to the air in drying, so that the operation may
be rapid. The most satisfactory method in
most cases is to hang the prints from a line or a
lath, either by means of cUps or by pins through
one or two corners. An alternative method is to
blot off as much moisture as possible, either with
a soft towel or blotting-paper, and then lay the
prints face upwards on a clean white cloth until
dry. A drying cupboard is the best place for
the latter method.— In any case, they should be
dried in a place as free from dust as possible.
(For imparting a high gloss to prints in drying,
see " Glossy Surfaces.")
DRYING RACK, OR DRAINING RACK
(Fr., SSchoir, igouttoir : Ger., Trooken-
gesiell)
A wooden, metal, or porcelain stand with
grooves, in which negatives, etc., are stood up
to drain and dry after washing. The ordinary
wooden folding pattern is shown at A, while B
A. Wooden Drying Rack
illustrates an ingenious expanding metal rack,
which may be adjusted to hold various sizes
of plates. Many washing tanks are fitted with
a removable metal rack which may be used for
drying. Negatives should not be placed closely
together in the racks when drying, or the process
Expanding Metal Drying Rack
will be very slow, and uneven patches sometimes
occur. The closeness of the usual grooves is in
this respect somewhat misleading. It is better
to spread out the negatives.
DUFAY DIOPTICHROME PROCESS
This employs a screen plate of French manu-
facture. A gelatinised glass is coated as to two-
thirds of its surface with a greasy material, which
acts as a temporary resist, in the form of Unes,
points, or grains of geometric or irregular shape.
The present plate consists of lines wi& rectangles
in between. The bare parts are dyed and the
whole surface varnished and treated with a
solvent of the greasy material so as to lay bare
the imstained gelatine. Half this surface is
then again covered with a greasy substance, and
the bare gelatine again dyed, again varnished,
the greasy material again dissolved, and the
last portion of the unstained gelatine dyed. A
compensating filter is used, and the plate is
issued with a special panchromatic plate fitting
into a frame with nickel pins which allow of
complete registration of the positive and colour
screen. Coloured plates to this work show the
formation of the Dufay plate, and a typical result
obtained with this plate.
Du Hauron, Ducos
Dust Spots
The plates must be manipulated in absolute
darkness or with the maker's special dark-room
filter. The developer recommended is : —
Metol
Sodium sulphite .
Hydroquinone
Potassium bromide
Liquor ammouise ('SSo)
Distilled water to
For use, mix with an equal quantity of water
and continue development for four minutes.
Rinse the plate for some minutes, and immerse
in —
• 53 grs.
6g.
if oz.
72 „
• 17 grs.
2 ,.
• 17 „
2 „
. 130 mins
. :s CCS
. 20 oz.
1,000 ,,
Potassium or ammo-
nium bichromate
Sulphuric add .
Water to .
44 grs. 5 g.
95 mins. 10 CCS.
20 oz. 1,000 „
When the image has dissolved, wash for
several minutes till all the yellow tint has dis-
appeared, and immerse in the first developer or
preferably in —
Metol
22 grs.
2-5
g-
Sodium sulphite
I oz.
50
Hydroquinone .
44 grs.
5
ft
Potassium carbonate
220 „
25
Potassium bromide
18 „
2
Distilled water to
20 oz.
1,000
CCS.
Re-development takes about three minutes, and
should be done in a bright light. The plate
may be reduced with " hypo " and ferricyanide,
and intensified with mercuric chloride followed
by ammonia.
DU HAURON. DUCOS
A Frenchman, bom in 1839, in Langon,
Gironde, and one of the first to describe iu detail
the three-colour process (1867). In 1864 he
patented a species of kinematograph. He was
also the inventor of the anaglyph, and the first
to describe a screen - plate process of colour
photography.
DUOTYPE (Ger., DupUx-Autotypie)
A half-tone in two printings, one being with
a light tint ink, and the other in a black or photo-
brown, the idea being to imitate the tones of
a photograph. Sometimes both printings are
from the same block, but the best results are
obtained from two blacks etched differently.
DUROLENE
A kind of unbreakable glass in which wire is
embedded. It has been recommended for studio
roofs, but its tint stops a large amount of actinic
hght.
DUST PREVENTION
Dust is often a great trouble in photographic
work, both in the field and in the work-room.
Dust in the camera and on the lens is the most
frequent cause of trouble, hand cameras being
more prone to the defect than others because of
the usual practice of carrying them unprotected.
Dusty lenses cause flat and misty pictures. Dust
will find its way into the lens through the slits
used for Waterhouse and rotating diaphragms,
and the only preventive is to fit, when possible,
a band of velvet ribbon round the lens tube
to cover up the slots as much as possible ; in
the case of Waterhouse diaphragms the band
may be kept completely over the slot when the
diaphragm is not in use. Rubber bands have
been recommended, but these contain substances
that tend to mark and discolour the lens mounts.
The plate-changing arrangements in hand
cameras, and shutters working inside, are often
the means of stirring up dust which settles upon
the lens and plate. Frequent dusting of the in-
terior of the camera and plate sheaths is advis-
able, but unless done carefully more dust will be
deposited than removed. Coating the inner-
most parts of the camera with glycerine or vase-
line has been suggested; such a coating wiU
naturally hold down the dust and prevent its
flying about, but inasmuch as it is liable to be-
come messy and to need frequent changing, the
method is not recommended. The focusing
screens of stand cameras are occasionally thinly
coated with vaseUne in order to make them more
transparent, and the coat serves as a kind of trap
for the dust ; in this case the cleaning is quite
easy, but the cleaning of the interior of the
bellows is quite another matter. Dark-slides
invariably attract dust, but they can easily be
dusted, and any coating of grease might inter-
fere with the sliding shutter or find its way to
the plate. Dark-slides having draw-out shutters
are the greatest offenders ; the light-trap at the
top of the slide, which closes the aperture when
the shutter is completely withdrawn, is made
usually of either velvet or rubber, and this
scrapes or wipes the dust from the sides of the
shutter as it is drawn out and returned, thus
in time forming an accumulation. Thorough
dusting of the light trap and the interior of the
slides is an obvious remedy. Dust settling upon
the plate causes many spots, and it is of but
Httle use dusting a plate before putting it into
the dark-slide if it is to be exposed to a minia-
ture dust storm in the camera.
Plate dusters are articles of commerce, but
if they are not kept scrupulously clean they put
more dust upon the plates than they take off
and do more harm than good. Plates rarely
need dusting with a brush ; when taking them
from the box or dark-slide, a gentle knock with
the edge upon a table wiU do aU that is neces-
sary. Of dusters, an old well-washed silk hand-
kerchief is one of the best.
Frequently unsuspected resting-places for dust
are the top rims of bottles and the crevice
between the cork and the bottle neck ; before
pouring a developer from a bottle, the rim and
mouth should be wiped, otherwise any accumu-
lated dust may find its way to the plate and
cause spots. The corks of bottles should be
kept covered with a paper or cardboard cap.
Many professional dark-rooms and aU plate-
making rooms have their floors k^t damp in
order to prevent dust.
The utmost care is necessary when mixing
chemicals, more particularly pyro and other
developers, to prevent small particles of the
developer in the form of dust flying about the
room and settHng upon sensitive surfaces.
DUST SPOTS
Miniature transparent spots on negatives due
chiefly to the causes given in the preceding
article. If the spots are actual holes in the
gelatine, showing the bare glass beneath, they
Duster, Plate
202 Dusting-on (Powder) Process
are due to dust in the process of manufacture
and are real pinholes ; but these are very rarely
met with nowadays. Dust spots are more or
less numerous and of various shapes and sizes,
and they occur where dust specks have rested
on the plate during either exposure or develop-
ment. In the former case they prevent the
light from reaching the emulsion, and in the
latter the developer is prevented from reaching
it. The remedy for spots caused in this way
(it is a mistake to call them "pinholes") is
careful spotting, but obviously prevention is
better than cure. Particles of developer dust
which may float about the dark-room and settle
upon undeveloped plates and bromide papers
invariably cause black spots, but such spots
will also appear when the developer has not
been properly dissolved, and it is very difficult
at times to discover the real cause of the trouble.
Black spots on a negative are best left alone,
and the resultant white spots on the print
touched out. Etching or pricking away with a
needle on the negative has been recommended,
but it needs particidar care, as otherwise the
film will be ruined.
DUSTER, PLATE {Ft., Torckon aux plaques ;
Ger., Plattenabstauber)
A strip of wood having a piece of plush
attached, and used for dusting dry plates before
insertion in the dark-slide. Sometimes a wide
camel-hair brush is employed, but this is still
less satisfactory, being more liable to put dust
on the plate than to remove it. Neither device
is recommended. (See also " Dust Prevention.")
DUSTING OR GRAINING IN PROCESS
WORK (Pr., Grainage ; Ger., Staub-
kornung)
There are several processes of photo-engraving
dependent on the laying of a ground consisting
of fine resin, bitumen, or other similar material.
Such a method is used for aquatint etching
instead of the old way of flowing on the resin
emulsified in alcohol.
For a process of colour work much practised
in Prance, called chromo-typogravure, a resin
grain is laid on zinc plates, and a set-oS is laid
down on the plates from a key plate to guide
the etcher in stopping out the various colours.
This is done by means of an acid-resisting varnish,
so that the resin ground forms the lighter tints.
In the photogravure process the laying of
the grotmd is an important operation. Pinely
powdered bitumen is generally used, and after
being deposited on the copper plate and fixed
by heat, a carbon print is developed upon it to
form the resist for etching.
The dusting for the foregoing processes is done
by means of a dusting box. This may be of
either the turnover pattern or the fan pattern,
the former being suitable for small plates and
mostly used by amateurs. The box is turned
over and over to shake up the bitumen, then
the plate is put in and the box allowed to stand
for a shorter or longer time, as may be demanded
by the character of the grain required. In the
fan dusting box the powder is stirred up in the
semicircular zinc bottom by means of a revolving
brush, and, after allowing to stand for a few
moments for the heavier particles to settle, the
plate is put in. The longer it remains in the
box the finer will be the grain. Powdered lac
is also sometimes used for dusting.
DUSTING-ON (POWDER) PROCESS (Pr.,
Procidi aux poudres ; Ger., Einstaubver-
fahrung)
Known also as the " Powder Process," based,
as are the other carbon processes, upon the
oxidising action of chromic salts upon organic
matters. In the present instance, the organic
matter loses its tackiness or stickiness under
the action of light and refuses to retain dust.
The process is largely used in the production
of photo-ceramics and for the intensification and
doctoring of faulty negatives when these are of
great value. Various substances are available
for the support of the powder picture, but none
is better than groimd opal or pot opal glass.
As the effect of the Ught in the process is to
cause the film to refuse to take powder, the parts
acted upon remain light ; this being the case,
a transparency (positive) must be used for
printing from and not a negative, as a print
from the latter in this process would be a nega-
tive. The requisites are sensitising mixture,
opals, powder, and a transparency of excellent
quality. Although opal has been named and
is recommended, glass, ferrotype, and other
supports can be used. In any case, it must
provide a proper contrast to the powder. Thus,
if the dust or powder used is silver or gold
bronze, the image may be produced on a dark
background, for which a ferrotype tinplate will
serve.
The support must be cleaned and sensitised
in a solution consisting of a gum, a hygroscopic
substance, and a Ught-sensitive medium. The
following formula is one of a great number
between which there is but little to choose : —
White sugar . . 200 grs. 20 g.
Gum arable . . 250 „ 25 „
Ammonium bichromate 200 ,, 20 „
Methylated spirit . i oz. 50 ccs.
Water . . . 20 ,, 1,000 „
An old, and possibly the original, formula, still
in use, is as follows : —
Water . . .10 oz. 1,000 ccs.
Dextrine . . . 240 grs. 48 g.
Grape sugar . . 240 „ 48 „
Potassium bichromate 240 „ 48 „
The first of these formula is said to possess
many advantages. The gum and sugar should
be covered by the water and dissolved by heat ;
when cool, the other ingredients are added. The
spirit is used simply to make the solution flow
over the plate more evenly, and more or less
may be used as desired. After washing, the
wet plate is flowed over with the sensitive mix-
ture, drained for a few minutes, and then baked
in an oven until bone dry. The operations up
to baking may be carried on in daylight, but as
the plate dries it becomes sensitive and should
therefore be removed and examined in a dull
light. The plate is then ready for exposure
imder a positive, and, as in many other cases,
this is the most difficult part of the process, for
so much depends upon atmospheric conditions.
The duration of exposure can be found only
by experiment, but as a rough guide it may be
Du8ting-on (Powder) Process
203
Dyes as Colour Sensitisers
said to be one minute in bright sunlight on a
summer's day, when a transparency of average
density is used. When exposure is complete,
the plate is " developed " by dusting on a
powder. The choice of a powder is almost
unlimited, but it must be exceptionally fine, to
ensure which it should be sifted through a musUa
bag. Ordinary powder colours from an oil-shop
may be used. Ivory black and Indian red are
good colours, used alone or mixed in varying
proportions, while some use levigated graphite.
For printing, the sensitive plate should be
warmed, or it may be warmed by being printed
in strong stmUght. An image will be seen
faintly upon the sensitive plate when removed
from the frame. The plate is held in the fingers
or on a pneumatic holder, and some powder
sprinkled over the surface, immediately spread
with a soft camel-hair brush, and kept on the
move until sufB.cient detail and density have
been secured.
Development proceeds rapidly as the plate
cools, and it should be assisted by a gentle
stream of air blown from the mouth across the
plate, the current not being strong enough to dis-
turb the powder or cause excessive moisture ; the
air must not be absolutely dry, and the powder
must be kept on the move with the soft camel-
hair brush. Almost any depth can be obtained
in any part of the picture by patient re-apphca-
tiou of the powder rather than by attempting
to make too much powder adhere at one time.
As the progress of development is visible and
imder perfect control, it is not difficult to bring
out or keep back certain parts, and in this way
very artistic results may often be easily obtained.
When development is complete, the powder
picture may be coated with plain collodion and
washed free from greasiness ; the plate is now
transferred to a 5 per cent, solution of potash
alum until the yellow bichromate salt has been
removed. Fixing with collodion as just described
may be dispensed with when a duplicate negative
is being made upon glass, all that is necessary
being to expose it again to the light to get rid
of e^ further tackiness. When, however, it is
desired to fix the picture — as, for example, when
it is upon an opal base — and it is not convenient
to use the collodion " fixer," the picture may be
washed over with the following solution : —
Water
I oz.
100 CCS.
Sulphuric add .
. 2 dims.
25 „
Methylated spirit
. 2 oz.
200 „
Mix in the order given. The plate is treated
with this until all the yellowness has gone, is
then washed gentiy in water, and dried by
gentie heat. The collodion fixer is preferable,
as with the acid solution there is a risk of
entirely losing the image. Flatness in a picture
is caused by over-heating or over-expositig the
plate or by developing in too dry an atmosphere ;
in this connection care must be taken to keep
white light from the image before fixing.
This process has been used for the production
of pictures in colour. In 1888 a process was
introduced by Germeuil-Bonnaud which con-
sisted in exposing a plate coated with treacle,
sodium borate and potassium bichromate, under
an ordinary positive transparency. It was then
dusted with various coloured pigments which,
it was claimed, adhered selectively to the differ-
ent parts of the picture, a claim that has not
been substantiated. Dr. Miethe has worked out
a variation of the idea. Glass plates are coated
with the following mixture : —
Gelatine ... 9 grs. 5-8 g.
Sugar candy . . 300 „ 194 „
Potassium bichromate 90 ,, 58 ,,
Water • • ■ 3i oz. 1,000 ccs.
The plates are dried in an oven and exposed
under a positive while warm. Three prints will
be required from three negatives representing
the three different colour sensations. Develop-
ment is performed by brushing on the plates
suitable transparent powder colours. The yellow
print is made first, stripped with collodion, and
affixed to a card with gelatine solution. When
dry, this is coated with a thin film of shellac,
and the red and the blue prints superimposed
upon it in the same manner.
A formula specially compounded for ceramic
work, but which will also serve for all papers
and articles, is : —
Gumming Mixture
A. Fish-glue . . i oz. 100 ccs.
Glucose . • 4 „ 250 g.
Glycerine . . 10 drops -5 ccs.
Water . . lo oz. 1,000 „
Sensitising Mixture
B. Am. bichromate . 1 oz. 100 g.
Water . . 10 „ 1,000 ccs.
Mix together equal parts, and use as already
described.
DYES AS COLOUR SENSITISERS
The peculiar property possessed by certain
dyes of conferring upon the silver hahdes in-
creased colour sensitiveness was discovered by
Vogel in 1873, has had a most important influ-
ence on the advancement of photography in
almost every branch, and since his time the
number of dyes which act as sensitisers has
been and is being continually increased, though
the practically valuable ones are but few. It
was but natural to expect that an examination
of the chemical constitution of the various
sensitisers would show some common property
or grouping of elements to which might be
ascribed the sensitising power, but up to the
present no definite conclusion can be come to.
It has been further suggested that the sensitive-
ness of the sensitisers themselves to light was
the cause of their action, but some of the most
fugitive dyes are not sensitisers, whilst others
which are very stable are. Then, again, it has
been pointed out that many of the dyes are
photo-electric, and that here electrons m^y be
set free which act on the silver halide, causing
increased ionisation of that part of the silver
halide which forms the latent image. The sub-
ject is so complicated, and the mass of material
available for examination is so meagre, that
the resulting definite conclusions are disappoint-
ingly small.
There are certain generally accepted facts
as to sensitisers, and these have been most con-
cisely summarised by Eder as follows : — ( i ) The
absorption spectrum of neither the alcoholic
nor of the aqueous solution of the dye nor of
Dyes as Colour Sensitisers
204
Dynactinometer
the dyed gelatine agrees with the position of
maximum action on the sensitive emiilsion.
(2) The position of maxamnm action of the dyed
silver bromide always lies slightly nearer the
red than the absorption maximum of any solu-
tion of the dye. (3) The position of maximum
of absorption of the dye in gelatine and the
maximum sensitising action generally differ by
about 30 /i /i or wave-lengths. (4) The absorp-
tion spectrum of a dyed silver halide coincides
with the maximum sensitising action. (5) The
dye must stain the silver halide itself to be a
sensitiser, but all dyes that thus stain are not
sensitisers. (6) Fluorescence, or fugitiveness to
light, of the dye appears to play no part.
As most of the important sensitisers are briefly
described under their respective names, refer-
ence should be made to these. The principal azo
sensitisers are glycine red, benzonitrol brown,
Pluto black, dianil black R, and wool black 4 B.
To the rosanihne family belong ethyl violet and
formyl violet. The phthaleine group is one of
the most important, as it comprises the cosines
and erythrosine. The acridine dyes are chrys-
aniHne, acridine yellow, and acridine orange.
The best sensitisers, particularly for red, belong
to the chinoline or quinoline group, and are
isochinohne red, dicyanine, and the isocyanines
orthochrom T, pinaverdol, pinachrome, homocol,
isocoi, etc.
DYES FOR COLOURING PHOTOGRAPHS
In choosing dyes for colouring photographs
on a gelatine basis it is important to take into
consideration first their stability when exposed
to light, and secondly their affinity to gelatine.
The following are the most suitable : acid violet
7 BN, wool blue N extra, patent blue, fast acid
violet, acid green, alizarine cyanine (blue violet),
tartrazine (yellow), chinoline yellow, brilliant
orange, Ponceau 5 R (red with violet tinge),
new coccine (bright red), erythrosine (bluish red),
fast brown, water soluble fast blue and water
soluble nigrosine (blue black). All these colours
will take well on gelatine if it has not been
hardened. For collodion prints it is advisable
to use albumen as a, vehicle for the dyes.
DYES. IMPROVING NEGATIVES WITH
{See " Retouching, Chemical.")
DYNACTINOMETER (Fr., DynactinomHre ;
Ger., Dynaktinometer)
An instnunent by which the actinic power of
light may be measured, or the rapidity of differ-
ent lenses compared.
EASEL. ENLARGING (Pr., Chevalet d'agran-
dissement, Chevalet a reproduction ; Ger.,
Vergrosserungs-Stativ)
A support to hold the bromide paper during
the operation of enlarging. In order to ensure
parallelism with the negative in the enlarging
camera or lantern, the easel is made to run on
rails ; or it is fixed, the lantern or camera being
moved instead. The easel may consist simply
A. Typical Modem Enlarging Easel
of an upright board supported by a firm base or
crosspieces, but it is a great convenience if it
possesses a swing movement, which will permit
the correction of vertical Unes that are shown
as slanting in the negative, through the tilting
of the camera when taken. Formerly the worker
was content to fasten up the bromide paper with
pins ; now many easels are provided witii spring
clamping bars, which save time and also hold the
paper flatter. Another arrangement is to attach
B. Enlarging Easel which Readily Assumes
Horizontal Position
to the easel a hinged frame carrying a sheet of
glass, this being fastened down over the paper.
A illustrates a typical modem enlarging easel,
with rising, falling, and swing movements ;
while B shows an easel of very sohd construction,
which, besides allowing for rise and fall and for
any degree of swing, may instantly be changed
to a horizontal position for pinning ttie paper, and
as easily returned to its former upright position,
in which it automatically catches. Some easels are
made with a ground-glass focusing screen, so that
the projected image may be focused from the
back ; these may, or may not, be provided also
with a dark-slide to carry the paper. The easel
is preferably painted black ; otherwise, when
only a part of the negative is to be enlarged, a
good deal of stray Ught will be reflected from the
easel. The white paper used to focus on should
preferably be removed, or covered with some-
thing black, before fastening up the bromide
paper. In the majority of cases, however, this
may be omitted without any ill result ; but it
is imperative if plates are used, as when making
enlarged negatives, etc.
It is sometimes necessary in enlarging to
correct the distortion in the original negative
by swinging the easel out of parallelism. In
a typical easel for process work, both a ver-
tical and horizontal swing can be obtained,
and the negative can also be turned in its own
plane to any axis. Max Jaffe, of Vienna, has
done some remarkable panoramic copying with
an easel of this kind, securing pictures with an
enormously wide angle by ignoring the original
distortion in the negative and correcting it when
copying, at the same time joining up the image
on one negative to another to secure a large
combination negative.
EAU BROME
Bromine water ; used at one time in the
daguerreotype process, for stopping the action
of hght.
EAU DE JAVELLE (Fr., Eau de Javelle :
Ger., Bleichwasser, JavelHsche Lang)
A clear, colourless fluid smelling of chlorine,
used as a reducer, " hypo " eliminator, and stain
remover ; known also as sodium hypochlorite,
ozone bleach, and Labarraque's solution. It was
one of the earliest of the bleaching solutions,
and was first made at Javelle, Paris ; hence its
name. There are several methods of making
it, the best for photographic purposes being :
Add I oz. of sodium carbonate to 4 oz. of water,
shake well, and add 320 grs. of bleaching powder
(chloride of lime), and shake well again. Filter,
shake up the residue with water, and again
filter. The filtrate is a solution of hypochlorite
{eau de Javelle). Acidified with oxalic acid, it
forms an active stain remover, but it is safer
to use it without the acid. Its use is not now
recommended, _ safer methods having super-
seded it.
EBONITE
A black compound of indiarubber or caout-
chouc, sulphur, and pigment, with occasionally
certain filling substances, used for the shutters
205
Ebony Stain
206
Eclipses, Photographing
of dark slides, developing dishes, etc. It is the
same as vulcanite except that the latter is made
in many different colours.
Ebonite has many uses in photography owing
to its waterproof and acid-proof character. Its
drawback, however, is its brittleness, though
this can be overcome, and a flexible ebonite
obtained, which is useful for some purposes.
Ebonite has been used for dipping baths for
wet collodion work, but has not proved popular
because of a supposed tendency for the bath to
be injuriously affected. More probably this is
due to the difficulty experienced in cleaning
such baths.
Ebonite dippers for the silver bath, however,
survive, and have the advantage of not being
so fragile as glass. Ebonite plate lifters for
flat dishes and trays are also largely used.
Draw-out shutters for dark-slides, iris diaphragms
and Waterhouse stops, developing dishes up to
about 15 in. by 12 in., and much larger flat
trays (with an outer wooden casing) for silver
baths, are made of this material.
In process work, ebonite is useful for parts of
etching machines which have to be exposed to
the acid.
EBONY STAIN
Ebony stain (Stephens's) is preferred to Indian
ink by some pen-and-ink artists. It makes a
good line, and dries with a glossy surface which
photographs well. It has the drawback of not
being waterproof, and of more quickly clogging
drawing pens than does Indian ink. It is cheap,
and if otherwise suitable it is worth while trying
to waterproof it by adding a solution made by
boiling together 2 oz. of shellac and -J- oz. of
borax in 10 oz. of water, and straining.
EBULLIOSCOPE (Pr., tbuUioscope ; Ger.,
Ebullioskop)
An apparatus for testing the purity of a liquid
or solution by ascertaining the temperature at
which it boHs. When a liquid contains dissolved
substances its boiling point is usually higher,
and a concentrated solution has a higher boiling
point than a weaker one.
EBURNEUM PROCESS
An obsolete process invented in 1865 by
J. M. Burgess, of Norwich, in which a carbon
or collodion transparency, transferred from a
sheet of waxed glass, was backed up with an
ivory-like mixture, which gave it the appear-
ance of being on ivory. Burgess's original
instructions were, briefly, as follows : — A good
collodion transparency is necessary, and the glass
upon which it is taken should be waxed to
fadlitate stripping. Either an iron or pyro
developer is used, preferably the following : —
PjnrogaUic acid . 3 to 6 grs. 7 to 14 g.
Citric acid . • 3 ,, 7 ,,
Glacial acetic acid . 20 drops 42 ccs.
Water . . . i oz. 1,000 „
Fix with cyanide, well wash, and tone with
gold. When dry, strips of paper are pasted
round the plate on the back and then turned
up so as to form a dish. The plate is placed
level and coated with the following mixture at
a temperature of 100° P. (38° C.) : —
Gelatine . . 5 „ 500 g.
Glycerine . . i „ 50 „
Zinc oxide . . i ,, 100 ,,
Water ... 10 oz. :,ooo ccs.
When set, the plate may be allowed to dry
spontaneously and the film detached. The pro-
cess was slow and difficult, for which reason it
was little used. Imitation ebumeum prints
widely known as " Ivorytypes " {which see) were
more popular.
ECLIPSES, PHOTOGRAPHING
The portrayal of the varying phases of an
eclipse, whether of the sun or moon, is always of
interest to the photographer. The exact times
at which these phenomena will occur can always
be ascertained a considerable time in advance
from the almanacs, thus enabling the photo-
grapher to prepare any special apparatus he may
desire to fit up for the occasion.
Dealing first with eclipses of the moon, the
chief interest in these lies in the gradual change
in shape as the moon traverses the earth's
shadow. When fully eclipsed the moon may be
either quite invisible, or showing of a more or
less bright coppery colour. The most satis
factory manner of obtaining a picture of the
eclipse with an ordinary camera is to set up the
camera on its tripod and focus sharply ; then
swing until the moon is near one end of the
ground glass. The end chosen should be that
from which the moon's image will travel in its
motion across the sky owing to the earth's
rotation. This is always from east to west, so
that, remembering that everything is inverted
in the camera, the first exposure should be
arranged near the right-hand side of the plate if
the observer is in the northern hemisphere.
I<oaiil the dark-sUde with isochromatic plates of
medium rapidity; draw the slide, and expose
with the cap. Give about a quarter of a second
exposure. After making one exposure, leave the
apparatus as it stands, with sUde stiU drawn, for
say five minutes. During this interval the
moon's image will have travelled towards the
left on the plate, and another similar exposure
may then be given. Repeat this procedure at
intervals of about five minutes until the eclipse
is over. On developing, which will be exactly
hke the development of an ordinary subject and
needs no special description, a series of pictures
of the moon will be found extending across the
plate, and of varying shapes, from fuU circle,
through crescents to the dusky total edipse. A
pleasing variation to the above procedure may
be made if the observer has a telephoto equip-
ment, as he can with it obtain larger pictures
of the moon's phases, showing more details of the
surface structure. It will not be possible, how-
ever, to obtain the whole series of pictures illus-
trating the progress of the edipse on a single
plate owing to the increased magnification. If
the series is required, then several loaded plate-
holders must be got ready to hand and the
plates changed as found most convenient.
With edipses of the sun, the problem is some-
what different, chiefly on account of the very
great actinic power of even a small section of the
unecUpsed solar disc. If the echpse is only
partial, the arrangement described above for the
lunar edipse may be repeated except in regard
Eczema Procurata
207
Edinol
to the exposure. This must be rendered as
short as possible. If a focal plane shutter is to
be employed, the slit in the blind must be made
as narrow as possible, and the tension run up to
the maximum. Should a diaphragm or cap
shutter only be available, then it wiH be advis-
able to stop down the lens to the smallest aper-
ture possible and also use the shutter at its
greatest speed.
The greatest interest, however, becomes cen-
tred in the solar ecHpse which becomes total,
the dark moon blocking out aU the usual brilliant
white disc. Then it is that one is able to see
that wonderful appendage to the sun, the corona,
and the ring of ruddy atmosphere, the chromo-
sphere. On a small scale these features may be
photographically recorded by means of cap
exposures, but they wiU have to be fairly rapid,
say a quarter of a second, owing to the rapid
motion of the moon. With a small mechanical
stand having provision for driving the camera
at the same rate as the drift of the moon much
longer exposures may be given, and the coronal
extensions portrayed to a greater distance from
the moon's limb. Owing to the special nature
of the coronal hght isochromatic plates should be
employed for this class of work, and, preferably,
the most rapid variety available. For recording
solar eclipses on -a. very large scale, special
cameras with lenses of great focal length have
been at various times employed. For example,
cameras with lenses of 40 feet focal length were
used by an American party under Professor
Campbell in India. The lens was situated at
the narrow end of a tube, propped up on the
top of a wooden skeleton tower. The plate
holder was in a canvas- covered portion near the
ground, and iu one case the moon's motion was
counter- balanced by moving the plate-holder by
a simple form of depsydra.
One of the most interesting and instructive
appHcations of photography to a total solar
edipse consists in the use of the prismatic camera.
In its simplest form this is the ordinary camera
with a. simple prism adjusted outside the lens in
such a position that the Hght from the edipsed
sun must pass tlirough both prism and lens
before it reaches the photographic plate in the
camera. By this means is obtained a series of
pictures of the sun's surroundings, instead of a
single one as before. Every different substance
present in the sun's atmosphere will show as a
different ring or series of rings, and it is by a
study of su(£ photographs — or spectrograms, as
they are technically called — that astronomers
have been able to learn what substances are
present in the solar atmosphere. In a particu-
lar example of the prismatic camera, the lens
aperture is 6 inches, and the focal length of the
lens is j\ feet. There is a single large prism
of 45° refracting angle rigidly attached outside
the objective, and the whole instrument is
fixed to a strong equatorial mounting driven
by a deUcatdy adjusted dockwork movement,
so that exposures of any desired duration can
be given.
ECZEMA PROCURATA
A name given to the skin disease caused by
the metol devdoper. For further particulars,
see imder the heading " Metol."
EDGING (Fr., Bordure ; Ger., Einfassung)
In wet collodion negative making, especially
for process work, the glass plates are generally
edged with indiarubber solution to prevent the
film from being washed off during the operations
of developing, intensifying, etc. Albumen and
gelatine are also used for the same purpose, but
with these materials it is generally the practice
Edging Brush
to coat the plate aU over as a substratum. A
useftd device for edging is shown above. A
small camd-hair brush has a strip of wood
bound to the side of it, and the two are pushed
through a cork, which stoppers a bottle or test
tube containing the rubber solution.
EDGING NEGATIVES FOR CARBON
PRINTING
Negatives intended for carbon printing require
an opaque margin, called a safe-edge. A narrow
margin of the print must remain white, as
otherwise it will be difficult to transfer the film.
This opaque margin may be produced by painting
the edges of the film witt water colour, or opaque
varnish may be applied to the glass side of the
negative. Another method frequently adopted
is to attach narrow strips of thin, opaque paper
to the negative, or to a piece of plain glass. In
the latter case this glass is placed in the printing
frame outside the negative, and one glass may
be used for many negatives.
EDINOL (Fr. and Ger., Edinol)
A developer, known also as " Paramol," under
which name it was originally introduced in
1 90 1, but the two agents are stated by some
not to be exactly the same. It occurs in a
faint ydlowish crystalhne powder, having the
formula CjHs OH CH^OH NHj, and it is soluble
in twelve times its weight of water. Its factor
number is 20, and it therefore stands midway
between the slow-working developers, such as
pyro, hydroquinone, and adurol, and the quick-
working developers, metol, amidol, etc. It can
be used as a single-solution or a two-solution
developer, and works well when combined with
hydroquinone. Edinol is extremely sensitive
to the action of bromide as a restrainer, so much
so that from 10 to 30 per cent, of a saturated
solution of sodium bicarbonate instead of
bromide has been recommended in cases of
over-exposure. It is dean-working and is par-
ticularly suitable for bromide and gaslight
papers and transparendes. The formulae for
one-solution and two-solution developers are
as follow : —
One-solution
Sodium sulphite . . 2 oz. 200 g.
Water . . . S „ 500 ccs.
Dissolve and add —
Edinol . . . I oz. 50 g.
Sodium carbonate . 2^ „ 250 ccs.
and then add water to make lo oz. This forms
a concentrated developer, and for use is diluted
with from five to ten times its volume of water.
Edison's Kinetoscope
208
Eikonogen Printing Process
Two-solution
A. Sodium sulphite . 2 oz. 100 g.
Ediuol . . .96 grs. 10 „
Water to . .20 oz. 1,000 ccs.
B. Sodium carbonate . . 10 % sol. ; or
Potassium carbonate . 5 % sol.
Use equal parts of A and B. Sodium carbonate
works slowly, and for quicker working potas-
sium carbonate may be substituted for it. (For
use combined with hydroquinone, see " Devel-
opers, Mixed.")
EDISON'S KINETOSCOPE (See "Kineto-
scope.")
EDWARDS'S FORMUL/E
These include a one-solution intensifier made
up from the following : —
A. Mercuric chloride . 60 grs. 3"9 g.
Water . . . 8 oz. 227 ccs.
B. Potassium iodide . 180 grs. 11 "7 g.
Water . . . 2 oz. 57 ccs.
C. Sodium hyposulphite 120 grs. 7 g.
Water . . . 2 oz. 57 ccs.
When all are dissolved add A to B, shake well
and add C ; allow to stand for an hour or two
before use. Soak the negative in this untU
intensified, and then immerse in a " hypo " fixing
bath for half a minute, finally washing well. If
local intensification is required, the solution
may be applied to the parts with a camel-hair
mop or a pad of cotton - wool. Edwards's
reducer or clearing bath is used chiefly for
removing yellow stains from negatives that have
been developed with pyro. The formula is : —
Aliim . . . . I oz. 55 g.
Ferrous sulphate . . 3 ,, 165 „
Sulphuric acid . . i drm. 6-25 ccs.
Water . . .20 oz. 1,000 „
This gives an apple-green solution, which is used
after fixing and washing. It keeps well if the
used liquid is not returned to the stock solution.
Another formula due to Edwards is given under
the heading " Redeveloper."
EFFECT (Pr., Effet ; Ger., Wirkung)
The general impression given by a print apart
from any examination of its details. It depends
mainly on the disposition of its principal masses
and its chiaroscuro (which see).
EFFLUVIOGRAPH
An invention by Mons. Tommasi, in 1886, by
the use of which all the effects of photography
were obtained through the electric efiauvia or
obscure discharge. Two metal brushes, placed
parallel in front of one another, were each con-
nected to the pole of a Holtz machine. A dry
plate of about the same height was placed per-
pendicularly to the brushes ; and on the dis-
charge taking place in darkness an image was
obtained by radiations.
The term effluviography is sometimes applied
to images obtained by what is more commonly
known as vapography (which see).
EGG, WHITE OF (Pr., Blanc des ceufs, Albu-
mine : Ger., Frisches Eiweiss, Albumin)
Commonly referred to in photographic pro-
esses as albxunen (which see). First used for
coating glass plates by Niepce de Saint- Victor
in 1848. About 1866 it was largely used for
albumenised paper, and one maker stated at
the time that he broke 2,000 eggs daily, merely
to obtain the whites. Mayall, whose albumen
negative process was widely used, stated that
the white of a duck's egg is more sensitive than
that of a hen's egg, and that the white of a
goose's egg was more sensitive than either.
In process work the whites of eggs are largely
used for making up the albumen-bichromate
solution in preference to dried albumen.
EGYPTIAN VIGNETTES (See " Black Vig-
nettes.")
EIKONOGEN (Fr., IconogSne ; Ger., Eikonogen)
A developer introduced by Dr. M. Andresen
in 1889 ; it appears in a yellowish white powder
or yellowish crystals when fresh, but rapidly
changes to a brownish tinge. Its formula is
CioHg (OH) NH2 SO2 ONa. It is sparingly
soluble in water, but readily so in the presence
of alkaUs, especially when heated. It can be
used in a one-solution or a two-solution form,
and is suitable for aU kinds of plates and bromide
and gaslight papers. It is widely advocated for
very rapid exposures, for which the following
one-solution mixture, which is ready for use, is
particularly suitable : —
Eikonogen . . .100 grs. 20 g.
Sodium sulphite . . 200 „ 40 ,,
Sodium carbonate . 100 ,, 20 ,,
Potassium bromide . 5 „ i „
Water . . .10 02. 1,000 ccs.
The small quantity of bromide added appears
to increase the density of the negative, but where
there is a suspicion of under-exposure, and when
soft portrait negatives are desired, it is better
omitted. Bromide acts very powerfully with
eikonogen, and further additions in cases of
over-exposure should be made cautiously. The
following is the formula for the two-solution
form : —
A. Eikonogen .
Sodium sulphite
Water .
B. Sodium carbonate
I oz.
4 „
20 „
3 ,.
50 g-
200 „
1,000 ccs.
ISO g.
Water .
20 „
1,000 ccs.
For use, mix i part of A, i part of B, and
2 parts of water. Potassium carbonate may
be used iu place of the sodium in the B solution,
and a more energetic developer obtained. When
eikonogen is used for wet plates they generally
need to be intensified, preferably with pyro-
silver. (For an eikonogen-hydroquinone com-
bination, see " Developers, Mixed.")
EIKONOGEN PRINTING PROCESS
A process invented in 1895 ^7 A. Prey, of
Paris. Aniline, or toluidine, is treated with
sulphiuric acid, and the almost colourless pro-
duct is dissolved in warm water. A mixture of
this solution with eikonogen, applied to albumen
paper, gives a inaction on exposure to light.
Cherry or blackberry juice is bleached by mixing
with eikonogen solution, but when paper coated
with the mixture is exposed to light the colour
returns. In the .same way, several iron, copper,
and tin salts, when mixed with eikonogen, are
CHURCH OF NOTRE DAME, CAUDEBEC-EN-CAUX BY H. W. BENNETT, F.R.P.S.
ARCHITECTURAL PHOTOGRAPHY (Exterior)
Eikronometer
209
Electrograph
sensitive to light. Freshly prepared potassium
formate with eikonogen also yields a sensitive
substance.
EIKRONOMETER (Pr., Eikronomitre : Ger.,
Eikronometer)
An early form of the Watkins dark-room
clock. (See " Clock, Dark-room.")
ELECTRIC INKLESS PRINTING
A process invented by W. Friese-Greene, in
which the electric current was made to pass
through the type forme and the impression
cylinder of an ordinary letterpress printing
machine. The paper was treated chemically,
probably with an iron salt, and when impressed
on the type was darkened by the electric action.
ELECTRIC LIGHT (Pr., Lumiire Slectrique ;
Ger., Elehtrisches Licht)
The electric light is the most practically useful
artificial Uluminant for photographic purposes.
Where pubKc mains are not accessible, a small
dynamo, driven by a gas-engine, offers the most
convenient means of installation. Apart from
the initial expense of the dynamo and engine,
this is naturally more economical than the public
supply, though involving greater trouble and
attention. The switches should be such as wiU
stand hard wear and rough usage, and an adjust-
able resistance is an advantage. There are four
principal types of lamps — fie arc, the incan-
descent or glow lamp, the Nemst lamp, and the
mercury vapour lamp. In portraiture, the arc
lamp is most used. For studio employment and
for ordinary black-and-white copying, the
enclosed arc is best, but for photographing
colour the open arc is superior. These two
patterns are fully dealt with under the heading
" Arc Lamps." Flame arc lamps, in wliich a
brilliant golden yeUow light is obtained by
incorporating metallic salts in the carbons, or
by introducing a central core of such salts, have
also attracted some attention among photo-
graphers, it having been stated that colour values
are better reproduced with them. A plate
sensitised for yellow has, of course, to be
employed. An arc lamp in use should not be
examined or adjusted without a piece of smoked
yellow glass brfore the eyes, or goggles of the
same material.
The incandescent glow lamp is yellower and
less actinic than the arc, but a number of these
suspended inside a dead white spherical or para-
bolic reflector, having a mushn diffusing screen
in front, can be used for portrait work, giving
a soft and pleasing lighting. Several lamps of
this kind are on the market. Ruby and orange
glow lamps are much used in the dark-room.
The new metallic filament lamps have greatly
improved the efficiency of incandescent electric
lighting, yielding better illumination with less
current than carbon filament lamps.
The Nernst lamp makes use of a thread of
yttrium and zirconium oxides, and similar
metallic earths. These lamps are employed
with the optical lantern and for enlarging ; they
are economical of current and carry their own
resistances.
The mercury vapour lamp is dealt with under
it& own heading. It requires very little current,
14
and is a useful light for printing, copying, or
enlarging. A certain prejudice exists against
its employment in portraiture owing to its
unpleasant colour, due to the absence of red
rays, but this is easily remedied by using one or
two ruby glow lamps in addition.
For copying, etc., the nearness with which the
lamp can be placed to the easel is of import-
ance from an economical standpoint, other
considerations being equal. Thus, the enclosed
arc can be brought closer than the open arc,
the flame arc still nearer, and the mercury vapour
lamp nearest of all.
In process work, the electric arc light is invari-
ably nsed for copying in preference to daylight.
(See " Arc Lamps.") Mercury vapour lamps
are also used to some extent. Incandescent
electric lamps are not sufficiently powerful.
ELECTRIC LIGHT FOR OPTICAL LAN-
TERN (See " Optical Lantern.")
ELECTRIC RADIATIONS (See "X-ray
Photography.")
ELECTRIC TELEPHOTOSCOPY (See
"Transmission of Photographs Electric-
ally.")
ELECTRO
A common abbreviation of the term " Elec-
trotype " (which see).
ELECTRO ETCHING
Numerous processes have been put forward
at various times for etching by means of the
electric current, but none has come into regular
commercial use. The earliest was a method of
etching the daguerreotype plate. Pizeau gilded
the image by depositing gold upon it, and then
etched ttie parts not covered by the gold, which
acted as a resist. Grove, Donne, and others
produced engraved plates in this manner, per-
forming the etching by galvanic action, but the
difficulty of biting the delicate daguerreotype
image to a sufficient depth and obtaining the
requisite ink-holding grain soon led to the
abandonment of the method. Prof. Jacobi, in
1839, engraved line plates into rehef by electric
etching, and about the same time Thomas
Spencer, of Liverpool, described a process of
galvanic etching by coating copper plates with
a resist ground and scratching lines through it.
In later times J. W. Swan used electric etching
for photogravure plates. Images scratched with
needle-points through an etching ground have
often been successfully etched. Sanger Shep-
herd some years ago described a process of etch-
ing a bitumen print on copper by depositing gold
on the parts laid bare by development and
etching the other parts. Dr. Strecker has
patented a process for electric etching with the
solution of a zinc salt. Zinc, copper, and steel
have been successfully etched, but the process
is slower than ordinary etching, and does not
appear to have any advantages.
ELECTROGRAPH (Pr., ^lecfrographe ; Ger.,
Elektrograph)
An apparatus for the telegraphic transmission
of photographs, invented conjointly, in 1901, by
H. R. Palmer, M. E. T. MiUs, and Dr. W. P.
Electrogravure
Element
Dunlany. The receiving and transmitting
maclunes are identical in construction, and may-
be used alternatively. The transmitter carries
a zinc enlargement of a half-tone plate, curved to
fit a cylinder, the depressed or etched portions of
the plate being filled with an insulating material.
Over the cylinder a stylus is made to travel,
much after the manner of a phonograph stylus.
At the other end of the wire, the receiving cylinder
is fitted with a pen, which travels at the same
rate as the transmitting stylus over a sheet of
paper placed beneath. When the stylus is in
contact with metal the circuit is completed, and
the pen of the Teceiving instrimient traces a dot
or line corresponding with that on the zinc plate ;
but when tiie stylus touches the insiiating
material in the etched portions the circuit is
broken, and no mark is made by the pen. As a
consequence, the picture on the half-tone plate is
reproduced at the receiving end, and from the
copy a smaller plate, suitable for press use, may
be made by reduction in the usual manner. Each
instrument is provided with a pen as well as a
stylus, and either may be used at will.
ELECTROGRAVURE
A process invented by Jos. Rieder for etching
on steel by galvanic means. It was shown at
the Paris Exhibition of 1900.
ELECTROLYTIC BREAK (See "Contact
Breaks.")
ELECTRO-PHOTOTYPY
A name given to Sutton's process (not used
commercially) of making half-tone printing
blocks. A half-tone negative was made by
photographing through a ruled screen on to a
gelatine plate. After being developed, and
before it was completely dry, the plate was
heated, this having the effect of sweUing the
dots into high relief. The plate was then used
as a mould for electrotyping.
ELECTROTINT
A fancy name given to the half-tone process
by an American firm.
ELECTROTYPE (Ft., Mectrotype, Galvano;
Ger., Galvano, Galvanische Riederschlag)
A copy or reproduction of a relief surface
made by the electrotyping process.
ELECTROTYPING (Fr., Electrotypage, Galvano-
plastie ; Ger., Galvanoplastik)
A process by which engraved plates, type
formes, etc., are reproduced. They are pressed
into a layer of beeswax, the resulting mould is
blackleaded by brushing or by spraying with a
solution of blacklead, to make the surface con-
ductive, £ind the mould is then suspended in a
solution of copper sulphate, a copper plate being
suspended opposite and near to the mould to
form an anode. The two are connected to a
source of electric current, and copper is then
deposited in a thin shell on the mould until
thick enough to be stripped off. This sheU is
filled up at the back with type metal to give it
suflicient thickness and solidity, and after being
planed at the back and mounted on a wood or
metal block is ready for printing from.
Photographic reliefs in gelatine have also been
electrotyped. (See " SweUed Gelatine Process.")
The late G. Scamoui, of St. Petersburg, suc-
ceeded in electrotyping from the image of a wet
collodion negative. Nickel, nickel steel, iron,
brass, and other metals have also been success-
fully deposited by electrotyping. In the Ord-
nance Survey Office, Southampton, original
engraved maps are reproduced by electrotyping.
The copper plate is silvered to prevent the
copper from adhering, and a thick shell is
deposited. This is in relief, and forms the
matrix from which any number of duplicates
may be made. The matrix is silvered and
deposited on in the same way as upon the
original. Major-General Waterhouse, when at
the Survey of India, successfully electrotyped
from a photographic carbon image developed
on the copper plate. (See also "Daguerreotypes,
Electrotyping.")
ELECTROTYPY
A process of reproducing daguerreotypes by
electro-deposition.
ELECTRO-ZINCOGRAPHY
A process of engraving on zinc in which the
electric current is used.
ELEMENT (Fr., tUment ; Ger., Element)
This term has been applied by chemists to
those substances which cannot, by any known
means, be split up into other and simpler forms
of matter. The following table is a Hst of them,
with the symbol and atomic weight of each.
The symbol, it may be explained, is the chemist's
shorthand or grammalogue, whilst the atomic
weight is that in which eadi element combines
with others to form salts or compounds. Thus
the chemist writes AgNO, for silver nitrate,
and this formula means that there are 108 parts
of silver, 14 parts of nitrogen, and 48 parts of
oxygen combined to form 170 parts of silver
nitrate. If now it is wished to form silver
bromide from this, using potassium bromide;
the equation or shorthand for the decomposi-
tion which would occur would be written : —
AgNOa -I- KBr = AgBr + END,
108,14,48 39.80 108,80 39,14,48
170 + 119
-h loi
and this shows that 119 parts of potassium
bromide would be required to convert 170 parts
of silver nitrate, and the result would be 188
parts of silver bromide, with lOi parts of potas-
sium nitrate as a by-product ; and no matter
what actual weight of silver nitrate was used,
the combination would always take place in
the above ratio — 170: 119.
Name
Symbol Atomic weii
Aluminium
. Al .
27
Antimony (Latin :
Stibium)
. Sb .
120
Arsenic
. As .
75
Bariimi
. Ba .
137
BeryUium
. Be .
9-1
Bismuth
. Bi ,
208
Boron .
. B .
II
Bromine
. Br .
80
Cadmium
. Cd .
,112
Element
211
Emulsion
Name
Symbol Atomic weight
Caesium
Cs .
133
Calcium
. ,
Ca .
40
Carbon .
.
C .
12
Cerium .
.
Ce .
140
Chlorine
.
a .
3S"5
Chromium
Cr .
52
Cobalt .
,
Co .
59
Copper
(Latin ":
Cuprum)
.
Cu .
63
Didymium
,
Di .
142
Erbium.
.
E .
166
Fluorine
. ,
P .
19
Gallium
, ,
Ga.
70
Germauiimi
.
Ge .
72-3
Gold (I<atin
Aurum]
Au ;
197
Helium.
He
4
Hydrogen
H .
I
Indium
.
la .
113
Iodine .
I .
127
Iridiiun
Ir .
193
Iron (I,atin: Ferrum)
Pe .
56
Lanthanum
.
La .
138
Lead (Latin
Plum-
hum).
.
Pb .
207
Lithium,
.
Li .
7
Magnesium
Mg
24
Manganese
.
Mn.
SS
Mercury
(Latin:
Hydrargyrum)
Hg.
20P
Molybdenum
Mo.
96
Nickel .
Ni .
59
Niobitua
.
Nb.
94
Nitrogen
, ,
N .
14
Osmium
, ,
Os .
• 195
Oxygen.
,
O
16
Palladium
.
Pd .
. 106
Phosphorus
.
P .
• 31
Platinum.
.
Pt .
• 193-4
Potassium
(Latin :
Kcdium)
K .
• 39
Rhodium
,
Rh.
. 104
Rubidium
, ,
Rb.
• 85
Ruthenium
,
Ru.
• 103-5
Samarium
, ,
Sa .
. 150
Scandium
. ,
Sc .
• 44
Selenium
Se .
79
Silicon .
Si .
, 28
Silver (Latin: Argen-
tum) .
.
Ag.
. 108
Sodium
(Latin :
Natrium)
Na .
• 23
Strontiimi
Sr .
• 87-5
Sulphur
S .
. 32
Tantalum
Ta .
. 182
Tellurium .
Te .
. I2S
ThalEum
Tl .
. 204
Thorium
Th .
. 232
Tin (Latin: Stannum]
Sn .
. 118
Titanium
.
Ti .
. 48
Tungsten
(Latin:
Wolfrunium)
W .
. 184
Uranium
U .
. 240
Vanadium
V .
51
Ytterbium
Y .
• 173
Zinc
Zn .
■ 65
Zirconium
Zr .
. 90
The Latin names in brackets are included to
show the derivation of the symbols. Only the
atomic weights generally used are given, as these
are continually under revision, and some are
stiU ia doubt, although only to the first or second
place of decimals. The newer gases and some
of the latest discovered elements — such as
radium, etc. — are not included.
ELEMI {See " Gums and Resins.")
ELIMINATORS (S«« " ' Hypo * Eliminators.")
ELLIOTYPE
A process of painting a picture upon glass,
in body and transparent colours, and printing
therefrom as though it were an ordinary nega-
tive ; named after its introducer. It was never
largely used, and is now obsolete.
EMERY (Pr., tmeri : Ger., Schmirgel)
An exceedingly hard mineral, varying slightly
in colour, a compact variety of corundum, and
very generally regarded as an iron ore. Chemic-
ally it consists of alumina, silica, and iron. Its
chief sotirce is the Isle of Naxos. It is reduced
to powder and used for grinding and polishing
metal, glass, etc. Opticians use it for the first
rough grinding of lenses. Square sticks of
emery, called emery files, are sometimes used
by wet collodion workers for taking the sharp
edge off glass plates ; but carborundum sticks
have been fomid better. Emery is sometimes
used in the form of a very fine powder instead
of pumice powder for cleaning copper and zinc ;
and collotype workers grind the surface of their
thick glass printing plates with fine emery to
give a matt surface to which the film can adhere.
EMETICS {See " Poisons and Their Antidotes.")
EMISSION, NODE OF {See "Nodal Points.")
EMULSION (Fr., Emulsion ; Ger., Emulsion)
A liquid, usually viscous, containing in
suspension an insoluble body in au extremely
findy divided state. Plates, films, and bromide,
gaslight and printing-out papers are coated
with emulsions. To such perfection has the
commercial manufacture of these articles attained
that it win hardly pay the average worker to
prepare his own ; but from an educational point
of view the manufacture of emulsions is extremely
valuable. In the following notes only tested
formulae are given, and it must be clearly under-
stood that perfection is only attainable after
considerable experience, and the tyro must not
expect to prepare either papers or plates as
excellent or as fast in working as those com-
mercially obtainable.
The various stages in emulsion making wiU be
outlined, and the reasons for each step explained.
Let it be assumed, therefore, that it is wished
to make a silver bromide gelatine emulsion.
The bromide is formed by double decomposition
or chemical interchange between an alkaline
bromide, usually potassium or ammonium, and
silver nitrate. If aqueous solutions of these two
salts were mixed in a haphazard fashion there
would certainly be obtained a coarse, granular
form of silver bromide which would at once sink
to the bottom of the vessel, and there might be
an excess of either silver nitrate or bromide. To
prevent the immediate deposition of the bromide,
Emulsion
212
Emul
sion
and to obtain a fine grain, a vehide — ^gelatine —
is added to the alkaline bromide solution, and
the fineness of grain largely depends upon the
proportion of gelatine used. If too much gela-
tine, or too hard a kind, be used during mixing
it is difficult to obtain high speed, as the gelatine
acts as a mechanical restrainer ; on the other
hand, if too little is used, a. coarse granular
deposit is formed, and the emulsion tends to
fog and thinness. When an alkaline bromide
and silver nitrate are mixed together they com-
bine in definite proportions according to their
molecular weights. The molecular or combining
weight of potassium bromide is 119, and that of
silver nitrate is 170. If these quantities were
weighed out exactly, whether in grains, ounces,
pounds, or tons, or grammes or kilogrammes,
exactly 188 parts of silver bromide would be
formed, and there would be found in the water
neither silver nitrate nor potassium bromide ;
but the slightest error in weighing might give
an excess of silver nitrate, which would be
fatal to the emulsion in development. It is
customary, therefore, to use an excess of bromide
or other salt in aU emulsions intended for develop-
ment ; this excess varies in most formulae, and
is governed by the process used, the quality of
the gelatine and tie speed required. Some
gelatines will give perfectly clean emulsions with
a much smaller excess than others. Then, as
one of the prime uses of the excess of bromide
is to keep the emulsion free from fog, a reasonable
excess is useful on this account, and increase
may make an otherwise foggy-working formula
satisfactory. Of recent years it has been con-
sidered that an increased excess of bromide
tends to give faster emulsions for negative work,
but it has at the same time a tendency to pro-
duce thinness in the high lights. A normal
ratio is 100 of silver nitrate to 80 of potassium
bromide, though it will be seen that the ratios
given in the formulse vary from this in some
cases.
When first mixed the emulsion is very slow,
no matter what formula is used, and would be
quite unsuitable for anything but lantern plates.
It is therefore subjected to a " ripening " process,
either by continued application of heat or the
use of ammonia. Exactly what occurs during
ripening is a matter of doubt, but it is generally
assumed that the silver bromide grain increases
in size and that this increase is accompanied
by greater sensitiveness to light ; the change
is probably more of a physical than chemical
nature.
It has been already stated that there is a
chemical interchange between the silver nitrate
and bromide, and this is represented by the
following equation, which may be said to be
the chemist's shorthand method of explaining
what occurs : —
AgNOa + KEr =
silver nitrate pot. bromide
170 119
AgBr + KNO3
silver bromide pot. nitrate
188 loi
The figures here are the molecular or com-
bining weight, and, as has already been
explained, 170 parts of silver nitrate combine
with 119 of potassium bromide to form i88 parts
of silver bromide and loi parts of potassium
nitrate. Alkaline nitrate thus formed must be
got rid of, and this is the purpose of the washing,
which also removes the excess of alkaline
bromide and the ammonia, if this latter has been
used for ripening. Were these salts not washed
out they would crystallise out on the plate
during the process of drying after coating, and
either prevent the access of light, or give rise to
crystalline markings which wotdd show in the
negative.
There are two distinct systems of making
emulsions : the acid or boiling process and the
ammonio-nitrate process. The former, as a
rule, is used for somewhat slow emulsions, and
the latter for the faster negative kinds. As to
the highest speed obtainable by the acid process,
no definite data are available, but certainly
200 H. and D. may be considered the limit, whilst
by the ammonia process from 300 to 400 H. and
D. can be reached. In the acid process the
mixing and the ripening are effected in an acid
gelatine solution, whilst in the other process
either the whole or part of the silver nitrate is
converted into ammonio-nitrate of silver. For
amateur work the ammonia process is somewhat
easier, and, if excessive speed is not required,
nice clean emulsions, giving good density, can
be obtained.
Before treating further on the actual mixing
of the emtUsion, it should be stated that the
TABLE I
^'s
of AgNO,
id to convert
of alkaline
of soluble
required to
t I gr.
3
of silver
produced
gr. soluble
of soluble
required to
■e I gr.
haloid
of silver
produced
1 gr. Qf
1^
eight
requin
I gr.
haloid
eight
haloid
conver
AgNO
eight
haloid
by I
haloid
eight
haloid
produc
silver
eight
haloid
from
AgNO
h
^
k
h
&
Ammonium bromide
98
^ 1734
•576
1-918
-521
J- I 'loe
Potassium bromide
119
1-427
•700
1-578
•633
Sodium bromide
103
I 620
■606
1-825
•548
Ammonium chloride
53-5
3-177
•315
2-682
•373
• -844
Sodium chloride
58-5
2-906
■344
2-453
•408
Ammonium iodide .
143-
1-172
•853
1-620
•617
1
Potassium iodide .
166
1-023
•977
I -41 5
•707
l- 1-382
Sodium iodide
150
I -133
•882
1-566
•638
J
Emulsion
213
Emulsion
alkaline bromides and iodides are interchange-
able, though as a rule that given in a. formula
should be adhered to ; still, the accompanying
tables, compiled by Ackland, will be found ex-
ceedingly useful, as they allow of the easy cal-
culation of the necessary amount of haloid for
any quantity of silver, or the substitution of one
for another.
Table I. enables the worker to calculate the
weight of haloid to convert any given quantity
of silver, or, vice versa, the quantity of silver
haloid produced from every grain of haloid, or
the weight of silver haloid produced from every
grain of silver nitrate. If, for instance, the
formula is : —
Potassium bromide
Potassium iodide
Ammonium chloride
Gelatine
150
10
25
200
The quantity of silver required to saturate the
above can be calculated by taking the figures
in the third column and multiplying by the
above. Thus : — •
Potassium bromide 150 x I-427 = 214-05
Potassium iodide 10 x 1-023 = 10-23
Ammonium chloride 25 x 3-177 = 79-425
Weight of silver nitrate required 303-705
The fourth column enables the worker to cal-
culate readily what excess of soluble haloid
there may be present in the emulsion ; whilst
considerable influence on the final result, both
as regards speed and density. If the speed
required is approximately obtained in the first
process of cooking, then pouring out the emul-
sion into flat pans to the depth of about i in.
wiU quickly arrest the ripening action, especially
if the pan or dish is stood in cold running water.
In summer-time it is even advisable t6 pack ice
around the pan, which for such small quantities
as given in these pages may be a clean (most
important) 15-in. by 12-in. dish. On the other
hand, if the emulsion is allowed to set in its
mixing pot, greater speed is obtained, especially
when ammoniacal emulsions are made, because
the heat is longer retained, and there is less
chance for the escape of the ammonia. It is as
well, however, in this case to cool the bulk of
the emulsion by running cold water around the
pot and constantly stirring ; ice water, too, may
be used, but care must be exercised, as when an
emulsion is poured out into flat, ice-cooled pans
to set there is danger in the case of negative emul-
sions of a want of density in the highest lights.
Still more important with regard to the
density and speed of the emulsion is the lapse
of time between the setting and washing ; and
in the case of negative emulsions the speed may
be nearly doubled, and consequently the density
of the high lights increased, by allowing the
emulsion to stand in the solid state in cold for
twenty-four to forty-eight hoxirs. i^xcept where
otherwise advised, the normal time is about
twelve hours ; that is to say, a negative emul-
TABLE II
S.^
s
s
g
s
1^
03 '2
l|
II
1^
!-§
II
!•«
II
1,1
11
1/3 -5
^•3
^■2
^
^5
■^
Ammonium bromide
I
-S23
-951
1-832
1-675
•676
-59
-653
Potassium bromide
1-215
I-
1-156
2-226
2-036
-821
-717
•794
Sodium bromide .
I -051
-865
I-
1-925
1-761
-71
-62
•684
Ammonium chloride
-546
-449
-519
I-
•914
-369
.322
•356
Sodimn chloride .
•597
-491
■568
1-093
I-
•403
•352
■39
Ammonium iodide
1-479
I -217
1-408
2-712
2-478
I-
-873
-966
Potassium iodide
1-695
1-394
I -612
3-104
2-839
I -145
I-
I -107
Sodium iodide
1-53
I -259
1-456
2-803
2-564
1-034
■903
I-
columns 5, 6, and 7 enable him to work back
when he has determined on a fixed content of
silver haloid.
Table II. is extremely useful for finding the
weight of one haloid that will replace another.
Supposing, for instance, that it is desired to
replace 80 grs. of ammonium bromide with the
sodium salt ; then in the first vertical column
headed " ammonium bromide " there will be
found against sodium bromide 1-051, which is
the weight of this salt that will convert as much
silver nitrate as one grain of ammonium bromide.
Therefore 1-051 x 80 = 84-08 would be the
quantity of sodium haloid to use.
Before entering into the making of emulsions
it may be as well to consider the subsequent
operations first, as they play an important part
in the quality of the finished emulsion. The
method adopted for setting the emulsion has
sion made one evening is ready the next morning
to be broken up and washed.
The easiest method of breaking up small
quantities of emulsion is to use coarse-meshed
canvas, the mesh being about \ in. square. The
emulsion should be coarsely cut up by means
of a silver knife (do not use a steel one), or
scored through with a wide-pronged silver or
plated fork, and then put into a sheet of the
canvas, the ends of the latter being gathered
together so as to form a bag. The bag is held
under the surface of a dish of clean water and
squeezed round and round so as to force the
emulsion through the mesh. PaiHng the canvas,
a fork can be efficiently used if the emulsion has
been set in a dish, as it can be scored longitudin-
ally and then across at right angles so as to cut
it up into little cubes, which should not be too
small, as otherwise they pick up too much water.
Emulsion
214
Emulsion
Commercially, -wlien large quantities of emulsion
have to be treated, a power or hand press is
used, and the emulsion forced through a perfor-
ated plate.
After shredding, th6 emulsion is washed.
According to the quantity to be treated, washing
may be effected either in flat trays or by means
of a caUco or linen bag and a deep jar. In the
first case, a sheet of linen should be placed over
the dish or tray, and the emulsion placed in
it and a stream of water allowed to run in at
one comer and out at the diagonally opposite
comer ; it is as well to raise sUghtly that end
of the dish at which the water flows in. In the
case of the bag method a square of linen should
be gathered up into a bag, the emulsion placed
therein, and some stout string tied round with
a sufficiently long loop to pass over a stick
that rests on the mouth of tiie jar and allows
the bag to hang down in the water. By this
method the soluble and detrimental salts
formed in the emulsion diffuse out into the
water. "Whichever method is adopted, it is
important that the water should be frequently
changed, and it is advisable to squeeze the
emulsion gently at intervals so as to press out
the water.
There is great diversity of opinion as to the
best duration of washing, some workers main-
taining that from eight to twelve hours is not
too long, whilst others reduce the time to two
hours or even less. The disadvantages of pro-
longed washing are that the emulsion, par-
ticularly in hot weather, picks up a large quan-
tity of unnecessary water which, unless an extra
quantity of gelatine is added afterwards, renders
the emulsion so sloppy that it is difficult to coat
it on glass, and, furtber — particularly with rapid
negative emulsions — the ripening process goes
on, and as the soluble bromides in excess are
being removed, there is great danger of fog
ensuing. From very careful tests the writer
has found that all emulsions can be thoroughly
washed by repeated changes (about twelve) of
water iu two hours, and small quantities — par-
ticularly it the weather is warm — can be thor-
oughly washed in one hour. The washed emul-
sion should be allowed to drain well, and is then
ready for melting.
The emulsion shreds should be placed in a
pot in a water bath at 90° P. (about 32° C.) and
the temperature gradually raised to I30° P.
(nearly 49° C), at which temperature the final
quantity of gelatine should be added and the
whole well stirred till the gelatine is dissolved.
It is just as well to keep the emulsion at this
temperature for at least half an hour, and it
can then be filtered through clean felt jelly-
bags, or, faiUng these, swansdown calico or
Canton flannel, previously washed to remove
any dressing. If there is any difficulty in getting
the emulsion to pass through the material,
pressure may be applied by squeezing with the
hands, but usually, with the emulsion at . the
temperature stated, there is no trouble pro-
viding the fiiter is first wetted with hot water
and well wrung out.
Gei,atino-chi,oride or P.O.P. Emulsion.—
The simplest form of gelatine emulsion is that
used for P.O.P., and the following formulae will
give excellent results : —
Valenta's Formula
A. Silver nitrate . . 307 grs. 32 g.
Citric acid . • 77 „ 8
Hot distilled water . 3 oz. 160 ccs.
' B. Hard emulsion gela-
tine . . . 922 grs. 96 g.
Distilled water . 14 oz. 700 ccs.
Allow to soak for half an hour, and then melt
in a water bath at 120° P. and add —
C. Ammonium chloride. 28 grs. 2-8 g.
Tartaric acid . . 28 „ 2-8
Sodium bicarbonate 14 ,, 1-4
Alum . • 18 „ 1-8 "
Distilled water . 3 oz. 140 ccs.
The ingredients in solution C must be dis
solved in the order given, and care should be
taken to use a sufficiently large vessel, as brisk
effervescence ensues. Both B and C should be
brought to 120° P. (nearly 49° C.) and mixed,
and then A, at the same temperature, added
slowly and with constant agitation. Allow the
emulsion to stand for from two to four hours in
a water bath at 1 10° P. (about 43° C.) with occa-
sional stirring, and then add —
Alcohol . . .15 drms. 100 ccs.
and filter through glass wool or two thicknesses
of Canton flannel or one thickness of swansdown.
Care must be exercised as to the Kght used, as
the fluid emulsion can readily darken iu colour
whilst digesting even in strong gaslight. The
duration of digestion or ripening is dependent
on the speed required. If coated when freshly
mixed, the emulsion is slow and gives rich and
vigorous prints ; if, on the other hand, it is
ripened for four hours it becomes much more
rapid, and gives a longer scale of gradation. If
it is desired to obtain a paper that will keep for
some time without discoloration, an equal
quantity of citric acid to that given above
should be added after digestion.
Another excellent formula is the following : —
Wade's Formula
A. Ammonium chloride . 25 grs. 2-6 g.
RocheUe salts . . 25 ,, 2-6 „
Alum . . . 50 „ 5-2 „
DistOled water . 2|^ oz. 125 ccs.
Dissolve, and add — r
B. Gelatine . . . 820 grs. 86 g.
Distilled water . 15 oz. 750 ccs.
previously dissolved at 110° P., and finally
add —
C. Silver nitrate . . 284 grs. 30 g.
Citric acid . . 150 „ I5'6 „
Distilled water . 2^ oz. 125 ccs.
The coating temperature of the above emul-
sions should be about 95° P. (35° C).
If an emulsion suitable for extremely thin,
flat negatives is required, the addition of a small'
quantity of the chloride of uranium, of nickel
or of cobalt, to any of the above formulse will
shorten the scale of gradation, but the most satis-
factory agent is calcium chromate, which must
be added with caution, as it is extremely ener-
getic in its action, o-i per cent, reducing the
scale of gradation by about one-third.
For matt surface papers the quantity of gela-
tine should be reduced so as to make an 8 per
Emulsions for Development ^'5 Emulsions for Development
cent, solution. More satisfactory matt emul-
sions can be obtained by incorporating with, the
emulsion lo per cent, of fine rice starch. The
necessary quantity of starch should be rubbed
into a cream witi a little water and a small
<iuantity of gelatine, taken from the emulsion
itself, and the whole should be heated to i6o° F.
(71° C.) for an hour and then added to the
emulsion. {See also " Collodion Emulsion.")
EMULSIONS FOR DEVELOPMENT
These may be divided into those for positive
work and those for negative work.
Positive Emumions
Positive emulsions may again be subdivided
into chloride and bromide emulsions, the former
including chloro-bromide also, and such as are
suitable for gasUght papers and plates.
Chloride Emulsion {Eder)
A. Sodium chloride . 288 grs. 30 g.
or Ammonium chloride 264 ,, 27-5 „
Hard gelatine . . 384 „ 40 „
DistiHed water . 8 oz. 400 ccs.
Hydrochloric add . 5 drops 10 drops
B. Silver nitrate . . 576 grs. 60 g.
Distilled water . 2 oz. 100 ccs.
C. Hard gelatine . . 384 grs. 40 g.
Distilled water . 10 oz. 500 ccs.
Dissolve C by heating to 120° P. (nearly 49° C),
and add B at the same temperature ; then add
A, also at 120° F., and allow to stand at this
temperature for ten minutes ; then rapidly cool
and set. This emulsion yields a satisfactory
gaslight paper or plate, which readily gives
warm tones. If the hydrochloric acid is omitted,
and 240 grs. or 25 g. of citric add is added, very
warm tones, from yellow to reddish brown, are
more easily obtained. If the above emulsion is
cooled down to 95° F. (35° C.) immediately after
mixing, and 60 minims or 6 ccs. of Uquor
ammordae (-880), and 2 oz. or 100 ccs. of distUled
water are gradually added with constant stirring,
a much more rapid emulsion is obtained, whidi
gives black tones more readily.
The great trouble in mixing aU chloride and
chloro-bromide emulsions is the formation of a
coarse grain, which is reduced by the developer
without exposure to light. For this reason the
beginner is advised to modify the above formula
as follows : Add the whole of the gelatine to
A and increase the quantity of water to 12 oz
or 600 ccs., and add the silver nitrate dry, in
small quantities at a time, with vigorous stirring.
When all the silver is added continue stirring
for fifteen minutes, and then add 8 oz. or 400 ccs.
of distilled water. As an alternative the emul-
sion may be set and washed as usual, and then
the extra quantity of water added. Either way,
there is less chance of the occurrence of coarse
grain, and the results are equally satisfactory.
There is but Uttle difference in the final result
whether the sodium or ammonium chloride be
used; the former gives a littie more contrast.
Much, harder working emulsions can be obtained
by adding to the above quantity of chlorised
gelatine 1-25 grs. or -05 g. of pure copper
chloride ; or greater contrasts may be obtained
by increasing this still further.
For some gaslight papers an unwashed emul-
sion is used, but there is far greater liability to
the formation of black spots.
Chloro-bromide Emulsions
Emulsions containing both bromide and
chloride of silver are more sensitive than pure
chloride emulsions, and whilst giving warm tones
with increased exposure, they give better blacks,
there being less tendency to greenish tones. The
ratio of bromide to chloride is a matter of taste,
but the more chloride the less the gradation,
and the more bromide the faster the emulsion.
Wraiten's Formula
Nelson's No. i gelatine 40 grs. 200 g.
rinse two or three times in water and add to —
Distilled water . . 4 oz. 856 ccs.
Dissolve at 125° F. (nearly 52° C.) and add —
Ammonium bromide
(neutral) . .110 grs. 55 g-
Sodium chloride • 3° „ 15 „
Hydrochloric add (10%
solution) . . 10 mins. 5 ccs.
Then add in a fine stream —
Silver nitrate , . 200 grs. 100 g.
Distilled water . . i oz. 220 ccs.
with constant stirring. Digest for ten minutes
at 150° F. (65-5° C), and add-
Hard gelatine . . 175 grs. 875 g.
vfhich has been previously washed and soaked
in water for half an hour and well drained.
When the gelatine has melted, set, and wash
for half an hour with six changes of water,
drain well and melt, and make the total bulk
up to 1,750 ccs. by adding water. Finally add —
Tannin . . . . . 1-03 g.
Wellington's Formula
Potassium bromide . 384 grs. 4° g-
Sodium chloride . 192 ,, 20 ,,
Citric acid . . 960 „ 100 ,,
Hard gelatine . . 1,344 „ 140 „
Distilled water . . 20 02. 1,000 ccs.
Heat to 150° F. (65-5° C), and add—
Silver nitrate . . 960 grs. 100 g.
Distilled water . . 20 oz. 1,000 ccs.
heated to 150° F. Digest for ten minutes, and
pour out into a dish to set.
Valenta's Formula
No. I. :—
Ammonium bromide . 480 grs. 50 g.
Ammonium chloride . 48 ,, 5 ,,
Nitric acid . . 10 drops 20 drops
Hard gelatine . . 1,615 grs. 168 g.
Distilled water . . 26 oz. 1,333 ccs.
Heat to 130° P (54-4° C), and add—
Silver nitrate . . 960 grs. 100 g.
Distilled water . . 26 oz. 1,333 ccs.
also at the same temperature. Allow to digest
one hour, and then pour out and set.
No. II., for greater contrasts : —
The above formula with —
Ammonium bromide 50 grs. S'2 g.
Ammonium chloride . 300 „ 30 „
Emulsions for Development ^'^ Emulsions for Development
In mixing both the Wellington and Valenta
formula the same procedure may be adopted
as for Wratten's.
The ratio of the silver haloids in these three
emulsions is as follows : — Wratten — chloride i,
bromide 2'i ; Wellington — chloride i, bromide
17 ; Valenta No. I. — chloride i, bromide 8-7 ;
Valenta No. II. — chloride 7, bromide i. Welling-
ton's gives very warm tones more easily than the
others with increased exposures.
Lantern Plate and Bromide Paper Emulsions
These may be pure bromide emulsions, but
it is preferable to use bromo-iodide, as the
iodide tends to keep the whites free from fog.
Some commercial bromide papers are also
chlorobromide emulsions. The following gives
a very satisfactory but slow emulsion, either
with or without the iodide.
Ammonium bromide 672 grs. 70 g.
Potassium iodide . I5'3 „ i'6 „
Hard gelatine . . 2 oz. 150 „
Hydrochloric acid (10%
solution) . .144 mins. 15 ccs.
Distilled water . . 30 oz. 1,500 „
Heat to 110° F. (about 43° C), and add —
Silver nitrate . . 960 grs. 100 g.
Distilled water . . 10 oz. 500 ccs.
also heated to 1 10°. Digest at this temperature
for one hour. If a more rapid paper is required,
then after digestion cool the emulsion down to
95° P- (35° C.) and add—
Liquor ammonias . 96 mins. 10 ccs.
Distilled water , . i oz. 50 „
then set and allow to stand for twenty-four
hours.
For enlarging, when a much more rapid paper
is required, a. slow negative emulsion, such as
given below, may be used. For coating bromide
paper the proportion of gelatine should not be
too high, although this depends upon the sur-
face required and the method of coating, about
1:18 or 20 being generally sufficient. For
matt emulsions, rice starch may be added as
already advised for gelatino-chloride paper. For
lantern plates a little more gelatine is required,
say about i : 14.
NEGATIVE Emtji,sions
The manufacture of negative emulsions is by
no means such an easy matter as positive
emulsion making, but with care slow emulsions
of very satisfactory quality can be produced.
The beginner is not advised to attempt very
rapid emulsions, as they are extremely difficult.
There are two principal methods for negative
emulsion making — the acid or boiling process,
and the ammonia method. The former will
give, as a rule, the cleaner plate, but it is not
possible to obtain so high a speed. With care
equally clean plates may be obtained by the
ammonia method and greater speed. The acid
process wiU be treated first.
Slow Emulsion
Potassium bromide . 720 grs. 75 g.
Potassium iodide . iS ,, 275 ,,
Nelson's No. I gelatine 317 ,, 33 ,,
Hydrochloric acid . 10 „ i cc.
Distilled water . . 11 oz. 550 ccs.
Heat to 120° F. (nearly 49° C), and add slowly
with constant stirring —
Silver nitrate . . 960 grs. 100 g.
Distilled water . 11 oz. 550 ccs.
also heated to 120° F. Digest in a water bath
at boiling point for half an hour, and then add
Hard gelatine . . 1,200 grs. 125 g.
which should have been well washed in water,
soaked for half an hoiir, and drained for half an
hour. Cool the emulsion, and set. This should
give an emulsion of about 25 H. and D.
An emulsion of about double the rapidity, and
giving somewhat greater contrast can be obtained
by cooling the above emulsion down to 95° F.
(35° C.) and adding—
Liquor ammonise (-880) 72 mins. 7-5 ccs.
Distilled water . . i oz. 50 „
and stirring well for about fifteen minutes, then
setting and allowing to stand for twenty-four
hours.
Rapid Emulsion
Potassium bromide . 1,200 grs. 125 g.
Potassium iodide . 24 „ 2-5 „
Hard gelatine . . 480 „ 50 „
Distilled water . . 10 oz. 500 ccs.
Heat to 140° F. (60° C.) and add in a fine stream
with constant stirring —
Silver nitrate . . 960 grs. 100 g.
Distilled water . . 7 oz. 350 ccs.
also heated to 140° F. Digest in a water bath
at boiling point for forty-five minutes, and
then add — -
Hard gelatine . . 480 grs. 50 g.
Distilled water . . 8 oz. 400 ccs.
The gelatine should be well washed in two or
three changes of water, drained, and then dis-
solved in the distilled water at 110° F. (43-3° C).
This should give plates of from 150 to 180 H.
and D., whi(i are rather soft working but clean.
Greater contrasts can be obtained by adding
ammonia as suggested for the slow emulsion.
Slow Ammonia Emulsion
Ammonium bromide . 816 grs. 85 g.
Potassium iodide . 29 „ 3 „
Hard gelatine . . 1,392 „ 145 „
Distilled water . . 20 oz. 1,000 ccs.
Heat to 110° P. (43-3° C), and add, with con-
stant stirring-
Silver nitrate . 960 grs. 100 g.
Liquor ammonias (-880) q.s. q.s.
Distilled water . 6 oz. 300 ccs.
at a temperature of about 70° F. (21° C). The
silver should be thoroughly dissolved and
enough ammonia added to redissolve the pre-
cipitate first formed. The exact quantity will,
of course, depend upon the strength of the
ammonia, but about 65 or 70 ccs. can be added
at first, and then further additions made very
cautiously, stirring well, till quite a dear solution
is formed. The temperature rises to about
90° P. (32-2° C), so that it is advisable to cool
this silver solution down by standing the vessel
in cold water for a short time. As soon as the
emulsion is mixed, the vessel should be placed
Emulsions for Development 217
Enameline
. 864 grs.
90 g.
24 „
. 480 „
• 480 „
2-5 ,.
so „
SO „
20 oz.
1,000 CCS
in cold water, running water for preference,
and the emulsion well stirred till quite thick
and then put away in cold water to set. If
allowed to stand for about sixteen hours before
washing, this should give a clean working plate
of about 30 to 50 H. & D., which will give great
contrasts and wide latitude of exposure.
Medium Rapidity Ammonia Emulsion
Ammonium bromide
Potassium iodide
Soft gelatine
Hard gelatine .
Distilled water .
Heat to 120° F. (nearly 49° C), and add, with
constant stirring —
Silver nitrate . . 960 grs. 100 g.
Liquor ammonise (-880) q.s. q.s.
Distilled water . . 6 oz. 300 ccs.
at a temperature of 80° F. (nearly 27° C). This
solution should be made as before described.
When mixed, the emulsion should be digested
in a water bath at a temperature of 120° P. for
half an hour, and then —
Hard gelatine . . 480 grs. 50 g.
which has been well washed but not soaked,
added. Cool down gradually and allow to stand
for sixteen hours before washing. This should
give plates of from 100 to 120 H. & D.
Rapid Ammonia Emulsion
Ammonium bromide . 1,152 grs. 120 g.
Potassium iodide . 24 „ 2-5 „
Soft gelatine . , 480 „ 50 „
Hard gelatine . . 240 „ 25 „
Alcohol . . . 2 oz. 100 ccs.
Distilled water . . 18 „ 900 „
Heat to 130° F. (54-4° C), and add—
Silver nitrate . . 960 grs. 100 g.
Distilled water . . 6 oz. 300 „
Iviquor ammoniae (-880) q.s. q.s.
at a temperature of 75° F. (nearly 24° C). Digest
in a water bath at 120° F. (nearly 49° C.) for
one hour, and then add —
Hard gelatine (well
washed only) . 1,680 grs. 75 g.
Cool the emtdsion and pour out into flat dishes ;
allow to stand for twenty hours. This should
give plates of from 200 to 225 H. & D.
There are many little dodges which can be
learnt only by experience and experiment, but
the following hints may not be useless.
In making acid emulsions it is advisable always
to run the silver into the bromised gelatine in
a fine stream with continuous stirring. In the
case of ammonia emulsions, it is not so important
to add the silver in a fine stream, but vigorous
stirring should be continued all the time.
If regularity of results is reqiured it is
important that the water bath should always
be kept at a constant temperature, and, further,
that the emulsion should be stirred about every
five minutes, otherwise the silver bromide may
•settie to the bottom of the vessel and give coarse-
grained thin-working plates that are absolutely
aiseless. It will be noted that distilled water
is advised in all the formula given in this article ;
this is important, as too often ordinary tap-
water is contaminated with iron and other
impurities, which lead to fog or loss of sensitive-
ness. It is advisable even to use distilled water
for washing the gelatine.
Greater rapidity can always be obtained by
reducing the quantity of gelatine during the
mixing, but there is great danger of the forma-
tion of coarse grain and fog. If the gelatine
is much reduced it is always advisable to add
about 10 per cent, of the total bulk of alcohol,
which not only prevents this but also obviates
the occurrence of dichroic fog with the ammonia
method.
Directions have already been given for setting
and washing emulsions. When the emulsion
has been washed enough it should be removed
from the water and left to drain for about an
hour, so as to free it from the adherent water
as much as possible. In fact, it is as well to use
a clean dry Unen cloth, and after the emulsion
has drained, place it in this and, collecting the
whole into the form of a bag, squeeze thoroughly.
The emulsion is then ready for melting and coat-
ing.
A test plate should always be coated first.
Melt the emulsion in a water bath at 120° F.
(nearly 49° C), then take out a littie and cool
down to 95° F. (35° C); coat a plate and put
away to dry. The bulk of the emidsion can now
be rapidly cooled down again and, when set,
alcohol containing o-i per cent, of carbolic acid
poured over the top to the depth of about half
an inch, the emulsion being then put away in a
dark, cool place. If it is to be ujsed soon the
alcohol may be omitted, but this will keep a
stock of emulsion in good condition for a week
or so.
ENAMEL, CERAMIC (See "Ceramic Process.")
ENAMEL COLLODION (See "Collodion,
Enamel.")
ENAMEL SURFACES
Highly glazed surfaces. Printing papers
having such surfaces are now obtainable, but
formerly the worker had to produce the glaze
himself. Enamel surface papers need carefui
washing, otherwise — especially in the case of
collodion paper — they are liable to crack ; they
also need mounting with a quick-drying mount-
ant, or else the moisture is hable to spoil the
glaze. Methods of enamelling prints which in
their normal state have ordinary or matt sur-
faces, will be found under the heading " Enamel-
ling Prints." Proper photographic enamels — that
is, bumt-in photographs upon porcelain, etc. — are
known as " ceramics." (See " Ceramic Process.")
ENAMELINE, OR ENAMEL PROCESS (Fr.,
Procede Smail ; Ger., Emailverfahrung)
A process originating in the United States,
by which a copper or zinc plate is coated with
a solution of fish-glue and ammonium bichro-
mate, exposed to Hght under a haU-tone nega-
tive, developed so as to clear away all the
soluble glue between the dots, and after being
dried is " bumt-in " — that is, the plate is held
over a gas flame until the image turns to a deep
chocolate-brown, almost black. When cool, the
Enamelling Prints
218
Endemann's Process
plate can be etched, the enamel image resisting
the etching solution. Gum is sometimes used
instead of fish-glue. A suitable formula for the
fish-glue solution is : —
Glue . . . . 5 oz. 500 g.
Water . . . 10 ,, 1,000 ccs.
Ammonium bichromate J ,, 25 g.
Add liquor ammonise (-880) until a golden yellow
colour is reached.
Some workers prefer a formula containing
albumen, and the following will serve : —
Le Page's fish-glue . 3 oz. 375 g.
Water . . . 8 ,, 1,000 ccs.
Ammoniuru bichromate 180 grs. 47 g.
Whites of 2 eggs
Beat the egg whites, add to the glue solution,
beat up again, allow to stand for eight hours
and then filter through absorbent cotton.
ENAMELLING PRINTS (Pr., Emaillure; Ger.,
Emailleiren)
The process of enamelling prints must not be
confused with burnishing, and other methods
of glazing. Bnamelling proper with collodion
gives the highest possible gloss. The method
described below is suitable for ah kinds of prints,
but particularly for collodion prints : Procure
some commercial collodion specially made for
enamelling, or make according to the instructions
given rmder " Collodion, Enamel," Thoroughly
clean a glass plate, rub it over with a little warm
wax or vaseline, polish well with a soft cloth,
apply a thick coating of the enamel collodion,
and allow to set thoroughly. Coat the glass
evenly and out of the way of dust. This coating
is to be transferred to the face of the print. By
the aid of gentle heat, make a solution of gela-
tine in water (20 grs. to i oz. ), and slip the coUo-
dionised glass plate film upwards into the warm,
not hot, gelatine solution ; immerse a dried
print also in the gelatine solution face down-
wards, allow it to soak, bring glass and print into
contact, film to film, lift out and squeegee
thoroughly until no air-bells are left, and then
set up to dry. When quite dry cut round the
edges of the print (through the collodion) with
a sharp penknife, Hft by one comer, and strip
from the glass. If properly done, the print will
come away easily, bringing the coUodion sur-
face with it.
As the coUodion (enamel) surface is easily
dulled if not mounted with a quick-drying
mountant, it is the practice of some workers to
back the print before or during enamelling with
waterproof paper or thin Bristol board, so as
to permit the use of any mountant. A good
method is to soak the immounted print in
gelatine, squeegee upon the collodion plate,
and then immediately after, while the print is
wet, to squeegee waterproof paper or thin Bristol
board on to the back of the print, using gelatine
as the adhesive. When the print and mount
are dry they can be stripped from the glass Uke
an unmounted print, and then be trimmed and
moimted.
ENAMELOID (Pr., Mnameloid; Ger., Ename-
loid)
A dead-black varnish suitable for the inside
of lens mounts, diaphragms, etc., said to consist
of celluloid dissolved in acetone, with the addi-
tion of vegetable black.
ENCAUSTIC PASTE (Tt., Colle encaustique ;
Ger., Enhaustische Kleister)
Known also as cerate paste ; a mixture for
srubbing on to the surface of prints in order to
give them a gloss, deepen the shadows, and
brighten them up generally. The gloss obtain-
able is very pleasing, but not so high as that
obtained by burnishing or enamelling. It is
particularly suitable for matt bromide and
platinotype prints, and at one time was widely
used for prints on albumen paper. In its sim-
plest form it consists of i part (by weight)
of ordinary beeswax reduced to a paste with
four parts of turpentine, the smell of which can
be masked by substituting 1 part of oil of
lavender for i part of turpentine. The wax
is soaked in the solvent and then melted geritly
by heat. Another simple paste is that made
according to Dr. Bder's formula : —
White wax . . i oz. 500 ccs.
Dammar varnish . 200 mins. 209 „
OH of turpentine . i oz. 500 „
Dissolve by heat and mix well. A more elabor-
ate mixture, and one vndely used, is that made
according to the Adam Salomon formula: —
Pure virgin wax
Gum elemi
Benzole .
Oil of lavender.
Oil of spike
Melt in a hot-water bath, mix thoroughly, and
strain through muslin ; or the gum may be
dissolved in the solvents and the melted wax
added after filtration. A small quantity of any
of the above mixtures is applied to the print by
means of a small piece of flannel or linen, and
is then worked into the print by continuous
rubbing, a polish being obtained finaUy by rub-
bing with a clean piece of flannel or a pad of
clean hnen.
The following mixture was at one time largely
used for painting with a brush over the shadows
of a print in order to deepen them ; it is not
encaustic paste proper, but can be used when
it is not desired to cover the whole of the print : —
SCO grs.
10 „
SOO g.
10 „
i oz.
i „
I drm.
240 ccs
360 „
60 „
Gum arable
i oz.
i6-S g-
Water
. 3 „
100 ccs.
Rock candy
I drm.
4 ,,
Acetic acid
10 drops
•7 ,,
Alcohol .
• 10 „
7 ,.
ENDEMANN'S PROCESS (Ti., Procede Ende-
mann ; Ger., Endemann's Prozess)
An anihne printing process, giving a black
image on a white ground. The paper is sized
with a solution of 1 oz. of sheet gelatine in 50 oz.
of water, and sensitised with : —
A. Sodium chloride
(common salt) . 480 grs. 846 g.
Potass, bichromate . 480 „ 846 „
Sodium vanadiate . 320 „ 564 „
Water . . . 20 oz. 1,000 ccs.
B. Sulphuric acid . 2 oz. 100 ccs.
Water . . . 10 „ 500 „
The acid must be introduced gradually into the
water, and the mixture, when cold, added to A.
Energiatype
219
Engineering Photography
The paper is floated on tlie surface of the sensi-
tiser, and hung up to dry in the dark. It is
exposed under a negative or tracing in a printing
frame for about seven minutes, and development
is carried out by exposing the print to the
vapour arising from a heated mixture consisting
of ^ oz. of aniline to 25 oz. of water (22 g. in
1,000 CCS.) for about one minute, which pro-
duces a brown image. The print is then placed
in a room filled with steam for about two hours,
or until the image turns black. To remove the
green colour that usually remains, wash carefully
in a solution of liquor ammonias (-880) 2 oz., to
water 12 oz. (166 ccs. hquor ammoniae to i,ooo
ccs. water).
ENERGIATYPE
A process (now obsolete) invented and named
by Robert Himt about 1851. It has been called
a ferrotype process, but ferrotypes are now
vmderstood to be pictures upon a blackened
tin surface. Good writing paper was prepared
by washing over with : —
Succinic acid . . 5 grs. 2-5 g.
Common salt . • 5 „ 2-5 „
Gimi arable solution ^ drm. 30 ccs.
Water . . . i oz. 500 „
When dry, the paper was sensitised on a solu-
tion of silver nitrate 60 grs., water i oz., and
dried in the dark. The paper was used in the
camera as a plate, an exposure of about 30
seconds being enough for a brightly lighted
landscape, and six times as long for a portrait.
The image remained invisible until developed,
the developer being made in the proportion of
I dram of a saturated solution of iron proto-
sulphate and 3 drams of gum arabic solution.
The picture was then fixed with ammonia and
finally well washed.
ENGINEERING PHOTOGRAPHY
Most of the technical considerations that apply
to architectiural photography apply equally well
to engineering subjects. The truth of vertical
lines must always be preserved by keeping the
\ V. 'SA
\ i
F F
A. Diagrams showing the Influence of View-
point in Engineering Photography
sensitive plate vertical, whether the view of the
machinery necessitates looking upwards or down-
wards. In many cases abnormal points of view
have to be taken, and the camera may have to
be raised several feet in order to show essential
features that cannot be seen from any other
position. One of the most important considera-
tions in engineering photography must always
be to show the essential features of the work
in an efiective manner. Technical knowledge,
or even a slight acquaintance with engin-
eering practice, will be exceedingly valuable to
the photographer who undertakes work of this
B
B. Camera Tilted Downwards
character. The object of the photograph is to
illustrate the working of the machine ; to
show most plainly its principal working parts
and the manner in which its object is attained.
Subject to these considerations, an oblique view
should always be taken, if possible, in preference
to a full front or side view. By choosing a
position that gives a good perspective, the relief
and projection of the various parts are shown, as
well as their solidity and their relation to each
other. In a view taken from the front, the sense
of relief is largely lost ; the maclune appears
flat, its functions are not well shown, and its
working is much more diffictilt to follow. The
diagrams at A show plainly the reasons for this ;
they represent a plan of a machine with the
camera F placed in different positions. Sharp
definition throughout is essential. Whenever
possible, machines should be painted a good
medium grey or lead colour, this assisting in
rendering detaU effectively throughout, and par-
ticularly in the shadows and light parts. The
colour should be quite dull, a glossy surface being
very undesirable. Bright parts may generally be
left untouched, as they then look more natural
than if painted white, as sometimes advocated.
Paint gives an effect suggesting wood.
In many subjects difficulties in working may
present themselves, and require ingenuity com-
bined with photographic skill to overcome. In
C. Method of Using Swing-back
photographing a subject with a long range of dis-
tances, the following method has been very
efficient. The subject was some electrically con-
trolled railway points, and it was very necessary
to show the mechanism between the rails as
large as possible. The camera was placed about
eight or ten feet from the principal part of the
subject, but signals and other objects five or six
Engraved Blocks
220
Enlarging
■hundred feet away were included, and all had to
be sharply defined. The distance was entirely
at the top of the picture, and the foreground at
the bottom, the camera being placed as in
diagram B. By tilting the camera downwards
and using the swing-back, as shown at C, sharp-
ness was obtained throughout by using a medium
aperture, as the foreground A in the diagram was
focused at a in the camera, and the distance B
at b. Previously it was found that with the
back and front of the camera parallel, //64 failed
to render the different planes reasonably sharp.
In all engineering subjects wide-angle lenses
should be avoided as much as possible. In photo-
graphing complete workshops or very large
pieces of machinery, they may be absolutely
necessary, but for single machines of small or
moderate size, a mediimi-angle or a long-focus
lens should always be used.
In many cases machines can be photographed
out of doors, and this is frequently preferable to
the Kghting in many workshops.
In most cases, engineers wish to have a clear
white background for all isolated pieces of
machinery ; this necessitates painting out the
background on the plate (see " Blocking Out,
or Stopping Out"), unless the work may be
left to the process-worker's retoucher.
Photographing workshops is treated in the
article " Factories, Photographing in," and notes
on the exposures for these subjects are given
under the heading " Exposure Tables."
ENGRAVED BLOCKS
A term correctly applied to wood-engravings,
but now commonly used to denote all kinds of
blocks, whether engraved by hand or pro-
duced photo-mechanicaHy.
ENGRAVING (See " Half-tone Process,"
" Photo-engraving," etc.)
ENGRAVING ON GLASS
Photographic processes have been employed
to produce an image on glass as a resist for
etching by means of hydrofluoric acid. The
bitumen process is one of the best for the pur-
pose of forming the resist image.
ENGRAVINGS, COPYING
In copying engravings and drawings the only
difference in working arises from the fact that
the subject consists of black lines on a white
ground, a type of subject that is usually con-
.sidered dif&cult on a gelatine plate, as it is far
from easy to obtain sufficient contrast with
ordinary plates. By adopting the following
method of working little difficulty should be
experienced in obtaining a negative that will
give aU the contrast required in the print. A
slow plate of the kind specially prepared for
this work should be chosen, and it should be
backed. A fine-grain ordinary, or a process
plate, will answer well. Correct exposure is
very important. The following method of
timing wiU ensure correct exposure. Place the
exposure meter flat against the drawing to be
copied, and note the time required to match the
standard tint. Using//i6 and a plate of the speed
of 40 H. and D., one half of the time that a Wynne
meter requires, or one fourth of the time required
by a Watkins meter to reach the tint, will be
the correct exposure for copying the same size
as the original. For other plates or for different
scales, the proportionate exposures can easily be
found from these data. Should the Mnes show
distinct signs of veiling, development should
be stopped, and the negative afterwards intensi-
fied, if necessary. (See also " Copying," etc.)
In process work, an engraving on thin, clean
paper, and with good black lines, without
printing on the back, may be copied by using
it as a diapositive. It is placed in contact with
a sensitised zinc plate and exposed to light for
a sufficient time. A negative image will be
developed, but this may be converted into a
positive one by flowing with a shellac varnish
containing some colouring matter to make it
visible. The latter will attach itself to the bare
zinc hnes, whilst that which rests on the sensitive
colloid film will be dissolved away by treating the
plate in a bath of weak add.
Playertype (which see) is also an easy process
for copying engravings on to sensitive paper.
ENLARGING
The operation of enlarging consists simply
in taking a print from a negative by means of
a lens instead of by placing a paper in contact
vrith the surface of the negative in the usual
manner. The essential parts of the apparatus
required are a holder for the negative from
which the enlargement is being made ; a camera
body or similar arrangement of which the nega-
tive holder forms one end, a lens being fitted
at the other ; and a board or easel for holding
the paper on which the enlargement is being
Principle of Enlarging
made. The positions of the easel and the lens
should both be adjustable, so that enlargements
of any desired size may be made. The illus-
tration explains the arrangement fully. N is
the negative, i, the lens, and P the paper. The
type of lens used for making an enlargement is
not important, beyond the fact that it ought
to cover the plate with crisp definition from
comer to comer with a fairly large aperture.
If it is necessary to use a small stop to obtain
good definition, the exposures required may be
inconveniently long. Also, a lens of long focus
should be avoided, especially if very large pic-
tures are desired from small plates, as the
apparatus would have to be very long. If the
focus of the lens is known, the apparatus may
be set up approximately in position for any
degree of enlargement by measurement, leaving
only the fine focusing ; it will then be easy to
Enlarging by Artificial Light ^^i
Enlarging by Daylight
ascertain what degree of enlargement forms the
limit of the apparatus.
The distance a from the centre of the lens to
the sensitive paper must be equal to the focus
of the lens multiplied by the degree of enlarge-
ment, with the focus of the lens added to the
result. The distance b from the centre of the
lens to the negative must be the distance a
divided by the degree of enlargement. The
distance A bears the same proportion to b as the
enlargement bears to the original negative. An
example will render this clear. A lens of 6 in.
focus is being used to enlarge a 4 in. by 3 in.
picture up to 12 in. by 9 in. The degree of
enlargement is three times linear. Three times
6 in. is 18 in., plus 6 in. brings the distance A up
to 24 in. ; and this distance divided by 3, the
degree of enlargement, gives 8 in. as the dis-
tance B. These general principles apply equally
to aU methods of enlarging. Details of making
enlargements on paper direct, or by means of
enlarged negatives, are given in later articles.
It is useful to know the relative exposures for
different degrees of enlargement, when all the
conditions are equal. Beginning with the pro-
duction of a print the same size as the original
as a basis, and calling the exposure for this I,
the relative exposures for other degrees of
enlargement, using the same stop throughout,
will be : —
Degree of
Enlargement
I
H
2
2i
3
4
5
6
Exposure
I
i-h
2i
3
4
6i
9
12
ENLARGING BY ARTIFICIAL LIGHT
The principal difference between enlarging by
daylight and by artificial hght consists in the
method of illuminating the negative evenly and
Enlarging by Incandescent Gas Light
with sufficient strength to obtain an enlarge-
ment in a reasonable time. A necessary-element
is a condensing lens for collecting the light and
presenting it in the form of an evenly and
briUiantiy illuminated disc immediately behind
the negative from which the enlargement is
being made. The source of hght may be an oil
lamp, a gas flame, or an electric lamp. The
first-named is the least satisfactory by reason
of its variable character and comparatively poor
quality. An incandescent gas burner is one of
the most satisfactory for general use. At times
the hght is projectal in the form of an enlarged
image of the mantle, and a similar dif&culty
may arise with an incandescent electric lamp.
This may be entirely obviated by interposing a
sheet of ground glass between the light and the
condenser, as near the latter as possible. Other
methods of lighting the negative are sometimes
adopted, but in practice they are far from
satisfactory. The diameter of the condensing
lens must be fully equal to the diagonal of the
plate that is being used — for example, 5^ in,
or 5 J in. for a quarter-plate ; but tiiere is no
advantage in any size in excess of this. The
usual arrangement is to enclose the hght in an
iron casing, one end of which holds the condenser.
By this method the light is excluded from the
room, so that the paper can be handled freely,
and the enlargements developed without any
risk of fogging, excepting when an exposure is
being made. As close to the condenser as
possible there is a carrier for holding the nega-
tive ; this carrier forms the back of a camera
body, the opposite end holding the lens for pro-
jecting the image. Beyond the lens an easel
or board is required for holding the sensitive
paper, and, as the distance between this board
and the lens, and between the lens and the nega-
tive, must be varied according to the degree of
enlargement, a method of extending the camera
body, and one for sliding the easel, have to be
provided. The easel should sUde on guides, as
it is imperative that it should be quite parallel
with the negative. The arrangement will be
more easily understood from the illustration, in.
which G is an incandescent gaslight, c the con-
denser, N the negative, I, the lens, and p the
paper on which the image is received.
The exposure will depend on the negative, the
paper, and the degree of enlargement. In
enlarging from quarter to whole-plate by incan-
descent gas, with lens aperture //8, the exposure
win vary from ten seconds for a thin negative
up to forty for a strong one, using a commercial
bromide paper. A test exposure on a small
piece of paper should always be made before
making the enlarged print. The test piece
should include the strongest part of the nega-
tive.
Any negative that wiU give a good contact
print on bromide paper will yield a good enlarge-
ment by incandescent gaslight with a con-
densing lens for concentrating the hght.
ENLARGING BY DAYLIGHT
This method gives greater opportunity for
varied methods of working to suit the conditions
of different photographers than does enlarging
by artificial light. The apparatus and the man-
ner of using it may range from the simple and
inexpensive fixed-focus enlarger up to a per-
manentiy arranged apparatus in which the dark-
room itself forms the camera in which the enlarge-
ment is made. The general principle is iUus-
trated in the article "Enlarging." It is the
method of adapting that principle to the require-
ments of the worker that varies. The most
simple is the fixed-focus enlarger, a piece of
apparatus in the form of a double hox, which
aUows one degree of enlargement only. This is.
an inherent disadvantage of a fixed-focus
instrument, but it has the advantage of great
convenience ; it is ready for use at a moment's.
Enlarging by Daylight
Enlarging Camera
notice, without any focusing or arranging. The
negative is placed film downwards at n (see
illustration A), the paper put in position at p ;
the apparatus taken out of doors, so that the
light from the sky overhead falls directly on
A. Diagram of Fixed-focus Daylight Enlarger
the negative, and the exposure made by operating
the shutter that closes the lens it. This apparatus
gives enlargements of one uniform size only,
this size varying with its construction and the
size of the negatives for which it is intended.
A second form of apparatus is an enlarging
camera (which see). Illustration B shows how
the apparatus is used : N is the negative, I, the
lens, and P the sensitive paper.
A third arrangement is one that is frequently
adopted by those who do much enlarging, and
who wish to have a much larger range in size
than that which can be obtained in an enlarging
camera. The dark-room, or a room that can
be darkened by closing the window with a
specially-made shutter, becomes the enlarging
camera. The camera in which the original
negative was taken, and an enlarging easel, eire
B. Diagram of Enlarging Camera
practically all the apparatus that is required.
The window of the room is closed by a shutter
(see illustration C), in which is a small opening
a little larger than the negative. Outside the
shutter a reflector of white card or a dull white
painted board is fixed so as to reflect the light
from the sky through the negative. Inside the
room the camera is supported on a table
opposite the opening in the shutter. The
negative N is placed in the camera back, film
C. Showing use of Reflector in Daylight
Enlarging
towards the lens, and a focusing cloth wrapped
round the camera back so as to prevent any
light leaking into the room. On the table an
easel holding the paper p is arranged to sUde
in guides, the image being projected by the
lens I, in the usual manner.
A difficulty in daylight enlarging is the ever
varying character of the light. A test should
always be made by a meter immediately before
making an exposure. It is only by this method,
and small test pieces as described in " Enlarging
by Artificial I/ight," that correct exposures can
be secured. Any negative that wfll give a good
contact print on bromide paper will yield an
equally satisfactory enlargement by daylight.
ENLARGING CAMERA (Fr., Chambre d'agran-
dissement : Ger., Vergrosserungskamera)
A camera for making enlarged photographs on
bromide paper, or enlarged negatives, from
smaller negatives or positives. It consists
essentially of a carrier or holder for the negative,
a dark-slide or frame for the bromide paper, and,
between these, a support for the lens, the whole
being covered in except the end at which the
negative is placed. In a fixed-focus enlarging
camera, of which A is a typical example, the
distance between negative, lens, and dark-slide
cannot be varied, and only one size of enlarge-
ment is possible ; but in other forms of appara-
A. Fixed-focus Enlarging Camera
tus, as in B, there is provision for altering these
distances to obtain enlargements of different
sizes. The cameras just considered do not re-
quire the room to be darkened if used indoors ;
they may, if preferred, be used outdoors. The
Enlarging Easel
223
Enlarging Lantern
non-portable enlarging camera, however, as
generally used in trade establishments, is placed
close against a window, from which all actinic
light except that illuminating the negative is
blocked out. With this form of enlarger an
B. Adjustable-focus Enlarging Camera
easel is usually employed instead of a darfc-slide.
Any ordinary camera may be used in this way
if a suitable holder or carrier is made for the
negative ; or the negative may be placed in the
dark-slide, this being inserted in the camera with
both shutters drawn, to serve as a carrier. To
obtain a uniform light, a white card or reflector
is fixed outside the window at an angle of 45°-
An alternative is to use a sheet of ground glass,
or to paste white tissue paper over the opening
which admits light ; when this is done the nega-
tive should be a few inches distant from the
opening instead of dose against it. Various
lamps are obtainable to fit behind the negative
carrier of daylight enlargers, thus enabUng them
to be used by artificial light.
ENLARGING EASEL {See " Easel, Enlarging.")
ENLARGING LANTERN (Fr., Lanterns
d'agrandissement ; Ger., Vergrosserungs-
apparat)
A lantern used in enlarging by artificial light,
to project a magnified image of the negative on
the bromide paper. It consists of a body carry-
ing the illuminant, a condenser to concentrate
the Ught on the negative and cause it to pass out
from the latter in a converging cone, and a pro-
jecting lens or objective to receive the cone of
light from the condenser and to form the enlarged
image. A illustrates the optical system of the
erdarging lantern, a being the Olimiinant, b the
condenser, C the negative, D the objective, and
E the projected image. The condenser must be
Sj-in. diameter condenser is required ; for a
half-plate, one of 8^ in. diameter ; and for a
whole-plate, one of 11 in. diameter. The con-
denser has nothing whatever to do with the size
A "■
A. Optical System of Enlarging Lantern
of sufficient size to illuminate the whole of the
negative, or part of the image will be cut off
towards the margins of the enlargement ; on the
other hand, there is no advantage in having too
large a condenser, but rather the reverse, as
light is wasted. For a quarter-plate negative, a
Enlarging Lantern with Rack and
Pinion Adjustments
of the enlargement ; this depends, other things
being equal, entirely on the distance of the
bromide paper from the projecting lens or objec-
tive. The objective should be capable of
covering the size of negative to be enlarged, and
of sufficient diameter and aperture to pass the
whole of the beam of Hght proceeding from the
condenser. The lens used in making the nega-
C. Simple Enlarging Lantern
tive is usually suitable for enlarging, the best
possible projection lens being probably a good
anastigmat. There are numerous illuminants
employed for enlarging, as oil, acetylene, incan-
descent gas, incandescent spirit, limelight, the
electric arc, the Nemst lamp, etc. Of these,
limelight and the electric arc are the most
efficient with regard to illumination, owing to
their approximating more nearly to a small
D, Lantern Body Attached to Camera
pomt of light ; but from the point of view of
general convenience and utility, incandescent
las is perhaps the favourite. The proper
adjustment of the niuminant is of importance,
or the enlargement will be unevenly lit. The
Enlarging Negatives
224
Enlarging on Paper
correct procedure is to place the negative in the
carrier and to focus roughly to the required size,
approximately centring the light and bringing it
to that distance from Qie condenser which seems
to give the best and most even illimiinatioa. The
negative is then removed, and the illuminant
moved back till a dark ring appears round the
disc of light on the easel. The illuminant is
now carefully centred till the ring is equal all
roimd, and is then pushed toward the condenser
E. Ellipsoid Enlarging Lantern
till the ring disappears and a perfectly even
lighting is secured, the negative being finally
re-inserted and sharply focused. Any after
alteration in the size of the enlargement will
require a fresh adjustment of the illuminant.
B shows a typical high-class enlarging lantern
which has rack and pinion adjustments through-
out, including provision for moving the lantern
body, the condenser, and the objective. The
negative carrier is furnished with rising, falling,
and swing movements, and a rise or fall is also
permissible with the lens. C illustrates a cheaper
enlarging lantern, of simple yet efficient con-
struction ; while T> represents a useful type
dispensing with the extension bellows and pro-
jection lens, and intended to take an ordinary
camera in front. In another form of enlarging
lantern, known as the ellipsoid enlarger, no con-
denser is used, the negative being lit by reflected
light from a curved opal reflector ; these
eSargers are made either for use with the
worker's own camera, or with a bellows and pro-
jection lens, as in E, where a pair of inverted
incandescent gas burners form the illuminant.
ENLARGING NEGATIVES
In order to make a large negative from a small
one, two operations are necessary. A trans-
parent positive must be made from the original
negative, and from that a new negative can be
made by enlarging to any desired size. The
character of the transparent positive is of the
greatest importance in determining the character
and quality of the new negative. The extreme
shadows or densest parts should be moderately
strong, but such an exposure should be given
that the highest light is veiled. No part should
be quite clear, and the transparency should be
didl rather than brilliant. The best method for
making the transparency is by contact printing
by artiiicial Hght on a rapid plate, thus securing
the truest reproduction of the gradation of the
original. For the same reason — the desirability
of reproducing all the gradations as correctly
as possible — the enlarged negative should par-
take of the same character ; the deepest shadow
should be veiled, otherwise there will be a dis-
tinct loss of tone values. The method of working
is given under " Enlarging by Daylight " and
" Enlarging by Artificial Light," excepting that
the transparent positive is placed in the position
there described for the negative and a plate in
the position given for the sensitive papei? Backed
plates should be used for making the transparency
and the enlarged negative, and the film side
should be towards the lens in each case. Film
towards film is the rule, as in printing. An
exception to this is when a reversed negative is
required for the carbon process. In that case
the transparent positive is reversed in the carrier,
the glass side being tiimed towards the lens.
Enlarged Paper Negatives. — ^Enlarged nega-
tives may be made on bromide paper from lan-
tern slides or other transparencies, the bromide
paper after exposure being treated with a weak
bichromate solution, as described under the
heading " Sterry's Process," in order to obviate
harsh results. By the W. Coats method, an
enlargement is made on rapid smooth bromide
paper, the exposure being short so as to keep
the shadows clear; amidol is used as the
developer and the print is washed for two
minutes ; the unfixed print is then toned in the
following bath, in winch it should remain for
seven minutes, at least : —
A. Pot. ferricyanide . 40 grs. 8 g.
Glacial acetic acid . i oz. 50 ccs
Water . . . 10 „ 1,000 „
B. Uranium nitrate . 40 grs. 8 g.
Glacial acetic acid . i oz. 50 ccs.
Water . . . 10 „ 1,000 „
Take equal parts of each just before use. The
solutions keep well separate, but not when
mixed. When toniug is complete, the print is
well washed and immersed for one minute in a
solution of 20 grs. (4 g.) of ammonium sulpho-
cyanide in 20 oz. (1,000 ccs.) of water. The
priut is washed again for two minutes and then
exposed to 4J in. of magnesium ribbon burning
at a distance of 12 in. from it. The print is
next rinsed and redeveloped in the original
amidol developer, fixed in hypo," and washed.
A metol-hydroquinone developer has been sug-
gested in place of the amidol.
An important point which must not be over-
looked in all enlarging processes is the increase
in contrast in the resultant print or plate. This
is caused by the scattering of the Hght by the
silver grains of the negative, which practically
act as points from which the hght spreads or
scatters out in fan-shaped bunifies, and there-
fore does not reach the lens. This may be over-
come by placing the negative film side next to
a sheet of fine matt opal glass.
ENLARGING ON PAPER
The most simple and satisfactory method of
enlarging is to produce an enlarged print on
paper direct from the original negative. It is
not only the most simple method, but it ensures
the truest reproduction of the gradation and
quaUty of the negative. There is only one print-
ing medium sufficiently rapid for direct enlarg-
ing— at least, by artificial Ught — and that is
paper coated with a silver bromide emulsion.
{See " Bromide Paper.") Enlarged prints pro-
Enlarging by Stripping
225
Erythrosine
duced on this paper are in every respect equal
to contact prints from the same negative, and
the development, fixing, and after processes
are precisely similar. The only difference is in
the methods of obtaining the print. These are
given imder " Enlarging by Artificial Light " and
" Enlarging by Daylight."
ENLARGING BY STRIPPING
A process of stripping a film from an ordinary
unvarnished negative, enlarging it, and attaching
it to a larger glass ; the process dates from 1882.
The following enlarging mixture is required : —
Hydrofluoric acid . i dim. 31 ccs.
Citric acid . . |^ oz. 125 „
Glycerine . . .1 drm. 31 „
Acetic acid . . |^ oz. 125 „
Water . . • 4 „ 1,000 „
The hydrofluoric acid needs careful handling.
The negative is placed in the solution and the
film -wfil gradually become released from the
glass and at the same time be enlarged. If
necessary, the film can be assisted to leave the
glass by means of a camel-hair brush. It is
next carefully rinsed in water and floated upon,
and squeegeed into contact with, a cleaned glass
of the required size. In this way a quarter
plate may be expanded to fill a half plate, and
larger sizes in proportion. When in contact
witii the new and larger glass it must be allowed
to dry naturally. As may be expected, films
enlarged in this manner give slightly tiiinner
results, and a rather dense origin^ is therefore
advisable. Films may be stripped from nega-
tives without any enlargement. {See under Qie
heading, " Film Stripping.") The older the nega-
tive the more difficult it is to strip and enlarge.
ENSEMBLE (Fr.)
The arranging or grouping of several figures
or of the constituent parts of a picture.
ENVELOPE SYSTEM (See "Daylight Chang-
ing-")
EOSINE (Fr., Eosine ; Ger., Eosin)
Synonym, yellowish eosin or eosine. CjHj
(CO Cj H Bra OK)2 O. Molecular weight, 708.
Soluble in water, alcohol, and ether. It usually
occurs as a red pow'der. The sensitising power
of eosine lies between E and D in the green and
yellow green, but does not reach the d line.
METHYi,ERyTHRiNE is the methylic ether and
primrose, or erythrine is the ethylic ether of
tetrabromofluorescein.
The eosines are a somewhat large class of
dyes known generally sis the phthalein group,
and derived from triphenylmetiiane. The first
dye of this group is : —
Fl,xroRESCEiisr (Fr., Fluorescine ; Ger, Fluore-
scein)
Solubilities, insoluble in water, soluble in
alcohol. A brick red powder of little photo-
graphic interest except as the starting-point of
other dyes. Its sodium salt is called : —
Uranin (Fr., Uranine ; Ger., XJranin)
C30 Hio O5 Nag. Solubilities, soluble in water,
alcohol, and ether. A brownish red powder
which is sometimes used for making yellow
screens or dark-room filters.
16
Assuming the formula for fluorescein to be
C, H4 (CO C, H3 OH), O, the hydrogen atoms of
the resorcinol group in brackets can be replaced
by the halogens chlorine CI, bromine Br, and
iodine I., and according to tiie number of sub-
stitutions there are formed monobromofluore-
scein, dibromofluorescein, known as eosine extra
yeUow, and tetrabromofluorescein yellowish
eosin ; these are used for sensitising collodion
emulsion for yellow-green ; and the mono-
bromofluoresceJn is an excellent green sensitiser.
Their action on gelatine plates is less satisfactory
thsm that of erythrosine. All these dyes have
a greenish fluorescence in solution, and form salts
when mixed with silver nitrate which are prac-
tically insoluble in water.
In process work, eosine is often used for dyeing
the fish-glue image in the enameline process ;
but methyl violet is more commonly employed,
and is preferred because it shows up the image
in greater contrast.
EPHEMERAL PHOTOGRAPH
A kind of phosphorescent photograph, pro-
duced by one of the many processes introduced
by the late W. B. Woodbury. Largely quoting
from his own words, the process is simple, and
the same piece of sensitised paper may be used
over and over again, while at the same time
always retaining its sensibUity. The material is
the phosphorescent powder, calcium sulphide,
obtained by calcining oyster-sheUs and treating
with sulphur. A sheet of paper is coated with
this by covering with gum or varnish, and dust-
ing the powder over it. If this paper is exposed
for a few seconds to light under a positive trans-
parency and then removed to a dark-room, a
luminous positive will be seen, lasting a longer
or shorter time, according to the exposure given.
Woodbury also produced luminous portraits and
views by the dusting-on process, substituting
the powder named for plumbago. (See also
" Luminous Photographs.")
EPSOM SALTS
The common name for magnesium sulphate,
which has been advocated as a preventive of
frilling ; the dry plate previous to development
is soaked in a saturated solution of the salts.
Also, a saturated solution of the salts made
with beer and a little gum water is used for
" frosting " studio and other plain glass windows.
EQUIVALENT FOCUS (See "Focal Length.")
ERYTHROSINE CPx., t:rythrosine : Get., Ery-
throsin)
Synonyms, erythrosin, bluish eosin, iodoeosin.
C, H, (COC, HI3 ONa)2 O. Molecular weight, 660.
Soluble in water, alcohol and ether. It is a
bluish red powder which, when pure, gives no
fluorescence in aqueous solution, and but slight
fluorescence in alcoholic. It forms an insoluble
silver salt, erythrosinate, or tetraiodofluorescin-
ate of sUver, which is used with collodion emul-
sion for colour sensitising. Erythrosine is the
most energetic yellow-green and yellow sensitiser
for gelatine emulsions, its action extending from
E to beyond d ; it leaves, however, a character-
istic minimum or lack of sensitiveness in the
blue-green between 6 and F. It may be added
Essence of Jeirgonelle
226
Etching Machines
to the emulsion at the time of mixing, in which
case 0-2 per cent, should be added to the bro-
mised gelatine before adding the silver nitrate,
or it may be added the last thing before coating,
or it may be applied in the form of a bath to
the finished and dried plate ; this method gives
the greatest colour-sensitising effect. The plate
should be soaked for two minutes in : —
Liquor ammoniae . 96 mins. 10 ccs.
Distilled water to . 20 oz. 1,000 „
drained and immersed in —
Erythrosine . . -96 grs. i g.
Liquor ammonia . 192 mins. 20 ccs.
Distilled water to . 20 oz. 1,000 „
and then well dried in the dark. A considerable
saving of time is effected in the drying if one
third of the quantity of water in the above
formula be replaced by alcohol or acetone.
Erythrosine M is the sodium or potassium salt
of tetrabromofluorescein as above ; erythrosine
G is a similar salt of diiodofluorescein.
ESSENCE OF JARGONELLE (See " Amyl
Acetate.")
ETCHING CBt., Morsure : Ger., Aetzung)
The incision of metals by means of acids or
other corrosive fliiids, as distinguished from
engraving, which implies incision by cutting
with a graver. Etching may be of two kinds :
(i) The older form consists in spreading an acid-
resisting coating, or " ground," on the metal
plate and scratching through it by means of
sharp points so as to lay bare the metal. This
is the process used by artist etchers, from
Rembrandt down to the present-day workers.
(2) The other and more modem method, in
which photographic processes play so large a
part, consists in forming an image on the plate
in ink, varnish, or other suitable acid-resisting
medium, and then etching away the bare parts of
the metal. The image may be applied by draw-
ing direct on the plate, by transfer from a greasy
itilf image on paper, or by photography with a
sensitive fihu. The last-mentioned method, now
by far the most common, is called photo-etching.
The methods of forming the image on the metal
are treated under various headings — for exEimple,
"Albumen Process," "Fish-glue Process," " En-
ameline," "Bitumen," etc.— and the etching
inks, solutions, metals, etc., are also separately
described. Etching may be either in relief or in-
taglio, the former being necessary for typographic
printing and the latter for copper and steel plate
printing. There are two divisions — line etdiing,
which reproduces lines, stipples, and solid patches
of colour ; and half-tone etching, which interprets
the tones of a photograph or painting by means
of a dot system. Colour etching is merely an
extension of one or other of these processes.
Photogravure etching {which see) is different
in principle. In ordinary etching the sunk
lines, or spaces between the lines, are practically
of uniform depth, but in photogravure etching
the depth is proportionate to the tones, the
shadows being sunk the deepest into the plate.
ETCHING BATHS
This term is applied to the etching solutions
and also to the troughs and trays used for
holding them. To prevent confusion, the vessels
themsSves are treated in the present article,
the solutions being described separately in the
article headed "Etching Solutions." The baths
are of wood, Hned with pitch or gutta percha;
of slate ; or of earthenware ; and they are
generally mounted on rockers, so that the solu-
tion may be washed to and fro over the plate. \
The ends are covered to prevent the splashing
of the acid out of the trough. In large shops
the troughs are mounted on a rocking machine
driven by motor and worm gearing, this ensuring
more uniform etching.
ETCHING INK
There are numerous formulae for etching inks,
these varying according to the particular branch
or process of etching for which they are required.
In America the term is limited to the ink used
for rolling up the albumen bichromate print
after exposure as a preliminary to development.
Excellent commercial inks are obtainable, so
that it does not pay to make one's own ink,
but it may be useful to know that such an ink
usually consists of beeswax, soap, shellac, Utho-
graphic ink, hthographic varnish, and similar
ingredients well mixed together. Etching ink,
as usually understood by English workers, may
also mean " starting ink," or soft etching ink,
and " finishing ink," or hard etching ink. These
inks can also be purchased ready-prepared. The
former consists of such ingredients as Russian
tallow, yellow beeswax, asphaltum, lithographic
or letterpress printing ink, and thin lithographic
varnish. The object of this resist is to form a
covering for the shoulders of the Unes by running
down the sides when the plate is heated. It is
usually applied by inking the surface with a
lithographic leather nap roller. The " finish-
ing ink " consists of beeswax, resin, asphaltum,
and lithographic printing ink. It is necessary to
warm the plate in order to get the ink to " take,"
and it is applied by means of a lithographic
glazed leather roller.
ETCHING MACHINES
Since about 1895 etching machines have come
much into vogue in photo-engraving establish-
ments. The earliest machine of the kind to be
brought into commercial use is the Levy Acid
Blast. (See "Acid Blast.") The Axel etching
machine, invented by Axel Holmstrom, has
a paddle-wheel working in the bottom of the
etching trough and tlSowing the acid against
the plate, which is placed almost vertically
against the side of the trough. The Mark
Smith machine is similar in principle, but
the plate is placed horizontally over the
etching trough, and remains stationary. The
Albert etching machine consists of a horizontal
trough which has a slow reciprocating motion.
The plate is laid face up on a platform at the
bottom of the trough. This platform is lifted
out of the solution when the lid is raised. This
lid has on its underside a series of ribs or vanes,
and it is given a rapid reciprocating motion
when laid down over the plate, so that the acid
is put into a state of violent agitation, causing
the plate to be etched more rapidly than it
would be in a rocking trough. The " Holt "
etching machine has a trough and a lifting plat-
Etching Metals
227
Euryscope
form similar to the Albert machine, but the
solution is agitated by means of a rotating disc,
on the underside of which are vanes for churning
up the solution. The " Danesi " machine rains
the acid down on the plate from a trough above,
into which the acid is pumped from the etching
trough below.
Various other forms of etching machines have
been proposed and patented, but the foregoing
have come into regular use.
ETCHING METALS
The metals used for etching are generally
zinc, copper, brass, and steel. Zinc is mostly
used for line work, copper for half-tone and
photogravure, brass for half-tone and for book-
binders' blocking plates, and steel for die
printing. Carefully smelted and rolled metal
is used, and the sheets are highly planished and
poUshed. For line and half-tone the plates are
usually from 14 to 16 B.W.G. ('083 in. to -065 in.)
in thickness, and the metal is purchased ready
for use.
ETCHING SOLUTIONS
For zinc etching nitric acid is invariably
used, the strength varying from i to 20 per
cent, according to the stage of the etching and
the nature of the work. The bath has to be
constantly rocked whilst the plate is being
etched. A " still " etching solution, which does
not reqxiire rocking, consists of : —
Nitric acid . . .130 parts
Water .... 100 „
Sal ammoniac . . . 20 „
Pyroligneous acid (wood
vinegar) . . . . 20 „
The bath should stand two or three weeks after
mixing. Another bath for zinc which need not
be rocked is : —
Sulphuric add ... 6 parts
Potassium nitrate . . 2 ,,
Water . . . . 20 „
Dissolve the potassium nitrate in water, and then
gradually add the add. Dilute with water till
bubbling ceases.
For etching an enamel film without " buming-
in " the image, the following bath is recom-
m.ended : —
Alcohol (40%) . . 400 parts
Nitric add . . . S to 7 „
For half-tone copper etching, iron perchloride
is dissolved in water until the solution registers
from 35° to 40° on the Beaume hydrometer
(up to 1-36 sp. gr.). About i^ lb. perchloride
to I pint of water will bring the solution to the
required strength. The soluticai is improved
for immediate use by adding ^ pint of an old
bath to every quart of new. Rocking the bath
makes the etchmg proceed more quickly. Heat
also aids the etchmg. Sometimes the plate is
etched face downwards, held in a damp.
Brass is also etched with perchloride of iron
at 35° Beaum^.
Steel can be etched with ferric perchloride
at 40° Beaume, or with a strong solution of
chromic add, or with acetic acid five parts,
fuming nitric add one part, diluted as may be
necessary with distilled water.
The term " etching solution " is also applied
to the solution of glycerine, with other ingredi-
ents, such as liquor ammoniae, caldum nitrate,
sodium chloride, etc., used for damping the
collotype plate. Again, " etching " is applied
to the operation of spreading over the htho-
graphic stone or zinc or aluminium plate a
slightiy add gum solution, which prepares the
surface for dean inking and printing, though it
does not actually etch into perceptible relief.
Such etching solutions for zinc contain a decoc-
tion of nutgaUs and phosphoric add, and for
aluminium phosphoric or hydrofluosilidc and
other adds.
ETHER (Pr., i:ther sulfurique ; Ger., Aether)
Synonyms, ethyl oxide, ethyUc ether, sulphuric
ether. Cj Hj O Cj H5. Molecular wdght, 74.
SolubiHties, i in 12 water; misdble in all pro-
portions with alcohol, chloroform, benzole, etc.
It is a Umpid, very Hght, and volatile transparent
liquid with characteristic odour and burning,
sweet taste. It is made by distillation from
sulphuric add and alcohol. The vapour being
very heavy and inflammable, ether should be
kept in a well-stoppered bottle in a cool place.
In large quantities it and its vapour are poison-
ous, the antidotes being an emetic or the use of
a stomach pump, free supply of fresh air, ammo-
nia, and artificial respiration. It may be pre-
pared from either ethyl or methyl alcohol, the
latter giving the so-called methylated ether
which can be used for all photographic purposes.
The spedfic gravity should be 720. It is used
for making coUodion and varnishes.
In process work, ether is largdy used for
making coUodion and collodion emulsion, the
kind usually employed being methylated ether,
sp. gr. 720, washed and redistilled. It is also
used for washing bitumen to increase its sensi-
tiveness, and with alcohol as a solvent for
bitumen in a process for graining the plate by
reticulation of the film.
ETHOXY LIMELIGHT
Limelight produced by raising a spot on a
cylinder of Ume to a state of incandescence by
means of a non-luminous flame of mixed ether
vapour and oxygen. The mixture is prepared in
a saturator (which see). Oxyhydrogen is a cor-
responding term indicating that a mixture of
hydrogen and oxygen is burnt.
ETHYL ALCOHOL (See " Alcohol.")
ETHYL OXIDE (See "Ether.")
ETHYLIC ETHER (See " Ether.")
EURYSCOPE
Under this name Voigtlander and other
optidans have issued lenses of the rapid recti-
linear type, of intensities varying from //4-5 to
//7. Similar lenses were issued by Ross as
" Universal Symmetricals '■ and by Dallmeyer
as " Extra Rapid Rectilinears." The rectilinear
portrait lens of the latter maker was reaUy a
euryscope with an aperture of f/3. Slower forms
of euryscope for wide-angle work, copying, etc.,
have also been made. Their greatest intensity
varies from //9 to //15.
Evaporating Dish
228
Exposure
EVAPORATING DISH
In wet collodion photography this is a most
important utensil for evaporating the silver
bath when it has become deteriorated by use
or by impurities. Usually the silver bath is
boiled to evaporate about half the volume of
solution, and then made up to strength again
with distilled water and additional silver nitrate.
Any alcohol and ether is thus driven off, and
the iodising salts dissolved out of the collodion
film are reduced in proportion to the volume of
Porcelain Evaporating Dish
the new solution. Amongst English and Con-
tinental workers the common laboratory form of
porcelain basin is used, the bottom, outside,
to which the greatest heat is applied, being left
unglazed. It is best to embed the basin in a
sand bath to avoid fracture by the application
of direct heat. In America stamped enamelled
iron dishes, called Agate ware, are largely used
without any apparent drawback, and of late
many EngUsh workers have taken to using cast-
iron enamelled dishes. A good way of testing
for faults in the enamel is to fill the enamelled
vessel with copper sulphate. The add will
attack the iron wherever it can reach it through
the small pores, and Httle beads of copper are
deposited in small spots, gradually increasing in
size until they become plainly visible. Such
dishes are obviously unsuitable.
EVERSET SHUTTER ('Pt.,Obturateurtoujours
arme, Obturateur automatique ; Ger.,
Selbstthdtigi-r Verschluss)
Any shutter that does not require setting
before an exposure can be made. An everset
shutter is an obvious advantage, since an unex-
pected opportimity of photographing a moving
object might be lost even in the short time
occupied in setting the shutter.
EXCITING
The old and practically obsolete name for
sensitising.
EXPANSION OF PAPER (See "Paper.")
EXPANSION, REDUCING DENSITY BY
(See " Reduction, Mechanical.")
EXPLOSIVE POWDER (Sei " Plashhght
Powders.")
EXPOSING, METHODS OF
The usual methods of exposing dry plates
in a camera are by means of a cap or shutter.
The cap method was the original one, and
although it is considered old-fashioned it still
has advantages. In landscape work the cap
may be made tp serve as a lens shade by holding
it above the front of the lens during exposure.
The correct way to uncap a lens is to imagine
that it is hinged to the top of the lens hood. The
cap is loosened by twisting and the lower edge
raised until it is clear of the lens, and replaced
again when exposure is finished ; in this way
the cap not only serves as a lens shade, but, by
raising and lowering at a suitable speed, one can
give more exposure to the foreground than the
sky, and at times obtain clouds on the negative
which would be missing on account of over
exposure if the sky had the same amount of
exposure as the landscape.
By the judicious use of a cap one may picture
a busy street as being empty, and such a method
is sometimes handy when one desires a photo-
graph of a building in a busy street without
showing the traffic. The lens in such a case is
stopped down to its very smallest extent, the
smaller the better, so as to require a very long
exposure, the longer the better ; exposure is
then made by a series of very brief exposures
with a cap. Assuming, for example, that an
exposure of one minute is considered to be
necessary, the plate is exposed for two seconds
and the cap carefully replaced, another two
seconds is given, and so on until the plate is
considered to be fully exposed. The brief
exposures will not be enough to picture moving
objects, and only those which have remained
still during the greater part of the minute will
show when the plate is developed.
Shutter exposures are invaluable ia cases of
portraiture, and of course absolutely necessary
for instantaneous work, as the quickest " ofi
and on " cap exposure possible is estimated to
be one-fifth of a second, but in the majority of
cases it is nearer half, or even a whole, second.
Silent-working shutters, preferably those which
work inside the camera, are the best for por-
traiture, as those which work noisily and outside
the camera are apt to startle the sitter, or other-
wise attract attention at the wrong time. Chil-
dren, for example, when posed in a position
looking away from the camera, will often turn
their heads when hearing the chck of the shutter.
When exposing for portraits and giving a time
exposure with a roller blind shutter, it is a good
plan to puU the cord gently so as to raise the
bund and to release it before it reaches the half-
way click, at which it remains open ; the spring
will pull the bhnd down again if the dick is not
passed, and in this way an absolutdy silent
exposure may be made. For exposures for seh-
portraiture, printing, enlarging, etc., see under
those headings, and also " Exposure Tables."
EXPOSURE
It is scarcely necessary to emphasise the great
importance of correct exposure in negative
making ; but it may be remarked that when the
plate has been correctly exposed, all subsequent
work is comparatively simple and straight-
forward, whereas with an incorrectly exposed
plate all the subsequent operations are difficult
and unsatisfactory, and the production of a good
print is sometimes impossible.
The correct exposure of a plate depends on
four varying factors : the subject ; the hght,
which varies according to the season, the time of
day, and the weather ; the speed of the plate ;
and the " rapidity," or working aperture, of the
lens.
Exposure
229
Exposure Meter
In the earlier photographic days no attempt
was made to work systematically from these
four varying factors, but exposures were largely
the result of guess-work. About 1880 the first
attempts were made to systematise the data
from which exposures were calculated, Dr,
Scott's table of light values, and W. K. Burton's
table of comparative exposures for different sub-
jects bdpg among the earliest examples of their
kind. Dr. Scott determined the fact that the
value of daylight varied itt direct proportion to
the height of the sun above the horizon. Con-
sequentiy, in equally clear weather, exposures
would require to be nearly four times as long in
the middle of December as in June ; and also at
six o'clock in June exposiires would be three
times as long as at mid-day. Dr. Scott pub-
lished a table, about 1883, giving proportionate
figures for each hour of the day for the middle of
each month. Although these figures were
necessarily incomplete, the interval from one
month to the next being much too long, this
table proved to be of valuable assistance for
many years.
Burton's tables provided a series of com-
parative exposures for different subjects — land-
scapes, marine pictures, interiors, and portraits —
under normal conditions. It gave the exposures
under the best possible conditions, and these had
to be multiplied by the figures given in Dr.
Scott's table for aU times excepting mid-day in
June. {See also " Exposure Tables.")
The most modem method of determining the
duration of an exposure is by means of a meter.
[See " Exposure Meter.")
In process work, and colour work, the lengthen-
ing of exposure due to prisms, mirrors, colour
filters, or ruled screens becomes an important
consideration. The larger the prism the more
light is absorbed. With a 3-in. prism the expo-
sure in the case of wet collodion work and
enclosed electric arc light is increased by about
2 J times ; but this would not be true, for
example, with an orthochromatic plate and green
filter. Mirrors when in best condition do not
greatly afEect the exposure, but they will do so
as they become tarnished and scratched. The
ratio of exposures for colour filters should be
determined by photographing black, white, and
a scale of neutral greys, whi(±L should, come ahke
on all three negatives. Ruled screens increase
the exposure by about one-fifth, and as small
stops are used the expostire will be much longer
than in ordinary negative making, though pro-
portionately the same. The nature of the
" copy " (the original) influences the exposure
in half-tone work. A deep red toned print will
require the longest exposure.
EXPOSURE, EFFECT OF TEMPERATURE
ON {See " Desiccated Dry Plates.")
EXPOSURE, INCORRECT
Correct exposure is the basis of all successful
work in photography. But in some subjects,
especially those with moving objects or very
dark interiors, it may be impossible to expose
sufficiently long ; and occasionally errors of
judgment may lead to both under- and over-
exposed plates.
Incorrectly exposed plates tan always be more
successfully treated if the error is known before
development is begun than if it is only recognised
when the operation has made considerable pro-
gress. Under-exposure is the more difficult to
treat, as there is insufficient light-action. If
the subject is one that is deficient in contrast,
or exposed in a dull light, the best method is
prolonged development either in a normal solu-
tion, or in one containing the normal amount of
developing reagent and excess of alkaU. If
the subject is strong in its contrasts of light and
shade, prolonged treatment in a normal solution
considerably diluted, or in a diluted solution
with extra alkaU added, is the only satisfactory
method. The diluted solution lessens contrasts
considerably ; and it allows prolonged develop-
ment without obtaining much strength in the
light tones. Detail is obtained without density,
and greater softness results than can be obtained
by any other method. If the resiiltant negative
is still too harsh, the methods given under the
headings " Hard Negatives," " Harmonising Con-
trasts," etc., must be adopted.
Over-exposure within moderate limits comes
within the latitude of the plate {see " Latitude
in Plates"), and requires no special treatment,
provided that the subject is one of good con-
trast of light and shade. If a plate has received
an exposure from one and a-half times to twice
the normal amoujit, development may be normal ;
and though the plate will look very strong, and
different from one that has been correctly
exposed, the resultant print will be little, it any,
inferior to that yielded by a normally exposed
plate. The time of printing wiU be much longer,
and that will be the only difference. In moder-
ate over-exposure in subjects deficient in con-
trast, for copying, etc., the only efficient means
of correcting over-exposure in development is
by treating it throughout by a modified solution.
Potassium bromide may be added to a normal
developer in any quantity up to 2 grs. to each
I oz. of solution ; or a more concentrated
developer may be employed, and 3 grs. or 4 grs.
of bromide added to each i oz.
Another method of working is to develop
either with a normal or a concentrated solution
until the extreme shadows begin to veil ; then
stop development and fix the plate, afterwards
intensifying to bring it to full printing strength.
EXPOSURE INDICATOR (Fr., Marquer auto-
matique, Compteur, Enregistreur ; Ger.,
Zdhlvozzichtung, Plattenzdhler)
A mechanical contrivance fitted to magazine
cameras to indicate the number of plates that
have been exposed. Usually, the number of the
plate in position for the next exposure is made
to show at a small opening, directly the pre-
viously exposed plate is moved out of the way by
the changmg arrangement. One pattern has the
numbers of the plates engraved on a metal wheel
inside the camera, which is moved round one step
by the action of the changing lever or handle, each
time this is worked. There are other patterns.
EXPOSURE METER (Fr., Phoiometre, Luci-
mitre, ActinomHre ; Ger., Expositions-
messer, Belichtungsmesser, AMinometer)
An instrument for ascertaining the necessary
duration of exposure when taking a photograph.
Exposure Meter
230
Exposure Tables
The terms " exposure meter " and " actino-
meter " are often used interchangealily, but the
latter refers to an appliance for simply testing
the actinic power of light, whereas the former
means an instrument that not only doeS this,
but indicates also the exposure requisite under
such conditions, with any given subject. While
an exposure meter may be an actinometer, an
actinometer is not an exposure meter. The term
actinometer now tends to be restricted to
appliances used for finding the light value when
printing, as in the carbon and similar processes,
where no visible image is at first obtained.
Of the many different kinds of exposure meters
proposed the best are those that provide for an
actual test of the light intensity ; among these
may be mentioned tiie Watkins and the Wynne
A, 'Watkins' Standard Exposure Meter
devices. The Watkins Standard Exposure
Meter A has an enclosed chain pendulum for
counting seconds or half-seconds, the cap or lid
shown on the left forming, when removed, the
weight of the pendulum. At the opposite end is
an opening under which runs a coil of sensitive
paper, which may be pulled out tlirough a slot
as required, in order to e^ose a fresh portion
under the aperture. To use the meter, a new
piece of paper is brought into position and
quickly covered with the thumb, pointing the
meter towards the source of the light that falls
on the object to be photographed. The pen-
dulum is then started swinging, and the finger
B. Watkins' Watch-form C. Wynne's Watch-form
Exposure Meter ■ Exposure Meter
at the same time removed from the test paper.
The number of seconds taken by the paper to
darken to the depth of the standard tint, as
painted in the cirde beside the opening, is now
carefully coimted. The pointer p is then set
against the plate speed number, the pointer d
to the diaphragm number, and the pointer A
to the actinometer time just obtained, when the
correct exposure will be indicated by the pointer
E. When the light is weak, or with specially
dark subjects, the exp.osure of the camera and
the meter may be carried out simultaneously, a
second tint being provided, which the sensitive
paper takes only one-quarter the time to match.
This instrument is very complete, and permits
of special calculations for other than ordinary-
subjects, such as enlarging, copying, etc.
A simpler form of the Watkins meter B re-
sembles a watch. Fresh paper is adjusted under
the opening by rotating the back of the case, and
the diaphragm number on the inner ring is set
against the plate speed ; the required exposure
wiU then be found against the actinometer
time.
Wynne's " InfaUible Exposure Meter " C
also resembles a watch. A smaU disc of yellow
glass (not shown in the illustration) is-cemented
to the revolving dial to cover the sensitive paper
until it is wanted. It is thus possible to see to
adjust fresh paper under the aperture without
its being prematurely exposed to light, and to
have it always ready by merely sliding aside the
yellow disc. The Wynne meter has the valuable
feature of showing at once the necessary expo-
sure with all the different stops. A table is
supplied with the meter assigning to the various
makes of plates a speed number, which repre-
sents also a diaphragm number. To use the
meter, the actinometer time on the inner ring, as
found with the sensitive paper, is set against the
plate speed on the outer circle. Against each
of the diaphragm nimibers on the latter will
then be indicated the correct exposure.
Obviously, if a stop corresponding with the plate
speed number is used, the exposure will be
identical with the actinometer time, and the
camera and meter may be exposed simulta-
neously.
EXPOSURE NOTEBOOK (Fr., Regisire des
expositions ; Ger., Expositionsbuch)
A notebook specially ruled for entering full
particulars of each exposure made, for the
after identification -of the different negatives, or
in order that any particular plate may receive
individual treatment. Spaces are usually pro-
vided for details of subject, date, time, Ught,
plate, number of slide, lens, stop, exposure, etc.
EXPOSURE, OVER- (See "Exposure,
'' Incorrect")
EXPOSURE TABLES
Tabulated series of comparative exposures for
different subjects, variations in the actinic value
of the light due to the season, and the different
lens apertures and plates. They materially
assist experienced workers when attempting
unusual subjects ; to the inexperienced they are
extremely valuable, rendering the problem of
exposure comparatively easy.
Of the many tables that have been produced,
attention will here be directed to the series
designed by Henry W. Bennett, these comprising
a table of comparative exposures for 'different
subjects, and a diagram and table of the variation
in the value of the Hght due to the season of
the year and the time of day.
Exposures for lens aperture //16, plate 200
Hurter and Driffield, and the best possible con-
ditions of light, etc., at mid-day in June : —
Clouds
Tabi,E I
Open-air Subjects
Second ,,
Boats at saa, distant ^
Exposure Tables
231
Exposure Tables
r> ,t t ■ Second the longer for one that is comparatively dark,
feabeach!'wavesT;tc. ! ! ! ! " 4 P J^it^ «^n^f windows or those seriously obstructed
- - ' • '• ■ • "-^ by outside objects. Dark woodwork in churches,
Landscapes : —
Open coiamon ; or open subject with no
strong objects .....
Average landscape : cottages or trees in pro-
minent position .....
Trees in full leaf near camera
Trees in full leaf very near ; part of trees only
included in picture .....
Woods ; photographs taken under strong m:
foliage I to 5<v>*fl
_ especially if near the camera, will always necessi-
, . tate a longer exposure than if the subject con-
A'-^sists of light-coloured stone. In domestic
r^ , interiors, the same principle regarding windows
J t, applies equally ; and the colour of the walls and
the furniture will also affect the exposure. In
J Lj, the case of an unfurnished room, the exposure
-nay be reduced to half that given in the tables.
he exposure for flowers and stUl-hfe subjects
Bmldmgs:— -,^111 ^e influenced by the colour, the degree of
Large buildings, general views . . . ^ r,'. contrast, and also by the manner in which the
Cottages, small buildings . . . . J , ijght from the window falls on it.
N^ow^^teSts l\ ''^^^^^ exposures, being correct for the best
Details of buildiigs '.'.'.'. j" to |-v Possible hght in June, must be multipUed by
Portraits • " * the figures obtained from the graph (called
Group or full-length figure . . . . j ;^ "Table II."), in which the thicker horizontalUnes
Head and bust ..... " '
Still-life, flowers, etc., full-size . 2 to 8
Larger objects, according to distance . J to i
Interior Subjects
Cathedrals and churches : — j,o j* 'Hu
Nave or general view . 45 sec. to 2 min.
Aisles, white glass windows. . i/g, i to 3 min.'
? represent the hours and the fine horizontal Unes
quarter-hours. The fine vertical lines corre-
spond to intervals of five days for each division,
the dates being given under every alternate
line. It is practicable to read off the correct
figure for any day, and for any time in the day.
Bach thick curved line has its multiplying figure
shown on it. This figure is indicated for any
)y the point at which the
lines cross the horizontal and vertical :
Tabi,E III
VALUE OF DAYLIGHT THROUGHOUT THE
YEAR
Aisles, stained-glass windows . ^^^ a to 7 nun.j7/„ date and time by the point at which these curved
Choir .... I1i». ■ 4 to 15 nun. •■ .. > . ^ . _
Crypt 10 to 60 min.
Ordinary rooms in modem houses . i to 3 min.
Workshops . " . . .30 sec. to i min.
Rooms or workshops with skyUghts 10 to zo sec.
Portraits in well-lighted room . 10 to 25 sec.
Still-life, flowers, etc., full-size, near
window . . . , ro sec. to r inin.
All the above times are sufficient to secure a
fully-exposed plate. The boats at sea described as
" near" are those that nearly fill the plate ; those
caUed " distant" are small in relation to the size
of the picture. In the landscape subjects de-
scribed as " open common," etc., are included all
those that have no object wilji any depth of
shadow within one hundred feet. Small bushes,
lower than the camera, can be disregarded, as
the camera, in looking downward, photographs
them from above, the direction in whidi the
light reaches them. In aU landscape work,;
heavy foliage will require a longer exposure than
Tabw II
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any other subjects at the same distance, on
account of its colour and strong deep shadows.
In all the interior subjects, a range of expo-
sure is given. The shorter is for a well-lighted
subject with large and unobstructed windows,
In Table III. it is only practicable to give
multiplying figures for each hour and for every
fifteenth day. The variations for intervening
times and dates can be estimated. This day-
light table disregards the effect of the weather.
When the hght shows any appreciable departure
from the best for the time of year, the exposure
should be multiplied by 2 ; if the weather is
dull, multiply by 3 ; and if very dull or gloomy,
by 4 or 5.
These exposures are for a plate having a speed
of 200 H. and D. Most modem rapid plates are
about this speed, but the makers give the rapid-
ities in almost all cases. The exposure for other
plates will be. directly proportionate to their
Exposure Tables
232
Extension, Camera
rapidity ; thus a plate 100 H. and D. will
require twice the exposure of one having a speed
of 200 H. and D.
These exposures are for //16, a medium aper-
ture. The relative exposures for other apertures
are given in Table IV.
Tabi,E IV
Value of Diaphragm Apertures
fl5-(> m //ii //16 //22 f/32 //45 //64
^ i 4 I 2 4 8 id
The exposure for any subject is first found
from Table I. ; this is multipHed by the time
value from Table II. or III. ; the resiilt is multi-
plied by 2, 3, etc., if dull weather, and finally the
total is multiphed by the stop value from Table
IV. Otherwise expressed : —
Subject X Time value x Weather x Lens aperture
Table I. Table II. or III. Table IV.
The result being the exposure required
Two examples will render the method of
working more easily understood, (i) For open
country lane with cottages ia the mid-distance,
September 14, 2 p.m., a fine, clear day, stop
//32, plate 200 H. and D. : —
Time:
Subject Sep. 14 Weather Stop f/32 Exposure
2 p.m.
I sec. X2X r X 4 = 1 sec.
(2) A cathedral aisle, well hghted by stained-
glass windows, April 17, 10.30 a.m., slightly dull
[2], lens aperture //22, plate 200 H. and D. : —
Time:
Subject Ap. 17 Weather Stop//22 Exposure
10.30 a.m.
2 min. X li X 2 X 2 = I2min.
Instead of using Table II. or III. and multi-
plying again for the weather, a meter may be
substituted as a means of measuring the intensity
of the light. The multiple of the unit time that
is required for darkening the sensitive paper to
match the standard tint is the figure to be used
in multiplying the unit exposure obtained from
Table I. The meter should always be held in a
vertical position, facing the camera. As an
example, the same data may be taken as in
No. I illustrating working from Tables I. and II.
A country lane with cottages, September 14,
2 p.m., stop //32, plate 200 H. and D. Assume
that a Wynne meter is used to test the light, the
unit time for matching the painted tint being
four seconds. It is hdd vertically, facing the
camera, and the time required for matching the
tint is eight seconds, twice the ruiit time.
Subject Meter
(Table I.) (units)
i sec. X 2
Stop Exposure
//32
X 4 = T sec.
A meter can be used in a very simple manner
for determining the exposure of objects within
twenty feet of the camera, by giving a definite
proportion of the time that the paper takes to
darken to the standard tint. The Wynne
standard tint requires four seconds, the Watkins
standard eight seconds, and the lighter of the
two tints supplied with the Watkins Bee meter
four seconds for matching with the sensitive
Wynne and
Watkins
Watkins Bee
standard
light tint
tint
one-half
one-fourth
one-fourth
one-eighth
one-eighth
one-sixteenth
paper in the best possible light. Consequently,
in the following table, different proportionate
figures must be employed according to the
meter used.
To use this table, which is very useful for still-
life, flowers, portraits, animals, machinery, etc.,
the meter is held dose to the subject in a
vertical position, facing the camera. The
actual time that the paper takes to match the
standard tint is noted, and a definite proportion
of this time is the correct exposure without
regarding it as a multiple of the standard time.
This proportion varies according to the distance
of the subject from the camera.
Tabi<E V
The exposure will be the following proportion
of the actual time that the meter paper requires
to match the standard tint : —
Distance of
subject from
camera
3 feet
5 ..
10 „
20 „ one-sixteenth one-thirty-second
These exposures are for //16, and a plate 200
H. and D.
These exposures are for objects of medium
colour ; for very dark subjects the exposure
should be doubled ; for very light, it may be
reduced to one-half.
Two examples will illustrate the method. A
portrait, head and bust only, is jbeing taken in a
garden. The sitter is about five feet from the
camera, and a Wynne meter, held close to the
sitter and facing the camera, requires four
seconds to match its standard tint. The expo-
sure for//i6 and a plate 200 H. and D. wiU be
one-fourth of this time = i second.
A small machine is being photographed in a
workshop, the same plate and stop 7/32 being
employed, and the machine being about ten feet
from the camera. The day is duU, the work-
shop not well lighted, and the meter, placed on
the machine while the camera is being arranged
and the image focused, requires fourteen minutes
to match the standard tint. One-eighth of this
time for ten feet distance, one minute and
three-quarters, multiplied by 4 for //32, gives
7 minutes as the exposure required.
EXPOSURE, UNDER- (See "Exposure,
Incorrect.")
EXPRESSTYPIE
A process of making grained half-tone blocks,
invented by Cronenberg. It consists in the
use of a grained screen, placed in contact with
tt gelatine dry plate so as to make a grained
negative. This is printed on to zinc or copper
in the usual way. The grain is of a reticulated
character resembling collotype.
EXTENSION, CAMERA (Fr., Extension ; Ger.,
Ausdehnung)
The distance between lens and plate, or the
length to which the bellows wxU rack out. (See
"Double Extension" and "Camera.")
Also the name given to an accessory for length-
ening this distance, when the bellows do not rack
Exteriors, Photographing
233
Eyepiece, Focusing
out far enough for the special work in hand.
There are many different kinds of camera
extensions, or " adapters," for this purpose,
some fitting on the front of the camera, others
at the back,
EXTERIORS, PHOTOGRAPHING
The general technical considerations that have
to be observed in photographing exterior views
of buildings, etc., are given under the heading
" Architectural Photography." There are, how-
ever, several special considerations which cannot
apply in the same manner in interior work.
Speaking generally, a long-focus, rather than a
short-focus, lens should be employed. At times
there are advantages in using a short-focus lens
for a comprehensive view of a high building, but
in small details or portions the longer focus is
always preferable when practicable. Of course,
there are many cases where limited space or
other conditions render it impossible to use any
other than a wide-angle lens. There is one
respect in which a wide-angle lens assists the
photographer to secure an effect that cannot
be obtained by any other means. In photo-
graphing a high building from the near point of
view necessitated by a wide-angle lens, the
impression is conveyed of looking upwards in a
manner that cannot be given by any photograph
taken from a more distant point. The effect
is realistic.
Whether photographing a complete building
or a small portion or detail, an obUque view
should practically always be taken. A square
front view is Uke an architect's drawing ; it is
never satisfactory, as it fails to give a fair
impression. An obhque view gives at once a
good impression of the relief and the form of
the building or detail. It conveys the impression
of solidity, and not simply the outline of the
front elevation. Sunshine is very effective, and
very useful in giving relief as well as good effect.
More especially is fiiis the case with large sub-
jects ; small details are frequently more satis-
factory in diffused Ught. Very fine effects can
sometimes be obtained by taking a photograph
when the sim is shining almost along the surface
of the subject, very slightly in front. The long
cast shadows from projecting details are strik-
ingly effective. A liberal proportion of fore-
ground should be included ia any pictorial view
of a building, or doorway, or similar detail.
And where possible, a foreground with Unes
running obliquely iuto the picture should be
chosen. It is the most simple and telling manner
of conveying the impression of the space that
exists between the object and the observer. As
in interior work, the point of view, the lighting,
and the general conditions should be chosen so
as to show in the most effective manner the
character, the quaUty, and the special features
of the architecture photographed.
EXTRA-FOCAL DISTANCE. OR "E.F.D."
The distance between lens and object, and lens
and image, minus the focal length of the lens.
The greater B.P.D. equals focal length multiphed
by ratio. The lesser E.P.D. equals focal length
divided by ratio.
EYE LENS
The lens, or combination of lenses, of an eye-
piece which receives the image from the field
lens and conveys it to the eye, as explained
under the heading " Byepiece."
EYEPIECE (Ft., Oculaire ; Ger., Okular)
The lens, or combination of lenses, which
receives the image from the microscope objec-
tive and conveys it to the eye. The best known
types of eyepieces are the Huyghenian, the
Ramsden, and the Kelluer.
The Huyghenian, which is the most popular,
is a negative combination composed of two
plano-convex lenses separated by the distance
of half the sum of their foci. The lower lens of
an eyepiece, that nearest the objective, is
known as the field lens, and the other is the
eye lens. A stop is placed between the field
and eye lens at the principal focus of the
latter.
The Ramsden, which is a positive and achro-
matic eyepiece, is a combination of two plano-
convex lenses with their convex surfaces inwards.
This form is especially useful for micrometric
purposes. The Kellner eyepiece is now rarely
used ; it gives a very large field, but the defini-
tion is not equal to that of the Huyghenian. The
eye lens is a combination of a biconvex (field
lens) and a biconcave lens (eye lens).
The projection eyepiece, as its name implies,
is designed exclusivtly for lantern and photo-
graphic work. The field lens of a projection
eyepiece consists of a plano-convex lens, the
eye lens being a biconvex combination of three
lenses. The field of this eyepiece is very limited,
but it gives fine definition ; the magnification is
small, from 2 to 6 diameters. The compensating
eyepiece is designed to be worked in conjunction
with apochromatic objectives. This eyepiece
derives its name from being over-corrected to
compensate for the under-correction of the
apodiromats. The compensating eyepiece works
well with high-power, but indifferently with low-
power, achromatic lenses. The eye lens of the
compensating ocular is plano-convex and the
field-lens a biconvex triplet, the eye lens and
field-lens being placed in close juxtaposition.
There are no universal standards for either
diameter or magnification of eyepieces. The
Royal Microscopic Society has adopted four
standard sizes for eyepieces — namely. No. I.
0-9173 in. (23-3mm.) ; No. II. 1-04 in. (26'4i6
mm.) ; No. III. 1-27 in. (32-358 mm.) ; No. IV.
1-41 in. (35-814 mm.). The variety of methods
of classifying tiie initial magnification or power
of an eyepiece is even more unsatisfactory than
the lack of uniformity in size. In most BngUsh
eyepieces the initial magnification is indicated
by letters a — E, a representing the lowest power
listed by the particular firm, giving a magnifica-
tion of 4 or 6 diameters ; the initial magnification
of E would be from 12 to 20. On the Continent
figures, not letters, are used to classify the power
of the ocular, but they give httle clue to the
magnification.
EYEPIECE, FOCUSING (See "Focusing
Magnifier.")
F
"F" NUMBERS
A popular method of marking diaphragms or
stops, the smaller / or the capital letter being
used with the number, as, for example, / 8, /ii,
etc. (For full particulars of measuring, relative
values, etc., see under the heading " Dia-
phragms.")
FABRICS, DARK-ROOM
Canary, orange, or red translucent cloth, used
instead of coloured glass for screening the light
in dark-room illumination. They are more
serviceable when used with artificial light, as
sunlight causes them quickly to fade and
become unsafe. The canary fabric is generally
used for slow bromide papers ; the orange for
rapid bromide papers, lantern plates, and slow
dry plates ; and the red for rapid dry plates.
Fabrics are, as a rule, quite as safe as glass, but
pinholes must be watched for, and the fabrics not
wetted in any way or exposed to strong sunlight.
FABRICS, PRINTING ON
Fabrics already sensitised for the bromide
and platinotype processes may be purchased,
and they are used in the same way as bromide
and platinotype papers. Fabrics are easily pre-
pared for photographic printing, and the blue-
print process is perhaps the simplest. The
fabrics mostly employed are cottons, linens,
silks, nainsooks, etc., but silk that has been
weighted with mineral matter is unsuitable ;
the finer the material the better. The fabric
needs to be thoroughly washed in hot -water,
ironed, and, to prevent the image from sinking
into the material, it should then be well sized, a
suitable size being —
Arrowroot
Gelatine .
Alum
Water to .
80 grs.
33 ,,
18 „
20 oz.
8 g.
3-3 „
1-8 „
1,000 ccs.
The fabric is immersed in this solution for about
five minutes, pinned down on to a flat board,
and dried before a fire, it being then somewhat
stiff. The ammonio-citrate and ferricyanide
sensitising solution (see "Blue-print Process")
is then brushed over it, and, after drying, it is
ready for printing upon. Printing, washing
(fixing), etc., are exactly as described for blue
prints upon paper. The printed fabric will not
withstand washing with soap and water, as the
alkali destroys the blue image.
In order to get the best and brightest of blue
prints upon fabrics, it is necessary to use a
negative with strong contrasts — that is, one
with clear shadows and dense high Hghts, and the
negative shoidd show broad efiects of light and
shade rather than an abundance of fine detail.
A process for the replacing of the blue ferro-
prussiate image by various dyes was pubUshed
in 1898 by Stewart E. Carter. Bleached cotton
or linen is brushed over with a ferro-prussiate
sensitiser, made as follows : —
A. Ferric ammon. citrate 164 grs. 164 g.
DistiUed water to . 1 oz. 500 ccs.
B. Potass, ferricyanide . 164 grs. 164 g.
Water to . . i oz. 500 ccs.
A and B are mixed in equal parts. The sensi-
tised fabric is exposed and washed just as a print
upon paper. The blue print is next immersed
in a weak solution of caustic soda (5 grs. to i oz.
of water) for a few minutes, then washed in
hot water, and placed for three minutes in a
solution of 13 grs. of sodium phosphate in 10 oz.
of water at a temperature of 170° F. (about
T]° C). This is followed by washing, first in
cold water and then in hot water, after which
the print is ready to receive the dye. A weak
gelatine solution is made (glue size 24 grs.,
water 10 oz.) and heated to 160° F. (71° C),
aiid the prints moved about in it for about
three minutes ; from 3 to 5 grams per litre
(1-3 to 2-2 grs. per ounce) of dinitroresorcin
(resorcin green) is added, and the temperature
raised to 180° F. (82° C). As soon as the shade
is considered fuU enough for a strong picture,
remove to boiling water to wash out all unfixed
dye. The high lights (whites) are next cleared
in a bath of neutral soap (used at a temperature
of i6o°F., 7i°C), and the print again washed
in hot water and finally in cold. Other dyes
may be used in place of the green named.
Gailo-cyanine gives blue and violet ; alizarin
gives purple, and also a brown sepia. The original
blue print may be toned, but the dye method,
although rather troublesome, gives the more
pleasing effects.
Carbon prints may be transferred to any kind
of fabric. This must be washed, dried, ironed,
and given several coats of the following sizing
mixture, allowing to dry after each coat : —
Cooking gelatine
Sugar
Glycerine .
Chrome alum .
Barium sulphate
Water to .
2 oz. 133 g.
I „ 66-5 „
I „ 66 ccs.
IS grs. 2 g.
4 oz. 266 „
15 ,, 1,000 ccs.
Dissolve by heat and mix thoroughly. Transfer
the carbon tissue thereon in the usual way. (See
" Carbon Process.")
Fabrics can be sensitised and used as ordinary
P.O.P. First soak the washed and dried fabric
in the following size for about three minutes : —
Gelatine .
Common salt .
Magnesium lactate
Water to .
100 grs. 10 g.
100 „ 10 „
100 „ 10 „
20 oz. 1,000 ccs.
234
Factorial Development
235
Faded Negatives and Prints
Dissolve by aid of heat and then well mix ;
after coating the fabric allow it to dry thoroughly.
The sized fabric is then sensitised by soaking
for three minutes in —
Silver nitrate . . 25 grs. 52 g.
Distilled water to . i oz. 1,000 ccs.
The fabric is next immersed for one minute in —
Citric acid
Sugar
Water to .
50 grs.
50 „
20 „
g-
and dried in the dark. The sensitive fabric is
then printed upon, toned, fixed, and washed
exactly as ordinary P.O.P.
An. easier method of coating fabric with a
silver solution is the following : A salting or
sizing bath is first made by rubbing up 180 grs.
of arrowroot or dextrine in a little cold water
until a smooth paste results ; make this up
to f pint with boiling water. If the mixture
does not at once become gelatinous it should be
kept hot (not boiling) and stirred till it does.
It should then be allowed to cool a Uttle, and
160 grs. of ammonium chloride dissolved in
about 4 oz. of water added to it. The mixture
is applied while warm to the washed and ironed
fabric, which is then dried and sensitised in
the following bath : —
A. Citric acid . . 25 grs. 50 g.
Distilled water . i oz. 500 ccs.
B. Silver nitrate . 60 grs. 125 g.
Distilled water . i oz. 500 ccs.
Mix the two solutions. To sensitise the fabric
use a Buckle or Blanchard brush. Pin the
fabric to a flat board, pour upon it a little of the
silver sensitising mixture rapidly and evenly,
spread it over the entire surface, and dry in
the dark. The fabric is printed upon as though
it were P.O. P., toned with an acetate and gold
toning bath, and fixed and washed like paper.
It is desirable after washing and before toning
to pass the print through a weak solution of
sodium chloride (common salt), which gives
reddish brown tones, or of sodium carbonate,
which gives brownish purple tones. {See also
" Diazotype," " Indigo Printing," etc.)
FACTORIAL DEVELOPMENT (See
"Development, Factorial.")
FACTORIES, PHOTOGRAPHING IN
Taking photographs in factories or workshops
presents difficulties from several independent
causes. The first is that work in progress can-
not always be stopped while the exposures are
made, and the consequent movement cannot
always be prevented. Then machinery and
shafting in constant motion introduce the serious
element of vibration, and, in addition, smoke
and moisture are inseparable from some kinds
of work, increasing the difficulties of securmg
good negatives. When the nature of the work
will allow it, the negatives should be taken
during the dinner-hour. The camera can be
set, everything arranged as desired, the subject
focused, and everything made ready for the
exposure beforehand. Then the plate can be
exposed under the best possible conditions. A
small stop is ahnost always necessary for secur-
ing good definition throughout.
When figures have to be included and the work
shown imder its normal conditions, the case is
different. The exposure must necessarily be
short so as to avoid movement of the principal
figures. FrequenUy, a large aperture is neces-
sary in order to shorten the exposure suffidentiy,
and it may be quite impossible to secure the
degree of sharpness in the different planes that
the photographer would desire. In that case,
the principal objects must be rendered as crisp
and sharp as possible, and the other parts must
simply take tiieir chance. Considerable assist-
ance may be given to the workmen that are
included by the manner of posing. If they can
be given a littie support, by resting on a tool, or
putting one of their hands on a machine, how-
ever sUght the support may be, it will materially
assist in avoiding movement during the exposure.
A longer exposure can be given without appre-
ciable movement. A single machine with one
or two figures should cause no difficulty. In
subjects of this kind, dupUcate exposures should
always be made.
Any windows that are in front of the camera
and included in the picture should be covered
during nine-tenths of the exposure, and, if
possible, the covering should be outside. Win-
dows in front of the camera, but not included in
the picture, should be covered during the whole
of the exposure, unless the lens can be shielded
from them as described under the heading
" Interiors, Photographing."
FADED NEGATIVES AND PRINTS. RE-
STORING
Faded prints are more commonly met with
than faded negatives, but whichever is treated,
success is more certain if the actual cause of
fading is known {see "Fading, Causes of")..
When negatives fade the trouble is usually due
either to insufficient fixing or to insufficient or
improper washing after bleaching with mercury
for the purpose of intensification. During the
year 1900 Sir WiUiam Crookes paid particular
attention to the subject of restoring faded
negatives — presumably those treated in the
usual way and not intensified — and the follow-
ing process is advocated by him. The faded
dry-plate negative is soaked for three hours in
distilled water, and then immersed for from ten
to fifteen minutes (in the dark-room) in the-
following bath: —
500 ccs.
3 g-
3 „
36 „
12 ,,
Water . . . I oz.
Pyro . . • 3 grs-
Sodium metabisulphite 3 „
Sodium carbonate . 36 „
Sodium sulphite . 12 „
The plate is next well washed, immersed in an
ordinary " hypo " fixing bath for half an hour,
and then washed in running water for from fom-
to six hours. It is then toned with gold, for
which purpose two solutions are required, one
of ammonium sulphocyanide (10 grs. to the
ounce), and one of gold chloride (i gr. to the
ounce) ; for use, i oz. of each is taken and
8 oz. of water added ; or, if desired, the com.-
plete bath may be made up as —
Water . . .10 oz. 1,000 ccs.
Am. sulphocyanide . 10 grs. 2 g.
Gold chloride . . i gr. -2 „
Faded Negatives and Prints
236
False Images, or " Ghosts "
The plate is immersed in this bath for about ten
minutes and finally washed for half an hour and
dried. The fixing in " hypo " can be omitted if
so wished, although it is desirable. The gold ton-
ing bath has the property of precipitating gold on
the image and rendering it of a blacker colour.
Negatives that have been intensified with
mercury may fade quickly, and to restore them
they should be treated with a solution of potas-
siimi sulphantimonate, commonly known as
SchHppe's salt. The faded negative is first
thoroughly soaked and then treated with 20 grs.
of Schlippe's salt dissolved in 2 oz. of water,
until the desired result is obtained ; finally
wash well.
The fading of prints has always been a trouble-
some matter. In the old days the necessity for
thorough fixing and the complete removal of
the " hypo " was not generally recognised, and
the question of fading became so important
that a committee was formed in May, 1855, to
enquire into the causes, the Prince Consort con-
tributing £$0 to the expenses of the inquiry.
Since then, of course, many improved papers
have taken the place of the old ones, and difierent
causes have arisen. Platinum prints are said
never to fade, but nevertheless they sometimes
appear to change their colour from the original
pure black to a brownish or yellowish brown
colour. According to Chapman Jones, such
prints may be completely brought back to their
original colour by unmounting and treating with
a mixture of hydrochloric acid and chlorine
water, made by adding a few drops of sodium
hypochlorite solution to dilute hydrochloric acid
(about one of acid to ten or more of water),
until the odour of chlorine is distinctly notice-
able. Neither hydrochloric acid nor chlorine
water alone is effective, though each does some-
thing towards the desired end. Several other
methods have been advocated, but aU are more
troublesome, and not nearly so effective.
The restoration of silver (printed-out) prints
is at all times a very risky performance. If they
ere old and yellow, and of value, they should be
copied — preferably through hght blue glass —
before any attempt is made to tamper with
them, because of the risk of spoiling the originals.
One process is to bleach the yellowed albumen
print in a mercuric chloride solution as used
for intensifying, well wash, and then to develop
in an old hydroquiuone or metol developer
(without bromide), or preferably to immerse in a
5 per cent, solution of sodium sulphite, and finally
wash well. This process is not reUable. An
elaborate process of restoring silver prints, and
one for which the inventor (H. Jandaurek)
was awarded a silver medal in 1888, is as follows.
Two solutions are required : —
A. Distilled water . 35 oz. 1,000 ccs.
Sodium tungstate 608 grs. 5 g.
B. Distilled water . i oz. 400 ccs.
Calcium carbonate (pure) 5 grs. 4 g.
Chloride of hme . 1-2 „ i „
Gold and sodium chloride 5 „ 4 „
The B solution should be kept in a yellow
bottle or in the dark for twenty-four hours.
The faded prints are tmmounted, well washed,
and placed in 8 oz. of the A solution to which
i oz. to J oz. of B has been added. They should
remain in this toning bath until they assume" a
good purple tone, and they are then well washed
and fiied with " hypo " (i oz. to 10 oz. of water)
until all the yellowness has disappeared, which
may take one hour or more ; finally, they are
washed well.
As stated above, all print restoration processes
are more or less unreliable, and need to be used
with great caution. Any details that have
vanished from the faded print cannot be brought
back, and all that the restoration process does
is to strengthen the weak parts of the print,
and as much as this can be done equally well by
making a copy in a proper manner.
FADING, CAUSES OF
All silver images, whether negative or positive,
are formed by metalUc silver in an extremely
fine state of division imbedded in a vehicle
of albumen, gelatine, or collodion. Everyone
knows how prone silver, even in the form of
spoons and forks or ornaments, is to tarnish,
and consequently it can be well understood how
much more readily the metal in a finely divided
state can be attacked. In many cases, particu-
larly in that of priats, the fading is undoubtedly
due to imperfect fixation or removal of the last
traces of " hypo " or the hyposulphite of silver.
It must not be overlooked that gelatine is a
hygroscopic substance, and that " hypo " in the
presence of moisture is decomposed, giving rise
to sulphur compounds which readily attack the
image. Whilst fading is not so commonly met
with in negatives, it can still be detected some-
times, and it is then advisable to bleach the nega-
tive with a chlorising mixture, such as hydro-
chloric acid and potassium bichromate, wash
well, and redevelop.
There is but littie hope of saving a fading
print, and care should be taken to ensure perfect
fixation and thorough washing, the former being
as essential as the latter. It will often be found
that prints mounted on cards show fading more
readily than those that are unmounted, and
this may be due to the card containing " hypo "
or some sulphur compound which is gradually
decomposed by the motmtaut or moisture, and
acts on the silver image. Frequently, too,
prints — especially collodion prints — will fade in
circular spots, and this can often be traced to
small particles of metal, such as the bronze
powder used for gilding the edges, etc., electro-
lytic action having been set up by the acid
moisture in the air between the two metals.
Varnishing negatives and prints is some pro-
tection. In the case of framed prints care should
be taken to see that the backboard of the frame
fits well, that the prints and mount are thoroughly
dry before being framed, and that all round the
edges, and over any cracks in the backboard,
good stout brown paper is pasted or glued.
FAHRENHEIT THERMOMETER (See
" Thermometer.")
FALLING FRONT (See " Rising Front")
FALSE IMAGES, OR "GHOSTS" (Fr.,
Images fausses ; Ger., Falsche Bilder)
Even the best doublet lenses sometimes show
what is known as a false image or " ghost,"
False Dispersion
when a bright object or light occurs in the pic-
ture. This is due to reflection of the bright
object from the front surface of the back lens,
and from this to the back surface of the front
lens, whence it is again reflected towards the plate.
In a properly designed lens, the distance apart
of the glasses and the position of the stop are
so arranged that the false image is difiused
before it reaches the plate, and so is very rarely
troublesome. To test for the presence of a
false image, focus a gas flame or a lighted candle,
placed at a distance from the camera equal to
about eight or ten times the focal length of the
lens. Cover the head with the focusing cloth,
and bring the image of the flame into the centre'
of the ground-glass screen. If the camera is now
turned slowly so that the image moves to one
side, tie ghost, if present, may on careful
inspection be seen moving in the contrary direc-
tion, and exactly opposite the principal image.
It very probably will not be in focus at the
same time as the chief image, but it may usually
be brought into focus by a slight movement of
the screw, and will then be foimd to be distin-
guished from the primary image by being erect
instead of inverted. This defect may often be
cured by slightly altering the distance between
the lenses, or by varying the position of the
diaphragm, the false image being consequently
spread over the whole of the plate and not
allowed to come to a focus. (See also " Flare
Spot.")
FALSE DISPERSION (See "Dispersion.")
FALSE PERSPECTIVE (See "Perspective,
False.")
FARMER'S REDUCER AND INTENSIFIER
About the year 1883 Howard Parmer intro-
duced what is undoubtedly the most widely
used reducer. It consists of " hypo " and po-
tassiimi ferricyanide in solution, and is some-
times referred to as the " ferricyanide " or
"hypo-ferricyanide," but more frequently as
the " Farmer " or " Howard Farmer " reducer.
It will be found described under the heading of
" Reducers."
Farmer's intensifier is not so well known. It
is one of the " silver " processes, and will be
found with others under the heading of " Silver
Intensifier."
FEERTYPE
A printing process, patented by Dr. Adolf
Peer in 1889, in which paper is sensitised with
diazo-sulphonic salts of aniline, amido-azo-
benzol, benzidine, and their homologues, in
conjunction with compounds of phenol, resorcin,
or naphthol. The diazo compound is set free
by the action of light, and forms a colouring
matter ; thus a coloured positive print is obtained
from a negative. After exposure, the print is
washed in water or dilute hydrochloric acid, by
which means the unacted upon and unchanged
preparation is removed. (See also " Diazo-
type.")
FERGUSON'S TONER
A copper toning bath for bromide prints. (See
" Copper Toning.")
237
Ferric Ammonio-oxalate
FERNS AND LEAVES, PRINTING FROM
Ferns and leaves make effective and decora-
tive photographs which are easily produced
without a camera, lens, or negative, the leaves
being printed direct upon the sensitive paper.
Lace may also be photographed in the same way.
Either fresh, preserved, or skeletonised flowers
and leaves may be used. A piece of plain glass
should be placed in a printing frame of the
desired size and the leaf laid flat thereon, the
sensitive paper (any kind answers, although
P.O. P. is preferable) coming next ; the back of
the frame is placed in position, and the whole
put out to print in the usual way. When
printed sufficiently, tone or develop, as the case
may be, and afterwards fix and thoroughly wash.
When the leaves are particularly moist it is
advisable to place a thin sheet of celluloid — a
clean film serves admirably — ^between the leaf
and the paper in order to prevent the paper from
becoming contaminated with the natural juices.
Almost equally good results may be obtained
from natural or skeletonised leaves, the differ-
ence being in the duration of printing. Bracken
and Virginia creeper leaves are particularly suit-
able, and a brief printing from fresh leaves gives
the outline of the leaves only, the image appear-
ing as white upon black. If, however, a reveisal
is wanted, the leaf may be placed in contact
with a dry plate and a negative made which
would produce a print showing black upon white.
The longer the exposure the more light travels
through the leaf, and the greater the detail
obtained. New leaves when suitably printed
give beautiful half-tones, because of the different
densities of the various parts of the leaves ;
whereas skeleton leaves produce only black and
white prints. Talbot, in 1836, used a fern leaf
when he proc'uced the first silver print on paper.
FERRIC AMMONIO-CITRATE (Fr., Citrate
de fer ammoniacale ; Ger., Braune citro-
nensdure Eisenoxydammoniak)
Synonym, ammonimn citrate of iron. 4Pe
C,H50, 3(NHj), C, H5O, 3Fe (OH),. Molecular
weight, 2,030. bolubilities, i in 4 water, insoluble
in alcohol. It takes the form of brownish red
scales, and is made by dissolving freshly precipi-
tated ferric hydrate in excess of citric acid and
neutralising with ammonia. It is sensitive to
light, and should be kept in the dark. It is
used in conjunction with potassium ferricyanide
in the iron printing processes.
Valenta has recommended a green salt, which
is a mixture of neutral ammonium ferric citrate,
add ammonium ferric citrate, and ferric citrate,
and has the formula sFeCjHjO, 2(NHi), C.HjO,
NH, C,H,0, 2H2O. Molecular weight, 1,956.
This occurs in bright, greenish yellow scales, and
gives much more sensitive papers with purer
whites than does the brown salt. It also is
sensitive to light and must be kept in the dark.
FERRIC AMMONIO-OXALATE (Pr., Oxa-
late ammoniaco-ferrique ; Ger., Ammo-
nium ferrioxalat)
Synonyms, ammonium oxalate of iron, oxalate
of iron and ammonia. Fea(CjOi)3 3(NH4)j
CjO, 8H2O. Molecular weight, 892. SolubiUties,
I in 2-1 water, insoluble in alcohol. It occurs
in bright green crystals, and is formed by
Ferric Ammonlo-sulphate
238
Ferric Salts, Printing with
dissolving ferric hydrate in ammonimn oxalate
solution, evaporating and crystaUising. It is
decomposed by light into ferrous ammoniiun
oxalate, and is used occasionally for blue prints,
a formula being : —
A. Ferric ammonium
oxalate . . J oz. 250 g.
Distilled water to 20 ,, i,ocxd ccs.
E. Potassium ferri-
cyanide . . ^ oz. 250 g.
Distilled water to 20 ,, 1,000 ccs.
Mix in equal parts jiist before use. It is also
used in the cold-development platinum and the
print-out platinum processes.
FERRIC AMMONIO-SULPHATE (Fr., Sul-
fate de fer ammoniacale ; Ger., Schwefel-
sdure Eisenoxydammoniak)
Synonyms, ammonium sulphate of iron. Fe SO^
(NHj)^ SO4 6H2O. Molecular weight, 328. Solu-
bihties, I in 5 water, insoluble in alcohol. It
occurs as pale greenish crystals, and is prepared
by dissolving 139 parts of ferrous sulphate and
75 parts of ammonium sulphate in a minimum
of water and afterwards crystallising. It has
been suggested as a substitute for ferrous sul-
phate on account of its greater stability, and it
has been used for developing wet plates,
FERRIC CHLORIDE (Fr., Chlorure ferrigue ;
Ger., Eisenchlorid)
Synonym, perchloride or sesquichloride of
iron, iron trichloride. Fe CI, 6H2O. Molecular
weight, 270-5. Solubilities, i in -63 water, i
in 4 alcohol, i in 4 ether. It takes the form
of yeUow crystalline lumps, which rapidly
deliquesce in the air. It is prepared by dis-
solving iron wire in hydrochloric add and oxidis-
ing with nitric acid. It has been recommended
for reducing negatives, but it gives rise to yellow
stains due to the formation of basic ferrous
salts. Its chief use is as a mordant in etching
half-tone and photogravure plates.
FERRIC OXALATE (Fr., Oxalate ferrique;
Ger., Ferrioxalat)
Synonym, iron sesquioxalate. Pej (CjOjjj.
Molecular weight, 376. Solubilities, very soluble
in water, insoluble in alcohol. It occurs in
greenish, glistening scales, which are extremely
sensitive to light, and it is therefore usually
preferred to mix it in solution and preserve in
the dark. It is the most light-sensitive of any
of the iron salts. It is used in the kallitype
process, but its chief use is as the sensitive salt
in the platinotype process. The following is the
best method of preparing the normal ferric
oxalate solution : Powder some ammouia-iron-
alum, weigh out 500 grs. or 520 g., place in a
tall cylindrical graduate, capable of holding
20 oz. or 1,000 ccs., and add 192 minims or
200 ccs. of liquor ammoniae (-SSo), and an equal
quantity of distilled water. Stir well for about
five minutes, and allow to stand for a further
five minutes. Then fill up with distilled water,
stir well, and allow the precipitated ferric hydrate
to settie down. Next decant or siphon off the
clear supernatant liquid, and repeat the process
until the wash water is no longer alkaline to
litmus paper. Then allow the precipitate to
settle till it occupies not more than 17 oz. or
850 ccs. Add 2,064 grs. or 215 g. of pure
oxalic acid in powder, stir well, and allow to
stand in the dark-room nntil the precipitate is
completely dissolved. Now filter the solution,
and wash the filter paper with distUled water
so as to make the total bulk of the solution
20 oz. or 1,000 ccs. This forms the "normal
iron solution " for platinotype, and contains
20 per cent, of ferric oxalate with about i'2 per
cent, of oxalic acid.
FERRIC PROTOACETATE (See "Ferrous
Acetate.")
FERRIC PROTOSULPHATE {See " Ferrous
Sulphate.")
FERRIC SALTS, PRINTING WITH
The light-sensitiveness of the iron (ferric)
salts is the basis of a large number of printing
processes, including chrysotype, cyanotype,
kallitype, the sepia printing process, amphitype,
the ink process, and platinotype. In all these
the ferric salt is reduced by light to the ferrous
state. The following table (due to Bder) shows
the comparative light sensitiveness of the various
iron salts : —
Ferric chloride and oxalic acid
Ferric oxalate .
Ammonium ferric oxalate .
Potassium ferric oxalate .
Ferric tartrate .
Ammonium ferric tartrate.
Ammonimn ferric citrate .
Ferric chloride and citric acid
Ferric chloride and tartaric acid
100
89
80
78
80
80
15
19
25
Many of the inorganic ferric salts are com-
paratively stable to light, but in contact with
organic matter are readily reduced, as in the
case of ferric chloride with oxalic or citric add.
According to Abney the spectral sensitiveness
of the iron salts is chiefly in the indigo blue,
about G J F, and extends to B in the green and
well into the ultra-violet.
Printing with salts of iron is known as the
iron-printing or heUographic process. The four
prindpal processes, each of which is described
under its own heading, are : the blue print pro-
cess (ferro-prussiate), white hues on a blue
ground ; Pellet, blue lines on a white ground ;
f erro-gallic, black Unes on a white ground ; and
brown Une (better known as, and described
elsewhere in this work under the heading of,
" Kallitype "), white lines on a brown ground.
An interesting process of printing with a
ferric salt is Shawcross's Amphitype {which see),
in which advantage is taken of the fact that
these salts have the property of attracting or
repelUng greasy inks. This is again shown in
the black line " True-to-scale," or Ordoverax,
process, where an undeveloped blue-print laid
on a gelatinous surface will so affect the latter
as to enable the lines to take ink while the other
parts repel it.
The table on p. 239 (due to Eder) gives a very
dear pr6cis of the prindpal iron printing pro-
cesses and the developers necessary to produce
full vigour of the images, which as a rule are
only faint. (See also separate headings.)
Ferric Sesquioxalate
239
Ferro-Gallfc Process
Sensitive
Product of
Developer used to produce full
Colour of
Name of
salt
light action
vigour of image
image
process
Ferric oxalate.
Ferrous salt (fer-
Potassium ferricyanide. (This
Blue
Cyanotype. (Gives
citrate, tartrate.
rous oxalate).
gives insoluble Berlin blue
white lines on blue
etc.
citrate, etc.
with ferrous salts, but a soluble
compound with ferric salts)
ground from a trac-
ing)
Ditto
Ditto
Potassium ferrocyanide. (This
gives a blue precipitate with
ferric salts, but a white with
fen'ous salts)
Blue
Pellet' s process.
(Gives blue lines on
white ground from
a tracing)
Ferric citrate
Ferrous citrate
Gold chloride. (Where the fer-
rous salt is formed metallic
gold is precipitated)
Brownish
Chrysotj^e
Ferric oxalate
Ferrous oxalate
Potassium chloroplatinite. (Me-
tallic platinum is precipitated
where the ferrous salt is formed)
Black
Platinotype
Ferric oxalate
Ferrous oxalate
Silver nitrate
Brownish
black
Kallitype orArgento-
type
Ferric and cupric
Cuprous chloride
Potassium siilphocyanide, fol-
Red brown
Obernetter's process
chloride
lowed by potassium ferri-
cyanide. (The cuprous chlor-
ide is converted into brown
cuprous ferrocyanide)
FERRIC SESQUIOXALATE {See "Ferric
Oxalate.")
FERRIC SODIUM OXALATE (Fr., Oxalate de
fer et de soude ; Ger., Natriumferrioxalat)
Synonym, sodio - ferric oxalate. Fe (CaOjjj
3Na2 CjjOi iiHjO. Molecular weight, 976. Solu-
bilities, I in I -69 water, insoluble in alcohol. It
occurs as large gieen crystals, unafiected by the
air. It is prepared by dissolving ferric hydrate
in acid oxalate of sodium. It is used in the
printing-out platinum process.
FERRIC SULPHATE (Fr., Sulfate ferrique;
Ger., Ferrisulfat, Schwefelsdure Eisenoxyd)
Synonym, sesquisulphate of iron. Fe^ (804)3
9H2O. Molecular weight, 563. Soluble ia water.
It takes the form of greenish crystals, or, in
the anhydrous form, it occurs as a greyish, white
powder. It has been suggested as a reducer, but
it gives rise to yellowish basic iron salts in the film.
FERRICYANIDE OF COPPER {See " Copper
and Potassium Ferricyanide.")
FERRICYANIDiE OF POTASSIUM {See
" Potassitun Ferricyanide.")
FERRICYANIDE REDUCER (Fr., Riducteur
ferricyanure ; Ger., Rothes Bputlangensalz
Abschwacher)
The action and use of this reducer are described
under the heading " Reducers."
FERRIER AND SOULIER PROCESS
A method of making lantern slides and stereo-
scopic transparencies, invented by Ferrier in the
«arly days of the albumen process of making
positives upon glass. The method has been
kept a trade secret, but is said to be a modi-
fication of the albumen positive process.
FERRO-CUPRIC PROCESS
An iron printing process devised by Obernetter
about the year 1865. Paper is coated by float-
ing on the following sensitive mixture : —
Water. .... 100 parts
Copper chloride (crystals) . 10 „
Ferric chloride solution (sp. g.
i'5) I „
Hydrochloric acid . . i ,,
The paper is then dried and exposed in the
same way as " blue-print " paper, a faint image
being visible. Immediately after printing it is
floated on the following developing mixture : —
Potassium sulphocyanide . 10 parts
Sulphiuric acid . . . i part
Water. .... 1,000 parts
To this is added 15 parts of the sensitive mix-
ture given above. If the print is not devel-
oped immediately after printing the image
is lost. Development at first should be by
floating, and when the image has partially
developed, the paper may be entirely immersed.
The paper is afterwards well washed and toned.
Red tones may be obtained by immersing the
developed print in a 10 per cent, solution of
potassium ferricyanide. For purple tones use —
Ferric chloride
Ferrous sulphate .
Hydrochloric acid
Water.
. I part
. ztoz^ parts
. 2 parts
10 to so parts
This bath will give a range of tones from red
through violet and purple to a greenish black.
Finally wash in weak hydrochloric acid.
FERRO-GALLIC PROCESS
A method of printing with ferric (iron) salts,
giving a black image upon a white ground ;
known also as the black-line process and the
Colas process. It is largely used by architects,
engineers, etc., for multiplying drawings. The
following mixture is made up, or larger quan-
tities in proportion : —
Ferric chloride (syrupy) 30 grs. 60 g.
Ferric sulphate . . 15 „ 30 „
Gelatine . . . 15 ,, 30 „
Tartaric acid . . 15 ,, 30 „
Water . . . i oz. 1,000 ccs.
Ferro-Gelaline Developer
240
Ferrotype Process
Soak the gelatine in the water, melt by the aid
of heat, and add the other ingredients. Coat
paper in the way recommended for the blue-
print process and dry in the dark. When
dry, expose under negative or tracing tiU the
ground is white and the lines appear yellow, and
then immerse in the following developer : —
Gallic acid . . 20 grs. 4 g.
Oxalic acid . ■ S „ ^ .>
Water . . .10 oz. 1,000 ccs.
till the lines are quite black ; wash, and dry by
blotting off between clean blotting-paper and
hanging up.
FERRO-GELATINE DEVELOPER
A solution of gelatine boiled with sulphuric
acid so as to lose its setting power, used by
Carey I,ea as an addition to the wet - plate
developer.
FERROGRAPHS (5ee "Ferrotype Process.")
FERROPRUSSIATE {See " Blue-print Pro-
cess.")
FERROTYPE PLATES
Thin plates of metal coated on their face with
a fine hard dark enamel. They were so called
through being prepared as a basis for " ferro-
types," or collodion positives taken direct in
the camera. {See " Ferrotype Process.") They
have, however, another use in modem photo-
graphy. A glossy-surfaced gelatine print may
be squeegeed while wet on to a ferrotype plate
in exactly the same manner as on to a sheet of
plate glass. No preparation of the ferrotype
plate is necessary beyond washing and polishing
with a soft fabric, and when the prints are dry
they leave the plate easily with a surface scarcely
inferior to that produced by contact with glass
FERROTYPE PROCESS (Fr., ProcSdi ferro-
type; Ger., Ferrotypie)
About the middle of the nineteenth century
the term "ferrotype" was applied to the process
introduced by Robert Hunt as " Energiatype "
{which see), but that process was but little used,
and the modern ferrotype is quite different.
Ferrotypes (known also as " tintypes ") are
pictures taken on sheet-iron plates varnished or
enamelled on both sides, the picture side being
the more carefully prepared. They are of
American origin, having been introduced by
J. W. Griswold in 1855, and were also known
as " Melainotypes " before the title of ferrotype
was generally adopted. It is beUeved that the
earliest reference made to ferrotypes is in Photo-
graphic Notes, dated January i, 1856, announc-
ing the invention by a Prof. Smith, of Ohio,
of a process of " producing a beautiful picture
on a piece of common sheet iron, . . . equal
to daguerreotypes, and much superior in some
respects." The journal calls the pictures
" Ferrographs."
Ferrotype pictures are positives produced by
the wet collodion process, a black or chocolate
enamelled iron plate being used as a support
for the picture instead of glass. The latter needs
backing up with black paper, velvet, or paint.
The finished results have the same appearance
in both cases, but the ferrotype image is reversed
as regards right and left, and the process is there-
fore not suitable for general application. Every-
one knows that this process has been widely
used for portraiture by itinerant photographers,
since by its aid they can take and finish a por-
trait in the space of a few minutes. The photo-
grapher generally takes particular care to arrange
the sitter " full face," or in any other position
in which reversal is not at first detected. For
ferrotype work proper the operator must be
within easy reach of his dark-room, as the plates
are prepared immediately before exposure.
The process, in brief, is first to prepare the
plate with collodion, sensitise in a silver bath,
expose while wet, develop with an iron developer,
and fix in a solution of potassium cyanide ; all
formulse and working details will be found under
the heading " Collodion Process (Wet)."
The Dry Process. — ^The introduction of ferro-
type dry plates has largely displaced the old-
fashioned wet process ; itinerant photographers
use them in conjunction with automatic cameras,
which comprise arrangements for developing and
fixing, thus obviating the use of the old portable
perambulator-like dark-rooms. Ferrotype dry
plates are bought in packets and used like other
dry plates, but instead of yielding a negative
on glass they give a positive direct upon the
black iron or tin support. An example of the
developers used for such plates is :
Sodium carbonate (pure) 4 „ 200 g.
Sodium sulphite ' . 2 „ 100 „
Hydroquinone . . J ,, 12-5 „
Potassium bromide . 290 grs. 29 „
" Hypo " fixing solution
(as below) . . ^ oz. 25 ccs.
Warm water to . 20 ,, 1,000 „
Allow to stand for two days and pour off the
clear solution for use. In cold weather half the
above quantity of bromide is required. After
exposure, the ferrotype dry plate is developed
until the high lights (which appear brown on a
white background) and half-tones are well out,
and the plate is then rinsed in water and fixed
in a " hypo " fixing solution (sodium hyposulphite
4 oz., water 20 oz.). Development takes from
eight to twelve seconds in hot weather, twelve
to twenty seconds in a normal temperatiire, and
twenty to sixty seconds in cold weather. After
fixing (duration, ten to thirty seconds), the plate is
rinsed for a few seconds and dried spontaneously
or by gentle heat. It is next varnished, and
then gives the appearance of having been pro-
duced by the wet collodion process. Sediment
sometimes appears on the film after washing,
particularly when over-developed, and gives the
plate a fogged appearance ; it may be removed,
before drying, with a pad of cotton wool.
A positive on a ferrotype plate is sometimes
used by artists as a means of tracing from.
Where a photograph is not to the correct scale
a positive enlargement can be more rapidly made
than a negative and print. As the image is
reversed in relation to right and left, it becomes
correct when traced over on gelatine by scratch-
ing the outline with a needle-point and filUng
with blacklead or other set-off powder, the gela-
tine being then turned over and rubbed down on
to drawing paper or Bristol board.
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Ferrous Acetate
241
Ferrous Oxalate Developer
FERROUS ACETATE (Pr., Acitaie de fer:
Ger., Ferroacetat)
Synonyias, ferric protoacetate, acetate of iron.
Soluble in water. Pe(CHsCOO)a. Molecular
•weight, 174. It occurs as green crystals, and is
obtained by dissolving iron in acetic add. It
was occasionally used in the wet plate days,
and was then formed in solution by adding
lead acetate to ferrous sulphate, when ferrous
acetate was formed and lead sulphate pre-
cipitated.
FERROUS AMMONIUM SULPHATE (Pr.,
Sulfate de fer ammoniacale ; Ger., Schwe-
felsaures Eisenoxydulammoniak)
Synonyms, anunonio-ferrous sulphate, Mohr'a
salt. Peso, (NHj), SO4 6H2O. Molecular weight,
392. It takes the form of pale blmsh green
crystals. It is made by crystallising ferrous
and ammonium sulphate. It was used in the
old wet plate days as being a more stable salt
than the ordinary ferrous sulphate. Seven parts
of the double salt are equal to five of the ferrous
sulphate.
FERROUS CHLORIDE (Pr., Protochlorure de
fer : Ger., Eisenchlorid)
Synonym, protochloride of iron. Pe Clj 4H2O.
Molecular weight, 199. Solubilities, i in 1-4
water, soluble in alcohol. It is a greenish crys-
talline salt, rapidly oxidised on exposure to the
air into perchloride. It is made by dissolving
iron wire in hydrochloric acid. It was suggested
as a substitute for ferrous oxalate in the oxalate
developer, and was occasionally used in the
powder process.
FERROUS CITRO ■ OXALATE DE-
VELOPER
A modification of the ferrous oxalate de-
veloper suggested by Abney : —
I. — Neutral potassium
citrate . . 9 oz. 450 g.
Neutral potassium
oxalate . .2^,, 112 „
Distilled water to 20 „ 1,000 „
2. — Perrons sulphate. 4 oz. 200 g.
Distilled water to 20 „ 1,000 ccs.
Por use, mix in equal parts. Cowan suggested
the following, and it is especially suitable foi
gelatino-chloride plates, as any warmth of tone
may be obtained by variation of exposure and
developer : —
I. — Por cold tones :
Neutral potassium
oxalate . 1,200 grs. 125 g.
Neutral potassium
citrate . 400 „ 42 „
Distilled water to . 20 oz. 1,000 ccs.
2. — Por warm tones :
Citric acid . 3,200 grs. 333 g.
Ammonium carbon-
ate . . 2,400 „ 250 „
Distilled water to . 20 oz. 1,000 ccs.
3. — Por extra warm tones :
Citric acid . 4,800 grs. 500 g.
Ammonium carbon-
ate . . 1,600 „ 166 „
Distilled water to . 20 oz. 1,000 ccs,
16
4. — Iron solution :
Perrous sulphate . 6J oz. 333 g.
Sulphuric acid . | „ 12-5 ccs.
Distilled water to 20 „ 1,000 „
Por nse, add i part of No. 4 to 3 parts of
Nos. I, 2 or 3.
FERROUS NITRATE (I^r., Azotate ferreux ;
Ger., Salpetersaures Eisenoxydul)
Synonym, protonitrate of iron. Pe (NOs)^
i8HaO. Molecular weight, 536. SolubiUties, i
in 6 Water, soluble in dilute alcohol. It occurs
as greenish white crystals. It may be prepared
by dissolving iron wire in nitric acid, but the
usual method is to mix 19 parts of ferrous
sulphate with 36 parts of barium nitrate in
solution, which gives 26 parts of ferrous
nitrate. It was used in the wet collodion
days, and gives an image much whiter in
colour than does the ferrous sulphate.
FERROUS OXALATE (Pr., Oxalate ferreux;
Ger., Eisenoxalat)
Synonym, oxalate of iron. PeCj0j2H20.
Molecular weight, 180. Practically insoluble in
water, but soluble in alkaline oxalate solutions.
Prepared by decomposing ferrous sulphate with
oxalic add, but generally obtained by mixing
potassium oxalate and ferrous sulphate, in the
form of ferrous potassium oxalate.
FERROUS OXALATE DEVELOPER
One of the oldest developers for plates and
bromide papers, announced in 1877 simultan-
eously by Carey Lea and Willis, of America and
England respectively, now almost entirely re-
placed by the newer organic developers. It has
the great advantage of giving an image in pure
metallic silver — that is, wi(iout any oxidised
stain which is so often the defect of the newer
developers ; but, on the other hand, it oxidises
rapidly, and gives in hard water a precipitate
of oxalate of lime. Also, it raises the inertia
of the plate, or, in other words, it does not bring
so mudt out of a plate as do the newer developers.
In the case of bromide papers, it is necessary to
use an add bath after development in order to
prevent the deposition of basic iron salts in the
fibres of the paper ; and this disadvantage has
led to its disuse. It can be prepared most con-
veniently by double decomposition between
potassium oxalate and ferrous sulphate. The
following may be considered a standard
formula : —
I. — Neutral potassium
oxalate . .502. 250 g.
Distilled water to 20 „ 1,000 cw:.
2. — Ferrous sulphate. 6 J oz. 330 g.
Distilled water to 20 „ 1,000 ccs.
Pure sulphuric acid 10 mins. i cc.
For use, add i part of No. 2 to 4 parts of No. :.
The iron must be added to the oxalate, and never
vice versa, so that the oxalate is always in
excess, because ferrous oxalate is insoluble in
water and soluble only in excess of an alkaline
oxalate. The developer is a deep orange solu-
tion which does not keep well. Another method
of making it is by heating the oxalate solution
to boiling point and adding dry ferrous oxalate
until saturated, and then cooling and botthng;
Ferrous Oxalate Intenslfier
242
Field Camera
but the first method is preferable. Bromides
can, of course, be used as with any other deve-
loper, and the addition of a very small quantity
of " hypo," -06 per cent., acts as an accelerator.
FERROUS OXALATE INTENSIFIER
In this process of intensification the nega-
tive, after bleaching in mercuric chloride, is
blackened by the application of the ferrous
oxalate developer, which reduces the white
silver and mercurous chloride image to metallic
silver and mercury. The advantage of this
process is that any amount of density may be
obtained by repeating the bleaching and blacken-
ing, each repetition adding more mercury, and,
so far as is known, the image thus obtained is
quite stable, and there is no selective action
either in the high lights or shadows. It is
important to wash thoroughly, preferably in
water acidified with hydrochloric acid, after
bleaching and before blackening. J. Chapman
Jones recommends bleaching the well washed
negative in a cold saturated solution of mercuric
chloride to each ounce of which one or two
drops of strong hydrochloric acid have been
added. Afterwards, the negative is washed for
one hour, blackened with a developer composed
of 6 parts, by measure, of a saturated solution
of potassium oxalate and i part of a saturated
solution of ferrous sulphate.
FERROUS POTASSIUM OXALATE (Pr.,
Oxalate de potassium ferreux ; Ger.,
Kalium-Eisenoxalat)
Synon3rm, potassio-ferrous oxalate. KjFe
(CjOiJjHjO. Molecular weight, 328. Obtained
in the ferrous oxalate developer by the admix-
ture of ferrous sulphate and potassium oxalate.
If the sodium salt is used, ferrous sodium
oxalate results.
FERROUS SODIUM OXALATE {See the
preceding article.)
FERROUS SULPHATE (Pr., Sulfate de fer ;
Ger., Schwefelsaures Eisenoxydul)
Synonyms, sulphate or protosulphate of iron>
green copperas, green vitriol. Pe SO^ /HjO-
Molecular weight, 278. Solubilities, i in i-8 cold
and '5 boiling water, insoluble in alcohol. It
occurs as large bluish green crystals, efflorescent
in air, obtained by treating iron wire with dilute
sulphuric acid. It is used as the developer for
wet collodion plates and to prepare the ferrous
oxalate developer. On exposure to air it becomes
oxidised and covered with a rusty powder of
basic sulphate, which shoiUd be rinsed off before
the crystals are dissolved.
FERROUS SULPHATE DEVELOPER
A developer used for wet collodion plates,
of which the following may be considered a typical
formula : —
Ferrous sulphate
Glacial acetic acid
Alcohol .
Distilled water to
350 grs. 40 g.
310 mins. 30 CCS.
310 .. 30 „
20 oz. 1,000 ,,
supposed to have some special advantage. The
development of a wet plate differs from that of
a dry, in that it is what is termed " physical
development " ; that is to say, the latent image
itself is not developed, but the silver nitrate
adherent to the film is reduced by the ferrous
sulphate and deposited in situ on the latent
image, so that the growth of the image is from
the top and not from the bottom or in the film,
as with the chemical development of a dry plate.
FIELD CAMERA (Fr., Chambre de touriste,
Chambre de voyage, Chambre portative ;
Ger., Reisekamera, Landschafts-hamera)
Field cameras are necessarily designed to
obtain the maximum of compactness and the
minimum of weight consistent with steadiness.
A, Square-bellows Field Camera
Since they wiU be more exposed to atmospheric
and climatic influences than indoor cameras,
the workmanship must be good, and the wood of
excellent quaUty and well seasoned. Rigidity is
of great importance. When extended, there
should be no shake or looseness at either front
or back if grasped firmly with the two hands.
The choice of pattern depends somewhat on the
nature of the work to be undertaken.
For technical, engineering, and suchlike pur-
poses, a square bdlows camera of somewhat
heavy construction is usually preferred. Illus-
tration A shows an apparatus which can be
used in the studio or on a tripod outdoors.
The rigid front is suited for carrying heavy
lenses, while the bellows racks backwards from
the front, a useful movement in wide-angle work,
where part of the image is sometimes liable to
be cut off by the projecting baseboard of the
A great many additions have been recom-
mended, such as copper or magnesium sulphate,
sugar, glycerine, albumen, etc, all of which are
B. Tapering-bellows Field Camera
ordinary type of camera. The back focusing
movement is also valuable in photographing
small objects at close quarters. The baseboard
folds over the focusing screen when closed, thus
preventing it from getting broken.
A lighter, yet still substantial, type of camera,
suitable for general work out of doors, is illus-
trated at B. The swing front is useful when
Field Camera
243
Figure Studies
photographing high buildings, and a sufficient
amount of rise is also provided for. The back,
which can be swung either horizontally or vertic •
ally, is arranged to slide close up to the front
if desired, for use with wide-angle lenses. A
well-known camera, noted for its great range of
movement and particularly adapted for archi-
C Field Camera with Extreme Rise of Front
tectural photography, is shown at C. The back
and front may be swung in every imaginable
position with ease, and at once rigidly damped
or locked. The extreme high rise of front wiU
be noticed. The front not only rises and fsills
by rack and pinion, but may be moved horizon-
tally or diagonally by means of a compound
sliding and revolving device.
A representative example of a moderate priced
triple-extension camera is illustrated at D. A
triple extension allows the bellows to be racked
out to about three times the focal length of the
average lens used with a camera of a given size,
and is an invaluable feature when using long-
focus lenses.
The cameras above mentioned are illustrative
of the chief tendencies of design in modem field
apparatus. A notable advance is shown on
earlier ideals of construction, especially with
regard to lightness, compactness, and the pro-
vision of mechanical conveniences. Double
D. Triple-extension Field Camera
book-form dark slides are usually preferred with
field cameras, and they should work without
either stiffness or looseness. {See also " Camera,"
"Dark-slide," etc.)
FIELD, DEPTH OF
tion, etc.")
{See "Depth of Defini-
FIELD LENS
The lower lens of a microscope eyepiece that
receives the image from the objective, as ex-
plained under the heading " Eyepiece."
FIELD OF LENS
The imaginary surface at which the sharpest
image that can be given is formed. With a
theoretically perfect lens, this would be a. plane,
but in practice the field is usually concave,
occasionally convex, and in the case of most
anastigmate, plane with an annular depression
at a considerable distance from the centre. In
the theoretically perfect field all the rays, axial
and marginal, come to a focus on a plane
which is at right angles to the axis of the lens.
This condition is fulfilled by one or two of
the modem anastigmats, especially those made
for copying. The most ordinary type of field
is concave, the concavity being away from the
lens. Before the introduction of the special
Jena glasses, this was considered normal, in
fact, inevitable, for so eminent an optician as the
late J. H. DaUmeyer stated that a lens having a
perfectiy flat field " does not exist, and cannot
be made." The amount of curvature of field
varies greatiy in dififerent types of lenses, being
most pronounced in portrait lenses of large
aperture, less in single landscape lenses, and
least of all in well-constructed rapid rectilinears.
Other things being equal, it will be found that
separating the elements of a double combination
lens has a tendency to flatten the field, at the risk
of increasing the astigmatism present ; while in
the case of single lenses the curvature is reduced
to a minimum by placing the diaphragm as far
as practicable from the lens. The field of a
typical anastigmat is flat in the centre for a con-
siderable distance from the axis, then comes a
" dip " and then a recovery to almost the original
plane. A field that is convex towards the lens is
rarely found in practice, generally occiirring in
modem anastigmats whici have been slightiy
over-corrected for flatness in the endeavour to
attain other qualities.
FIGURE STUDIES
Portraiture is mainly directed to securing a
" likeness," while figure studies are generally
intended to show character, costume, occupation,
and so on. Renderings of figures in homely
surroundings, or engaged in somewhat humble
everyday occupations, are generally classed as
" genre." The great thing to avoid in successful
figure work is any suggestion of posing or of
camera-consciousness. Sometimes figures are
dealt with as what may be called character
studies, in which case care must be taken that
position, Ughting, view-point, and general treat-
ment are ^1 directed to securing the particular
characterisation desired. In other cases the
figures, singly or collectively, are treated in
" settings," or surroundings suggestive of their
habits and employments. Whatever their occu-
pation, work, or play, they should appear
natural, and not suggestive of merely perform-
ing for the occasion. This does not imply that
a certain amount of posing and arrangement
must not be resorted to, but that there should be
no evidence of such.
In the case of character studies, careful observ-
Figures in Landscapes
244
Film
ation of the subject is necessary to realise pre-
cisely what is to be rendered in each particular
case. Study is also equally essential where
occupation is to be suggested. There are cer-
tain poses and movements that are more effec-
tive and suggestive than others, and these must
be watched for and noted. The sweeping move-
ments of a mower, for example, cannot be shown
completely, but the " arrested motion " should
be suggestive of action and not of a stationary
pose. A blacksmith with his hammer poised in
the air is more suggestive of energy and force
than if his hammer is resting on the hot iron.
In every such case the most characteristic
position must be diligently sought for. The
human interest always makes figure studies
attractive, but it is extremely difficult to secure
iinquahfied success without careful observation
and continued practice and experience. It is,
in fact, a branch of photographic work that
demands special aptitude, but one that well
repays the utmost care that can be devoted
to it.
FIGURES IN LANDSCAPES
There are some landscape subjects that appear
quite complete without figures of any kind ; in
fact, in some cases, the introduction of the
smallest figure would be detrimental. Frequently,
however, a landscape without figures gives the
impression of a mere setting — an empty stage.
It has been said that in a perfectly composed
landscape there is one, and only one, correct
position for a figure or figures. It is, in fact, an
exceedingly difficult matter to introduce figures
into a landscape with complete success. They
must be neither too prominent so that they
attract undue attention, nor too insignificant
so that they fa0 to take their place in 5xe com-
position. Above all, the figures must be appro-
priate to their surroundings ; they must not
only be in the picture, but of it.
The relation which figures bear to the land-
scape varies. They may be so unobtrusive as
merely to convey a necessary suggestion of life,
or they may be so prominent as to claim more
attention tian the actual landscape. In the
latter case, they are rather figures with land-
scape, although the landscape is an important
integral part of the whole picture. When several
figures are included they should not be scattered
indiscriminately, but should bear some relation
to each other as weU as to their surroundings.
To this end it is helpful to study the character,
placing, and arrangement of figures in land-
scapes by good artists, and also carefully to
examine photographic examples in which figures
have been satisfactorily introduced.
FILIGRANE
A photographic process for water-marking
paper, invented by W. B. Woodbury. A gelatine
relief of the design is made by the Woodbury-
type process, and when thoroughly hard and dry
is passed through a rolling press with the paper
to be water-marked. The result is that the
paper is pressed thinner in some parts than in
others, the thin parts appearing much lighter.
On holding the paper up to the light a water-
marked image is seen. The reUef can be used
a large number of times.
FILM (Pr., PelUcuU ; Ger., Film)
This term is applied to the surface which
carries the sensitive silver salt : thus the film
side of a paper or plate (Fr., Pellicule ; Ger.,
Schicht) ; but it has also become very generally
applied to distinguish any flexible support from
glass plates. The subject of flexible supports
can for historical purposes be most readily
dealt with by dividing it into the following
classes: (i) negative paper; (2) stripping
films ; (3) cut films ; (4) roll films.
Negative paper was, of course, one of the
first forms of negative material, and was intro-
duced by Fox Talbot, in 1839, who also sug-
gested making the finished negative more trans-
lucent by waxing it. Le Gray, in 1854, intro-
duced the wax paper process, in which the
paper was waxed prior to sensitising. In 1849,
Fox Talbot and Malone took out a patent for a
resin-coated paper which was used by Newton
in 1850, Le Gray in 1852, and Tillard in 1854.
Crawford in 1854 used coUodion-coated paper,
and Geoffray in 1856 impregnated paper with
rubber solution, fastened it to a glass plate
coated with glycerine, coated it with collodion,
and afterwards stripped it. Corbin in 1858 used
collodionised paper ; and Marion in 1863 also
used dry collodion paper. I,aoureux in 1878
used a wax paper, which was rubbed with
French chalk, coated with collodion according
to the bath process, and the fixed negative was
squeegeed down to a sheet of gelatinised glass
whilst still damp, allowed to dry, and then
stripped from the glass. In 1879, Ferrier, oi
Paris, patented a film of collodion and gelatine,
and in the same year Stebbing intiroduced
gelatino-bromide films on a hardened gelatine
skin. Palmer, of Liverpool, in 1881 produced
a film of gelatine and oxgall. In 1882 Morgan,
of Morgan and Kidd, introduced negative paper,
and Wamerke in 1884 made paper coated on
both sides with emulsion, so as to avoid the
curling of the paper and negatives. In 1885
Woodbury and Vergara utihsed a paper made
transparent with resins, etc. ; and ordinary
negative paper was produced by Wilde, of
Gorhtz. Eastman in 1885, Moh in 1898,
Lumi^e, the Thornton Film Co., in 1900
(paperoid films), and Gaedicke in 1889, used
thiu varnished tracing paper.
Stripping films were made by Mihnson in
1877, Perran and Pauli in 1880, Thiebault in
1886, Wilde in 1887, Moh in 1898, Balagny in
1898, Hofmann in 1901, Goldbacher in 1901,
the Thornton Film Co. in 1901, and Wellington
in 1901. In all these the paper was prepared
either with a soluble gelatine film, or wax,
rubber, or resin, which allowed the finished
negative to be stripped from the paper sup-
port.
Cut celluloid .films were first suggested by
Fourtier (Prance) in 1881, but Carbutt (U.S.A.)
seems to have been the first to introduce them
commercially in 1888, though he had made some
in 1884. In 1882 Pumphrey (Birmingham)
introduced a "flexible glass" support, consisting
of gelatine and collodion, and Moh in 1890,
and Raphael in 1892, used thiu sheets of mica.
Froedman in 1887 introduced a support of
bichromated gelatine which had been rendered
insoluble by exposure to light ; Stebbing in
Film
24S
Film Manipulation
1879 used a hardeaed gelatine film between two
films of collodion; and Wilde in 1883 used
insoluble gelatine and collodion. Balagny in
1886 used alternate layers of collodion, varnish,
and gelatine. In recent years most plate
makers have produced cut celluloid films one-
hundredth of an inch in thickness.
Roll films seem to have been first suggested
by Melhuish and Spencer in 1854, and by
Merritt and Wamerke in England and Captain
Barr in India in 1875. Barr was the first
to suggest the present system of usiag a black
material at the back of the film, which was
continued beyond the ends of tie sensitive
material (then paper) to protect it from light.
Roll celluloid films appear to have been con-
ceived first by Goodwin (U.S.A.) in 1 887, although
the patent was not granted till 1898 ; wli2e
this patent was lying in the American patent
ofiEice, Reichenbach, of the Eastman Kodak Co.,
applied for a similar patent, which, like Good-
win's, included the " non-curling " layer of
gelatine on the back of the celluloid. Cody, of
the Blair Camera Co., patented in 1894 the
use of the now well-known daylight loading
cartridge. Many of the manufacturers who are
mentioned as making cut stripping films also
prepared roll films, but the celli3oid, about
TTf^j- in. thick, is now almost universally used.
The treatment of films, as regards develop-
ment and fixing, is precisely the same as for
plates. The only point to which attention should
be directed is the keeping power of the emulsion
when this is coated on celluloid, and thoi^gh
this is generally recognised to be practically
limited to twelve months after coating, instances
have been recorded of films — especially cut films
— being fit for use after five years. This possibly
can be explained by the d&erent state of dry-
ness of the support.
In process work, the word " film " is appUed
in several ways. There is the film obtained by
stripping negatives. The " Ivotus " film was
introduced by Mawson and Swan to facilitate
the obtaining, by stripping, of film negatives,
these films being of hardened gelatine of sub-
stantial thickness.
The gelatine films known as " Shading
Mediums," often simply called " films," have
lines, stipples, or patterns moulded on their
surface, so that they can be inked and the
pattern transferred by rubbing down with a
stylus, or by pressure with a small rubber
roller.
The " Norwich Film " is a transparent gela-
tine film grained on one side for drawing upon
in pendl, crayon, or ink, according to the degree
of fineness or coarseness of the grain. By making
the drawing with a greasy ink the surface can
afterwards be flowed over with a non-actinic
alcohol soluble varnish, which will not aSect
the drawing. The latter can then be washed
away with turpentine, leaving the lines or granu-
lations transparent, so that the film becomes a
negative which can be printed from by any
photographic process. If the film is drawn on
with lithographic crayon or lithographic transfer
ink, the drawing may be transferred in the usual
Uthographic manner by damping the gelatine
and mnning through a press in contact with
stone or zinc.
FILM CAMERA (Pr., Chambre d. pellicule:
Ger., Filmhamera)
In its primary sense, a camera specially de-
signed for use with films, whether flat or in the
roll. Such cameras are mostly of the hand type,
and typical examples of the various kinds will
be found under the heading " Hand Camera."
Any ordinary camera may, however, be used
with films by the simple expedient of employing
a roll-holder instead of a dark-slide ; or, if flat
films are preferred, a. suitable changing box,
adapter, or film pack may be used.
FILM CARRIER (Pr., Porte-pelUcule : Ger.,
Filmrahmen)
A kind of sheath, usually of thin metal
turned over at the edges on tluree sides, used for
holding flat films in dark -slides or in hand
cameras. Some carriers are indented from the
back so that the film is kept dose to the front,
in order to be in register with the focusing screen ;
others require the insertion of a piece of black
cardboard between the film and the carrier.
Another type of carrier consists of a flat metal
back over which folds a hinged frame. The film
is laid on the back and the frame closed down
on it, securing itself by a dip at the edge.
The term film carrier is also sometimes applied
to roll-holders and adapters for holding films.
FILM HARDENERS (See "Hardeners.")
FILM HOLDER (Pr., Pince a pellicule; Ger.,
Filmshalter)
A metal or wooden clip used to hold the ends
of roU films when devdoping in the length.
Another kind consists of a flat piece of metal
turned over at two edges, to hold a short por-
tion of film, cut from the length, flat during
devdoping. The term film holder is also some-
times given to the roller slide, or roll-holder
(which see).
FILM MANIPULATION
The use of films, both flat and Tollable, has
become during recent years more and more
popular, and there has been much discussion
as to whether these or plates are the more
advantageous, although, results alone con-
sidered, there is no difierence between them.
The developers, fixers, intensifiers, etc., suit-
able for dry plates will suit films also, for the
reason that the emulsions are the same although
the support is glass in the first case and cellu-
loid in the second.
Flat Films. — Plat films are treated exactly
as though they were plates. There may be
difficulty in keeping them wholly immersed
in the solutions, on account of their buoyancy,
which tends to make them float on the surface
of the Uquid, thus leading to uneven develop-
ment, markings, and yellow stains. It is best
first to place the required amount of developer
in a dish and to slip the film face upwards into
it well under the surface ; or the film may be
placed in a dry dish and the devdoper poured on.
By rocking tiie dish the film is kept on the
move, and the devdoper made to flow evenly
over it. Some workers use a narrow wooden
frame A, which tightly fits the bottom of the
dish ; the film is then pinned face upwards to
Film Manipulation
246
Film Manipulation
the frame and the developer poured on. But
this method ought not to be necessary except
that films tend to curl very much when wetted.
The disadvantage of using a false bottom entirely
of wood is that unless it fits very tightly in the
bottom of the dish it may float on the surface
and do more harm than good.
Cutting Roll Films. — Only when roll films are
threaded, the whole length of film being worked
backwards and forwards through the developer,
which should cover the bars. In a contrivance, C,
embodying the same principle, a bent rod carries
a roller acting as a bar to keep the film under
the developer ; with both these contrivances it
is necessary to hold one end of the strip in each
hand after the manner shown at P. A con-
A. Frame to fit Develop-
ing Dish
B. Dish with Two Cross-
bars.
C. Dish with Roller
unrolled in a proper way is there little or no
danger of cutting through the images. The
cutting up of a roll film before development is
necessary only when each exposure is to be
developed separately, after the manner of fiat
films. D shows the proper and E the improper
method of cutting up a roU film. The roll should
be held in the left hand and the end of the
wound-up film pulled with the right, the black
paper being on the top and the film beneath.
Only one number should be unwound at a time,
and when the division marks at the edges are
seen (between the numbers), the film is placed
in contact with the black covering paper and
both cut through evenly with a pair of scissors ;
by this method the paper and film are in con-
tact and in agreement as in the camera. The
wrong way of cutting up a film {see E) is to bring
the loose white film to the top of the black
paper, because when this is done the images
wifl invariably be cut through, as the division
markings will not be true. The film must be
swung round below the paper, in the direction
shown by the dotted lines.
Developing Roll Films. — The object of cutting
FILM
D. Proper Method of Cutting Film
up films is to avoid the awkward operation of
developing them in the strip form. With the
shorter lengths there is, however, no difficulty
in developing them whole, but when longer than
36 in. it is better to cut them up or to use one
of the numerous film-developing devices on the
market, which, of course, are suitable for the
shorter lengths also. At B is shown a dish
having two cross-bars, under which the film is
trivance on a different principle is shown at G ;
one end of the film is attached to a spring
drum, which is made to revolve, and the film
passed through the developer by alternately
pulUng and slackening the other end. These
and other accessories are very convenient, but
in their absence the following method may
be adopted. A dish is filled with the developer.
The whole length of film is detached from the
black paper, one end is taken in each hand, and
the filrn is passed, sensitive (matt) side down-
wards, through the developer, a see-saw move-
ment of the arms being maintained, and the film
passed to and fro through the developer until
the whole series of images is fully developed. It
is a good practice to develop the whole strip
imtil the barest outlines are visible, and the
spaces dividing the pictures can be distinctly
seen ; the film can then be cut with scissors, the
partly developed pictures placed in cold water,
and each one developed separately in an ordinary
>'
E. Incorrect Method of Cutting Film
flat dish. It is advisable to keep the partially
developed films on the move while in the water,
as, if allowed to stand, they may remain curled
up or on the surface, in which case markings and
stains would appear.
Fixing. — Films may be fixed in the strip, or cut
up. Even if the film is developed in strip form,
it may be advisable to cut it up before or during
fixing, for the sake of convenient handling ; but
Film Manipulation
247
Film Stripping
opinions differ on this point. Films need more
care than plates when ^ing, because, should the
films float on the surface of the fixer, exposure
to the air will cause markings, yellow stains, etc.,
which cannot easily be removed. An acid fixing
F. Developing
Film
H. Film held in
Cork CUp
bath (potassium metabisulphite and " hypo ")
is better than an ordinary fixing bath of plain
"hypo," as the metabisulphite prevents stains.
Washing and Drying. — Kims cannot be washed
and dried in a rack like plates, and some trouble
is often met with in keeping them under the
surface of the water. Numerous devices have
been introduced for washing films properly. A
useful contrivance is shown at H ; a cork is cut
in halves lengthways, after cutting a notch in
the top ; then an indiarubber band is placed
around the halves as shown, the whole now
forming a clip. The film is inserted in the cork,
which will float on the surface of the water and
I, Films Pinned up to Dry
hold the film beneath the surface. Films are
best dried by pinning them, face (emulsion sur-
face) outwards, to a sheU, as shown at I, or
special clips may be used in place of pins. All
flat films should be kept under slight pressure
when not in use. If a film is stored in a toll, it
should always be wound sensitive surface outside,
as it will then lie flatter when printing. Films
are better varnished, and for wet films a borax
and gum lac solution is best, but for dry films a
dammar varnish may be used. {See " Varn-
ishes.") By the aid of special tanks, the develop-
ment of films may be carried out in daylight.
FILM PACK
A device for exposing a number of cut films
successively. A holder, somewhat similar to a
dark-sHde, is loaded with a packet of cut films.
This can be done in daylight. Projecting from
the packet are paper tabs, and by pulling these
out and tearing them off the films are successively
brought into position for exposing, and then
carried round to the back of the pack. When all
the films have been exposed, the pack may be
removed from the holder (still in daylight), and
a fresh one substituted. This provides a con-
venient means of exposing an indefinite number
of cut films without having to resort to a dark-
room. Some cameras are made for using a fihn
pack only, in which case the holder is usually
an integral part of the camera ; but the holder
or adapter is also siiitable for use on other
cameras interchangeably with dark slides. A
special tank has been devised for the develop-
ment of cut films as used in the pack, although,
of course, its use is a convenience rather than a
necessity.
FILM SHEATH (Fr., ttui d peUicule, Porte-
pellicule ; Ger., Filmscheide, Filmrahmen,
Blechrahmen)
A metal sheath for holding flat films in maga-
zine hand cameras ; practically identical with
certain forms of film carrier (which see). Ordin-
ary plate sheaths may be used for films if a
piece of black cardboard is inserted behind each
film. In some patterns of hand cameras, the
changing mechanism is designed for use with
sheaths of a definite thickness, and will not work
with thinner sheaths.
FILM STRIPPING
Films may easily be stripped from their glass
supports and transferred as required, this course
often being necessary when the glass of a nega-
tive is cracked and the film is imdamaged. In
reversing a negative for single transfer carbon
or collotype work, the stripping method is also
useful. If desired the film may be enlarged in
course of transference, as described under the
heading " Enlarging by Stripping." In cases
where it is not desired to enlarge the film, the
hydrofluoric acid used for stripping must be
diluted with methylated spirit, whidti, to some
extent, counteracts the tendency to expand.
The following is suitable : —
Methylated spirit . 5 oz. 1,000 ccs.
Water . . i^ drms. 37-5 „
Glycerine . . i| „ 37'5 „
Hydrofluoric acid i — 1| „ 25 — 37'$ „
Make this up without the acid and keep as a
stock solution, adding the acid just before
using. The negative to be stripped should not
have been varnished, or, if it has been, the
varnish must be removed before treatment. It
should be noted that hydrofluoric acid attacks
Film Stripping
248
Filter Paper
glass, and any mixture containing the acid must
therefore be kept in an iudiarubber or ebonite
cup or dish, or in a glass vessel that has been
coated internally with paraffin wax (the wax is
melted, poured in and out again, leaving a coat-
ing on the sides). Some sheets of waxed paper
are also needed before the work of stripping can
be begun, also a glass plate coated with gum or
gelatine on to which the film is to be transferred,
for owing to the use of a large proportion of
spirit the removed film will not adhere to plain
glass. Lay the negative to be stripped on a
perfectly level surface, and with the aid of a
straightedge, and by means of a sharp penknife,
cut through the film to the glass at -J- in. from
the edge all round ; then pour enough of the
stripping mixture on to the film and spread over
evenly with a camel-hair brush, or a piece of
paper or cotton-wool. In about five minutes
the film will become loose, and the narrow bands
of film at the edges may be stripped away, this
being a good test as to how the stripping mixture
is working on the film. If after five minutes the
film refuses to move, a little more acid may be
added to some more of the solution, and spread
over the film. No attempt must be made to
hasten the loosening of the film at the edges by
pulling ; the acid must do all the work. When
the margin comes away without the slightest
resistance, it is a sign that the main film is in
a state to be removed. A penknife may be in-
serted under one comer of the film just to see if
this will come away easily from the glass. The
film being still on the plate, drain off superfluous
acid, and pour on more of the stripping mixture,
this time without the acid. This in turn is
poured off, and a sheet of the waxed paper
brought down upon the loosened film, and lightly
squeegeed down. The film wiU adhere per-
fectly to the waxed paper, and they can be
removed together on to the new glass and
squeegeed over lightly ; the paper is then pulled
gently away, leaving the film upon the prepared
glass.
When a reversal — as regards right and left —
is wanted, the film on the original negative
should be transferred to a plain piece of white
paper covered with the spirit mixture minus
the acid ; the waxed paper is then laid over
the removed film, and the two papers, with the
film in between, squeegeed into contact; the
papers are then separated carefuUy, in such a
maimer that the loose film remains on the waxed
paper ; it is then transferred to the prepared
plate in the manner described above, care being
taken to keep the film flat and in perfect contact
with its support.
Owing to objections to the use of hydrofluoric
add, many prefer to do without it, and they
employ some such method as the following. The
film is liable to slight enlargement, by about
one-thirtieth of its length, which matters little
if it has been cut round the edges in the manner
already described. The negative is placed in
the following bath : —
Caustic soda
Formaline
Water
20 grs. 23 g.
20 drops 21 CCS.
2 oz. 1,000 „
rolled back with the finger. But do not do so ;
instead, when it appears to be loose, transfer to
the following bath : —
Glycerine . . 60 — 70 drops 63 — y^ ccs.
Hydrochloric acid . 50 „ 52 ,,
Water . . . 2 oz. 1,000 „
in which it can be entirely detached, and as it
floats in the liquid either side may be attached
to the new glass. In order to ensure the film
sticking to its new support, it is advisable that
the following substratum should be applied to
the glass : —
Formaline
,
. 10 drops
I cc.
Gelatine .
,
• 4 grs.
4-5 g.
Water
.
2 oz.
1,000 ccs
Swell the gelatine in the water, dissolve by
heating, and add the formaline ; coat the glass,
allow to dry, transfer the wet fiilm to it, press
down, and allow to dry naturally. A fixed
and washed unexposed dry plate also serves as
a support.
Films are removed from celluloid supports by
soaking in the caustic soda and formaline mix-
ture already given, and then in the hydrochloric
acid and glycerine bath ; the films, slightly
enlarged, are washed and transferred to glass
or celluloid.
A convenient method of using hydrofluoric
acid for stripping is to manufacture it as
required, which can be very easily done by
making a solution of sodium, ammonirun or
potassium fluoride, about 10 grs. to the ounce of
water (20 g. to 1,000 ccs.), and acidulating with a
few drops of some strong acid, such as sulphuric
or nitric, applying the mixture to the nega-
tive. Hydrofluoric acid is generated and strips
the film, and the solution may be thrown away
when it has done its work. The dry fluorides
keep well in ordinary glass bottles.
FILMOGRAPH (Fr., Filmographe ; Ger., Fil-
mograph)
The name given to an early pattern of film
camera by Humphrey.
FILTER {See " Colour Screen or Filter.")
FILTER PAPER (Pr., Papier d filtrer ; Ger.,
Filtrierpapier)
Paper folded into a fimnel for the purpose of
0tering liquids. Practically only two kinds of
filter paper are known to photographers, the
The formaUne toughens the film, and in about
ten minutes the film could, if it were desired, be
Methods of Folding Filter Papers
white and the grey, cut in circular form. They
are sold in packets of one hundred, the size
ranging from about 2^ in. to 20 in., and the
prices from about 3d. to 2S. 6d. per packet.
There are many ways of folding such papers
Filter, Vacuum
249
Finger-print Photography
into cones for fitting funnels, two of the most
general being here illustrated. A shows the
commonest style, the paper being first folded
into halves and then into quarters ; it is then
placed in the funnel and one side opened out.
In B the circle is first folded into halves and then
laid flat again, leaving a crease to show the
diameter. The ends of the diameter are then
brought together and the halves opened out.
FILTER. VACUUM
A device by means of which liquid is forced
through a filtering medium by atmospheric
pressure.
A simple form of filter for viscous fluids, such
as the flsh-glue solution used by process workers,
is that shown at A. A strong glass flask of about
one litre capacity has a nipple connection blown
into its side near the neck. To this nipple a
Sprengel " pump " of glass is attached by means
of a rubber tube. The construction of the
"pump" is shown at B. The inner tube is not
continuous, but consists of two tapering tubes,
A. Vacuum Filter
B. Sprengel Pump
one being sealed to the upper end of the outer
tube and the other to the lower end, their tapered
ends meeting and being enclosed one within the
other for a short distance. The air drawn from
the flask can thus pass between them. The
vertical nozzle of the " pump " is connected with
a water-tap. The rubber tubes must be tightly
bound on, or they will be blown ofi by the pres-
sure. The funnel containing the filtrate is
thrust through a rubber bung placed in the neck
of the funnel, and it is desirable to have a per-
forated porcelain plate in the funnel to prevent
the filtering medium, which may be cotton-wool,
glass-wool, or felt, being sucked down the neck
of the funnel. The filtrate having been poured
in, the water-tap is turned on and the rush of
water through tbe " pump " draws the air out
of the flask, creating a vacuum in it. Thus the
filtrate is powerfully sucked through. It is
desirable to have a dip on the tube leading from
the flask to the " pump," so that the tube can
be pinched when Uie water is turned oS, or the
water in the tube will be sucked back and dilute
the filtered liquid.
FILTRATION (Pr., Filtration; Ger., Fil-
trieren)
A process used to remove from a liquid or
solution any insoluble or extraneous matter.
Usually an tmsized, pure, porous paper is used.
{See " FUter Paper.") For ordinary purposes
a small tuft of absorbent cotton-wool stuffed
into the neck of a funnel wiU usually suffice.
For filtering emulsions well-washed swansdown,
or a felt filtering bag, may be used. It should be
noted that developers should only be filtered —
or strained, to use a more correct term — through
loosely packed wool, otherwise they may oxidise.
Glass-wool (finely spun threads of glass) is used
for filtering collodion or corrosive liquids which
would attack paper or cotton-wool.
FILTRATION, UPWARD
A method of filtration which it is convenient
to adopt in the albumen process. A glass
cylinder, open at both ends, has two thicknesses
of washed muslin tied over one of the ends.
The albumen is placed in a vessel slightly larger
in diameter than the cylinder, and Sie latter is
then lowered into the vessel, muslin end down-
wards. The weight of the cylinder forces the
albumen solution to pass upwards through the
mushn into the cylinder.
FINDER, VIEW (See " View Finder," " Direct
Finder," " Iconometer," etc.)
FINGER - PRINT PHOTOGRAPHY (Pr.,
Photographie A marque de doigt : Ger.,
Fingerspur Photographie)
The photography and systematic registration
of finger-prints has become of immense import-
ance in tiie detection of crime. The meUiods
employed may be divided into two classes: (i)
those used when the individual whose finger-
prints are to be examined or registered is pre-
sent to give more or less voluntary assistance ;
and (2) iiose in which the finger-prints have been
involuntarily left behind by Uieir originator.
The procedure adopted at New Scotland Yard
under the first circumstances is very simple. The
best black printers' ink is spread in a thin, even
film on flat tin-plate or copper by means of a
roller. The finger to be recorded is pressed
down Ughtiy and steadily on the film of ink,
taking care not to move it sideways at all. After
a few seconds the finger is raised and pressed
down on a smooth white card or paper, when a
sharp, clear impression should result. This is
known as a " plain " impression. Another kind
is obtained by placing the bulb of the finger on
the inked slab, facing to the left, and turning
it gently over until it faces to the right. The
finger is then pressed gently on the paper, roll-
ing it from left to right as before, thus making
what is called a " rolled " impression. With an
unwiUing subject, trouble may arise from the
finger being deliberately moved.
For experimental work, a good substitute for
the above method is allow a drop of printing ink
to fall on a smooth card or glass, and to spread
it out with a finger. Finger-prints on white
paper may be photographed on a photo-mechan-
ical plate, giving a short exposure to secure
contrast and developing with hydroquinone.
Prints from the negatives may be made on gas-
light paper. Another and quicker way is to have
the inked finger pressed on a dean sheet of glass
instead of on paper. Several thicknesses of
gummed paper in strips are then stuck on the
glass at the sides, and it is placed in a printing
frame. In the dark-room, a slow, ordinary
Finger-print Photography
250
Finishing Photographs
plate, backed, is laid film side downwards on the
glass, the gummed strips serving to protect the
film from Sie still wet ink. Having inserted the
back and fastened the frame, an exposure of
about half a second is given at two feet distance
from a fish-taU gas burner. This may be done
by turning down the gas to an almost invisible
blue point, holding up the frame, and then
turning the gas up and off as rapidly as possible.
On development with hydroquinone a good
sharp negative should be secured. The frame
must, of course, be kept still. The prints here
shown were obtained from negatives made in
this way; A, B, C, and D are finger-prints, E
and P being thumb-prints. A and B are from
the same finger at difierent times ; the lines will
be found to tally, and the mark of a slight cut
at X is plainly seen in both.
If, however, the finger-prints have to be
searched for patiently and carefully, and are
eventually found in awkward places, on un-
Another class of finger-prints which call for
great care, since the record is so easily disturbed
and lost, are those in dust. If on a dark sur-
face, these are readily photographed with a
direct front lighting. When tt.ey occur on a
window-pane or other colourless glass, a dark
background should be placed at the back, a
short distance away, and the light should come
obliquely from behind. In rare cases semi-
invisible finger-prints may sometimes be ren-
dered conspicuous by chemical treatment, if
there is any idea of the occupation of their
suspected producer. Thus, for example, a
tanner fresh from work might reasonably be
expected to leave traces of tannin in his finger-
prints, which, under favourable conditions, could
be rendered black by treatment with a solution
of a ferric salt.
It is found that a solution of silver nitrate,
of say 6 per cent, strength, will occasionally
cause the appearance of an imsuspected finger-
c D
Finger and Thumb Prints
favourable surfaces, and in aU probability faint
and nearly invisible, the work becomes much
more difficult. When trouble arises owing to
any unusual colour of the ground on which the
finger-print occurs, an orthochromatic plate
must be used in conjunction with a suitable
colour filter, to secure contrast, each case being
treated, of course, according to its particular
requirements.
The majority of involuntary finger-prints are
greasy ones. To photograph these, if on a Ught
surface, such as china, enameUed furniture, etc.,
they should be dusted lightly with dry, finely
powdered plumbago or graphite ; a flat, broad
camel-hair brush is charged with a little of the
powder, and, holding this a short distance above
the finger-print, the handle is tapped gently
with the forefinger of the disengaged hand. Or,
instead, the hand holding the brush may be
nudged or shaken. The surplus powder is care-
fully blown away with a small bellows ; on no
account should the breath be used. Greasy
finger-prints on a dark surface — old oak furni-
ture or black ironwork, for instance — may be
treated in the same manner, using, however,
dry, finely powdered whitelead instead of the
plumbago.
Finger - prints in blood on a dark surface
should be placed where there is no extraneous
light, as in a cellar or dark room, and lit from
the front with magnesiimi ribbon or the electric
arc, of course screening the direct rays from
the lens of the camera.
print on ordinary paper, or will intensify a semi-
invisible one.
FINGER TIPS OR STALLS (Pr., Doigtiers ;
Ger., Fingerlinge)
Rubber sheaths, like the tips or fingers of
gloves, worn when developing, working in wet
collodion, sensitising with bichromate, etc., to
protect the fingers from staining and as a safe-
guard against the entrance of poisonous chemicals
into cuts or wounds.
FINISHING PHOTOGRAPHS
Photographs are frequently finished with
crayon or water-colour, and of recent years,
the aerograph (which see) has been extensively
employed for the purpose, this providing an easy
means of introducing soft backgrounds. While
details of the actual methods will be found under
the heading " Working-up Prints," it may be
said here Siat photographs to be finished by
hand should be on matt paper, as otherwise the
touching-up shows prominently. Ordinarily, the
medium (generally water-colour) should match
the tone of the print, but for photo-mechanical
reproduction this is not necessary. The aim in
finishing a photograph should be to strengthen
or to modify as may be necessary, and not to
introduce work that is not of a photographic
character ; this naturally forbids all outlining.
In process work, many special considerations
have their bearing upon the extent of the
Firelight Effects
251
finishing and the methods employed. Much
information is given in the article under
the heading " Aerograph," and further notes
of a j)ractical character will be found at
" Working-up Prints."
FIRELIGHT EFFECTS
EfEects represented in photographs appearing
to have been taken by the fireside and by the Ught
of the fire. Firelight is too weak to illuminate
the sitter for photographic purposes without an
undue exposure, and artificial aids are necessary.
Daylight is the most satisfactory light for the
purpose, and the illustration shows the method
employed by H. Essenhigh Corke. A suitable
window is selected and blocked up with brown
paper or other opaque material, leaving, how-
ever, a space about 2 ft. square, the bottom of
which should be level with the top of a table or
platform arranged close to the window. The
light admitted by the space is the " fireUght,"
but the space itself does not show in the photo-
graph. A fender and hearthrug may be arranged
Arrangement for Firelight Effects
to make the deception more complete, loose tiles
or wallpaper with a tiled pattern being placed
in the fender. The sitter should be placed as
near to the " fire " as possible, so that the
light may be concentrated upon him. A dark
background should be used.
FireUght effects may be taken at night by
the aid of magnesium. Throwing magnesium
powder into a real fire is rarely satisfactory,
and a better way is to use a magnesium lamp
in an empty fireplace, firing the powder when all
is ready for exposiire. Any other lights in the
room may be left on, as the average artificial
light will do no harm. In some cases it will be
advisable to use a weak supplementary flash
in the room in order to assist the very deep
shadows. If there is a good draught up the
chimney no magnesium smoke will escape into
the room and show in the picture, but if the
draught is poor it will be well to fit a Sheet
of plain glass in the fireplace, in such a way as
to trap the smoke. The finished print should
be stained with an aniline dye of a suitable
tint, so as to give it a firelight colour, and various
experiments in toning may be tried.
FIRES, PHOTOGRAPHING
The domestic fire is an awkward thing to
photograph satisfactorily, owing to the moving
smoke and the non-actinic colour of the red-hot
Fish, Photographing
coals. The best efiects are obtained by allowing
the fire to bum as bright and as smokeless as
possible, and then scattering a Uttle saltpetre
on it.
The photographing of conflagrations is, in
daytime, no more difficult than ordinary land-
scape or architectural work, the only precaution
necessary being, in addition to getting out of
the way of firemen and water, to take up,
if possible, a position on the windward side, in
order that the smoke blows away from the
camera and appears more or less as background.
Large fires at night generally give out sufficient
light to allow of brief exposures.
FIREWORKS, PHOTOGRAPHING
Fireworks really photograph themselves when
once the camera is ready. A stand camera
must be used, or a hand camera fixed upon some
suitable support, as it is impossible to hold a
camera in the hand stiU enough for the neces-
sary exposure. The camera must be focused
for what is known as " infinity " ; this is best
done in daylight by focusing some distant object
and fixing the camera at that focus or making a
mark on the baseboard, so that the lens may be
put in position at night when there is Uttle or
nothing to focus. When the firework display
begins, the camera is set up in the required
position, and the first few rockets looked at on
the focusing screen in order properly to judge
the correct position. The plate is then inserted
and a time exposure given — a minute or more,
as desired, or until a sufficient number of dis-
charges has been obtained on the plate. Only
one or two fireworks on a plate would look very
mean, and it is better to get a good number of
discharges, not interfering to any extent with
one another. As large a stop should be used
as possible, and a rapid plate, backed so as to
prevent halation, although with small stops
and slow plates some of the very bright rockets
may be obtained. The curves taken by rockets
in their ascent are very graceful, and care should
be taken to get far enough away to include
them when they are high and burst. The plates
are developed as usual, care being taken not to
under-develop, but to secure as much contrast
as possible. Firework exposures frequently
appear disappointing when in the developer,
and the plate may seem to be slow in developing
and to lack density, but such exposures gener-
ally fix out well. Printing should be deep, so
as to get a black background.
FISH. PHOTOGRAPHING
This is a branch of Nature photography ofier-
ing a field of pecuUarly interesting work. The
most important part of the outfit is a good stand
camera, with a modem anastigmat, working at
//6. Isochromatic plates should always be used,
where possible, in conjunction with a compensat-
ing filter (isochromatic screen). The size of the
aquarium or tank, in which the fish are to be
placed for photographing, must necessarily be
governed by the predominant size of the sub-
jects. It is a great mistake to have too large a
tank] for it will cause needless labour and trouble,
but at the same time it must be kept in mind
that unless the fish has ample room to move
freely, it will become alarmed, and will certainly
Fish-eye Camera
252
Fixed-focus Camera
assume unnatural positions, while in its struggles
to escape from its cramped surroimdings it may
injure itself. The photographic tank should have
all four sides of glass, so as to admit as much Ught
as possible, and one of the long sides must be of
good " patent plate " glass free from scratches,
air-bells, and ofiier blemishes, which would show
in the photograph, as it is through this side that
the photographs will be taken. This tank should
be kept purely for photographic purposes, and
not used as a regular stock aquarium, and must
be kept perfectly clean inside and out. Cleanli-
ness is most important. The water with which
the photographic tank is iilled should first be
strained through a piece of hnen, so that there
are no floating particles. The fine shingle used
for the floor must be well washed before being
placed in the tank, to rid it of mud and fine
sand. The plants must for the same reason be
well washed ; their roots may be cut away, and
the base of the stems weighted with a strip of
soft lead folded round and embedded in the
shingle. It is as well to place the plants rather
towards the back of the tank, as oQierwise they
are apt to get in the way and partially obscure
the subject to be photographed. The subject
itself will generally be found to look aU the
brighter and better for a gentle sponging to clean
off any dirt that has deposited in the natural
slimy secretion with which the body may be
coated. The photographic tank should be placed
in such a position that as good top and side
lighting as possible are obtained. The camera
should be placed directly in front of and at the
centre of the long side of the tank that is
fitted with the " patent plate." This glass must
be perfectly clean and free from smears. It is a
good plan to keep a soft washleather specially
for the purpose. Instead of introducing plants
into the photographic tank, a plain tinted back-
ground may often be used with advantage. If
plants are used, care must be taken to select only
those which would be found growing in the
favourite haunt of the particular fish to be photo-
graphed, otherwise a most unnatural effect will
be produced. Fanciful or elaborate backgroimds
should never be employed, as they only serve
to distract the attention from the fish, and pro-
duce a very artificial effect.
Before attempting to photograph a fish, it
should be kept under observation for some time
in a roomy, well-oxygenated aquarium, so that
its habits and characteristic positions may be
studied and noted down. When first placed in
the photographic tank, the fish will probably
dash wildly about, sink to the bottom, and
skulk away into the comers. It is no use at-
tempting to begin photographic operations until
the fish has got over the fright of being trans-
ferred from the stock aquarium to the photo-
graphic aquarium, and has become somewhat
accustomed to the strong hght illuminating the
latter. P. M-D.
FISH-EYE CAMERA (Pr., Chambre d ceil de
poisson : Ger., Fischenauge-kamera)
J. Alan Stewart, M.A., has pubhshed a method
of obtaining photographs resembling the views
that would be seen by the eye of a fish. Objects
against the light of the sky are only perceived
by the fish when they fall within the hmits of a
right-angled cone, whose apex is at the fish's
eye, while the base is a circle on the surface of
the water, of a little larger radius than the
depth of the fish. To produce a photographic
imitation of these conditions, a box having a
pinhole instead of a lens was employed. Although
light-tight except to rays entering by the pin-
hole, the box was not watertight, but admitted
water freely. The sensitive plate was placed
5 in. from the pinhole and the camera was
immersed in a larger box filled with water, the
exposure being tben made on an object — a
phantom minnow, for example — 3 or 4 in. below
the surface of the water in the exterior vessel.
An isochromatic plate was used, satisfactory
results being obtained with five minutes' expo-
sure in bright sunUght.
R. W. Wood advises the following procedure :
A small pail is taken, and into this, rather over
half-way up, is fitted a metal disc having a
perforated pinhole. The photographic plate is
laid at the bottom of the pail in the dark-room,
and the pail is filled with clean water, both
above and below the metal disc. The pail, which
is now practically a camera, is stood on the
ground and covered with a sheet of glass, which
must touch the surface of the water, so that
air does not come between — this preventing
ripples. Very interesting vertical pictures may
be made with the apparatus. To work horizon-
tally (in the manner in which » fish would
observe things through the sides of an aquarium),
a watertight box is made, with an opening in
one end. A piece of looking-glass is then taken,
and a pinhole is made in the film of amalgam on
the back, the glass being then cemented over the
opening in the box with the unsUvered side out-
ward. In the dark room, a plate is inserted, the
box fiUed with water and the cover replaced.
A httle more water is added, through a small
hole provided for the purpose, in order to dis-
place any air that is present. Some remarkable
results are obtained with this camera, which will
photograph objects close to the tripod, besides
those nearly due right and left, and directly
overhead. Naturally, there is a certain amount
of distortion, especially at the margins of the view.
FISH-GLUE (Pr., Colle de poisson ; Ger.,
Fischleim)
The product obtained by boiling fish-skins
and other waste remaining from fish-curing, and
manufactured principally at Gloucester, Mass.,
U.S.A. The glue thus procured is permanently
Uquid, and in a more or less viscous form. It
is largely used by photo-engravers for the enamel,
enameline, or fish-glue process, but for this pur-
pose it is clarified by boiling with albumen. The
glue is preserved with oil of wintergreen.
FISH-GLUE PROCESS
This is described under the heading of " Enam-
eline," by which name it was originally intro-
duced as a secret process.
FITCH-HAIR BRUSH
A brush made from the hair of the polecat.
FIXED-FOCUS CAMERA
A camera in which the relative positions of
lens and plate or film are fixed. Such cameras
Fixed White
253
Fixing
are usually of a cheap class, although some of
the smaller ones are fitted with lenses of high
quality. The advantages of a fixed-focus
cam.era are mainly simplicity and readiness for
work at a moment's notice. These cameras are
frequently fitted with supplementary lenses, or
magnifiers, which permit of near objects being
focused at fixed distances, usually 3, 6, 9 and
12 ft.
FIXED WHITE (See " Barium Sulphate.")
FIXING
The term " fixing " is a misnomer, as, instead
of making permanent something that is desired,
it removes something that is not desired, and
which, if left in the negative or print, would
seriously impair it. Fixing, in photography,
means the removal of any sensitive salt unacted
upon by light, or by the developer, thus render-
ing the negative or print unalterable by the
further action of light. The quantity of silver
reduced (developed) in a negative bears a very
small proportion to that originally in the plate
— ^very small both in film depth and surface
measurement, only the highest lights going all
the way through the film, while in the shadows
and darker parts little more than the surface is
touched. Thus in the average developed film
there remains a large proportion — estimated at
75 per cent. — of unaffected silver bromide which
must be removed before the negative can be
examined with safety in daylight, or be used for
printing.
Several substances possess the property of
dissolving this unreduced silver. Sodium hypo-
sulphite has the greatest solvent action except
ammonia, which for many reasons it is not
advisable to use. Although many solvents of
silver are known, ammonia, potassium cyanide,
and sodiiun hyposulphite (better known as
"hypo") are the most notable. Ammonia,
however, is not practicable, because to remove
the superfluous silver quickly a very strong
solution must be used, and such a solution
seriously damages a gelatine film. Potsissium
cyanide, though used as a fixer for wet plate and
ferrotype work, is too expensive for modem dry
plates and papers, and in addition is undesirable
because of its exceedingly poisonous nature
and its liability to eat into the half-tones.
The colour of the negative after fixing with
cyanide is by reflected light whiter than when
"hypo " is used, but by transmitted light, as when
printing, it is browner and consequently more
actinic. All things considered, however, it is
not so good as " hypo." It was in the year 1819
that Sir John Herschel discovered in sodium
hyposulphite a solvent for unreduced silver, but
the first use of it is credited to J. B. Reade,
who in 1837 made the first fixed silver prints
from paper negatives. " Hypo " was at that
time a very rare salt, and racpensive, costing
about half a crown an ounce ; iu 1845 it dropped
to 6d. per ounce, in 1857 to 6d. per pound, since
when it has become very cheap indeed.
The usual procedure in fixing negatives is to
place them film upwards in a flat dish filled with
the " hypo " solution, but while such a method
serves very well, particularly when the solution
is frequently agitated, the work is performed
more quickly and efiiciently if the plates are held
vertically in the solution, which should be in
porcelain tanks (as B), or lead-lined zinc tanks.
These tanks must be deep and formed with a ridge
in the bottom {see B), on which the plates rest
while the grit and other impurities setUe below
them. Plates fixed in flat dishes often appear
correctiy fixed except for small white (unfixed)
patches caused by impurities resting on the film.
A. Wooden Tank
B. Porcelain Tank
and preventing the action of the " hypo.'' In
a vertical tank a dozen plates may be fixing at
one time, and take up but litUe room. When a
flat dish is used the plate should be film side
down, but not with the film in contact with the
dish, and then impurities cannot easily attach
themselves to the film ; even this is not so good
as vertical fixing. A shows a form of dish for
fixing plates upside down ; the long V-shaped
wooden trough, covered with pitch or made
waterproof and watertight in some other way,
is filled with the fixing solution, and the plates
rested on the sloping sides film side downwards.
An advantage of such a dish is that it may be
used for any and all sizes. Such a dish is more
cumbersome, and takes up more room, than a
vertical trough.
It is not necessary to deal here with the com-
position of " hypo " fixing baths, as formulae
have been given under the headings " Acid
Fixing Bath " and " Alkaline Fixing Bath."
While fixing is apparently the simplest of all
photographic operations, it is frequently done
in an inefficient manner, thus leading to many
failures. A common mistake is to remove the
negative or print from the " hypo " solution too
soon. A negative is not fixed the moment the
silver appears to be dissolved away and the
plate clear. The process of fixing with " hypo "
includes two distinct and important functions.
The first is the formation of a double salt of
sodium hyposulphite and silver by the reaction
of the creamy white silver bromide with the
" hypo," at which stage the negative is clear
and apparentiy fixed. The double salt so formed
is insoluble in water, and therefore cannot be
removed by any amotmt of washing ; it cannot
be seen, and the negative appears perfect and
ready for washing and drying, but if washed and
dried at this stage the double salt will on exposure
to light appear in due course as a yellowish stain,
and in time the image will fade more or less to
an extent corresponding to the amount of the
double salt in the film. The second function
is the dissolving away of the detrimental salt
first formed. Although insoluble in water, a
longer soaking in the " hypo " solution converts
it into another double salt that water will easily
remove ; hence the absolute necessity of leaving
Fixing
254 Fixing Before Development
the developed plate in the fixing bath for an
additional time after the plate appears to the eye
to be fixed and dear. Ordinarily, the proper
length of time to secure perfect fixation is double
that taken by the white substance to dissolve.
Thus, for example, if it takes ten minutes'
immersion in the " hypo " bath to clear away
the last traces of the silver bromide, the plate
must be allowed to remain for another ten
minutes in order that fixation may be complete.
Some workers advocate a second fixing bath
rather than a prolonged soaking in one bath, but
if the first 'bath is fresh, properly mixed, and of
the correct strength, a second fixing bath should
be quite unnecessary. If the fixing bath is so
weak or so loaded with impurities that it is unable
to perform its work, it should be discarded, as
it is in a condition to do harm a second bath
cannot correct.
Where a variety of developers are in use, and
if no care is taken to wash the plates thoroughly
free from developer before placing them in the
fixing bath, there is a possibility of trouble arising
if the same bath is in use for aU plates ; but there
is quite as much risk of having the transparency
of the gelatine impaired by failure to wash off the
developer even when a freshly made bath is
used.
A common mistake is to employ " hypo "
fixing baths too strong. The silver bromide is
less soluble in, say, a 50 per cent, solution than
in a 25 per cent, solution. The latter, 4 oz. of
" hjrpo " to 16 oz. of water, is a suitable strength
for films and plates, but for papers half or even
a quarter strength will serve. When a very
weak " hypo " bath is used, the double salt
referred to is likely to remain in the film, because
there is no excess of " hypo " to act upon it.
The bath should not be weaker than i in 5 for
plates and i in 10 for prints. A fixing bath
made of the usual strength, the ingredients being
properly weighed or measured and not taken
by guesswork, and used in sufficient quantity
to cover the plate, will contain an excess of
" hypo " that wiU act upon the double salt if
time enough be given.
A solution of " hypo " will not attack the
actual image which has been developed so long
as the plate is well covered with the solution,
but when a negative wet with the fixing bath
is exposed to the air, the " hypo " in solution,
in conjunction with the oxygen of the air, does
attack the developed (reduced) silver which
forms the image, with the result that the nega-
tive becomes thinner. This action is not very
rapid, and no appreciable harm is done when
the negative is taken out of the bath for examina-
tion, and a reasonable time may elapse before
it is placed in the washing water ; but irrepar-
able damage is done when the plate is left in the
fixing bath, or in the washing water after fixing,
only partly covered with the liquid. The
covering of the plate with a solution of " hypo "
and glycerine, and leaving it exposed to the air,
is, in fact, a little-used method of reducing.
As regards the exhaustion of the fixing bath,
Messrs. A. and I,. I^tmiidre carried out some
experiments (published in February, 1907), and
found that, to avoid subsequent yellowing of
negatives on modem gelatine plates, it is advis-
able (i) to fix not more than one hundred
9 by 12 cm. plates in one litre of 15 per cent
solution of " hypo " (this is roughly equal to
about 120 quarter-plates in 35 oz.) ; (2) to fix
not more than fifty of such plates (sixty quarter-
plates) in one litre of a 15 per cent, fixing bath,
plus I'S per cent, of bisulphite ; (3) to fix not
more tiian seventy-five plates (ninety quarter-
plates) in one litre of a 15 per cent, fixing bath
plus 1-5 per cent, bisulphite and -5 per cent,
chrome alum. The moment when the fixing
bath is used up and should be thrown away can
be determined by placing a drop of the bath
on white paper, and exposing for some time to
light and air ; if the spot turns brown, the bath
is exhausted.
The function of the fixing solution is the same
for prints as for negatives, although the silver
salts may differ chemically and may be attacked
under different conditions. The porous paper
allows the " hypo " to act on both sides of the
film., but this is more than counterbalanced by
the larger amount of water that must be dis-
placed before the " hypo " can begin its work
of dissolving the silver brqmide.
While, on the whole, a plain solution of
" hypo " is sufficient for the fixing of negatives
and silver prints, several additions have from
time to time been recommended, some with a
view to hardening the film and so prevent frilling
and blistering, others to prevent or remove stains
from the film, and still others to keep the solu-
tion itself from being discoloured in cases where
it is employed over and over again. The most
harmful, and at the same time the most frequently
recommended, addition is common alum, which
decomposes the " hypo," liberating sulphur, and
forming injurious compounds that may possibly
interfere with the fixing, and lead to degradation
of the negative or print.
As the result of a series of experiments, Messrs.
Haddon and Grundy have stated that the l\est
strength at which to use a " hypo " bath is 10 per
cent., and that such a bath will at a normal
temperature completely fix a print in ten min-
utes. As to the exact amount of " hypo " to
be used for each print, this depends on many
circumstances, but on an average 2 oz. of " hypo "
dissolved iu 20 oz. of water will thoroughly fix
420 sq. in. of print — ^^that is, one sheet of paper
24 in. by I7-J- in., equal to about thirty quarter-
plate prints or about ten or eleven h^-plate
prints. Otherwise stated, it requires approxi-
mately from 80 grs. to 90 grs. of " hypo " in the
form of a 10 per cent, solution to fix a half-plate
print at normal temperature, immersing the print
for ten minutes.
In process work, wet collodion negatives are
invariably fixed in potassium cyanide, the usual
formula being i oz. of 30 per cent, cyanide in
20 oz. of water.
FIXING BEFORE DEVELOPMENT
It has been found that whatever the action
of light may be on the sensitive silver salts, the
result is such that it is not destroyed by fixa-
tion ; and it has been suggested that when on
tour it may be convenient or safer merely to
fix the exposed plates and then develop them
on the return home. In such a case the developer
is a physical one, and the most satisfactory ia
that given on the next page.
Fixing Before Toning
2SS
Flake White
A. Anunonium sul-
phocyanide . 2,304 grs. 240 g.
Silver nitrate . 384 „ 40 „
Sodium svilphite . 2,304 „ 240 ,,
"Hypo" . . 480 „ so „
Potassium bromide 57 ,, 6 ,,
Distilled water to 20 oz. 1,000 ccs.
B. Metol . , 144 grs. 15 g.
Sodium sulphite . 3 oz. 150 ,,
Distilled water to 20 „ r,ooo ccs.
For use, mix 6 parts of A with 54 parts of
water, and add 30 to 40 parts of B. As a
practical process this is hardly worth trial, as
the exposures must be at least four to six times
longer than usual.
FIXING BEFORE TONING (See "Toning
after Fixing.")
FIXING. COMBINED DEVELOPING AND
{See " Developing and Fixing Com-
bined.")
FIXING, COMBINED TONING AND {See
"Toning and Fixing Combined.")
FIXING, DEFERRED
A process for treating a negative after devel-
opment so that fixing may be carried out later.
The method is largely used by tourists who desire
to see whether exposures have been correct, but
who do not wish, for the time being, to go to the
trouble of fixing and washing. The plate is
developed as usual, washed for about five min-
utes, and placed in any one of the three following
baths, thus rendering the developer inert : —
(i) Potassium bromide -f oz., water 5 oz.
(2) Alum i oz., citric acid 30 grs., water 5 oz.
(3) Cadmium bromide i oz., ^cohol 5 oz.
In hot weather add 1 5 drops of formaline. Five to
ten minutes' treatment is sufficient. The safest
bath is the bromide bath (No. i ) ; should the alum
bath (No. 2) be used and the plate not be properly
washed, ugly stains may appear. With formulae
Nos. I and 2, a slight rinsing after the " defer-
ring " bath is necessary, the plate being then
dried and fixed at leisure. The advantage of the
cadmium bath (No. 3) is that the plate need not
be washed either before or after treatment, and
the alcohol serves to dry the plate in a very
few minutes. Daylight does not injure negatives
temporarily finished in this way, and they may
even be printed from, preferably upon bromide
or gaslight paper.
FIXING WITHOUT TONING
All printing-out papers do not need toning,
and in some cases good colours may be obtained
by fixing only. {See " Self-toning Papers.")
Plain salted paper fixes out a pleasing sepia
colour, if not too heavily sized. Paper prepared
with silver chloride alone comes out of the
fixing bath a blue colour, while if the organic salt
is chiefly used a foxy red results. A combination
of these two colours in right proportion results in
a pleasing tone on fixing. Effective red tones
may be obtained on ordinary matt P.O. P. by
fixing without toning. Printing should be
deeper than usual, and the prints washed well
before fixing, in order to remove the free sUver.
FIXING-HARDENING BATHS
Solutions for hardening the films of plates and
papers and at the same time fixing the image.
Their use does not yield such permanent results
as the use of separate fixing and hardening
baths. {See " Hardeners.") The best known
formtdae are : —
Alum "Hypo"
Alum (saturated sol.) 20 oz.
Sodium sulphite (sat-
urated solution) . 6 „
"Hypo" sol. (i in 5) 20 ,,
100
100
ccs.
Chrome Alum "Hypo"
Add-
Strong sulphuric acid 60 drops
Water . . . 2 oz.
•I
SO
cc.
ccs.
to—
Sodium sulphite . 2 oz.
Water . . • 6 „
5°
ISO
ccs.
It
and pour the mixture into —
"Hypo" . . .16 oz.
Water . . . 48 „
400
1,200
ccs.
Finally add —
Chrome alum . . i oz.
25
ccs.
Water . . . 8 „
200
»»
" Hypo " Acid Sulphite
" Hypo " (in powder) i lb. 250 g.
Sodium add sulphite 2 oz. 32 „
Water . . . 64 „ 1,000 ccs.
The second and third baths, being in an acid
condition, must not be used for printing-out
papers, and are suitable only for plates and
bromide and gaslight papers. The " hypo "
and plain almn bath may, however, be used
after toning.
Another form of fixing-hardening bath, which
is largely used in hot countries and in England
during hot weather, is the following: —
Sodium hyposulphite .
Potas. metabisulphite
Chrome alum .
Water
2 oz. 220 g.
i „ 28 „
i „ 28 „
10 „ 1,000 ccs.
First dissolve the " hypo " in 5 oz., half of the
water made hot, next the metabisulphite in half
the remaining water (cold), and add to the
"hypo" mixture; lastly dissolve the chrome
alum in the remaining water (cold), and add
to the hypo-metabisulphite mixture. Careless
mixing causes turbidity, whereas the solution
should be clear and of a greenish colour. The
above being acid is suitable for negatives and
bromide and gaslight prints, but not for P.O.P.
FLAKE WHITE
Basic lead carbonate, used as a white pig-
ment for retouching photographs, etc.
In process work, flake white has been super-
seded by other pigments, and is now seldom used
for retouching photographs for reproduction
owing to its tendency to become yellow. The
more modem white pigments employed, such
as albanine, ullmanine, blanc d'argent, etc., are
described under their respective headings.
Flap Shutter
256
Flash Lamp
FLAP SHUTTER (Pt^Obturateur dvolet; Get.,
Klappverschluss)
A shutter in wliicli tlie exposure is made by
the rise and fall of a hinged flap. In an early
pattern, the flap was actuated by an elastic band
stretched from the upper part of the shutter over
A. Single Flap
Shutter
B. Double Flap
Shutter
a peg or projection at the bottom of the flap,
the latter being released by depressing a catdi.
The flap feU again by its own weight. This kind
of shutter is now seldom seen, except in studio
apparatus. A greatly improved modem pattern,
arranged to work noiselessly by the pressure of
a pneumatic ball, and remaining open as long
as the ball is pressed, is illustrated at A. The
catch seen on the right is to keep the shutter
raised during focusing or for time exposures,
by engaging with a bent wire. A double flap
shutter is shown at B. Another form of flap
shutter is really nothing more than a hinged
covering for the lens, lined with velvet and
worked by means of a rod projecting outside the
camera. With this, however, exposures suffi-
ciently quick for studio work are readily given.
FLARE SPOT
A light patch usually near the centre of a
photograph, and caused by internal reflection
in the lens. It may usually be obviated by
altering the position of the diaphragm, so that the
reflected light becomes evenly distributed over
the entire field. One form of flare takes the
shape of a well-defined inverted image of a
window, portion of sky, or other bright object.
This is usually termed a " ghost " and may be
obviated by the method above indicated. Flare
usually appears when using a small diaphragm ;
hence many lenses which work satisfactorily
down to //16 exhibit flare when stopped down
to a smaller aperture. {See also " False Images.")
FLASH LAMP (Fr., Lampe iclair : Ger., BUU-
lampe, Magnesiumlampe)
In its original sense, a lamp for burning mag-
nesium powder, which is blown through a spirit
or gas flame. A simple type of flash lamp may
be made as shown at A, with a short metal pipe
bent to a right angle and surrounded with cotton-
wool soaked in methylated spirit. A charge of
powdered magnesium is placed in the pipe, and
the free end is attached to a rubber tube ter-
minating in a ball. The spirit is then Ht, and
pressure on the ball at the desired moment
drives the magnesium into the flame and ignites
it. A number of such lamps may be arranged
to flash simultaneously by connecting aU the
pipes to a single large ball, a pair of bellows, a
bicycle pump, or an air reservoir. It is always
preferable, when extra light is desired, to use
several lamps, rather than to increase the charge
of powder in a single lamp ; as, in the latter
A. Simple Type of Flash Lamp
case, much of the powder may simply be driven
through the flame without being consumed, and
so be wasted. Flashlight mixtures should on no
account be used in enclosed lamps ; these are
only suitable for plain magnesium powder. A
popular commercial flash lamp of the enclosed
type, which gives either an instantaneous or a
continuous flash, is shown at B. To use this,
the metal chamber is half filled with magnesium
powder, and about an ounce of methylated spirit
is poured into the vessel holding the wick, taking
care that none gets into the discharge orifice or
over the sides of the reservoir. The rubber tube
is then closed by means of the spring clip, and
the bladder is inflated until it fills the net. The
wick having been lit, a flash of the required
duration can now be obtained by pressing the
clip. After exposure, the flame is extinguished
by replacing a metal cap.
The term flash lamp is now also used for open
arrangements in which a flashlight mixture, con-
sisting of magnesium powder mixed with potas-
B. Enclosed Flash
Lamp
C. Open Flash
Lamp
slum chlorate, or other detonating ingredients,
is burnt in a metal tray or pan, by means of a
fuse which is operated from a small accumulator,
the mechanical striking of a match or percussion
cap, or other means. A typical flash lamp of the
open type is illustrated at C. The ignition of the
powder is obtained in a somewhat novel fashion.
A milled disc of a special pyrophorous or spark-
giving metal is caused to rotate against a similar
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Flashlight Candles
2S7
Flashlight Photography
metal surface by means of a coiled spring, thus
giving ofi a small stream of sparks as it revolves.
The spring is wound up by a key and the powder
is spread on the tray around the milled disc,
when pressure on the pneumatic bulb at once
starts the mechanism and ignites the flash
mixture. For professional flashlight purposes,
longer trays are commonly used, the powder
being laid in a thin, heaped-up line. The lamp
is raised to a suitable height by a jointed metal
rod attached to a stand ; and a screen or cover
of musUn, or other Ught, translucent material, is
supported on a frame over the tray to diffuse
the illumination.
FLASHLIGHT CANDLES {See "Candles,
FlashUght.")
FLASHLIGHT PHOTOGRAPHY
The taking of photographs by means of
flashes of artificial Ught, the Ught being generally
produced by burning magnesium or flashlight
mixtures. Magnesium was made known in 1808
by Sir Humphcy Davy, but for half a century or
more it was regarded as a curiosity. In 1859
Bunsen, of Heidelberg, and H. E. Roscoe, of
Manchester, pointed out the value of magnesium
as a source of Ught for photographic exposures.
Improvements in the manufacture of the metal
took place (a company being formed in Man-
chester for the purpose in 1 863), but its expensive-
ness (magnesium in the form of ribbon then cost
half a crown per foot) kept its use restricted.
A. Brothers, of Manchester, has been credited
with taking the first successful photographs with
magnesium, for early in 1864 he obtained a
stereoscopic negative of a Derbyshire mine, and
in May of the same year a portrait of Prof.
Faraday, at the Royal Institution. In the
foUowing year the interior of the great Pyramid
was taken by Prof. P. Smith by magnesium
Ught, since when the metal, in the form of both
ribbon and powder, has become cheaper and
consequently widely used. The Ught given off
is of intense brUUancy and of high actinic power.
Magnesium for photographic illumination pur-
poses may be obtained in three different forms —
pure magnesium powder ; flattened wire, known
as ribbon ; and a combination of magnesium and
other substances, in powder. The ribbon is the
safest, but does not ^ow of such short exposures
as the powders ; however, it is commonly
employed in photographing dark comers of
rooms, caverns, ceUars, etc., where the length of
the exposure is not of much consequence, and
it is sometimes useftd as an accessory to day-
Ught, as a means of illuminating objects in deep
shadow, since, on account of its burning slowly,
it may be moved about while the exposure is
being made, and so give diffused Ughting.
Another advantage of using ribbon is that the
actinic value of the Ught obtained by burning a
definite quantity remains constant under the
same conditions, so that by measuring the length
— or, preferably, weighing the quantity — of the
ribbon before burning, the photographer can
easily obtain data that will assist him in making
the results of later exposures sure.
For flashUght work proper — that is, for what
are known as " instantaneous exposures " —
the powders must be used. It is not necessary
17
to employ a shutter as in making instantaneous
exposures by daylight ; in most cases the
ordinary Ughts of an apartment are too feeble
in actinic rays to affect the plate, and the lens
is left open until after the flashlight. Magnesium
flashes are open to objections : the quantity of
smoke produced, and the difficulty of diffusing or
spreading the Ught over a sufficiently wide area
magnesium
Flaahlight
A. Simple Arrangement for Flashlight
Portraiture
to obviate harsh shadows and hard contrasts.
Again, there is the risk of explosion, but such an
accident can scarcely occur with careful, proper
firing. Pure magnesium powder gives a bright
and highly actinic flash, but it must be blown
through a flame. FlashUght powders containing
substances in addition to magnesium are reaUy
explosive mixtures, and they must be ignited
by applying a light, for should they be blown
through a flame a dangerous explosion will
result. A flashUght compound must not be
used in a closed storage reservoir or magazine
lamp, because in these the flame would travel
to the bulk and explode it. Only the pure
magnesium powder should be used in such lamps.
For the beginner, the ribbon is the safest and Uie
pure powder the next safe.
As regards the amount of powder to be used,
this depends upon nearness of subject, stop,
plate, etc., but the table given below (compiled
by J. H. Crabtree) may be taken as a guide : —
•s-1
Size of Room
g-s
Weight of Magnesium
.s «
required
11
Lmgth
Breadth
Heighi
Feet
Feet
Feet
Feet
Grains
Oz. (approx.)
9
15
6
10
15
—
15
20
6
10
30
—
20
25
ID
10
75
—
25
30
12
10
120
i plus
30
35
12
10
180
35
40
15
10
230
i plus
40
45
15
12
300
—
45
50
20
12
370
—
50
60
20
12
460
I plus
55
65
20
12
560
I J plus
60
70
30
15
680
li plus
65
75
30
15
780
if plus
70
85
30
15
900
2 plus
75
90
40
15
1020
2f Dunus
80
95
40
15
1200
2i
85
100
45
20
1340
3 plus
90
120
45
20
1500
3i minus
95
125
50
20
1650
3*
100
130
60
20
1850
4i
Flashlight Photography
258
Flashlight Photography
The conditions assume a lens at// 11 and a fairly
rapid plate, the exposure being so short as to be
regarded as instantaneous. It is also important
to bear in mind that the quantities specified
must be completely burned in the flame with an
ample supply of air, and not half consumed or
wasted.
Lighting and Arrangement of Subject. — Success
in group and portrait photography by flashlight
depends chiefly upon the arrangement of the light
and sitter. A frequent mistake is to have the
light at too low a level ; it should be at least i ft.
above the level of the sitter's head, and not on
a level with it or lower. The higher the light
(in reason) the more truthful will be the effect,
and the less like the generality of flashlight
photographs, which are distinguished by the
glaring whites of the eyes and the harsh blacks
and whites. In portraiture it is a good plan
to place the flash powder on steps as at A {see
preceding page), or if ribbon is used the operator
may stand on the steps and wave the ribbon
about, or the ribbon may be tied to a stick and
waved about on high. At B is shown the plan
1
Group
__/
2id9
flashlamp
n
®/sf
Flashlamp
B and C. Plans and Arrangements for
Flashlight Portraiture
of a suitable arrangement for taking portraits by
flashlight ; a reflector of White material is needed
on the shady side of the face, or if there happens
to be a white wall surface on that side it will
serve the purpose. Whitewashed ceilings serve
admirably as a top light, as they reflect down-
wards an enormous amount of actinic light when
the magnesium is fired. The Hght is placed and
flred at a point on one side of the camera, but
slightly nearer than the camera to the figiire,
yet not so near as to be included in the view ;
the flash must not be reflected in the lens, or
the plate will be fogged. By varying the posi-
tions of camera, sitter, hght, etc., any number
of different effects can be obtained in one room.
If there is nothing acting as a reflector on the
shady side of the sitter, it will be necessary to
interpose a sheet of white tissue paper or muslin
between the flash lamp and the subject in order
to diffuse the Hght and obtain softness in the
photograph. Frequently it is the nearness of
the light as well as its low position that gives
a ghostly effect to flashlight portraits. The
diffuser is useful in the majority of cases, and
although it stops a little of the light and may
mean a few extra grains of powder, the results
obtained will be softer and better. In group
work, two or more lamps may be necessary, in
which case one lamp should be much nearer to
the group than the others (see C), all the lamps
being fired at the same moment. Professionals
frequently employ electrical arrangements to syn-
chronise the ignition when more than one lamp
is in use. The near lamp serves as the main
hght, and the other as a kind of auxiliary lamp
to assist generally and light up to a small extent
what woijdd be the shady side.
In flashlight photography all the gas, electric,
and other lights may be left burning, as they do
not much affect the plate dmring the extremely
short exposure. If the image cannot be seen on
the ground glass sufficiently distinct for focusing,
the sitter or sitters can hold a candle or a lighted
match on a level with the face, and the flame can
then be focused. The plate is then put in, the
dark-sUde shutter is drawn, and the cap taken
from the lens or the shutter opened, the exposiire
being made by firing the powder or ribbon. Only
that part of the exposure made during the
burning of the magnesium need be taken into
consideration.
One of the great drawbacks to the use of flash-
light is the immense amount of white smoke
given off. All windows and doors may there-
fore with advantage be opened ; and the smoke
of one flash must be got rid of before another
exposure is made. The smoke is quite harmless.
Some of the patent commercial mixtures cause
less smoke than others, while some of the more
expensive and complicated flash lamps have
smoke-catching devices. A home-made smoke-
catching device is formed by placing the flash
lamp in a large box stood on its end with its
open side towards the subject ; after exposure
the lamp is immediately taken out, the box
closed with a cloth or tightly fitting lid, and the
whole taken to an open window or outside and
emptied ; but the arrangement prevents much
valuable Ught reaching the ceiling and walls.
Outdoor work with flashlight differs but
slightly from the above, but more light is
required, and there is Httle or no trouble with
the smoke. More powerful (consequently more
explosive) mixtures, of the firework type, can
be used, as the risk of danger to human beings
is so much less.
Plashhght work is not confined to portraits,
groups or evening work generally, but is of great
service in illuminating dark comers in interiors,
such as crypts, workshops, underground work-
ings, etc., m the daytime. For this purpose
ribbon is better than powder, but care must be
taken to keep the naked light and the smoke
from it out of the view of the lens, with which
object the flash lamp may be fired behind a
pillar or something of the sort.
Any developer will, with care, serve for deve-
loping flashlight exposures, but as there is always
a risk of under-exposure and harsh contrasts,
little or no bromide should be used, and the
developer should be diluted with water. The
following hydroquinone-eikonogen developer has
been widely recommended for flashlight expos-
ures, but metol-quinol and similar developers
can be made to give equally good results : —
A. Hydroquinone
1 oz.
ii-i g.
Bikonogen .
i „
ii-i „
Sodium sulphite
2i „
S5-5 ..
Hot water to
45 „
1,000 CCS
Flashlight Powders
259
Flattening Prints
Dissolve the sodium sulphite, then the eikono-
gen, and finally the hydroquinone.
B. Sodium catbonate 2^ oz. 5 5 "5 g.
Hot water . . iS » 333 ccs-
For use take 3 oz. of A, i oz. of B, and 3 oz.
of water ; this forms a normal developer which
should give a good negative in from eight to ten
minutes.
FLASHLIGHT POWDERS
The chief two kinds of flashlight powders are
(i) pure magnesium powder and (2) mixtures of
magnesium and other substances. Magnesium
powder used alone is blown through a flame, the
brightness and duration of the flash depending
upon the quantity of powder burnt and upon
the length of time taken in passing it through
the flame. Some arrangements for firing permit
of a slow passage of the powder through the
flame, in which case the Hght is continuous, and
not an instantaneous flash ; others permit of a
large quantity of the powder being passed through
a flame very quickly, in which case there is fre-
quently a, risk of much of the powder being
wasted.
Flashlight mixtures are explosive, and in their
action behave Uke gunpowder ; they must not
be blown through a flame, but must be placed
in a heap or a ridge and the hght applied, the
result being a momentary flash of high actinic
power. Such explosive mixtures must always
be looked upon as being more or less dangerous.
The addition of chemicals to the magnesium is
for the purpose of increasing the rapidity of the
<combustion and the actinic power of the light.
When such mixtures are made by the worker,
the ingredients should be purchased in the
powder form and then mixed carefully together
on paper with a dry feather. Large quantities
should never be mixed for fear of explosions, and
for the same reason there should be no lumps of
any kind in the mixtures. The ordinary photo-
grapher will be well advised in buying his flash-
Ught mixtures ready prepared. Some of the
best known formulae are : —
(i) Magnesium
6]
sai
Potassium chlorate .
9
(2) Magnesium
6
Potassium chlorate .
4*
Potassium perchlorate
4i
{3) Magnesium
6
Potassium chlorate
12
Antimony sulphide .
2
(4) Magnesiimi
16
Potassium perchlorate
12
Potassium nitrate
12
(5) Magnesium
48
Ammonium nitrate .
3
Strontium oxalate
5
Sodium oxalate
5
(6) Magnesium
40
Potassium perchlorate
60
Sodium chloride (salt)
5
Barium tartrate
7
can escape quickly. No. 4 bums rapidly, and
is less hable to explode. No. 5 is for isochro-
matic plates, and a yeUow screen should be used
in the lens. No. 6 is for isochromatic plates, but
a yellow screen need not be used.
Aluminium is said to give less smoke than
magnesium, but it yields only about two-thirds
of the actinic hght. The following mixture of
aluminium and magnesium not only gives less
smoke than a mixture containing chlorate, but
the smoke quickly passes away and the powder
is non-explosive : —
Copper sulphate (anhydrous) 6 parts
Magnesium powder . . 3 „
Aluminium powder . . i „
This gives much less smoke than mixtures con-
taining chlorate, and the smoke passes away
quickly, thus allowing of a series of successive
exposures in a room. {See also " Aluminium
Flashhght.")
There are many other formulae for flashlight
mixtures, but they are similar to the above.
Great care is necessary when firing fiashUght
mixtures ; and when no proper lamp is used the
powder is best placed on a small iron slab or
tray and fired by means of touch-paper {which
see), or by means of a long taper or of a match
fixed to a stick, the operator turning his head
away when the actual flash takes place.
Slow-burning mixtures may be made, the
following being a typical formula : —
. 100 parts
• 70 „
Magnesium powder
Ceric nitrate
Strontium carbonate
30
Nos. I and 2 are good average mixtures for
home work or professional porteaiture. No. 3
gives a very good hght, but its fumes are poison-
ous, and it should tiierefore be used in the open
air or in a well-ventilated room where the fumes
Eighty grains of this powder bum in about six
seconds.
Flash-sheets are made by soaking thin blotting-
paper in a strong solution of saltpetre, drying,
and then spreading over the paper pure dried,
unoxidised magnesium powder, leaving the
edges free. Such a sheet constitutes a com-
bined slow-match and flashhght, it burning
slowly until the smoulder readies the powder,
which then bursts into a bright flame. Flash-
sheets are quite safe in use ; a commercial form
is a mixture of fine magnesium powder and cellu-
loid spread on glass and allowed to dry.
FLATNESS
A term applied to a print in which there is
but httle contrast between the lights and
shadows. It is the opposite quaUty to briUiance.
An over-exposed and under-developed negative
gives a flat result.
FLATTENING PRINTS
Prints that are not dried under pressure
invariably curl up. Prints on coUodion paper
may be dried between blotting-paper under
pressure, but gelatine prints— ordinary P.O. P.,
bromide and gasUght papers — cannot be treated
in this way, because of the sticky gelatine sur-
face. Sometimes even collodion prints will curl
badly when removed from pressure. A rough
and ready method of flattening is to roll the dry
prints all together film side outwards, and
secure with an elastic band ; after a few hours
they will be found on unrolling to be flat. A
better method is here illustrated. The curled
Flexible Support
260 Flowers, etc., Photography of
picture is laid face downwards on a dean flat
surface, and a flat ruler is then placed along one
edge of the print and pressed down firmly.
Flattening Prints
Next, the whole print is drawn sharply under the
ruler, as illustrated, the ruler being kept station-
ary. The process may need to be repeated
once or twice.
FLEXIBLE SUPPORT (See "Temporary
Support.")
FLORENTINE FRAMES (Fr., Cadres floren-
tins ; Ger., Florentinischer Rahmen)
Ornate gilt frames with open-work foliated
ornament ; suitable for photographs worked-up
in water-colours, crayons, etc., when not on too
large a scale.
FLOWERS OF SULPHUR (See "Sulphur.")
FLOWERS AND FRUIT, PHOTOGRAPHY
OF
In this work success depends on the lighting,
the arrangement of the subject, and the method
of exposure. Flowers and fruit may be photo-
graphed indoors or out, in their natural sur-
roundings or otherwise ; but the best results
are obtained by arranging them indoors and in
a suitable light. A convenient method of
arranging the lighting is shown at
A and B. On a table near a window
on the shady side of the house the
flowers (or fruit) are arranged, the
background being a sheet of brown or
other coloured paper, according to the
tint required in the photograph. It
is advisable to have papers of several
difierent colours at hand, and to bear
in mind their different photographic
values. The light should come in at
the window and be fairly strong, as
then, by means of tissue paper over
the lower half of the window and a
white cardboard reflector on the
shady side of the subject, the light
may be controlled to a nicety. The
positions of the camera, flowers, back-
ground, etc., are all subject to experiment
in obtaining various eiiectis. It is not always
advisable to show the vase which contains
the flowets or the means of supporting the
fruit. In the case of a few blooms, they may
be stood in a narrow-necked bottle ia order to
keep them upright, and the stalks must be
long if the neck of the bottle is not to be
included in the picture. Other supports include
a bowl of wet sand ; bent strips of sheet lead ;
and a large potato, the stalks in all these cases
being long. For the purpose of picturing the
vase as well as the flowers or fruit lying upon
the table, there should be no dividing line
between table and background, for which pur-
pose the paper forming the background should
be brought in a gentle curve underneath the
vase, etc. Even if a line would enhance the
pictorial value of the picture, it should not be
abrupt. The table-clotti must not be of a pro-
nounced pattern, or of a colour contrasting too
strongly with the background.
Cameras are sometimes used vertically for
photographing flowers that are lying, for example,
on the floor. Similar results may generally be
obtained with an ordinary camera used in the
usual way, by arranging the vertical back-
ground to take the fruit or floral sprays ; this
may be done by using stout, stiff cardboard
covered with coloured paper as the backgroimd
and pushing pins through from the back, their
points serving as rests and being covered by
the objects photographed, although if they are
not hidden they will be scarcely noticeable.
Cut flowers may be preserved for photographic
purposes by sprinkling them with fresh water,
and while wet placing in a vase containing the
following solution : Water 4 oz., curd soap
2 drms., common salt 8 grs. The soap is cut
into shreds and dissolved in the water, adding
a small pinch of borax and the salt. If the
flowers are to be kept for several days their
stalks should be rinsed under the tap daily for
a minute or so, the petals sprinkled, and the
flowers put back into the vase.
The lens stop plays an important part in
the pictorial rendering of flowers. //16 gives
general sharpness, but a smaller one may
in some cases be necessary. Exposure should
not be unduly prolonged, as some flowers —
poppies, for example — are apt to droop during
a long exposure and show signs of movement
upon the plate. Isochromatic plates are the
^^^Vbm7~
oi
Flowers ^
1
1 1
n
A and B. Arrangement for Flower Photography
best for most flowers, but ordinary plates
may be used for some with good results, every-
thing depending upon the colour of the flowers.
For reds, blues, yellows, and various shades
of green an isochromatic plate is indispensable
to give the proper values of the colours. Much
may be done on ordinary plates by giving a
suitable exposure — that is, one sufficiently long
to enable tiie colours of little actinic value to
register themselves on the plate. E. Seymour
has used a yellow screen and isochromatic plate
for only about 10 per cent, of his exposures, as in
Fluid Lens
261
Fluorotype
his opinion the use of a screen robs the picture of
half-tone and gives an effect unsatisfactory to the
observer of nature. Opinions differ, however,
but there can be no doubt that to give the
plate a full exposure for the deepest shadows and
to develop until the highest light is of the correct
density, is a thoroughly reliable method of
working. In ordinary photography the goal of
development is detail in the shadows, but if
this is appUed in flower photography, the high
lights may become blocked up and too dense.
Detail in tke highest lights is the secret of success-
ful flower and fruit studies ; there will always be
detail in the shadows if the exposure has been
sufficient. The plate should on no account be
over-developed, and the following pyro-soda
developer is specially recommended : —
A. Potassium metabi-
sulphite . .IS grs.
Pyro . . . 130 „
Water . . .20 oz.
B. Sodium sulphite . 2 J oz.
Sodium carbonate
Water .
2
20
i-S g.
13 „
1,000 CCS.
125 g-
100 „
1,000 CCS.
For normal exposures take 3 parts of A and
I part of B. For under-exposure, add more
of B and dilute with water.
FLUID LENS
A glass shell, which may or may not have
optical qualities in itself, filled with liquid.
This arrangement is of considerable antiquity,
and has from time to time had photographic uses.
A fluid condenser made by Daguerre is still in
Section of Fluid Lens
existence ; while Scott Archer, Thomas Sutton,
and later Dr. Griin, all constructed lenses in
which liquids played an important part. With
the Sutton lens {see illustration) an extremely
wide angle was obtained, but in the Archer and
Griin lenses the special object was to gaiu
" rapidity." In the illustration, A indicates
glass, B water, and c the diaphragm. The Griin
lens was said to contain cedar oil.
FLUID MEASURE [See " Weights and Meas-
ures.")
FLUORESCEIN (See " Fosine.")
FLUORESCENCE
Certain substances have the power of altering
the wave-lengths of the hght or electric rays which
fall upon them. Such bodies, when illuminated
by ultra-violet light, become visible iu darkness
to the naked eye by emitting yellow, green, blue
or blue-violet rays, commonly termed fluores-
cence. Quinine sulphate, calcium tungstate,
and barium platino-cyanide are typical fluoresc-
ing substances. Many aniline dyes, particularly
fluorescein, have considerable fluorescing pro-
perties, eosine, for instance, giving a green
fluorescence. In most cases the colour of the
fluorescence given by dyes is complementary to
the colour of the dye itself.
FLUORESCENT SCREENS
These are largely used in radiography. They
are made by coating a suitable fabric witii
barium platino-cyanide, calcium tungstate, or
other substances which fluoresce when exposed
to X-rays. These screens, when used in a dark
chamber, permit of the visual examination of
objects placed between the X-ray tube and the
fluorescing screen, the form and, to a limited
extent, the structure of objects appearing as
shadows on the screen. Of late years fluorescing
screens have been popular for shortening the
exposure in X-ray photography ; they are placed
in contact with the sensitive film of the dry plate,
and the fluorescence in conjunction with the
direct action of the X-rays on the plate materially
shortens the exposure. Fluorescent screens
made of quinine sulphate are used to detect the
presence of ultra violet light.
FLUORESCENT TUBES
Vacuum tubes, for use with electric currents,
which contain traces of gases after almost com-
plete exhaustion. When a high potential current
is passed through such a tube it glows with
various coloiurs, each gas giving off a distinctive
fluorescence. Fluorescent tubes are much used
in spectroscopic analysis to determine the nature
of gases. These spectra consist of bright lines
only. X-ray tubes fluoresce owing to the smaU
quantity of residual air they contain after
eichaustion.
FLUORHYDRIC ACID
Acid.")
(See " Hydrofluoric
FLUORIC ACID
Another name for hydrofluoric acid {which see).
FLUORIDE {See "Potassium Fluoride," etc.)
FLUOROTYPE
An obsolete process (invented by Robert Hunt
in 1844) for obtaining pictures upon paper in
the camera, so called from the introduction of
the salts of fluoric acid. The solutions were : —
A. Potassiuni bromide 20 grs. 20 g.
Distilled water . [ oz. 500 ccs.
B. Sodium fluoride . 5 grs. 5 g.
Distilled water . i oz. 500 ccs.
These were then mixed together, spread
on plain paper, and dried ; the prepared paper
was next treated with 60 grs. of silver nitrate
dissolved in i oz. of water. The paper was given
about half an hour's exposure in the camera,
then soaked in water, a weak solution of iron
protosulphate brushed over it, washed in water
acidulated with hydrochloric acid, and fixed in
either plain water or a weak solution of sodium
hyposidphite ; finally it was washed well.
Fluosilicic Acid
262
Focal Plane Shutter
FLUOSILICIC ACID
More correctly known as " Hydrofluosilicic
Acid " (which see).
FOCAL APERTURE
The effective aperture of a lens expressed as
a fraction of its focal length. When the object
is at a. considerable distance from the lens this
is a fixed quantity for each stop, but when copy-
ing, the focal aperture becomes less in propor-
tion to the size of the image. Thus a lens working
with its largest opening at//8 on a distant object
has its intensity reduced to //16 when copying
to equal size, and to 7/32 when enlarging to three
diameters. The relative exposure necessary with
any given lens working at varying camera
extensions may be obtained by increasing the
exposure required for a particular aperture at
the normal focus in the proportion of Uie squares
of the normal and temporary focal lengths
respectively. Thus, if a lens having a normal
focal length of 6 in. is used with a camera exten-
sion of 9 in., the exposure with any stop will
be increased in the proportion of 81 to 36 ; in
other words, 2J times the normal exposure will
be required.
FOCAL LENGTH (Pr., Longueur du foyer:
Ger., Brennweite)
The distance between the centre of a lens and
the screen or plate upon which the image of a
distant object is sharply depicted. This defini-
tion, however, is only correct in the case of a
very thin lens, in which the thickness of the
glass does not come into consideration, and
in which there is only one element. In the case
of modem photographic lenses, " focal length "
is often taken to mean " equivalent " focal
length ; that is to say, when a lens will render
the image of a distant object on exactly the
same scale as would a very thin spectacle lens,
the two are said to be of the same equivalent
focal length. Equivalent focal lengths vary in
direct proportion to the size of the image
obtained; thus, assuming that a 6-in. lens
gives a 3-in. image of a distant object, an i8-in.
lens will give a 9-in. image of the same object.
This fact enables the measurement of the focal
length of any lens to be effected by simple com-
parison of its image with a similar image made
by a lens of known focal length, or, better still,
with a pinhole image. A practical method is to
substitute for the lens a fairly small pinhole, the
camera being extended to a convenient length
(a length of 10 in. simplifies the slight calculation
necessary), and to take a negative of some distant
object having two easily recognisable points, such
as chimneys or telegraph poles, these being
shown a few inches apart. The distance between
these two points is carefully measured and
becomes a constant factor in determining the
focal length of any other lens which can be
focused upon the same object. Assume that the
distance between the points is 4'5 in. Taking a
lens of unknown focal length, it may be foimd,
for example, that the images of the two selected
points are 3 in. apart ; then as 4-5 is to 3 so is
10 to ^. 3 X 10 -5- 4-5 = 6-66 in. An approxi-
mately correct result may be obtained by focus-
ing a near object so that it appears in natural
size upon the screen ; then one-fourth of the
distance between the object and the focusing
screen is the focal length of the lens.
The focal length of negative lenses may be
ascertained by neutralising them by placing
positive lenses in contact with them until one
is found that practically loses its convergent
powers ; then tiie concave lens is said to have
a negative focal length equal to that of the
positive lens which it neutralises. Dallmeyer's
method is to place a diaphragm, containing two
small openings, in contact with the negative lens,
which is then turned to the sun ; the light pass-
ing through these two small openings is received
upon a white card, which is moved away from
the lens until the two spots of light are double
the distance apart as compared with the open-
ings in the diaphragm ; then the distance between
the diaphragm and the card is the negative focal
length
FOCAL PLANE SHUTTER
A shutter that works immediately in front
of the plate, and now commonly fitted to the
highest class cameras. It is believed to owe
its practical form to B. J. Edwards, who in i88i
published a description of his apparatus ; but
some eighteen or twenty years previously the
principles were known to William England, who
used a crude device working on the same principle
a long time before Edwards's ideas were published.
England's device was a board containing a
horizontal slit which travelled in front of the
plate in the same manner as the drop shutter of
the present day travels in front of the lens,
and it was caught in a kind of bag suspended
from the camera. A shutter of a similar nature
had previously been experimented with by Dr.
Mann, who recognised its power to utilise the
whole of the light admitted by the lens. Prom
1882, in which year Edwards lectured upon his
invention before the old South London Photo-
graphic Society, until 1892, the focal plane
shutter seems to have been lost sight of, but
in the latter year the Thomton-Pickard Company
placed upon the market their now well-known
shutter of this type, and, simultaneously,
Stolze and Ottomar Anschutz, quite unknown
to each other, were both working to the same
end — the simphfication and perfection of the
shutter, more particularly, perhaps, in the
means of adjusting the sUt.
The principle of the shutter is as follows : —
A roller blind, containing a slit or aperture the
whole length of the plate, is made to travel
immediately in front of the sensitive surface.
Assuming ttiat this gives an exposure of j^th of
a second, by reducing the slit to one-fifth of its
original width the exposure is reduced to i^th
of a second ; again, by increasing the tension of
the spring by five or ten times an exposure of
^th or rsWtli of a second respectively is
obtainable. Most subjects come within the
range of ^th to ^^irth of a second. The
efficiency of the focsd plane shutter is greater
than that of the lens shutter ; some types of lens
shutter pass for only a very small proportion of
the totsu exposure the whole of the light that
the lens is capable of transmitting, mu^ of the
time of exposure being taken up by the shutter
in uncovering and then covering the lens, there
being only a brief period when the lens is quite
Foci
263
Focus
nncovered. With the focal plane shutter the
whole of the light admitted hy the lens is avadl-
able for action upon any particular portion of
the plate uncovered by the sUt ; and another
advantage is the high speed at which the shutter
can work, rendering it indispensable for " in-
stantaneous " work of any kind.
It is sometimes affirmed that the focal plane
shutter gives distorted results, but its advocates
afiSnu that the distortion (if any) is practically
negligible. In practice, distortion may be
divided into two classes : (a) that in whidi the
outline of any one body is rendered untruth-
fully, and (6) that in which the relative position
of a group of figures or objects is incorrectly
delineated; this latter may, of course, include
the former, and of the two is the more serious.
While it matters but little if an image of, say,
a rapidly moving railway train is sUghtly longer
or shorter than would be the case were Oie train
photographed at rest, it is a serious matter if
the result of a closely contested cycle race is
rendered incorrectly. To minimise any possible
error, the following points on the correct use of
the shutter should be remembered. If the image
(on the focusing screen) of the subject being
photographed is rapidly moving in the same
direction as the sUt in the shutter, the slit must
be made to move at a much greater speed than
if the image and slit were travelling in opposite
directions. The use of a shutter travelhng at
great speed in an opposite direction to that of
the image has a tendency to shorten the object,
while, on the other hand, the use of a shutter
travelling in the same direction as the image
may lengthen it. But such distortion is so
trifling that it would be practically impossible
to discover it. When engaged in high-speed
work a good distance at which to work is about
seven or eight yards from the subject. Using a
6-in. lens at a distance of eight yards, for
objects moving at right angles to the camera
these exposures would be about correct : —
Trains, horses galloping, cycle rac-
ing, etc. .... rAnr sec.
Men racing, jumping, etc. . ^^ sec.
Diving ..... ^ sec.
If the object is taken end on — that is, coming
towards, or receding from the camera — exposures
three times as long as the foregoing may be
given. By doubling the distance from the
object, the length of exposure may be doubled.
To develop plates which have received a
minimum of exposure, a very energetic developer
must be employed. The following formula is
recommended, using equal parts of A and B : —
B.
PjTogallic add . 40 grs.
Ketol . . . 35 „
Potassium meta-
bisulphite . 90 „
Potassium bromide 15 „
Water to . .20 oz.
Sodium carbonate . 3 oz.
Water to . . 20 ,,
4-4 g.
3-8 „
10 „
1-6 „
1,000 ccs.
164 g.
1,000 ccs.
FOCI, VARIABLE (See " Telephoto Lens.")
FOCIMETER (Pr., FocimUre : Ger., Fohus-
messer. Bren-nweitemesser)
An instrument invented by Antoine J. P.
Claudet, and used to test whether the chemical
and visual foci of a lens coincide, that is, whether
the lens is achromatic. It consists of a. series
of cards with different letters or numbers
arranged radially on a horizontal rod, one behind
the other, as illustrated. The middle card is
focused sharply with the full aperture of the
FOCI
The plural of focus (which see),
FOCI, CONJUGATE (5ee "Conjugate Fod.")
Claudet's Fodmeter
lens to be tested, a plate being then exposed and
developed. If the card focused is perfectly sharp
in the resulting negative the lens is properly
achromatic ; but if one of the other cards is
sharper, the chemical focus of the lens does not
agree with the visual focus. By focusing the
card that is rendered sharply in the negative
and noticing the extent to winch the screen has
to be moved from its former position, the
difference between the two fod and the exact
degree of correction required will be ascertained.
Several modifications of this apparatus have
been suggested.
FOCISCOPE
A focusing eyepiece introduced by Penrose,
the lens consisting of three elements cemented
together, forming a very powerfid magnifier of
fairly flat field. It is useful for examining half-
tone dot images.
FOCOMETER (Pr., FocomHre: Ger., Fokomesser)
A lens-testing apparatus designed by Thomas
R. Dallmeyer, for ascertaining the focal length
of a lens, and the degree to which the various
aberrations are corrected, or otherwise. It is
essentially a type of optical bench.
FOCOPLANE
Focal plane ; see " Focal Plane Shutter."
FOCUS (Fr., Foyer ; Ger., Brennpunkt)
Plural, fod. The point at which the rays of
light emitted by any luminous body converge
after passing through a lens to form the image
of such a body. The position of the focus is
simply demonstrated by using the lens as a
burning glass. The focus of a lens is a position
and not a distance, although the word is often
so misused (see " Focal Length " ). The focus for
distant objects is often called the prindpal or
solar focus.
Focus Adjuster
264
Focusing Glass
FOCUS ADJUSTER (Fr., Ajusteur de foyer ;
Ger., Fohvisordney)
An arrangement for lengthening or shortening
the focal length of a lens, by the use of a single
supplementary lens, or a series of such lenses of
varying foci. A device described by John
TraiU Taylor consisted of a movable brass sKding
piece, for which an opening was provided in the
lens mount between the combinations. In the
sliding piece were four apertures, each fitted with
a thiu achromatic negative lens. The appliance
was designed for use with a doublet composed
of two sKghtly meniscus lenses, which by them-
selves did not give a flat field. With the focus
adjuster, the focal length of the objective was
increased to 7, 9, 12, or 15 inches, according to
which of the four concave lenses was used, the
field at the same time being flattened and the
marginal pencils corrected at a fairly large
aperture.
FOCUS, DEPTH OF (See " Depth of Defini-
tion, etc.")
FOCUS, EQUIVALENT (See " Focal Length.")
FOCUS TUBE (See "Crookes- Tube.")
FOCUSER (See " Focusing Magnifier.")
FOCUSING (Pr., Mise au foyer, Mise au point;
Ger., Einstellung)
The action of adjusting the extension of the
camera until the image is sufficiently sharply
defined on the ground-glass focusing screen. A
focusing magnifier assists in determining when
the image is sharp by allowing slight differences
in crispness to be more easily seen. As all the
planes of a subject cannot be equally well
defined, it is important to recognise which
should show the most critical definition. Objects
near the eye should naturally show greater
sharpness than those farther away. But, in
addition, the principal object in a picture should
show the best definition, should any differences
exist. Where there is a number of objects at
different distances, and it is desired to secure
a imiform degree of sharpness between the near-
est and the farthest, it is advisable to focus on
a point beyond the nearest object, about one-
fouith of tie distance from the nearest to the
farthest.
In process work, several schemes have been
proposed for automatic focusing. Some elabor-
ate mechanical inventions have been devised for
moving the camera to and from the copyboard
at the same time as the focusing screw is turned
to move the ground glass of the camera, but none
of these arrangements has come into practical
use. A more convenient method, which can be
appHed to any camera and stand with little
alteration of existing arrangements, is the
Scalometer system, invented by I,. Emmett.
The scalometer is an instrument made in box-
wood, opening like a two-foot rule, there being
on the two limbs similar scales of equal divisions
numbered from the ends of the Umbs. A cross
rule divided into inches or centimetres bridges
the angle formed by the opening of the two
Umbs. In operation the points or ends of the
limbs are applied compass-like to the sides of
the original, and then clamped at this separation.
The cross rule is then made to sUde up and down
until it indicates across the angle formed by the
limbs the measure of the desired reduction. At
this point the proportional number on the two
limbs is read off, and is marked on the back of
the original. Then all originals which bear the
same proportional number can be photographed
Scalometer for Facilitating Focusing
together. By means of a printed scale supplied
with the instrument it is possible to mark
off the copying stand with numbers correspond-
ing to those on the limbs of the instrument,
so that the camera can be instantly set to the
proportion number marked on the original,
without the necessity of focusing.
FOCUSING CAMERA (Pr., Chambre d foyer
rigldble ; Ger., Einstellungs-kamera)
Any camera in which different distances can
be focused for, as distinguished from fixed-
focus cameras, which do not permit of adjust-
ment. Self-focusing cameras are those which
extend automatically to the correct focus for
any given distance, on setting a pointer or
turning a key on a marked dial. Such adjust-
ments are usually only to be found on hand
cameras.
FOCUSING CLOTH C]?T.,Voile,Voilenoir,Voile
de chambre. Voile de mise au point ; Ger.,
Einstellungstuch, Kopfhwh, Schwarze Lein-
wand)
Synonym, black cloth. A doth used to cover
the back of the camera and the operator's head
when focusing, in order to exclude extraneous
light, which would interfere with the visibility of
the image on the ground-glass screen. It is
also employed to shield the top of the dark-slide
when withdrawing the shutter, and not infre-
quently to wrap up the sKdes after the exposures
have been made. It is usually made of black
velvet or twill, which may or may not be liaed
with yellow or red doth, or of waterproof doth.
A cloth is more convenient in use when provided
with cords at the comers for tying to the camera
in windy weather ; whilst a loop in the middle of
one side, to sUp over the lens, is always useful.
For a small camera, the focusing doth may be
about 3 ft. square.
FOCUSING GLASS
A name for the focusing magnifier (which see).
The term is applied occasionally to the focusing
screen of the camera.
Focusing Jacket, or Rack Mount 265 Focusing Uncorrected Lens
FOCUSING JACKET, OR RACK MOUNT
(Pr., Tube A crimailUre ; Get., Zahnstange
Obfektivrohr)
A form of lens mount provided with an inner
tube carrying the glasses, which slides to or fro
by an attached rack and pinion. This kind of
mount is found on lantern, enlarging, and
Cinematograph objectives, and some portrait
lenses. For lantern and kinematograph use,
the jacket is sometimes suppUed empty, to allow
of the insertion of different objectives in loose
interchangeable tubes or cylinders.
FOCUSING MAGNIFIER [^., Loupe, Loupe de
mise au point ; Get., Einstelloupe)
Synonyms, focuser, compound focuser, focus-
ing eyepiece, focusing glass. A lens used when
more accurate focusing is desired than is obtain-
able on the ordinary ground-glass screen, as may
be necessary in photo-micrography, process
work, etc. It is usually composed of two plano-
convex lenses of identical focal length, mounted
with their plane sides outward at a distance
apart equal to two-thirds of the focal length. The
ABC
Focusing Magnifiers
lenses should preferably be achromatic, though
this is not indispensable. To use the magnifier,
a piece of plain plate glass having a few fine
black lines ruled on it is substituted for the
ground-glass focusing screen ; or, as an alterna-
tive, several microscopic cover glasses may be
cemented at suitable spots on the ground glass
by means of Canada balsam, having first made
a pencilled cross on the ground surface where
each glass is to be attached. The magnifier is
adjusted by sUding or rotating the upper tube,
till the ruled lines or pencilled cross, as the case
may be, are in sharp focus, when it only remains
to see that the image on the screen is in focus
at the same times as the lines or cross. The
magnifier gives an enlarged image, and naturally
a brighter one than can be obtained on ground
glass. A shows a magnifier with screw adjust-
ment and clamping collar ; B shows one with
an Archimedean screw movement ; C has an
erecting lens to show the image the right way
up ; while D is provided with a bayonet tripod
by which the magnifier may also be raised to
examine prints, half-tone blocks, etc., if required.
FOCUSING NEGATIVE LENS (See "Nega-
tive Lens.")
FOCUSING SCALE (Pr., tchelle de mise au
point : Ger., Einstellskala)
A graduated scale or dial fitted on hand
cameras, enabling objects at various distances
to be focused, by the movement of a pointer,
without inspecting the screen.
FOCUSING SCREEN (Fr., Vevre douci. Glace
doucie ; Ger., Visirscheibe, Mattscheibe,
Mattglas, Mattglasscheibe)
The screen upon which the image formed by
the camera lens is focused, before exposing the
plate, in order to secure sharp definition. It is
usually of glass ground on one side to a matt
surface. Some of the ground-glass screens
supplied with the cheaper cameras are extremely
coarse. A finely ground glass is, however, on
the market in the usual cut sizes at very reason-
able prices. A good substitute, having the
advantage of being light and unbreakable, is a
sheet of matt celluloid ; but care must be taken
that this does not buckle, or it will not agree in
register with the dark -slide. For this reason
cdluloid is scarcely suitable for large cameras.
Temporary makeshifts, to replace a broken
focusing screen, are : white tissue paper or
tracing paper stretched taut, a fine cambric
handkerchief, or plain glass dabbed lightly with
putty. For Lohse's method of forming a focus-
ing screen the following is necessary: —
Gelatine . . -45 grs. 450 g.
Barium chloride . 15 „ 150 „
Ammonium sulphate. 7i „ 75 ,,
Water to . . • 3i oz. 1,000 ccs.
The gelatine, sulphate and three-fourths of
the water are heated together until dissolved ;
the barium, dissolved in the remaining fourth
of the water, is then added. After mixing and
cooling, the mass is pressed through muslin so
as to form threads, then washed and melted
again. Finally a trace of salicyUc acid in alcohol
is added, the whole is filtered, and is then ready
for coating upon plain glass. The solution is
slightly troublesome to prepare, but such a
screen may with care last a lifetime. A less
troublesome method, due to P. R. Salmon, is
to apply to plain glass a varnish consisting of —
White lac . . • 70 grs. 80 g.
Picked gum sandarac . 12 „ 14 „
Alcohol . . . 2 oz. 1,000 ccs.
C. Welbome Piper has suggested stiU another
method ; a dry plate should be fogged uniformly
all over by immersion in a developer for a long
time, fixed, bleached in a solution of 5 grs. of
iodine and 10 grs. of potassium iodide in i oz.
of water, treated with very dilute ammonia,
washed, dried, and varnished. A screen pre-
pared iu this way, or in any of the other ways
above mentioned, is far superior to ground glass.
In process work, the ground-glass screen used
has a transparent centre formed by cementing
a thin microscopic cover glass to it with Canada
balsam. Extremely fine focusing can then be
done by means of an eyepiece. A cross should
be made on the ground glass with a blacklead
pencil before cementing down the glass, so that
the focus of the eyepiece may be adjusted to it.
FOCUSING UNCORRECTED LENS
When using an uncorrected lens, that is, one
in which the visual and actinic foci are not
Coincident, an allowance has to be made after
focusing so as to bring the sensitive plate into
the plane of actinic focus. The amount of this
varies with the refractive index of the glass, but
as such lenses are commonly made of crown
Fog
266
Fogged Negatives
glass, it is usually safe to place the plate ^ to
^ of the focal length nearer to the lens. The
correction may also be made, as in the case of
SteinheH's original periscope, by focusing at full
aperture and then stopping down to f/44, or
smaller. Another method is to place a very
weak lens in front of the working lens whUe
focusing and removing it before exposure. This
corrector must temporarily shorten the focal
length to the necessary degree.
FOG (Fr., Voile ; Ger., ScMeier)
A general reduction of the silver salt by the
developer, particularly on those places which
should be dear glass in the negative or white
paper in the print. The various kinds of fog
are discussed in later articles.
FOG, AERIAL (Pr., Voile airien : Ger.,
Aetherisch Schleier)
Mist, or fog, particularly noticeable in the
distance in landscapes, due to the reflection of
the ultra-violet and blue rays by minute par-
ticles of water, vapour and dust. It is a factor
to be recognised, particularly in telephotography
and mountain work, and in such cases the use
of colour-sensitive plates and a yellow screen,
which cuts out the ultra-violet and blue, is
advantageous. On the other hand, the peculiar
softening effect of aerial fog is extremely pleasing
from an aesthetic point of view, and care should
be exercised therefore not to eliminate its effects
unduly.
FOG, CHEMICAL (Pr., Voile chimique : Ger.,
Chemischer Schleier)
A reduction of silver all over the surface of
the plate or paper, which may be due either to
chemical fog inherent in the emulsion, to too
strong a. developer, or to the access of actinic
light or the use of an unsafe dark-room Ught.
Pog inherent in the emulsion cannot be ciured,
but its ill effects may be somewhat obviated
by exposing fully and adding potassium bromide
to the developer. A clean working plate should
stand three minutes' development in the dark,
without previous exposure to light, in a normal
pyro-soda developer, and then present but the
slightest trace of deposit. Chemical fog, caused
by using too strong a developer, may be obviated
by weakening the developer and by the addition
of a Uttle bromide,
FOG, COLOUR, DICHROIC, GREEN, AND
RED (Pr., Voile rouge ; Ger., Rotschleier)
A peculiar form of fog, which is green by
reflected light and red by transmitted light. It
is in all cases due to silver deposited in a colloidal
state, and shows itself most prominently in the
shadows of a negative. It may be due to the
emulsion itself, to traces of " hypo " in the
developer, excess of a solvent of the silver
haloid, such as sulphite, etc., or it may arise
through partial fixation and reduction of the
soluble silver salts by traces of the developer.
This last form is often to be met with in films
when one lies over another in the fixing bath.
Dichroic fog is in almost all cases sensitive to
light, and though this is not readily noticed, it
can be proved at once by covering up part of
the negative showing this defect, and exposing
to sunlight. It is extremely difficult to remove,
but treatment with the following is the most
efi&cacious remedy : —
Sodium sulphite . i oz. 50 g.
Potassium cyanide. 100 grs. 10 „
Distilled water to . 20 oz. 1,000 ccs.
Abney has suggested bleaching the negative
in a mixture of ferric chloride and potassium
bromide. Well washing, and then redeveloping
with ferrous oxalate, which reduces the dicluroic
to a general fog.
FOGGED DRY PLATES, RESTORING
Plates which have been accidentally exposed
to Ught (Ughtstruck is a term sometimes used),
may be made almost as good as new, with the
exception that their speed is reduced, by treat-
ment for about five minutes in either of the
following restoring baths : —
Chromic acid . .15 grs. 6'2S g.
Potassium bromide .30 „ i2"S ,>
Water to . . .5 oz. 1,000 ccs.
Potassium bichromate 20 grs. 8-3 g.
Hydrochloric acid . i drm. 25 ccs.
Water to . . . 5 oz. 1,000 „
Afterwards, the plates are thoroughly washed
and dried. All the operations must be carried
out in the dark-room. Plates that have been
exposed in the camera, but have not been deve-
loped, may be restored in the same way, but the
immersion must be of longer duration. Plates
restored in this way need from five to ten times
the normal exposure. Several other methods
are possible, one of which is to soak the plate in
a 2 per cent, solution of ammonium persulphate ;
Condys fluid (as bought), with the addition of a
few grains of potassium bromide, also answers.
Abney has recommended a bichromate bromide
mixture made by dissolving 10 grs. of potassium
bichromate in i oz. of water, 10 grs. of potassiimi
bromide in another ounce of water, and adding
the two together.
Pogged dry plates can be made specially suit-
able for transparency work by soaking for about
ten minutes in —
Potassium bromide
. 120 grs.
12 g.
Potassium iodide
• 15 ..
1-5 „
Hot water
i oz.
25 ccs.
When dissolved add —
Hydrochloric acid . ^ oz. 25 ccs.
Potassium bichromate 120 grs. 12 g.
Water to . . .20 oz. 1,000 ccs.
Wash and dry.
The plates are made very slow by any of the
processes named, and thus they give greater
contrasts ; hence their suitability for copying
black-and-white work. They should also be
developed with a clean-workmg developer, such
as adurol or hydroquinone.
FOGGED NEGATIVES, TREATMENT OF
The method of treating fogged negatives must
depend on the cause or nature of the fog. Deve-
lopment fog, and fogging or staining caused by
the plates being stale, are most successfully
treated by thiocarbamide. A stock solution
Fogged Prints, Treatment of 2^7
Formosulphite
may be prepared, as it will keep weU. The
formvila is : —
Thiocarbamide
Common alum
Citric acid
Water to .
i6
i oz.
i „
31 g-
31 ,.
IS ,,
1,000 CCS.
In very bad cases of fogging, this solution
may be used without dilution ; but in ordinary
cases one part stock solution to one or two parts
of water will be preferable.
Fogging from over-exposure, or from exposing
the plate too freely to the dark-room light, is
best treated by Farmer's reducer, this consisling
of " hypo " and potassiimi ferricyanide.
Fogging by exposing the plate too much
during development or in loading the camera is
most difficult to treat successfiUly. (See also
" Exposure, Incorrect.")
FOGGED PRINTS, TREATMENT OF
Fogged prints are generally not worth the
trouble of treatment, excepting bromide and
gaslight paper prints in which the white parts
are degraded Uirough the paper being stale.
In all other cases the prints should be thrown
away and replaced by new ones. The treat-
ment should be the same as that given for plates
showing development fog, or fog arising from
the plates being stale. (See " Fogged Nega-
tives, Treatment of.") The thiocarbamide bath
should be used, but the solution should be
more dilute, in most cases, i part of the
stock solution already given should be taken
and 3 parts of water added. The thiocar-
bamide bath should be used after fixing and
well washing the print.
FOLDING CAMERA (Pr., Chambre pUante,
Chanibre folding ; Ger., Falte-kamera,
Klapp-hamera)
Any camera made to dose by folding, as
opposed to studio and process cameras, which
do not close in this way, and to box-form hand
cameras. A folding hand camera is commonly
understood to be of a specially light and portable
construction, although the term is used very
indefinitely. A style of hand camera in whidi
the front extends on four struts is known in
Germany as a " klapp " camera. (See also
"Hand Camera.")
FOREGROUND
The part of a subject nearest the spectator.
The term is stretched to include water. As
foreground objects are naturally seen with the
greatest clearness, the treatment of this part of
a picture demands careful attention. Especially
is this the case with stereoscopic pictures. Fore-
ground objects may be brought into greater
prominence if the camera is lowered consider-
ably, espedaUy when (as in the case of a group
of flowers) they are intended as the subject of
the picture. It is sometimes difficult to get a
near foreground and also the distance quite
sharp wittxout considerable stopping-down of
the lens ; and in such a case tiie top of the
camera back may be swung away from the lens.
If there is to be lack of definition anywhere in
the picture the foreground is usually the last
place where it is permissible.
FOREGROUND SHUTTER (Pr., Ohturateur
des devants : Ger., Vortergrund-verschluss)
A shutter designed to give a longer exposure
to the foreground of a landscape, or similar out-
door composition, than to the sky, thus enabling
both to receive a more correct exposure than
would otherwise be the case.
FOREIGN PLATES, ETC (For sizes, see
" Sizes of Plates and Papers.")
FORMALINE, FORMALDEHYDE, FORMIC
ALDEHYDE, FORMIC ANHYDRIDE,
OR ANTIPYR (Pr., Formal; Ger., Alde-
hyde formique. Formalin, Formaldehyd)
Best known as formaline. Ordinarily it is
met with in aqueous solution, which is prepared
by passing the vapour of methyl alcohol mixed
with air through a heated tube containing
copper gauze. The liquid is colourless, has a
characteristic smell, and, as obtained com-
mercially, contains about 40 per cent, of formalde-
hyde. Formaline vapour attacks the mucous
membranes of the eyes, nose, and throat, and
causes intense irritation.
Photographically, it is used chiefly for harden-
ing gelatine films, it replacing and being safer
than alum. A suitable strength is 10 per cent.,
and it may be used immediately after fixing
for both negatives and prints. It has also
been suggested as a constituent of developers,
the most useful formula being —
Hydroquinone .
Sodium sulphite
Formaline
Water to .
40 grs. 16 g.
400 „ i6o „
50 drops 20 CCS.
S oz. 1,000 „
The above is a one-solution developer ready for
use, no bromide or alkali being required when
formaline is present. The above developer is
suitable for negatives of black-and-white draw^-
ings, or for giving strong contrasts in other
subjects.
FORMIC ACID (Pr., Acide formique ; Ger.,
Ameisensdure)
Synonym, hydrogen carboxylic acid. H COOH.
Molecular weight, 46. A clear liquid obtained by
distilling oxalic add with glycerine. It is a
dangerous caustic, and must be handled very
carefully. It was used in the old wet-plate
days, and has been recommended as a preserva-
tive for pyro, but whilst a good preservative,
the addition of an alkali turns the solution
muddy and black.
In process work, formic add is sometimes used
instead of acetic add for the stripping of wet
coUodion negatives. Its disadvantage is that it
is injurious to the hands.
FORMOSULPHITE (Pr., Formosulfite; Ger.,
Formosulphite)
One of Messrs. Lumiire's patented products,
which takes the place of an alkali in the developer.
It is sold in tiie form of a white crystalline
powder, and, as its name suggests, is a prepara-
tion of paraformaldehyde, sodium sulphite, and a
small quantity of an alkaline bromide. It acts
also as a preservative, prevents stain, and hardens
the film.
Formyl Chloride
268
Freezing or Cooling Mixture
FORMYL CHLORIDE OR TRICHLORIDE
(See " Chloroform.")
FOTHERGILL PROCESS CPT.,'Procide Fother-
gill ; Get., Father gill's Pyozess)
A dry process introduced by Thomas Pother-
gill in 1858. The plate having been coUodionised
and sensitised in a neutral silver nitrate bath,
as usual in the wet-plate process, was washed
with rain water and allowed to drain for about
half a minute. Some plain albumen, obtained
by well beating the white of i egg with 2 drms.
of water, and allowing to subside, was then
ppured on the collodion film, and, after remain-
ing for thirty seconds, was washed off under a
gentle stream of rain water, sufficient remain-
ing in the pores of the collodion to answer the
purpose of preserving its sensitiveness. The
plate was then allowed to dry and was fit for use.
Such plates would keep some time, and could be
exposed dry without previous preparation.
FRAME (Ft., Cadre ; Get., Rahmen)
The selection of a suitable frame for a finished
print is an important matter. Portiyiately, the
special demands of photographers in this respect
have been fully met, and there is now no lack
cxf choice in appropriate frames. It must be
remembered that the chief purpose of a frame,
with or without a mount, is to isolate the picture
from its surroundings. Therefore, a frame
defeats its own end when it attracts attention
from the print to itself. For this reason an
ornate, or so-called " fancy " frame, is generally
unsuitable. The great majority of photographic
prints are seen to best advantage in a simply
designed frame of a dark colour. The various
mouldings may be roughly classified into those
. that are flat and practically flush with the
picture, those that throw it forward, and those
that throw it back. If the print is framed close
up, that is, without showing any margin, a
wide moulding is generally best. A narrow one
in such a case does not adequately isolate the
print, and has a " skimpy " effect. On the other
hand, a mounted print demands a much narrower
moulding. The more mount there is the narrower
may the moulding be, as the mount and frame
may be regarded as a whole.
Gold frames, and those with a highly varnished
surface, are not often suitable. Far more effec-
tive, as a rule, are well-made frames of good
solid oak, stained brown or black, and poUshed
by friction with a brush or a rough doth, or by
the sparing application of beeswax and turpen-
tine. (See also "Framing.")
FRAMES, PRINTING (See " Printing Frames.")
FRAMING
In addition to the actual selection of a suit-
able frame for a photograph (see "Frame"),
there are one or two other points to take into
account. First comes the question of the glass.
This should not only be free from flaws and
waviness, but it should be as colourless as possi-
ble. If a sheet of the usual picture-framer's
glass be laid down, so as to cover half of the
print only, a great difference will be noted
between the covered and uncovered halves. Not
only is the colour of the priat affected, but there
is a marked alteration in the values. Generally
the tones are degraded or flattened, especially
in the case of delicate grey prints. When a
clearer glass cannot be used, the print should be
kept somewhat brighter than it is intended to
appear in its framed state. When the glass is
placed in the frame it is well to run a narrow
fillet of paper round the edge, pasting it down to
the glass and the sides of tie rebate. Take care
that it does not show from the front, its object
being merely to keep out dust. The backboard
having been bradded securely down, glue or
paste brown paper over the entire back.
FRAUNHOFER LINES
When a solar spectrum is viewed in a spec-
troscope with a very narrow slit it will be seen
to be crossed by thousands of transverse dark
lines. The most prominent of these were named
by Fraunhofer according to the letters of the
alphabet, and are now called by his name.
No matter what the dispersing medium may be,
prism or grating, these lines always fall in exactiy
the same colour ; they are therefore extremely
convenient " milestones " or data for naming
any colour, and enable one to define a colour
exactiy. For instance, the term " yellowish
green " conveys no strictiy definite idea ; whereas
the term " a yellowish green like D ^ E " — that
is, midway between the Fraunhofer lines D
and E — indicates a definite and fixed tint. The
cause of Fraunhofer lines was determined by
Klirchoff and Bunsen, who discovered that any
substance in a state of incandescent vapour
absorbed exactiy those rays which it emitted
when in a state of luminescence. For example,
if a pellet of metallic sodium is burnt in an elec-
tric arc it emits two dazzUng orange-yellow
rays, known generally as the D hues ; but if
the light thus emitted is allowed to pass through
a cloud of somewhat cooler sodium vapour these
briUiant yellow Unes instantiy become black —
that is to say, their light is absorbed. This
fundamental law applies to all substances, and
by its aid it has been possible to detect the
elements burning in the sun and in still more
distant stars. (See also "Spectrum.")
FREEZING OR COOLING MIXTURE (Fr.,
Milange r^frigSrant ; Get., Kaltemischung)
A mixture which, by absorption of heat in
liquefying, produces a low temperature. It is
largely used in hot countries, and sometimes in
England during hot weather, to cool solutions,
particularly for use with gelatine plates and
papers. The ordinary " hypo " fixing bath is
itself a cooling mixture, for when freshly mixed
the temperature of the water falls considerably.
The most common freezing mixtures are the
following : —
Proportions
by Weight
Snow or pounded ice
Common salt (sodium chlor-
ide)
Snow . . . . ••31
Crystallised calcium chlor- >
ide 4 J
\}
1}
Water
Ammonium Nitrate
Sodium sulphate . .
Hydrochloric acid
Temperature
Produced
-•4''F. -r8°C.
-54°F. -48''C.
5°F. -I5°C.
i^4°F. -I7°C.
French Chalk
269
Fumell's Developer
A good method of lowering the temperature
of solutions is to place the bottles containing
them in a freshly made " hypo " bath.
FRENCH CHALK (See " Chalk, French.")
FRILLING
A trouble to which negatives are liable while
undergoing treatment in the various solutions ;
the edges of the gelatine film leave the glass plate
and are cockled. It is due to the uneven temper-
ature of the solutions, excess of soda or other
alkali in the developer, handling the negatives
with the warm fingers, the use of strong fixing
solutions, or to rapid washing, the water being
allowed to impinge upon the edges of the plates
in such a way as to lift the films. Frilling may
be prevented by hardening the film before or
after development with formaline, or a com-
bined fixing and hardening bath may be used.
If no precautions are taken and the gelatine
is found to be frilled, it may be more or less
remedied by treating with methylated spirit.
Frilling is allied to the far more common defect
of blistering, and the remedies given under a
separate heading for the latter apply equally
well for the former. Frilling often appears on
print-out papers when they are torn, as, for
example, when a half-plate piece is torn into
halves for use as quarter-plates. Printing papers
should always be cut clean, because rough edges
allow the water to get easily under the films,
so causing frilling.
Two old-fashioned but serviceable methods of
preventing plates from frilling may be mentioned.
One is to soak the dry plate before development
in a saturated solution of Epsom salts, and the
other is to rub a wax or tallow candle round the
exposed dry plate on the film side, before wetting
it with the developer. Neither of these, however,
is as reliable as immersion in a 10 per cent, solu-
tion of formaline. {See also "Hardeners" and
" Blisters.")
FRONT, CAMERA (Fr., Planchette d'dbjectif ;
Ger., Objektivbrett)
That part of the camera which carries the
lens. It should be provided with a rising and
falling movement, and a cross movement is an
additional advantage. In field cameras, it
should preferably also be arranged to swing, in
order that the lens may be tilted if desired with-
out needing to incline the camera. The fronts
of large cameras are commonly furnished with a
removable panel for the lens, an arrangement
which, by the employment of several panels,
permits various lenses of diflterent sizes or foci
to be used interchangeably on the same camera.
{See also " Cross Front," " Detachable Front,"
" Rising Front," and " Swing Front")
FROST SCENES
The photographing of frost scenes is dealt
with under the heading " Snow and Hoar Frost
Photography." Frost on window-panes may be
successfully photographed by placing a black
cloth outside the window at an angle of 45" and
photographing the frost from the inner side.
F.R.P.S.
Fellow of the Royal Photographic Society.
The Fellowship was instituted January i, 1895,
and is open to those who, being already members,
satisfy the Council of their ability in, or con-
tributions to, any branch of photographic work,
an annual subscription of two guineas being
payable.
FULL APERTURE
When no stop is used, a lens is said to work
at " open aperture " or " full aperture."
FULMINATING COTTON
Another name for gun-cotton {which see).
Sometimes used in flashlight photography.
FUMING
Photographically, the exposing of albumen
paper to the fumes of ammonia ; paper so treated
gives brighter prints and tones to richer colours
more easily. The sensitive paper to be fumed is
pinned to the inner side of a box lid ; in the
bottom of the box is placed liquor ammoniae in
a saucer, or it is sprinkled upon blotting-paper.
The box is then closed, and the paper exposed
(in the dark, of course) to the action of the
ammonia fumes for about ten minutes, or longer
if the weather is cold. Fuming is now almost
obsolete, but at one time it was recommended
for papers other than albumen, and even for
plates.
FURNELL'S DEVELOPER
A developer widely advocated about 1890 iot
positive work ; it is claimed to keep for years,
allow great latitude in exposure, give clear glass
shadows, and not frill the film.
No I :—
Sodium sulphite
Powdered alum
Distilled water .
SO grs.
10 „
3 oz.
Dissolve, filter, and then add —
Pyro
Sodium nitrate
24 grs.
36 „
10 g.
2 „
250 CCS.
4-8 g.
77 „
This is made up as a stock solution, and it will
keep indefinitely.
No. 2 : —
Liquor ammonise (-880) i^ drms. 15 ccs.
Ammonium bromide 30 grs. 6 g.
DistUled water to 15 drms. 150 ccs.
To develop, take ^ oz. of the No. i (pyro) solu-
tion, made up to 2 oz. with water, and add 10
drops of the No. 2 (ammonia) solution, and apply
to the plate, adding more of the latter if neces-
sary. After development, do not wash but rinse
in a satiurated solution of alum, then wash and
fix in the following bath, after which wash and
dry : —
Sodium hyposulphite 2 oz. 220 g.
Sodium carbonate . i„ S5 » ,
Alum (saturated sol.) | „ 50 ccs.
Water to . .10 „ 1,000 „
7 (See " Gamma.")
GAEDICKE'S INTENSIFIER
One of the silver intensifiers, the formula
being : —
Ammon. sulphocyanide loo grs. 46 g.
Silver nitrate . . 48 „ 22 „
Sodium sulphite . Soo „ 230 ,,
" Hypo " . . 100 „ 46 „
Potassium bromide . 7 „ 3 .>
Water . . . 5 oz. 1,000 ccs.
To prepare for use, mix as follows : —
Stock solution as above 48 drops 100 ccs.
Water to . . . I oz. 1,000 „
Then add —
Rodinal ... 16 drops 33 ccs.
Immerse the negative therein until intensified
and then wash.
GALL {See " Ox-gall.")
GALLATE OF IRON PROCESS
Better known as the " Ink Process " {which
see). The term has been loosely applied to other
iron processes of printing.
GALLIC ACID (Pr., Acide gallique ; Ger.,
GalHschsdure)
Occurs in fine, silky, yellowish crystalline
needles. CsHj (OH), COOH H^O. Solubility
I per cent, in cold water, 33 per cent, in boil-
ing water. Largely used in the early days of
photography as a developer for paper nega-
tives, and it was with this acid that Talbot in
1835 made some important discoveries in con-
nection with the latent image. It is occasion-
ally used in modem processes, as, for example,
in the development of P.O.P., intensification of
collodion and gelatine plates, and as an ingre-
dient in the ferrous citrate developer for chloride
plates.
Gallic acid is often used by lithographers for
preparing the surface of zinc plates for printing,
instead of the nutgall decoction recommended
by the old workers ; the effect is the same, and
the trouble of preparing the decoction is saved.
GALLO-NITRATE OF SILVER PROCESS
Another name for the old calotype or talbotype
paper process, in which paper was sensitised
with silver nitrate, immersed in potassium
iodide, washed, dried, exposed, and developed
with a mixture of silver nitrate, gallic, and
acetic acids and water. {See " Calotype.")
GALLS (NUTGALLS)
In zincography — lithographic printing from
zinc plates — a decoction of nutgalls, mixed with
gum arable solution, is used for preparing the bare
parts of the zinc so that they tepel the greasy
printing ink used for rolling-up. To make the
decoction, steep 4 oz. of nutgalls in 3 quarts of
water for twenty-four hours, and then boil up
and strain. For use, add |- pint of tliis solution
to i pint of gum solution, of the thickness of
cream, and 3 drams of a solution of phosphoric
acid.
GALVANOGRAPHY
Under this name there have been put forward
several processes based on the idea of painting
on a silvered copper plate with oil colour in thick
masses so as to give relief. When dry, or nearly
so, the surface is dusted with finely powdered
blacklead to make it electro-conductive, and a
thick copper shell is deposited on it. This is
subsequently used as an intaglio printing plate.
A process of this kind was patented by Prof.
Herkomer and Henry T. Cox in 1898. The basis
of the method was described by Franz von
Kobell, of Munich, as early as" 1842.
GALVANOGRAPHY, PHOTOGRAPHIC
A process of utilising a gelatine relief as a
mould for making electrotypes. Several in-
ventors have adopted the title, but Paul Pretsch
had probably the best right to it. His process
consists in coating a glass plate with gelatine
containing bichromate, with a silver salt and
other chemicals. When dry it is exposed imder
a transparency, and then immersed in cold water
to dissolve out the unaltered chromium salts
and cause those parts protected from the light
to swell up in proportion to the tones of the
picture. The high lights do not swell at all, and
have no grain. The plate thus produced is, of
course, an exact reverse of that required for
printing. The surface is next made conductive
with a metallic coating, so that an electro-
deposit can be made upon it, thus producing a
copper shell which can be backed up with type
metal to form a printing plate.
GAMBOGE (Pr., Gomme gutte; Ger., Gummi-
gutt)
Synonyms, camboge, gummi gutte. A gum
resin obtained from several species of guttiferse
trees, occurring in bright orange lumps with
conchoidal fracture ; used as a colouring pig-
ment.
The coating of lithographic writing transfer
paper is coloured with gamboge in order that the
prepared side may be distinguished from the
unprepared one. Gamboge has been recom-
mended as an addition to Indian ink for drawings
intended for photo-reproduction.
GAMMA (Pr. and Ger., Gamma)
The term adopted by Hujter and Driffield to
define the gradation, or degree of contrast, of a
270
Gas Cylinders
271
Gelatine
negative. Gamma infinity, or 700, as it is
usually written, is the ultimate density-giving
power of the plate. (See " Plate Testing.")
GAS CYLINDERS (See "Cylinders, Gas.")
GASLIGHT PAPERS
Papers coated with a chloride or chloro-bro-
mide emulsion, which can be manipulated in weak
gaslight. For suitable emulsions, see under the
lieadmg " Emulsions for Development." Gas-
light paper (so called) is really a very slow bro-
mide paper, and is developed, fixed and toned (if
necessary) like bromide paper, except that the
•developer must be stronger, and the develop-
ment is more rapid. Exposure can be made by
putting the paper into contact with a negative
which is held a few inches from a gas burner or
good oil lamp, but development must not take
place in a light equally strong or the print wiU
be fogged ; either the light must be turned
down diiring development, or the operation
must be carried out at some distance from the
light or in a shadow. Artificial lights other
than gaslight, or even very weak daylight, will
serve equally well ; in fact, the common practice
is to expose to the Ught of magnesiimi ribbon
and develop by aid of weak artificial light. A
metol-hydroquinone developer is usual, and this
must be accurately prepared, particularly as
regards the potassium bromide ; too little
bromide causes impure whites, while with too
much the blacks will be of a greenish hue.
Development should take place almost in-
stantaneously. An add fixiag-bath is advisable,
but not necessary. The colour of the print
depends on exposure and development ; longer
exposure and a weaker developer invariably
produce warmer tones. With most papers a
warm brown tone may be obtained by giving
three times the normal exposure and diluting
the developer with twice the bulk of water.
GASLIGHT, PORTRAITURE BY
The use of gaslight is possible for portraiture.
With ordinary gaslight (without mantles), ex-
posures are long even under the most favour-
able conditions, the light being poor in violet
rays and comparatively^non-actinic. Gaslight has
advantages for isochromatic work, as without a
yellow screen it gives practically the same result
as daylight with a screen, isochromatic plates
t>eing used in both cases. With a very rapid
plate, and the lens stopped down to//8, the neces-
sary exposure with two gaslights (not incan-
descent) 3 ft. from the sitter would be about
two minutes. Particular care is necessary in
posing, using a reflector, and in development,
as the results are bound to be a trifle hard and
■" contrasty."
Incandescent gaslight is better for portraiture,
as a full-size mantle gives an illumination of
about sixty candle-power when at its best, and
is about one and a-half times as eflective
photographically as a gas flame of the same
visual intensity, because of the whiteness of the
light and its ridmess in the blue or actinic rays.
The exposure depends, of course, upon the num-
ber of burners. The spedal fittings obtainable
from factors are in the form of brackets containing
a, score or more lights, which make possible quite
brief exposures — say one or two seconds ; but
an enormous amount of heat is produced. Fair
resvilts may be obtained with one or more
ordinary domestic burners, but the exposure is
somewhat long, a minute at least, with two
lights near to the sitter, a very rapid plate, and
the lens at //8.
It will be noted that all gaslights are in-
candescent, the light in a plain iiame being
produced by heating particles of carbon to in-
candescence ; but it is convenient to adopt here
the ordinary nomendature by which the term
" incandescent " is restricted to burners of the
Bunsen type, fitted with manties of rare earths.
Acetylene outfits for portraiture are similar
to the incandescent gas fittings in arrange-
ment. The light is very actinic, and as a rough
guide it may be said tiiat when using fourteen
acetylene lights, a rapid plate, and a lens at//8,
an exposure of about five seconds is required in
an ordinary room ; the distance of the lights
from the sitter greatiy affects the length of the
exposure. (See also " Artifidal Light, Photo-
graphy by.")
GAUGE, PRESSURE
The lantemist ascertains the contents of gas
cylinders by means of a gauge. He may know
that the cylinder is of 20 cubic feet capadty, and
the full cylinder gives a gauge pressure of 120
atmospheres ; after the exhibition, the gauge may
indicate, say, 50 atmospheres. Then the content
50 50
equals -f— x 20 = -g- = 8J cubic feet.
A pressure gauge is used on the motor aero-
graph pump, the degree of pressure being indi-
cated in pounds per square inch on a drcular
dial. With the aerograph foot pump a simple
form of pressure gauge is used, consisting of a
U-shaped tube filled with a coloured fluid, one
end being dosed and the other attached to the
air reservoir. As the pressure varies it is indi-
cated by marks on a scale placed behind the
tube.
On the large vacuum and pneumatic frames
used by process workers there is generally a pres-
sure gauge, reading in pounds per square inch
on a drcular dial.
The Levy add-blast etching machine has a
gauge consisting of a column of mercury in a
glass tube, communicating with a U-tube in the
iron casting of the gauge. As the pressure
increases or decreases the mercury rises or falls,
and the pressure in pounds per square inch is
read on a scale alongside the glass tube.
GAUSS POINTS {See "Nodal Points.")
GELACOL
A preparation of gelatine treated with acetic
add to destroy its setting property. It is used
for coating glass plates witli a substratum, par-
ticularly in collodion emulsion work.
GELATINE (Fr., Gilaiine ; Ger., Gallerie,
Gelatin)
A colloid of extremdy complex nature, con-
taining carbon, hydrogen, nitrogen, and oxygen,
with a small proportion of sulphur. It is known
commerd^y in fine shreds or thin, flat sheets,
marked with the diamond pattern of the strings
Gelati
ine
272
Gelatine, Bichromated
on which it is dried. Photographic gelatine is
usually prepared from selected hides, whereas
inferior sorts are prepared from bones, tendons,
and cartilages. It is insoluble in cold water,
which it absorbs and then swells up to a sUmy
mass ; it is soluble in aU proportions in hot
water, but insoluble in alcohol and ether. The
principal constituents are two substances known
as glutine and chondrine ; the former is not
precipitated by the alums, whilst the latter is,
and gelatines rich in chondrine are the best
for photographic purposes. A simple test for
this is to add to a warm 10 per cent, solution of
gelatine an equal volume of a saturated solution
of chrome alum, when the solution should in-
stantly set to a jelly. It is only possible to
indicate the general characteristics of a gelatine
suitable for photographic purposes, as the true
test of its suitability is to make a practical trial
with a small batch of emulsion. A good gela-
tine shoidd absorb not less than six times its
weight of water, and not much more than twelve
or fifteen times.
There are three kinds of photographic gela-
tine : hard, medium or middle hard, and soft.
Hard gelatines should not melt below 82° P.
Device for Determining Melting Point
of Gelatine
(nearly 28° C.) ; if they do not melt at 88° F.
(31° C.), there is a risk of their having been
hardened with alum. Soft gelatines should
melt at from 62° to 75° F. (say 17° to 24° C).
A I per cent, solution should set to a jelly when
cooled down to 56° P. (13-3° C), and remain
without any sign of putrefaction for twenty-
four hours.
The determination of the melting point is
somewhat difficidt, arnl Child Bayley has sug-
gested an excellent practical device here shown
in the testing position. This may be made
of copper or zinc, and the sloping portion is
to prevent heat from the Bunsen burner passing
direct to the front of the tank. Across the
front of the tank should be scratched a line
about I in. from the top, and on this line should
be placed some discs of gelatine. Gummed labels
are cut into strips about ^ in. wide and about
i|- in. long, and their ends are then gummed
together, with the gummed surface outside, so
as to form rings. The tank should be placed
with the front and marked surface up, and the
paper rings placed on the line and then carefully
filled by means of a pipette with a warm 10 per
cent, solution of gelatine. When the gelatine
is thoroughly set, the rings should be cut down
with a sharp knife and stripped off, and the
tank set upright and filled with cold water, and
this heated by means of the Bunsen burner.
The discs must be carefully watched, and when
they begin to melt and run down over the line
the temperature should be noted. A mean of
six trials may be taken as correct.
Another method is to use a thermometer in a
very narrow test tube, just i mm. (^ in.) wider
all round than the thermometer bulb, which
should be of elongated shape. Then fill the tube
with the gelatine solution and, while hot,
immerse the thermometer well into the tube,
and set. Afterwards place the tube in warm
water, and gradually raise the temperature ; then
when the gelatine melts, the tube will drop off,
and the temperature can be noted.
Gelatine is used for preparing baryta paper,
for emulsions, both negative and positive, in
collotype, photogravure, and other photo-
mechanical processes, and it is the chief in-
gredient of an excellent mountant.
Solutions of sulphocyanides and barium
chloride dissolve gelatine in the cold, as do also
acetic, oxalic, hydrochloric, and sulphuric acids.
Zinc chloride and chloral hydrate destroy its
setting power. The setting is increased by the
alums, magnesiimi sulphate, and numerous other
salts. It forms a compound, gelatinate of
silver, which is sensitive to hght, with silver
nitrate.
In process work, gelatine has numerous uses
— ^namely, for coating collotype plates, for pre-
paring photo-lithographic paper, for the carbon
tissue in the photogravure process, for the making
of gelatine reliefs, for use as a substratum on
glass plates, for the making of films for shading
mediums, for making Utho-transfer papers and
films for tracing, for stripping negative films,
for making colour filters, for glazing prints, etc.
Particulars of these applications and uses are
given under the respective subject headings.
GELATINE, BICHROMATED
Gelatine treated with an alkaline bichromate
forms the basis of the carbon process and of all
photo-mechanical printing methods. Fish-glue
is employed in some processes, but that is a sub-
stance closely allied to gelatine ; and other
colloids are sometimes substituted, as in the
gum-bichromate process. Gelatine, in its nor-
mal condition, will absorb cold water readily,
and dissolve easily in hot water. Gelatine
treated with an alkaline bichromate retains these
quahties if kept in the dark ; but if exposed to
light, it no longer absorbs cold water, or swells
in consequence, and it also becomes insoluble.
These properties are utilised in different printing
methods. In the carbon process, and in some
photo-mechanical methods, an image in gelatine
is produced by exposing a film of bichromated
gelatine under a negative, and then dissolving
away those psirts on which the Ught has not
acted by means of hot water. In others, a
gelatine relief is produced by means of the
unequal swelling of a gelatine film that has been
exposed under a negative when soaked in water.
Details of the various processes in which these
qualities are utilised are given under thetf
respective headings.
In process work, many processes depend on
the properties of bichromated gelatine. Among
these may be mentioned collotype, photogravure.
Gelatine Emulsions
273
Geological Photography
photo-lithography, and photo-relief. For the
half-tone process gelatine has not been found
so satisfactory as fish-glue, the latter having no
setting property, and being easily developed
with cold water. An attempt was made of late
to utilise for half-tone a gelatine in which the
setting property had been destroyed, but it was
foimd to be more subject than fish-glue to changes
of temperature, and also liable to become putrid
very readily.
GELATINE EMULSIONS (See "Emulsion.")
GELATINE MOUNTANTS (See "Mountants.")
GELATINE PAPERS
Printing papers which are coated with gelatine,
which acts as a vehicle for the silver salts. All
bromide and gaslight papers, and most makes
of ordinary P.O.P., are gelatine papers. Some
makes of P.O. P. are coated with collodion.
Nearly all self-toning papers have collodion
emulsions, but a few have gelatine. Gelatine
papers are sticky when wet, and the emulsions
dissolve in hot water.
GELATINE PLATES AND FILMS
Glass plates or celluloid coated with gelatine
emulsions, as distinguished from collodion
plates.
GELATINE RELIEFS
Probably more ingenuity has been displayed
in devising processes for making gelatine reliefs
to serve as printing surfaces than in any other
form of photo-mecianical work, and yet there
is not one of these processes that is in regular
commercial use at the present day. These pro-
cesses date from the experiments of Pox Talbot
and Poitevin. In general the basis of the pro-
cess is the preparation of a thick film of bichrom-
ated gelatine on plate glass, exposing it under a
negative or positive when dry, and developing
with warm water so that the imexposed parts
wash away, leaving those portions standing that
have been acted upon by light. The rdief is
hardened with alum or other agents, and dried.
(This is the " Wash - out Gelatine Process,"
which see.) In some processes, however, the
unaltered gelatine is not washed away, but is
allowed to swell up, and thus form a matrix
for casting in plaster. (See " Swelled Gelatine
Process.")
The foregoing were chiefly used for line repro-
duction processes, but others are intended for
making half-tone reliefs. Dallastype and Dallas-
tint, and Pretsch's photo-galvanography are
processes of the kind that are described under
separate headings ; and Woodbury also devised
a process of this nature for typographic printing.
The half-tone image is either formed by printing
through a screen, or by reticulating the surface
of the gelatine. In Woodburytype (which see)
the gelatine relief is utilised, but in an essentially
different maimer from the foregoing ; pigment
is introduced into the film, and development is
similar to that of carbon tissue. Stannotype is
a variation of Woodburytype. Photo-filigraue
(see "Piligrane") is another process depending
on a gelatine relief. (See also " Aerograph,"
"Leimtype," " Mosstype," " Stannotype," etc.)
18
GELATINEGRAVURE
Transparent gelatine is placed over a photo-
graph, and a drawing made by scratching. When
this is complete the lines are filled with litho-
graphic transfer ink thinned with turpentine
and applied with a dabber. Printing is done by
running the gelatine through a roller press in
contact with paper.
GELATINO - BROMIDE PAPERS AND
PLATES
Papers or glass plates coated with gelatiuo-
bromide emulsions.
GELATINO-BROMIDE PROCESS (Fr., Gila-
tino-bromure ; Ger., Bromsilbet gelatin)
A term used in the early days of dry-plate
photography to distinguish the method of manu-
facture of the emulsion from collodion It is
now also used to include bromo-iodide plates.
GELATINO-CHLORIDE PAPER
Paper coated with an emulsion of silver
chloride in gelatine.
GENRE WORK
The word " genre " comes through the French
from the Latin " genus," a kind. In painting
it has been used to signify figure subjects of a
homely or domestic character, generally engaged
in their ordinary occupations. The term has
been adopted to signify the same subjects
treated photographically. Similar considera-
tions apply as in dealing with single figiires and
groups. There are the same difficulties of
securing satisfactory pose and arrangement, and
a suggestion of natural action. The " setting "
of the figures and the choice and arrangement
of the accessories also play an important part.
Careful studio arrangements and the employ-
ment of good models have frequently led to the
production of excellent genre pictures, but the
best and easiest way is to study and treat the
real subjects and tiieir ordinary surroundings
both in and out of doors. The works of some
of the painters of the Dutch school offer very
fine examples of the effective treatment of genre
subjects. The thing to aim at is harmony
and tinity. (See also " Figure Studies.")
GEOLOGICAL PHOTOGRAPHY
Photography as appUed to geological inves-
tigation may be roughly classed under the
following headings: (i) Photographs showing
plains, valleys, escarpments, base levels, moim-
tains, lakes, rivers, glaciers, etc., taken for the
purpose of illustrating the origin of landscape,
and the action of atmospheric and other pro-
cesses of denudation. (2) Photographs of the
faces of cliffs, quarries, railway cuttings, and
other exposed surfaces, to show the way in
which strata have been laid down, and changes
which have taken place producing unconformity,
overfolding, faults, dip and strike, anticline and
sjmcline, crushing, deavage, and joints. (3)
Photographs of fossil remains, both in situ and
after cleaning, to show the types of animal and
plant life existing during the formation of the
strata in which their fossil remains are embedded.
(4) Photo-micrographs of thin sections of rocks,
showing their structxure, composition, and any
Germeuil-Bonnaud
274
Glass
minute animal and plant remains that may be
present.
For most geological photography, a good stand
camera, having a long extension of bellows,
swing back, and rising front, will be found most
serviceable. A good lens is aU-important, as
the value of a geological photograph depends
Ufon its perfect clearness and sharpness of
detail. The lens should be provided with a deep
hood for use in the field, which will prevent
flare, • and flat, foggy-looking negatives, caused
by reflections and rays of light falling obliquely
on the front surface of the lens. The tripod
should be substantial and rigid, so that there
win be no fear of vibration during exposure,
for it is always best to stop down the lens and
give a full-time exposure, so that a crisp, sharp
negative, fuU of detail and gradation, may be
obtained. It is often desirable when photo-
graphing a portion of the face of a difE, or part
of the strata laid bare in a quarry or railway
cutting, to include in the photograph some
familiar object of which the size is well known,
to act as a kind of rough scale by which one may
judge the relative thickness of a deposit, or
the size of a fossil seen in situ. For this pur-
pose, some workers use their geological hammer,
but as hammers vary a good deal in size and
shape, it is much better to include a twelve-
inch or two-foot rule. Orthochromatic plates
should always be used. P. M-B.
GERMEUIL-BONNAUD
(Powder) Process.")
{See " Dusting-on
GHOST IMAGES IN LENSES (See "False
Images, or 'Ghosts.'")
GHOST PHOTOGRAPHY
Photography.")
{See " Psychic
GIFFORD'S SCREEN
A so-called monochromatic light screen, made
by immersing a slip of cathedral green glass,
which is of bluish green tint, in a solution of ani-
line green. It is used in photo-micrographic work,
and passes a spectral band about E in the green.
GIGANTOGRAPHY
A process of making enlarged half-tone nega-
tives for poster printing. Two cameras are
required — one a small one, according to the size
of the original image, and the other large enough
to take the enlarged negative. The lens of the
small camera is connected to an aperture in the
front of the large camera, on the principle of the
usual enlarging camera. An evenly graded
transparency, thin but full of detail, is placed in
the dark-slide of the small camera, the shutters
drawn out, and the slide placed in position. The
half-tone screen is placed in its holder in front
of the positive, and the distance of the screen is
set proportionately to the extension of the
camera to secure the desired enlargement. A
powerful light is reflected through the positive
by illuminating with arc lamps a sheet of white
paper placed behind it. The image is then
focused, and the ruled screen adjusted until the
desired dot image is obtained. The advantage
of the process is that it saves the necessity of a
very large and expensive ruled screen.
GILLOTAGE
The earliest process of line zinc etching, in-
vented by Charles Gillot, of Paris, and patented
in France in 1850 ; known as panikonography,
or the French or Parisian method of zinc etch-
ing. The principle of the method is that an
image in lithographic ink on zinc is strengthened
for acid resisting by repeatedly rolling up with
ink and then dusting with resin, the plate being
heated to melt the resin, so that it runs down
the sides of the Unes and protects them against
undercutting by the acid.
" GIPHANTIE "
A book written in 1760 by a French-
man, Tiphaigne de la Roche, the title being
an anagram of his own name. It contains a
forecast of photography. One paragraph says :
" You know that the rays of Hght reflected from
different bodies form pictures, paint the image
reflected on all polished surfaces, for example,
on the retina of the eye, on water, and on glass.
The spirits have sought to fix these fleeting
images ; they have made a subtle matter by
means of which a picture can be formed in the
twinkling of an eye. They coat a piece of canvas
with this matter, and place it in front of the
object to be taken. The first efiect of this cloth
is similar to that of a mirror, but by means of
its viscous nature the prepared canvas, as is
not the case with the mirror, retains a facsimile
of the image. The mirror reflects images faith-
fully, but retains none ; our canvas reflects
them no less faithfully, but retains them all.
This impression of the image is instantaneous.
The canvas is then removed and deposited in a
dark place. An hour later the impression is
dry, and you have a picture the more precious
in that no art can imitate its truthfulness." A
still earlier writer, F^n^lon, had a vision of
photography, but did not so clearly express it ;
his book bears the title of " Un Voyage Sup-
pose," and was written in 1690.
GISALDRUCK
A photo-lithographic process, invented by
B. Gisevius, of Berlin, for direct printing on
aluminium without a negative. The actual draw-
ing is printed through on to a sensitive film on
the metal, and the negative image is converted
into a positive. It resembles the Vandyke pro-
cess {which see).
GLACIAL ACETIC ACID {See " AceUcAcid.")
GLAISHER, JAMES
Bom in I^ondon, April, 1 809 ; died at Croydon,
February 7, 1903. Was for twenty-three years
(1869 to 1874 and 1875 to 1892) president of
the (now) Royal Photographic Society. He
was largely responsible for the photographic re-
cording instruments in Greenwich Observatory.
GLASS (Fr., Glace, Verre ; Ger., Glas)
Ordinary glass is a fused mixture of silicates
of calcium or lead with the siHcates of sodium
or potassium. While practically imafEected by
acids, except hydrofluoric, it is attacked by strong
alkalis, which dissolve out the silica. Some
glasses are yellowed by prolonged exposure to
Ught ; this is frequently the case with old lenses.
Glass
3;s
Glass, Cleaning
Crown Glass is made usually from sand, lime,
and a sodium salt, with sometimes lead oxide.
Flint Glass contains potassium carbonate, red
lead, sand, and saltpetre. It is easily fusible,
and is not so suitable for chemical purposes,
for which a soda-lime or potash-lime glass is
preferable.
Opal Glass is obtained by fusing an oxide of
tin or zinc with the pot-metal ; a " flashed "
opal, consisting of a thin opal layer imited to
plain glass, is also manufactured.
Optical Glass first received specific attention
from Pierre Ivouis Guinand, of Les Erenets, in
Switzerland (bom 1748, died 1824), who obtained
improved results by stirring the fused mixture
with a rod of crucible clay. J. Praunhofer (bom
1787, died 1826) succeeded in avoiding striae
and in procuring glass of a uniform refractive
index by the simple expedient of using larger
pots for melting ; he also investigated some of
the optical effects resulting from variations in
the ingredients and their proportions. In 1842
a son of Guinand introduced boracic add into
the glass, which, however, did not then meet
with favour. In 1851 Maes, of Clichy, produced
a colourless and homogeneous zinc crown glass,
containing zinc oxide and boracic add ; this
was used in Charles Chevalier's photographic
objectives. L. Sddel in 1856, and J. Petzval in
1857, pointed out that new glasses, having a
different relation between their refractive and
dispersive powers to those then in use, were
required for the perfection of the photographic
objective, but it was not till Otto Schott and
B. Abbfe began their joint work in 1 881 that any
real progress was made. In 1886 the famous
Jena works were started by Schott, Abb6, and
R. Zeiss, imder a liberal subvention from the
Prussian Government. Since then the pro-
duction of optical glass of almost any required
refractive or dispersive power has been rendered
possible by the use of new chemical ingredients.
People often talk loosely of the Jena optical
glass, as if there were only one variety, although,
as a matter of fact, several hundreds of different
varieties of optical glass are known, these
induding all the or&iary flints and crowns,
besides the spedal glasses that have made the
manufacture of the modem anastigmats possi-
ble ; it is these spedal glasses that are generally
meant by the term " Jena glass." With the
older makes of optical glass, increased refractive
power was always accompanied by a high degree
of dispersion, but in the new Jena glasses a
very high refractive power is obtained with a
comparatively low dispersion.
(For the optical properties of glass, see
"Lens.")
Cements for Glass. — A cement for glass needs
to be as colourless as possible, the best from
this point of view being Canada balsam, which
should be dried in an oven, allowed to cool, the
glass gently heated, the remelted balsam thinly
appUed, and the surfaces brought together. This
is the universal cement for lenses. Other ex-
cellent cements (but not suitable for lenses) are
water-glass, which, however, tends to roughen
the glass, and an emidsion of gelatine in suf-
fident acetic add to cover it, the process of
digestion being assisted by standing the bottle
in warm water.
In process work, glass is an important material.
To secure good contact between the negative
and metal plate in direct printing, the glass
must be flat, and plate glass is preferable, though
for the general nm of work a good selected
sheet glass is used. Plate glass of about i in.
thickness is used for assembling a number of
stripped films on to one plate. For process
printing-frames, thick plate glass is used up to
li in. thickness in the largest frames, and this
glass must be well annealed in order to with-
stand the strain of the pressure and the heat
of the arc lamps used for printing. The glass
must also be free from surface scratdies and other
imperfections which would show in the print.
GLASS, CLEANING
Glass for photographic purposes must be
scrupulously dean. Glass upon which prints
are squeegeed for glazing is best deaned by
soaking in very dilute nitric acid and scrubbing
with soap and water ; after drying, it is dusted
over witii French chalk and poUshed. When
glasses are to be used for coating and sensitising,
as in the wet collodion process, rouge or whiten-
ing or fine tripoli powder mixed with methy-
lated spirit to the consistency of thick cream
is recommended ; the paste is rubbed over the
glass, rinsed off with water, and a final polish
is given with chamois-leather.
A good mixture for thoroughly deaning glass
for ordinary purposes is —
I part
• I ,-
• li „
• i „
Apply with a piece of flannel, and polish with a
soft rag, chamois-leather, or soft paper crumpled
up.
To dean films off old negatives, soak in hot
soda-water for a few minutes, and scsrub with a
brush ; or, if they are not varnished, soak them
for an hour or two in water made slightiy add
with nitric add ; the films can then be rubbed
off with a strip of wood, or placed in hot soda
water and scrubbed. When the negatives have
been varnished, it is necessary to use a strong and
hot solution of common washing soda or caustic
potash, and leave the negatives in this until cold,
when the films wUl leave the glass. Do not let
the caustic potash solution touch the fingers.
In process work, in which collodion and collo-
dion emulsion are used so largely, it is necessary
to take great pains in deaning glass. New glass
is best soaked in a 5 per cent, solution of hydro-
chloric acid contained in grooved lead - lined
troughs; and it is then rinsed with plenty of
water and poUshedwith methylated spirit 20 oz.,
tripoli 10 oz., iodine 2 drams. Prepared chalk
or whiting may be used instead of tripoli, and
equal parts of methylated alcohol and ammonia
instead of iodine.
For removing collodion films from old nega-
tives, nitric add is generally used in the pro-
portion of I oz. add to 6 oz. water. A good
film-removing pickle, free from fumes, consists
of—
Soft or rain-water
Powdered pumice stone
Chalk or whitening
Liquor ammoniae .
Sulphuric add
. 4 oz.
200 CCS.
Potassium bichromate
• 4 „
220 g.
Water ....
20 „
1,000 CCS.
Glass, Etching on
276
Glossy Surfaces on Prints
After treatment, swill and put in the draining-
rack. Next, with a linen rag charged wiQi
whiting of the consistency of Ouck cream, rub
well both sides of the partially dry negative
glasses ; then put into a clean bath composed
of nitric acid 4 oz., water 40 oz. Finally, swill
under a tap and then albumenise.
GLASS, ETCHING ON {See " Hyalography.")
GLASS, GREEN {See " Green Glass.")
GLASS, PHOTOGRAPHS ON
In 1 848 Niepce de St. Victor produced photo
graphs upon glass in the form of negatives, but
glass as a support for photographs was suggested
by Sir John Herschel in 1839. About 1850
Archer produced positives on glass by the collo-
dion process.
Photographic negatives are now almost
entirely upon glass or celluloid. Photographic
positives on glass are produced in many ways, as
described under the headings " Lantern SUdes,"
" Wittdow Transparencies," etc.
GLASS POSITIVES
Photographs on glass, such as lantern slides.
The early glass positives were produced by the
collodion process, and the deposit forming the
image was white and the shadows clear glass,
there being a backing of black velvet, cloth, or
paint.
GLASS, RUBY {See " Ruby Glass.")
GLASS, SILVERED
Photographers and process workers are well
advised not to prepare their own mirrors and
prisms, but the question of silvering is im-
portant. The silvered surface must be thick
and durable to withstand the frequent pohshing
for removal of tarnish. Mirrors should be
thoroughly warmed before polishing, and the
polishing pad and rouge must be quite dry and
warm. The very finest optical rouge should be
used, and the pad should be rubbed on a clean
glass plate brfore applying it to the mirror.
The pad should be kept in a wide-mouthed glass
jar with glass stopper when out of use, so that
no gritty dust can reach it. The silvering on
the hypoteneuse of prisms should be backed with
an electro-deposit of copper and then varnished.
GLASS. SOLUBLE {See "Water-glass.")
GLASS, YELLOW (See " Yellow Glass.")
GLASSWARE, PHOTOGRAPHING
Photographically, glassware is similar to silver
ware, and the instructions for lighting, etc., given
under the latter heading apply almost as weU
to glass vessels. Glass may sometimes be
improved by frosting or dewing, as described for
silver ware, but in most cases it is advisable to
fill the glass vessels with a non-actinic solution,
in order to prevent the details and high Mghts
on the far side conflicting with those nearest the
camera. A non-actinic solution may consist of
a very dilute solution of potassium perman-
ganate, but it must be only slightly tinged,
otherwise it wiU appear as ink. Another plan
is to dust the glasses lightly with powdered talc,
using this for partly fiUing up engraving in order
to make it show more distinctly upon the nega-
tive. The background should be of a dark tint.
In process work, numerous expedients are
resorted to for photographing glassware for
catalogue illustrations. A piece of ice put
inside the vessel will cause moisture to condense
on the outside, and so stop reflections. Dabbiug
the glass over with putty is also effective on
smooth surfaces, but does not avail with cut-
glass. Coating the glass with a varnish and
blackleading with a brush has also been resorted
to. Spraying the glass with the aerograph also
serves the purpose.
GLAZING PRINTS (See " Glossy Surf aces on
Prints.")
GLAUBER'S SALT
Another name for sodium sulphate {which see).
First produced by Johann Rudolph Glauber, a
German chemist, about 1661 ; hence the name.
GLOBE LENS
One of the earliest non-distorting, wide-angle
lenses, introduced by Harrison, of New York,
iu 1862, and highly esteemed until superseded
by the wide-angle rectilinear. Its chief defects
Globe Lens
were slowness (full aperture f/36) and liability
to flare. It was symmetrical in construction,
the outer surfaces of the two components being
so placed as to form part of a sphere, as shown.
GLOBE POLISH REDUCER (See " Baskett's
Reducer.")
GLOSSY PAPERS
These are almost always prepared with gela-
tine. Their gloss may be enhanced in finishing
by the procedure given under the heading
" Glossy Surfaces on Prints." A glossy surface
possesses the advantage of imparting great depth
and transparency to ttie shadows, and of render-
ing all detail crisply throughout the scale of
tones. It also gives greater visual contrast in
the print. For this reason, prints with glossy
surfaces are very desirable for reproduction pur-
poses, and for many kinds of commercial photo-
graphy, engineering subjects, architectural de-
tails, etc. There are several papers on the market,
both for daylight and for artificial light printing,
with semi-glossy surfaces.
GLOSSY SURFACES ON PRINTS
For finishing prints with a glossy surface, a
paper prepared with a naturally glossy surface
should be employed. The most simple and
satisfactory method of working is as follows :
The prints, after fixing and washing, should be
immersed in a formaline bath (formaline ^ oz.,
water 5 oz.) for two or three minutes, washed
Glucose
277
Goddard, John Frederic
for a quarter of an hour, and then dried. A
glass, celliiloid, or ferrotype plate is washed and
polished with a soft fabric, first rubbing on with
a flannel a solution of 20 grs. of beeswax in i oz.
of turpentine. The print is soaked in water
until thoroughly Ump, and then a liberal quantity
of water is thrown on the polished plate, and
the print placed face downwards on the plate,
care being taken that there is plenty of water
between the two surfaces. The print is next
firmly squeegeed into contact, interposing a
sheet of rubber cloth between the print and the
roller squeegee. When quite dry, the print will
leave the plate very easUy, and its surface will
possess a high gloss. This suriace is hard and
durable, due to the employment of the forma-
line bath, but it is weU to back the print with
a waterproof sheet so as to prevent ttie mount-
ant from affecting the glaze.
GLUCOSE (Fr., Glucose: Ger., Glycose)
Synonym, dextrose, grape sugar. CeHuOo.
Molecular weight, 180. A thick, syrupy, yellowish
Uquid, obtained by the action of dilute sulphuric
add on starch. It was suggested as a developer
or addition to developers for wet plates.
GLUE, FISH (See " Pish-glue.")
GLYCERINE (Pr., GlyUrine : Ger., Glyzerin)
A colourless, odourless, thick liquid of charac-
teristic sweet taste, miscible in all proportions
with water and alcohol, and slightly soluble in
ether. Glycerine as purchased from a chemist
or at an oilshop is good enough for photographic
purposes. It has many uses in photography,
for example, in developing platinotypes, as a
constituent of developers, as an addition to
gelatino-chloride and collodio-chloride emulsions,
in mountants, and to prevent films curling.
In collotype work, glycerine is used for the
" etching " or damping of the plate previous to
inking. A sidtable solution consists of 3 parts
glycerine to 2 parts water.
GLYCEROL {See "Glycerine.")
GLYCINE, OR GLYCIN (Fr., Glycine ; Ger.,
Glycin)
A developer, known also as paraoxyphenylgly-
dn, having the formula C, H4 OH NHCHj COOH.
It appears in the form of glistening grey powder,
which, when carelessly' kept, turns to a brownish
black and loses its developing powers. The
powder is insoluble in plain water, but soluble
in a solution of sodium sulphite, or on the
addition of an alkali. It is a slow-working
developer, having a factor of 7, and works after
the manner of ferrous oxalate ; it has the advan-
tage of giving good dear negatives with little or
no fog, and good density. It is widely used for
stand and tank development and for the repro-
duction of black-and-white subjects ; it may be
used in a one-solution or two-solution form.
One-Solution Developer
Hot water . . 30 oz. 1,000 ccs.
Sodium sulphite . ij „ 45 g.
Potassium carbonate 2j „ 90 „
Glycin ... 4 „ 18 „
The above is ready for use.
Another one-solution formula gives a stock
solution in the form of a cream, and is known
as —
Hiibl's Stock Glycine Solution
Sodium sulphite . 2j oz. 688 g.
dissolved in —
Hot water . . 4 „ 1,000 ccs.
then add —
Glycine . . . i „ 275 g-
Heat to boiling point, and add —
Potassium carbonate . 5 oz. i,375 g.
Add the potassium carbonate gradually in small
quantities on account of the carbonic-add gas.
When cold, this forms a thin paste ; when
required for use, shake and dilute i part with
12 parts of water, using more water for soft
development and less water for hard develop-
ment. For stand development, mix with 50
to 55 parts of water.
Two-Solution Developer
A. Glycine . . 380 grs. 44 g.
Potass, carbonate . 144 „ 16 $ ,,
Sodium sulphite . 5 oz. 275 „
Water . . . 20 „ 1,000 ccs.
B. Potass, carbonate . 2J „ 137 g.
Water . . . 20 „ 1,000 ccs.
For use, mix equal parts of A, B, and water.
Potassium bromide is added in cases of over-
exposure.
Messrs. Newton and Bull have recommended
glycine as a developer for all isochromatic plates,
as follows : —
Glycine . . .192 grs. 18 g.
Potass, carbonate . . 2 oz. 88 „
Sod. sulphite (anhydrous) 240 grs. 22 „
Potassium bromide . 12 „ i „
Water to . . . 25 „ 1,000 ccs.
Development is controlled by time, using a
factor of 6.
In process work, glycine is an excellent developer
for collodion emulsion and for process dry plates,
but it is expensive compared with hydroquinone,
which is more generally used.
GLYCOCINE {Pi., Glycocine ; Get., Glykokoll)
The decomposition product of the action of
sulphuric acid on gelatine. It was used as a
preservative for collodion dry plates. (See also
" Amido-acetic Add.")
GLYCOCOLL (See " Amido-acetic Add.")
GLYPHOGRAPHY
An electroty ping process invented by E. Palmer,
of London, about 1844. A copper plate is coated
with a white composition consisting of white wax
and zinc white, and the coating is scratched
through with needles so that the Imes are formed
in deep furrows. The plate is brushed with
blacklead, and forms a mould for electrotyping.
(See also " Wax Process " and " Cerography.")
GODDARD, JOHN FREDERIC
Inventor of the polariscope ; improved the
daguerreotype process by discovering (in 1840)
Goetz's Reducer
278
Gold and Sodium Chloride
the accelerating properties of bromiae, by which,
with iodine, he obtained a bromo-iodide of silver
on the surface of the silvered plate, thereby
reducing the necessary exposure to about one-
sixtieth — from twenty minutes to twenty seconds.
This invention, in conjunction with Pizeau's
gold chloride and " hypo " invigorator, made the
daguerreotype a commercial success, as it then
became possible to give reasonably short ex-
posures, whereas previously long exposures were
needed, and the sitter's face had to be whitened
with powder, and placed in full sunlight.
GOETZ'S REDUCER
A reducer for negatives introduced in 1894
by H. Goetz. A strong solution is made by
mixing i oz. of copper sulphate with 5 oz. of
distilled water: —
No. I—
Common salt
Copper siilphate solution
Distilled water
No. 2 —
Sodium hyposulphite
Distilled water
i oz. 28 g.
i „ 55 „
10 „ 1,000 CCS.
96 grs. 22 g.
10 oz. 1,000 CCS.
The carefully washed plate is placed for from
twenty to thirty seconds in solution No. i, then
rinsed and transferred to No. 2, in which the
reduction takes place, and the process should
be well controlled, the action being a rather
quick one. The longer the plate has been left
in No. I the more rapid will be the reduction in
No. 2. For sHght over-exposure increase the
salt and decrease the copper sulphate in No. i ;
the contrary holds good in a case of under-
exposure. Finally, the negative should be
thoroughly washed.
GOLD (Fr., Or ; Ger., Gold)
Au. Molecular weight, 197. It occurs native
in grains or nuggets. A heavy yellow or orange-
yeUow metal, which, as a metal, is not used in
photography. Its salts are used for toning
prints. Most of its salts are sensitive to Hght,
particularly the chloride, in the presence of
organic matter, and therefore aU gold solutions
should be kept in the dark,
GOLD CHLORIDE (Pr., Chlorure d'or : Ger.,
Goldchlorid)
Synonyms, trichloride or perchloride of gold,
auric chloride. AuCl, HCl 4HaO. Molecular
weight, 412. Solubilities : very soluble in water,
alcohol, and ether. It occurs as needle-like
yellow crystals obtained by dissolving metallic
gold in aqua regia and evaporating the solution.
The crystals are very hygroscopic, and should
be kept in a stock solution. There is a brown
form of gold chloride, AuCl, HCl XB.2O, which
contains less water than the yellow salt and is
less hygroscopic. This should contain from 50
to 51 per cent, of metallic gold. Both salts are
used in toning. Gold chloride has a great
tendency to form double salts with the alkaline
chlorides, which are more stable. (See " Gold
and Potassium Chloride " and " Gold and Sodium
Chloride.")
GOLD AND " HYPO " BATH (See " Gold
Hyposulphite." )
GOLD HYPOSULPHITE (Fr., Hyposulfite d'or
et de sodium, Sel de Gilis et Fordos ;
Ger., Unterschwefligsdure Goldoxydulnairon,
Goldsalz)
Synonyms, sel d'or, hyposulphite of gold and
soda. AuS203Na2SsjOs2HjO. Molecular weight,
522. Solubilities, very soluble in water, almost
insoluble in alcohol and ether. It occurs in white
needles, and is obtained by adding a strong
alcoholic solution of gold chloride to an excess
of sodium hyposulphite. It was usually pre-
pared in solution by adding a 2 per cent, solution
of gold chloride to a 6 per cent, solution of
" hypo." It was used for toning or " gilding "
the old daguerreotype image, and is sometimes
recommended for printing-out papers.
GOLD AND IRIDIUM BATH
The addition of iridium and potassium chlorides
to a gold bath has been recommended for toning
prints, but ag it presents no practical advantages,
and merely increases the cost, it has found no
general use. The following is used for toning
ceramic substitution pictures, and gives a warm,
black tone : —
Iridium chloride
Gold chloride
Lactic acid
DistUled water to
34 grs. 3-5 g.
20 „ 2 „
22 mins. 2 CCS.
20 oz. 1,000 „
GOLD AND PLATINUM BATH
The addition of chloroplatinite of potassium
to the gold sulphocyanide bath was stated to
give rich black platinum tones, whereas, as a.
matter of fact, all that takes place is the more
rapid deposition of the gold. A bath similar in
composition to that given under the heading
" Gold and Iridium Bath," the iridium being
replaced by potassium chloroplatinite, is also
used in producing ceramic photographs. Plati-
num baths are sometimes used after a gold
toning bath for P.O. P. papers.
GOLD AND POTASSIUM CHLORIDE (Pr.,
Chlorure d'or et de potassium ; Ger.,
Kaliumgoldchlorid)
KO AnOs 2H2O or KAuCla 2H2O. Mole-
cular weight, 414. Solubilities, very soluble in
water, alcohol, and ether. Yellowish needles
obtained by mixing four parts of gold chloride
in concentrated solution with I-I2 parts of
potassimn chloride, evaporating, and crystallising.
It is used for toning.
GOLD RESIDUES (See "Residues.")
GOLD AND SODIUM CHLORIDE (Fr.,
Chlorure d'or et de sodium ; Ger., Natrium
goldchlorid)
Naa AuCls 2H2O, or NaAuClj 2H2O. Mole-
ciUar weight, 398. Solubilities, very soluble in
water, alcohol, and ether. Yellowish orange
crystals, obtained in the same way as the potas-
sium salt (see "Gold and Potassium Chloride"),
using 4 parts of gold chloride and i part
of sodium chloride. Both these salts may be
adulterated with free potassium or sodium
chloride, which may be detected by dissolving
them in absolute alcohol, when any alkaline
chloride will be undissolved.
Gold Toning
279
Grain in Negatives
GOLD TONING (Pr., Virage A Vor ; Ger.,
Tonen (Schonen) mit Goldsalz)
The purpose of the gold toning bath is to
convert the somewhat unpleasant yellowish red
colour of the fixed silver image into a more
pleasing brown, purple or bluish purple. This
has been erroneously described as gilding,"
whereas the action is purely chemical, the gold
taking the place of the silver of the image,
and Qie silver being converted into chloride in
place of the gold. If instead of a plain solu-
tion of gold chloride the auric chloride AuG,
were used, the reaction could be expressed as
follows : —
Aua, + 3 Ag = 3 Aga + Au
From this it will be seen that one atom of
gold replaces three atoms of silver, and the fine
details in the high hghts would disappear and
the image lose considerably in vigour. If, on
the other hand, the gold is reduced to the
aurous chloride AuCl, the reaction would be
represented by —
AuCl + Ag = Aga + Au
and one atom of gold would replace one atom
of silver. It has been stated that an intermediate
atirous chloride, AuClj, is formed, but it is such
an unstable salt that its existence is doubtful.
To convert any toning bath into the proper
toning condition — that is, when the gold is
reduced to the aurous state — it is " ripened "
either by aUowiug it to stand or by the use of
hot water to dissolve the salts, which should
make the bath either neutral or distinctly
alkaline. In the case of the sulphocyanide bath,
a double salt of sulphocyanide of ammonium
or potassium and gold is formed; this may
also be in the auric or aurous state, and a
similar chemical action takes place. Of recent
years a more reasonable method of using the
gold bath has been generally adopted, this
allowing a definite quantity of gold to a definite
area of print, instead of using one bath for a
number of prints in succession and then adding
fresh gold. It is important to wash prints weU
before toning, so as to free them from the excess
of silver nitrate, which would decompose the
gold chloride and prevent its deposition on the
print. When a toning bath has been used, all
the gold is not exhausted ; but some which has
passed into a stable aurate will not deposit.
Obviously this may be collected for the sake of
the residues, or the old bath may be used
instead of water to make a new bath, the former
plan being preferable. (See also " Residues.")
GOLD TRICHLORIDE OR PERCHLORIDE
{See " Gold Chloride.")
GOLD AND URANIUM BATH
A mixture which has been frequently sug-
gested for obtaining warm black tones on matt
surface print-out gelatine or coUodion papers : —
Gold chloride . 2| grs. -25 g.
Uranium nitrate
Sodium chloride
Sodium acetate
Distilled water to
24 „ -25 „
10 „ I „
10 >. I .,
20 OZ. 1,000 CCS.
Dissolve the gold and uranium in a little water,
neutralise with sodium bicarbonate, and add to
a hot solution of the other salts. The bath is
ready for use when colourless and cold.
GOUPIL PROCESS
A method of making facsimiles of water-
colour drawings. A photogravure plate is care-
fully inked by hand with small dabbers or tam-
pons, and in the more delicate parts with
brushes, using differently coloured inks accord-
ing to the character of the portions of the plate
to be inked. When the inking is complete the
coloured print is obtained at one impression.
The plate is then cleaned and inked again for
the next picture. This method of printing is
very slow and costly, as skilled artists have to
be employed for colouring the plates. The
results, however, are very fine, and in some
cases hardly distinguishable from the original
water-colour drawing. The process is still
practised.
GOUPIL GRAVURE
A photogravure process suggested to Goupil
and Co., of Paris, by W. B. Woodbury, about
1870, and largely worked afterwards by that
firm. A gelatine reUef was made in the same
manner as for the Woodburytype process,
except that a fine gritty powder was added to
the gelatine to give the necessary grain. Prom
this rehef a mould was taken and an electrotype
shell deposited on it.
GRADATION
That variation of tones in a print by which
are suggested differences in colour and in light
and shade. A print has a long scale of gradation
when there are many intermediate tones between
deepest shadow and highest hght. {See " Key.")
GRAIN IN COPYING
Copies of photographs frequently have a
"grainy" effect, due to the dry plate reproducing
the grain of the paper on which the original
photograph was printed. To reduce the effect as
much as possible, the original should be placed
for copying in a good diffused front light ; it is
the character of the lighting that is generally
to blame when the grain is reproduced promi-
nently, as the stronger the light from one point,
usually one side, the more pronounced is the
grain. A method of obviating grain is to smear
the face of the original with glycerine and
squeegee it face downwards on plain glass, the
copy being then made through the glass.
In process work, the suppression of grain is
more easily attained, now that the use of the
electric arc has become common, than it was
when dayUght copying was in vogue. By the
use of two arc lamps, one on each side of the
copy, the illumination can generally be adjusted
to overcome the effect of the grain. Also the
originals may be photographed under plate glass.
GRAIN IN NEGATIVES
In the early days of rapid plates a grain was
perceptible in the negative, it being coarser as
the speed of the plate increased ; but the defect
has now almost vanished, although it may still
be produced under certain conditions. " Grainy "
negatives are more frequent in hot weather than
Grained Negative
280
Green Glass
in cold ; in the stunmer, and particularly when
development is forced and the plate happens to
be under-exposed, excessive coarseness of grain
may often be seen. The temperature of the
atmosphere during the drying of the negative
afEects the grain, and the more quickly a nega-
tive is dried the coarser wiU be the grain ; there-
fore, when a negative is to be used for printing
upon glossy paper, or lantern sUdes are to be
made from it, the cooler the atmosphere employed
for drying the better. One theory (there are
several) is that when negatives dry slowly on a
hot day, the gelatine becomes partly decom-
posed, allowing the particles of the silver bromide
to come together ; these particles have an
affinity for each other, and are enabled to come
together when the gelatine which keeps them
apart has been to some extent destroyed. Thus
the particles form coarse particles, and impart
to the negative a " grainy " or woolly appearance.
Bxcess of alkali also increases grain ; therefore,
in order to produce a negative as grainless as
possible, let the exposure be fuU, use a normal
developer at no higher temperature than
65° P. (18° C), and dry as quickly as possible
in a cool, clean current of air.
In process worh, it is a disadvantage to use a
plate that gives too granular an image. Hence,
process dry plates are relatively slow in order
to secure a fine-grained emulsion. In collodion
emulsion work also, the grain must be kept fine.
GRAINED NEGATIVE
A term often employed to denote a half-tone
process negative, or a negative made through a
ruled screen for breaking up the image into a
fine grain.
GRAINS PER OUNCE
See under the heading " Solutions, Making
up," where the number of grains per ounce of
solutions of the usual " percentages " will be
found.
GRAM. OR GRAMME
A metric weight, eqviivalent to 15-432 grains
avoirdupois, apothecaries', or troy ; written g.
or gm. in formulee. (See also " Weights and
Measures.")
GRANULATION, OR GRANULARITY (Pr.,
Granulation ; Gr. Granulieren)
A term usually applied to an image of which
the grain is coarse and distinctly visible to the
naked eye. It may be due to the emulsion or
to the action of the developer. It is also occa-
sionally used for images broken up into a
grain photo-mechanically.
GRANULOTYPE
A term appUed to a half-tone etching on
grained zinc, the image being formed by means
of the bitumen process, printed under a tone
negative.
GRAPHOSCOPE
An instrument containing a double convex
lens large enough to permit both eyes at the
same time to look through it at a single photo-
graph, in this way obtaining, it is said, an
illusion of relief, but not that soUdity observable
in a stereoscope. The suggestion of relief may
be due to the non- achromatic lens causing over-
lapping of the different rays.
GRAPHOTYPE
A process suggested by A. H. Wall, in which
a block of compressed chalk was drawn on with
a specially prepared ink, which hardened the
chalk wherever the lines were made, whilst the
clear parts could be brushed away until a high
relief printing block was obtained. The chalk
no doubt contained size, and the ink some hard-
ening substance, such as chrome alum, tannin, or
formaline. In another process of this kind the
block of chalk is treated with water-glass, to
harden it after brushing it into relief.
GRATING, DIFFRACTION {See "Diffrac-
tion Grating.")
GRATING, PRISM
A diffraction grating on the hypotenuse of
a prism of 60°, used for direct-vision diffraction
spectroscopes. An ingenious method of making
these gratings was devised by Thomas Thorp,
of Manchester. He flows a plane metallic
diffraction grating with celluloid, which when
dry is stripped off as a film and cemented to the
prism ; it gives an image hardly inferior to that
produced by the original grating.
GRATING. SCREEN
A term sometimes appHed to the ruled screen
used for half-tone process work.
GREEN FOG {See "Fog, Colour, etc.")
GREEN GLASS
Printing through green glass increases the
contrasts on P.O. P. The use of coloured glasses
was suggested by I^emann in 1861, since when
it has been repeatedly adopted for obtaining
rich prints from thin and flat negatives. About
1890 the use of greenish yellow glass was advo-
cated for obtaining, in conjunction with matt
papers and the uranium toning bath, not only
vigorous prints, but also black tones resembling
platinotype. Glossy P.O. P. also prints very
much brighter and better under green glass,
and the method is of great advantage when
valuable negatives of a flat, thin, or ghostly
character are used and intensification is not
allowable. A green glass cuts out the violet and
deep blue rays of light, allowing the bright blue,
green, and yellow rays to travel through the
negative and act upon the sensitive paper, with
the result that the organic salts of silver are
acted upon more than the chloride. The organic
salts have a shorter scale of gradation than the
chloride has, hence the prints have stronger
contrasts and the shadows are richer than would
otherwise be the case. The most suitable shade
of glass for the purpose is that known as " signal
green " or " single flashed chromium green."
With the green glass, which is placed over the
negative, printing is considerably prolonged.
The method answers only with print-out silver
papers. Green glass has also been advocated in
place of ordinary glass for dry plate making ;
it has several advantages, one being that it
prevents halation.
Green Tones
281
Group Arrangement
GREEN TONES
Green tones are generally difficult to obtain
and not of great permanency except by the
carbon process. Carbon tissue in many shades
of green may be purchased, and greens by the
process are easy to obtain, of even quahty and
quite permanent.
P.O.P. — ^The green tones obtainable on P.O.P.
are uncertain as to exact tone, and they are not
permanent. The best method is to tone as
black as possible in the usual way, and then to
stain the print with an aniline dye. Another
method is to print very faintly, and then, without
washing, immerse the print in a lo per cent,
solution of potassium bromide for three minutes.
The faint image is then developed with a metol-
hydroquinone developer as used for bromide
paper, then washed and fixed in the usual way,
without toning.
Bromide Paper. — ^The following is a typical
method, which not only gives a good green, but
intensifies considerably at the same time. Make
lo per cent, solutions (48 grs. in i oz. of water)
of (i) uranium nitrate, (2) ammonio-citrate of
iron, (3) potassium ferricyanide, {4) nitric acid.
For use mix together No. i 12 drops. No. 2
12 drops. No. 3 24 drops, No. 4 24 drops, and
add water to make i oz. Immerse print until
of the desired colour, wash, and dry. A much
brighter green may bo obtained by mixing
together J oz. of No. 2, ^ oz. of No. 3, and 5 oz.
of a 10 per cent, solution of acetic acid. Tone,
rinse, and transfer to a 10 per cent, solution of
chromic acid ; rinse, and immerse in a 5 per
cent, solution of alum ; then wash and dry.
GREENHOUSE AS STUDIO {See "Studio
Design and Construction.")
GREENLAW'S PROCESS
A modification of the calotype process for
obtaining paper negatives. Thin paper was im-
mersed for about an hour in a solution of potas-
siujn iodide and potassiimx bromide, containing
sufficient iodine to give it a dark claret colour.
It was then dried, sensitised as required in an
acidified silver nitrate bath, rinsed, and again
dried. After exposure in the camera, the paper
was developed with gaUo-nitrate of silver, rinsed
well, fixed with " hypo," and washed.
GROUND GLASS
Besides its use for the focusing screen {which
see), it is also employed to diffuse the light in
dark-room lamps, in enlarging apparatus, and
in printing. Sometimes it is employed in glazing
the studio, when direct sunshine has to be
excluded or an objectionable view blocked out.
A piece of ground glass may be placed behind
the negative in the retouching desk, to give a
softer and more uniform hght. Ground glass is
also used to give a matt surface to P.O.P. prints.
GROUND GLASS, COPYING THROUGH
In making half-tone process blocks from a
half-tone print, very finely ground glass may be
used to prevent the crossing of the two dot
images from forming an objectionable pattern.
The plain side of the glass is placed in contact with
the print, and the ground side is rubbed with a
trace of glycerine.
GROUND GLASS PLATES (Pr., Plagues i
verre dipoH ; Get., Mattglasplatten)
Plates having the emulsion coated on finely-
ground glass instead of plain glass, or on a
specially prepared matt substratum. The latter
idea was originated by E. J. Wall. Softer prints
are obtained from the resulting negatives, while
the matt siurface offers great faciUQes for work-
ing on with pencil. Such plates are especially
suitable for stereoscopic and other transparencies.
Plates coated with a matt emulsion beneath the
sensitive emulsion are obtainable commercially
under the name of " Matt-ground," or " M.G."
In process work, thick plate glass ground on
one side with emery powder is used as the sup-
port for the collotype printing film.
GROUP ARRANGEMENT
There is some truth underlying the saying
that " two are a group, three a crowd." The
difficulty of securing a perfect rendering of a
single figure is enormously added to by every
further addition. In fact, when many figures
are to be included at the same time it is hardly
possible to secure anything more than a num-
ber of mere portraits. When the group is a
small one it is often possible to secure a natural
arrangement in which each member has some
common point of interest or occupation. In
such a case, however elaborately the sitters may
be " arranged," the result should appear natural
and fortuitous, as though it had merely been
taken at a happy moment. The figures must
not be placed with any appearance of balance
or symmetry having been deliberately aimed at,
but at the same tune they must not seem in-
dependent and isolated.
In the case of larger numbers, such a homo-
geneous composition is practically out of the
question. The worst arrangement that can be
made is, unfortunately, the most common one.
This is placing the figures in one or more straight
lines right across the pictiure. A narrow band
of small figures with a wide expanse above and
below is never satisfactory. It is better, when-
ever possible, to take advantage of a sloping
bank or a flight of steps, so as to increase the
height of the group on the plate. Such a group
must not appear ill-balanced or lop-sided.
Another common fault to be avoided is the use
of a short-focus lens, which exaggerates the
difference in apparent size between the nearer
and more distant figures. A long-focus lens
and a more distant standpoint give a more
natural effect.
A football or cricket team, a wedding group,
a family party, and so on, admit only of a more
or less formal treatment, the desideratum being
a collection of good portraits. This does not
apply to renderings of groups for what may be
called pictorial purposes, such as fishermen on
the beach or women in a market place. In
such cases any attempt at deliberate arrange-
ment is often impossible, and oftener inadvis-
able. The only satisfactory method is to watch
carefully the ever-varying arrangement of the
figures composing the group and to seize the
most promising opportunities that offer. Appro-
priate and characteristic poses should be watched
for, with careful regard all the time to the relative
positions of the members of the group. The
Griin Lens
282
Gums and Resins
figures will from time to time naturally fall into
satisfactory arrangements, and these moments
must be waited for and taken instant advantage
of. As has been said, the difficulty of obtaining
a perfect arrangement increases with the number
of figures included, but it is seldom possible to
make this arrangement deUberately without
introducing a suggestion of unnatural posing
and stiffness. In a satisfactory group arrange-
ment it must be remembered that all the figures
must not claim equal attention ; some should
be prominent and others duly subordinate.
GRUN LENS
A fluid lens (which see), said to be filled with
cedar oil; it works at a large aperture and
has been used for theatrical photography.
GUAIACOL (Pr., Galacol ; Ger., Guajakol)
Synonym, methylcatechol. A faintly yellowish,
limpid liquid obtained from beechwood creosote
by fractional distillation. It was supposed to
be a developer, but more careful purification
proved that it was an impurity that acted, and
not the guaiacol itself.
GUAIACUM RESIN
The resin obtained from guaiacum or lignum
vitse is sensitive to light, and North has patented
a process in which guaretinic acid, obtained from
the above, was the light-sensitive compound with
or without the admixture of dyes. It has found
no practical application.
GUM CUTCH (See "Catechu.")
GUM ELASTIC (See " Indiarubber.")
GUM GALLIC PROCESS
A dry collodion process used by Hardwick in
i860, and improved by Manners Gordon in
1 868. The plate is edged with albumen and
coated with collodion, to each ounce of which is
added i gr. of cadmium bromide ; next it is
sensitised in a silver bath in the usual way.
After that the following gum gaUic solution is
iised as a preservative : —
GUM OZOTYPE
Gum.")
(See " Ozotype Process,
A.
B.
Gum arabic
Sugar candy
Water .
Gallic acid
Water .
20 grs.
5 „
6 drms.
i'3 g.
■32 „
21 CCS.
3 grs.
•2 g.
2 drms. 7 CCS.
A and B are mixed together and poured over
the plate, this being next drained and allowed
to take its own time to dry. The exposure
necessary is from four to twenty times that for
a wet plate. The developer specially recom-
mended is : —
A. Gelatine . . .64 grs. 4 g.
Glacial acetic acid . 2 oz. 57 ccs.
Water . . . 14 „ 400 ,,
B. Iron protosulphate . 30 grs. 2 g.
Water . . . i oz. 28 ccs.
One part of A is mixed with three parts of B,
preferably one or two days before use. Before
developing, immerse the plate in lukewarm water
for a short time in order to soften the gum.
Additional density is generally desirable and is
obtained with a pyro-silver intensifier. The
plate is finally fixed in " hypo," and washed.
GUM PLASTIC (See " Guttapercha.")
GUM SILVER PROCESS
A " plain paper " printing process by means
of which print-out pictures may be obtained on
almost any kind of paper, ordinary writing-paper
answering quite well. Three solutions are
required for sensitising : —
No. I. Powdered gum arabic ifoz. 54 g.
Water . . • 3i ,, 100 ccs.
No. 2. Solution No. i . 84 mins. 5 ,,
Glacial acetic acid . 50 ,, 3 „
No. 3. Silver nitrate . .15 grs. i g.
Water, distilled . 50 mins. 3 ccs.
In preparing solutions Nos. i and 3, the gum
and the silver must be pulverised. Add No. 3
to No. 2, mix well together, and apply it with
a fairly stiff brush to the paper, which is then
dried in the dark ; a brush bound in metal
should not be used, but if none other is avail-
able see that the metal binding does not touch
the solution or the paper. The paper prints
well as soon as dry, but better still, and the tones
are richer, if used about thirty hours after pre-
paring. The paper is printed in the same way
as ordinary P.O. P., and good red tones may be
obtained by printing to a suitable depth and
fixing in a weak " hypo " solution (48 grs. in
5 oz. of water). Colder and purplish tones may
be obtained by toning in a gold or platinum
bath, or even in a combined bath. The finished
tone depends largely upon the quality of the
negative.
GUMS AND RESINS
The photographer uses gums and resins chiefly
in the form of varnishes.
Amber, a fossil resin, ranging in colour from
colourless to reddish-brown, is slightly soluble
in ether and turpentine ; treated in the same
way as copal in varnish making, it dissolves in
turpentine, petroleum and benzine.
Anime, or Zanzibar copal, is of two kinds,
fossil and " recent," the former being superior ;
of pale yellow or yeUowish-brown colour and
having a rough surface-called " goose skin." It
is very hard, and, for varnish making, needs to
be treated in the same way as copal ; but it is
slightly soluble in ether, benzine, chloroform,
cold turpentine, etc.
Copal, a fossil gum, of pale yellow colour, hard
and transparent ; soluble slightly in cold tur-
pentine and fully soluble in turpentine when fused
or " run " in a copper pan over a fire, a process
that must be left to the varnish manufacturer.
Dammar is known in several forms, ranging
in colour from colourless or pale yellow to dark
brown and black. It is soluble in oil, ether and
benzene.
Dragon's blood is of various kinds, the chief
being of blackish-brown colour and, being in
sticks about i in. thick ; soluble in alcohol,
benzene, chloroform, carbon bisulphide, etc.
Elemi is of many kinds and of a white or
greyish appearance ; it is soluble in alcohol.
Guaiacum is described under its own heading.
Gum arabic, small rounded nodules of yellow
Gum-bichromate Process
283
Gun and Revolver Cameras
or brownish-yellow colour, is soluble in water
but insoluble in alcohol.
Gum benzoin, or gum benjamin, occurring in
large blocks of grey or brown colour, with almond-
shaped particles of a cream colour, is easUy pul-
verised between the fingers, and has a fragrant
odour ; soluble in alcohol and slightly so in
ether and turpentine.
Gum sandarach, a soft, bright gum, resembles
tears or pears in shape, and is semi-transparent ;
soluble in alcohol, and slightly so in benzine,
petroleum, and turpentine.
Gum tragacanth, or gum dragon, moss-like
pieces of whitish colour, is opaque, hard, and
tough ; it forms a thick emulsion with water.
Lac is a brown giun, laiown in many forms —
including sheUac (shell lac), seed lac, lump lac,
stick lac, etc. — which are prepared from a
resinous incrustation on the twigs of certain
trees. It is soluble in alcohol and ether, and
partially so in turpentine. White lac or bleached
lac is used in preparing colourless varnish.
Mastic is in the form of tears of a pale yellow
colour, brittle, and easily melted ; soluble in
alcohol and turpentine. It is used in preparing
mastic varnish.
Resin, an amber-coloured or brown oxidation
product of turpentine, is brittle, easily melted,
of lustrous appearance in a thin coat, and is
soluble in alcohol, turpentine, etc.
GUM-BICHROMATE PROCESS
Familiarly known as " bi-gum," this process
depends on principles first laid down by Poitevin
in 1855. Briefly, it consists in coating paper
with a mixture of gum and pigment sensitised
with potassium bichromate solution. This
paper is printed under a negative, the bichrom-
ated coUoid becoming more or less insoluble in
proportion to the light action. In this way a
print may be obtained with a single coating, but
it is usual to re-coat the print thus made and
again print and develop. This may be repeated
almost indefinitely, either for the purpose of
reinforcing certain parts of the image, or for
producing prints in more than one colour. The
paper used must be weU sized, in order that the
pigment may lie on the surface and not sink into
the substance of the paper so as to stain and
degrade the high lights. If the paper is not
already sufficiently sized a formula suggested by
Mummery is 3 to 5 per cent, of gelatine in
water with 5 drops of formaline to the ounce.
This is brushed evenly over the paper.
The experienced gum worker frequently
evolves his own formula for coating the paper.
It is best to arrive at this experimentally by
proceeding in some such manner as the follow-
ing : 2 oz. of good dean gum arable in tears is
enclosed in a muslin bag and suspended in 6 oz.
of cold water for about two days. This provides
the gum solution. Next, a saturated solution of
ammonium or potassium bichromate is made.
Lastly, the pigment may take the convenient
form of moist water colours in tubes. A mix-
ture may then be made of 10 parts gum solution,
5 parts bichromate solution, and a quantity
of the pigment to be judged always by the length
of the " worm " of colour squeezed from the
tube. Less bichromate will make the paper
less sensitive. The ingredients of the mixture
must be thoroughly incorporated by rubbing
down on a slab or sheet of glass with a palette-
knife.
The sized paper is coated with this mixture
by means of a camel-hair mop, a hog-hair softener
being passed over the surface afterwards in both
directions to make it smooth and even. All this
must be done quickly before the coating hardens.
After about half an hour the paper should be
thoroughly dried by heat and placed in a calcium
tube if it is to be kept, although it is best to use
it as fresh as possible. It must be borne in
mind that the paper is very sensitive to light.
Duration of printing depends to some extent
on the composition of Sie coating. As the image
is not visible an actinometer must be used as in
carbon printing, or a piece of P.O. P. exposed
simultaneously under a negative similar in print-
ing speed to the one in use. As a rule, the
bichromate paper will be sufficiently exposed
when the P.O. P. image looks of the right density.
The gum print is now placed face downwards
in a dish of cold water. The pigmented gum
will soon begin to leave the paper slowly. It is
here that the worker begins to exercise that
control over the development that constitutes
the chief value of the process. He may employ
cold or tepid water by laving, sprajring, spong-
ing, or brushing. By such means he retains only
such of the pigmented gum as he requires for the
rendering of his idea of the subject.
If furSier printing is contemplated the print
is dried and the processes of coating, printing,
and developing repeated as before. Here comes
in the difficulty of obtaining perfect registration
of the second or subsequent images, and some
device is necessary for securing that the print
shall be replaced exactly in its original position
on the negative. Even then there is the expan-
sion and contraction of the paper to be reckoned
with.
When the final development is complete the
print is soaked in a 5 per cent, solution of potash
alum to remove the bichromate stain, and then
rinsed in water.
The use of various papers, the number of pig-
ments available, the different effects resulting
from modifications in coating and development,
the power of multiple printings in one or more
colours — aU these afford opportunity for con-
siderable exercise of control over the final result.
But the very existence of these variable elements
precludes the possibility, even if it were desir-
able, of laying down any hard and fast rules for
working the process. The individual worker
must gradually formulate his methods by careful
experiment and observation, in which case he
will ultimately find the process most plastic,
interesting, and valuable. (See also " Arabin
Gum-bichromate Process.")
GUN AND REVOLVER CAMERAS (Pr.,
Fusil photo graphique. Revolver photo-
graphique, Chambre revolver ; Get., Feuer-
gewehr-kamera, Revolver-kamera)
The photographic revolver — the first instance
of an efficient automatic apparatus for chrono-
photography — was designed in 1874 by P. J. C.
Janssen, the astronomer, to obtain a record of
the transit of Venus. The observation was
made in Japan, the instrument being placed
Gun and Revolver Cameras
284
Guttapercha
under cover, as shown at A, and directed on a
heliogtat, to keep the sun's image stationary.
Forty-eight pictures were taken in succession
on a circular plate, which was caused to make
one revolution in seventy-two seconds, and
stopped at the correct intervals by a Maltese
A. The Janssen Photographic Revolver
cross movement. The exposures were given by
a rotating disc with twelve openings, moving
at a different speed to the plate. A fixed
partition, having a single aperture, was placed
between the plate and the shutter disc, so that
a different portion of the plate, then at rest,
was exposed each time an opening in the shutter
passed the fixed aperture. The operation was
repeated four times to obtain a satisfactory
record. On this model Marey founded later his
photographic gun B. A long-focus lens was
placed at the end of the barrel, thus rendering
it feasible to photograph small objects from a
distance, and the tube was arranged to telescope
for focusing. The clockwork mechanism is
illustrated at C, the back cover being removed.
On pressing the trigger E, a circular shutter
with one aperture commenced revolving. Be-
B. Marey's Photographic Gun
hind this rotated a disc F with twelve openings
(only haU is here shown), the sensitive plate
revolving at the back of the disc by friction.
The perforated disc and plate were moved
intermittently by a pawl G, on an arm worked
by an eccentric, and each time one of the openings
in the disc P came to rest in line with the lens
the aperture in the shutter passed in front of
it, making an exposure. During its movement
the plate was protected from Ught by the opaque
part of the shutter. (See also " Chrono-photo-
graphy.")
Detective cameras and naturalists' cameras
of various kinds have been proposed from time
to time under one or other of the names given
at the head of this article.
GUN-COTTON
A nitro-cellulose, the hexanitrate, which is
extremely explosive. The term is sometimes
wrongly applied to pyroxyhne. /
GUTTAPERCHA (Pr. and Ger., Guttapercha)
A natural product having many similarities to
indiarubber, but capable of being made plastic
and malleable by heat, and retaining, when cold,
any shape given it while hot. Whereas gutta-
percha is plastic, indiarubber is elastic ; and
whereas indiarubber easily combines witii sul-
phur, guttapercha will neither combine nor
intimately mix with that substance. Gutta-
percha is the coagulated juice of the Isonandra
C. Mechanism of Marey's Gun
gutta, which grows in the tropics, particularly in
the Malay district. Its principal uses in photo-
graphy are as a material for dishes and bottles
to contain hydrofluoric acid, and as a mountant.
For the latter purpose, a piece of very thin sheet
guttapercha, the size of the print, is placed on
the mount, next the print is laid over it, and
then comes a sheet of blotting-paper, over which
a hot iron is passed slowly and firmly. The heat
softens the guttapercha, which then adheres to
both mount and print. An objection to the
method is the liability of the guttapercha to
perish.
A cement, made by dissolving 2 parts of
shredded guttapercha and 2 parts of powdered
Syrian asphalt in a mixture of 10 parts of oil
of turpentine and 5 parts of carbon bisulphide,
makes an excellent cement for leather and other
materials.
Guttapercha has been used for coating paper
in order to transfer collodion films. It has also
been used for stripping negatives, instead of
using rubber solution. By the addition of gutta-
percha to collodion the latter is rendered not
only tougher, but more sensitive.
H
HADDON'S FORMUL/E
Many useful formulse due to A. Haddon are
in use, three of the best known being given
below : —
Reducer for Negatives and P.O.P.— This con-
sists of potassium ferricyanide and ammonium
sulphocyanide, and is compounded as follows : —
For negatives —
Potassiimi ferricyanide lo grs. n g-
Ammonium sulphocyanide 20 „ 22 „
Water . . . 2 oz. 1,000 ccs.
This reducer has the merit of keeping well. The
plate is immersed in the solution in the usual
manner, rocked until reduction is sufficient, and
then washed for ten minutes. A dry negative
should be first soaked in water.
For P.O.P.—
Potassium ferricyanide 4 grs. 4'4g-
Ammonium sulphocyanide 20 ,, 22 „
Water . . . . 2 oz. i ,000 ccs.
Platinum Toning Bath for P.O.P. — ^This is a
toning bath on the lines suggested by Henderson.
The formula is : —
Platinum perchloride
15 grs.
I g
Sodium formate
500 „
32-5 ,
Water .
175 „
ii'S ,
Formic acid .
150 mins.
9 ccs
Before treatment, the prints must be washed
in a salt and water bath (salt i oz., water 20 oz.)
prior to toning. Fix and wash as usual.
Mercury Intensification. — ^For the purpose of
eliminating from a mercury-bleached negative
the last traces of a compound formed by the
mercuric salt combining with the gelatine,
Haddon has strongly advocated the use of hydro-
chloric add. The bleached negative must be
washed for ten minutes, and then immersed for
three or four minutes in a bath consisting of
I dram of hydrochloric acid and 10 oz. of water.
Kext it is rinsed in water and transferred to a
second acid bath, rinsed again, and placed in a
third, then washed in several changes of water,
and finally blackened as described under the
heading " Intensification."
HALATION (Fr., Halation, AurMage ; Ger.,
Lichtfleck)
A halo-like, blurred effect, frequently seen
surrounding a brightly lit portion of a photo-
graphic image, caused either by reflection from
the back of the glass plate or by lateral spread-
ing of Ught in the film. The defect has been
observed from the earliest days of photography,
but it became more common on the introduction
of glass plates. It is believed that the first men-
tion of the word in print occurred in the year
1859. Halation is usually seen in its most
aggravated form in a photograph of a dark
interior which includes a bright window. The
latter will not be clearly outlined, and all round
it there will be fog. Halation also appears
sometimes when the roof of a house or a tree
cuts against the sky ; around a white collar or
dress in a portrait ; and, in fact, in all subjects
where a very bright line comes in sharp contrast
with a deep shadow. The chief cause of hala-
tion is the reflection from the back of the plate-
of the bright beam of light that reached it.
In the illustration, the plate is shown in a ver--
tical position, A being the film side and B the
plain glass side or back of the plate. E S repre-
sents a ray of light coming from the lens and
striking the film at F, part of it being reflected
along the line F G and being dispersed in the
camera. The light being strong and the sensi-
tive film translucent, some of the light passes
through the film and strikes the back of the
plate at j. If all the Ught continued its way
A
.'''"
.'-'' ,.'-'G
""-'
.-'■'
B F
\^
Xx^
E
C
0
Diagram Showing Chief Cause of Halation
and went out at the back, it would do little or
no damage, but instead at j another reflection
takes place, as at j H, and the light passes again
through the film and causes fog on the other
parts. Assuming that a bright window in a
dark interior is being pictured on the plate, and
that the part below F represents the window, and
the part above P the dark wall of the room,
some of the light rays E F from the window
would pass through the plate to j and be reflected
to H, thus causing the sharp outline of the win-
dow to be blurred. When the bright object
comes at the side of the plate, the halation is
usually worse than when it comes in the centre,
because rays of Ught which strike the plate
almost at right angles to its surface at CD are
reflected back through the film at practically the
same places through which the Ught first passed.
As the degree of obUquity increases, the amount
of reflection increases also, until at a certain
angle, varying with the refractive index of the
glass, the whole of the light is reflected. The
285
Half'plate
286
Half-tone Screen
thicker the glass plate the greater will be the
extent of the halation, because of the wider
angle formed by the reflected rays ; this explains
in part why the thin celluloid films do not show
appreciable halation. A contributory cause of
halation is under-exposure and forced develop-
ment, conditions that are more often responsible
for the defect than are the direct causes. As a
rule, the quicker a plate is developed the less
will halation show.
It vfiH be seen that the principal causes of
halation are (a) the translucency of the emul-
sion, and (6) the reflective power of the back
of the glass. Some remedies are at once obvious,
(i) To replace the glass with paper or other
non-reflecting support. (2) To stain the film
or in other ways to make it so opaque as not to
allow the rays to penetrate the glass. (3) To
prevent the back reflection by coating the plain
glass side with a non-reflecting or absorbing
medium. Others have also been suggested.
The third remedy, that of coating the back of
the plate before exposure with some non-actinic
and non-reflective substance, is in general use, and
has been found the most convenient and effective
in practice. Formulae for suitable mixtures are
given under the heading " Backings, Plate."
In process work, it is found advisable to back
dry plates with caramel or other medium to
prevent halation, which would rob the half-tone
dots of their sharpness. A sharp dot is an essen-
tial in half-tone work.
HALF-PLATE
A commercial size of dry plate and printing
paper, measuring 6 J in. by 4f in., and largely
used for " cabinet " portraits and occasionally
as a stereoscopic size.
HALF-TONE PROCESS (Pr., Proc^di en demi-
teintes or Simili ; Ger., Halbtonverfahrung
or Autotypie)
A process in which the half-tones of a photo-
graph are reproduced by breaking up the image
into dots of varying size, transferring this dot
image to a metal plate, and etching the dots
into relief for typographic printing. The shades
of colour or tone between black and white in the
photographic image are termed half-tones. To
reproduce these half-tones in a block for typo-
graphic printing, in which a uniform layer of
ink must be employed, it is necessary to break
up the image into fine dots of varying size —
largest, and therefore printing darkest, in the
shadows, and smallest, therefore printing light-
est, in the high lights ; the intermediate sizes
printing the halt tones.
The credit of the idea of breaking up the image
into dots by means of a network screen is due
to Pox Talbot, who proposed it in a patent
dated 1852. He used crape, or gauze, but also
suggested the use of a glass plate ruled with
fine opaque lines, which latter is the means
employed to-day for executing the process.
Various experimenters carried on the process
with gauze, or with lines on glass obtained by
photographing lines ruled or printed on paper,
and with hnes ruled through a blackened ground
on glass, but it was not until 1893, when Max
Levy, of Philadelphia, patented and introduced
commercially his process of engraving and etch-
ing the lines into the glass and filling in the
furrows with black pigment that the process
became a commercial success. The Levy screen
consists of parallel hues ruled diagonally on two
glasses, which are sealed together face to face
with Canada balsam, thus forming a network
of crossed lines. Varying degrees of ruling are
used, from fifty-five lines per inch (for coarse
newspaper work) up to 400 Unes per inch,
according to the degree of fineness required
in the block. Ordinary magazine illustrations
are made through a screen of about 133 to 150
per inch ; the half-tone plates accompanying this
work were made through screens of 175 and 200.
In carrying out the process the screen is
placed in a holder in front of the sensitive plate,
and, by means of mechanism in the back of the
camera, is moved nearer to or further from the
plate according to the extension of the camera
and the degree of the ruling — long extension of
the camera requiring greatest distance of the
screen, and fine rulings the smallest distance.
Some cameras are fitted with screen adjustment
gear. Square, cross, star, and other shaped
diaphragms are put in the lens, alternately with
the usual round diaphragm, the object being to
promote the better formation of the dots.
The negative is made either by the wet or
dry plate process, or with collodion emulsion,
the first-named process being generally preferred,
and it needs to be developed, intensified, and
cleared to sharpen up the dots. A copper or
zinc plate is coated with a solution of fish-glue
and ammonium bichromate (see " Enamehne "
and "Fish-glue"), and exposed to Ught under
the negative. The image is developed by dye-
ing the plate with anilme violet and washing
with water until the dots stand out clear on the
bare metal. The plate after being dried is held
in pincers over a gas-stove imtil the image is
" bumt-in " or converted into an enamel which
is extremely acid-resisting.
The etching is done with dilute nitric acid for
zinc, or with ferric perchloride for copper, and
it is carried to such a depth as will prevent the
printing ink from filling up the spaces between
the dots.
To increase contrast and to bring out detail,
the plates are usually " fine etched." Parts
that are sufficiently etched in the first or " deep "
etching are stopped out with acid-resisting var-
nish, and the remaining parts again etched ; this
may be repeated several times.
The plate is finally trimmed to size, the edges
bevelled with a special plane or machine, and
fastened to a wooden moimt or block by naUs
driven through the bevelled edge ; or a metal
block may be used. The mount brings the
plate to type height, so that the block can be
printed along with type. W. G.
HALF-TONE SCREEN
A glass plate, or pair of plates sealed together,
ruled with parallel lines, usually crossed, to form
a network or grating, which is placed in front
of the sensitive plate to break up the photo-
graphic image into a series of dots, in order that
the half-tones may be reproduced. The com-
mercial half-tone screen was introduced by Max
Levy, as stated under the heading " Halt-tone
Process."
Hallotype
287
Hand Camera
HALLOTYPE (See " HeUenotype,")
HALOGENS (Fr., Halogines ; Ger., Halogene)
The four elements, bromine, chlorine, fluorine,
and iodine, are thus caUed because they form
very marked salts with metals.
HALOID (Pr., Haloide; Ger., Halogenverbindung)
Synonym, halide. Applied to compounds
containing one of the four halogens ; for in-
stance, a silver or alkaline haloid or haHde is
spoken of.
HAND CAMERA (Fr., Chambre i main, Chambre
dStective : Ger., Handkamera, Detectiv-
kamera, Geheimhamera.)
A camera sufficiently light and portable to
be used in the hand, instead of on a stand. A
collapsible pocket camera having a cloth body
was suggested by Edwards as early as 1855. In
i860 and 1861 hand cameras of fixed focus with
bodies of wood or metal were constructed by
Bertsch and by Ottewill, and in the latter year
magazine changing-boxes were in use. Enjal-
bert in 1887 used a leather changing-bag attached
to the camera, with a lever for lifting the plates
as exposed. The first approximation, however,
to the convenience of the modem hand camera
appears to be due to Thomas Bolas, who in
1 88 1 described several forms of what he termed
" detective cameras," with twin lenses, a focus-
ing arrangement, and a pneumatic release for
the shutter. A reflecting prism was placed in
front of the lens so that it might be pointed at
a right angle to the direction of the object to
be photographed, and thus worked without
exciting suspicion.
The simplest pattern of hand camera is the
box form, which is usually of fixed focus, the
lens being incapable of movement and so
adjusted Siat all objects beyond about seven
yards distant wiU be rendered sufficiently
sharp. A typical box form camera for films A
has two finders K and i, for sighting the object.
for plates being shown at B. In this model,
focusing is effected by turning a milled screw
o; a hinged door at the front allows access
to the lens and shutter, and permits the storage
of the pneumatic ball and tubing in the recess.
Folding Hand Camera for Films
A trigger release is worked by a push at the
side ; p is the lever actuating the plate-changing
mechanism, and Q, pivoted to tixe door, acts
as a dust excluder.
The details of the plate-changing mechanism
differ considerably: C illustrates one effective
arrangement, introduced by McKellen. The
metal sheaths s containing the plates have pro-
jecting pins T at their bottom comers, which
rest on grooved guide plates v at the sides of
the camera. At the end of each groove is a
circular hollow, in which turns a revolving disc
V, the two discs being moixnted on the same
shaft. Each disc has a notch in it capable of
receiving the pins of the sheaths. The sheaths
are pressed forward by the spring w, when the
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Box-form Fixed-focus
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B. Box-form Focusing Camera
C. McKeUen Plate-
Changing Mechanism
one for vertical and one for horizontal pictures.
The inner case is shown partly withdrawn,
M being the key by which the film is wound.
Box-form hand cameras are also made to hold
a magazine of plates in sheaths or for use with
ordinary dark -slides. Besides the fixed -focus
type, they are obtainable with a focusing
arrangement working by scale, one of this kind
front one bears at the top against a stop-rail x
and is supported at the bottom by its pins
engaging in the notched wheels. To change a
plate, the wheels are turned simultaneously by
means of a handle outside the camera, thus
carrying down the front sheath, the pins of
which remain caught in the notches until the
top clears the stop-rail x. The sheath now falls
Hand Camera
288
Hand Camera
into the bottom of the camera, and the handle
is turned in the reverse direction until the
■wheels engage with the pins .of the second
sheath, which is then in position for exposure.
A representative example of a folding hand
E, Winding Mechanism for Films
camera for films is shown at D. The principal
movements and fittings are : j, key for winding
film ; K, focusing screw ; L, rising-front pinion ;
M, finder ; N, spirit level ; o, lens with dia-
phragm shutter ; P, cross-front movement ; Q,
bush for tripod screw, for attaching the camera
to a stand if required ; R, focusing scale.
The winding mechanism for films usually
varies little from the system shown at B. Having
removed the sliding back, a charged spool of
film S is placed in a recess at one side of the
camera and fits on two small pegs. An empty
spool T fits a recess at the opposite side, and is
turned by the winding screw tr which engages
in one of its ends. Having inserted both spools,
the end of the black paper on the full one is
drawn out tmtil it can be pushed through the
slot seen on the empty spool, and the key is
given a single turn. The back is then replaced
F. Folding Camera for Plates
and the key turned until the first number on
the black paper appears at the small ruby
window in the rear of the camera ; it is then
known that the first film is in position for
exposure. The remaining numbers are wound
forward as required, and when the last exposure
has been made winding is continued until all
the black paper has been wound off the original
spool, when the camera back may be opened
and the exposed spool withdrawn.
A folding camera for plates is illustrated at
G. "Hand or Stand" Camera
P. A more substantial and elaborate example
of what is known as the " hand or stand "
type is shown at G ; this can be employed for
nearly all descriptions of work, being either
held in the hand or supported by a stand.
Yet another class of hand camera is that in
which a focal plane shutter is used, for high-
speed exposures, as required in press work and
sports photography. A typical folding focal
plane camera is shown at H. In use, it is held
up to the level of the eye, the subject being
viewed through a direct-vision finder, consist-
ing either of a small concave lens with cross-
Unes and sight, as illustrated, or a rectangular
wire frame. There is a growing tendency
among press workers to prefer the focal plane
to the reflex camera on account of its lightness
and lesser bulk, besides the fact that it is held
at a more generally useful height. The reflex
and twin-lens cameras have, however, the great
advantage of giving a full-size image in the
finder, which may be watched and focused
H. Folding Focal Plane Camera
right up to the moment of exposure. These
cameras form a class by themselves, and will
receive separate treatment. {See also " Detec-
tive Camera," " Magazine Camera," " Pocket
Camera," " Reflex Camera," " Twin-lens
Camera," etc.)
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Hand Camera, Work with
289
Hard Water
HAND CAMERA, WORK WITH
It considerably enlarges the scope of the
photographer's work to become expert in the use
of the hand camera. But the hand-camera
■worker matures only with time, patience, prac-
tice and experience. Moreover, there are special
considerations to be taken into account before
it is possible to do consistently good work with
a camera that not only has to be used in the
hand, but has to be brought into operation with
trjHing rapidity. One of the most important
points is familiarity with the camera itself. It
should be known and understood down to its
smallest detail. Every operation involved in
making an exposure and changing the plate or
film must be so familiar that it can be pMformed
rapidly and almost mechanically. There must
be practically no risk of bungling or blundering.
The use of a reflex camera removes any doubt
as to what is sharply focused and what is in-
cluded on the plate. With other patterns it is
necessary to learn to estimate distances with
approximate accuracy. It is also useful to
know the depth of focus at different distances
and with different lens apertures ; and to know
the distance (with the particular lens in use) at
which a full-length figure will come the right
size on the plate. When there is any uncer-
tainty as to the precise distance of the object
to be focused, it is weU to err on the near side,
as the depth of focus is always greater on the
farther side than on the nearer side of the point
focused upon.
In the absence of a full-sized finder it is
advisable to have the small finders as accurate
as possible. In practice it is better that they
should show rather less than is actually included
on the plate. When the plate used is a very
small one it is more than ever necessary that
the subject should be accurately placed upon it,
as there is no room to be wasted. Many failures
result in the use of small cameras from this
cause, particularly when reUance is placed on
finders so minute as to be worse than useless.
It is generally worth while to fit such small
cameras with a removable finder that will show
on a reasonably large scale just What will appear
on the plate.
It is also of vital importance to be able to
hold the camera level and steady during expos-
ure. The duration of exposure that can be
given with safety depends largely on the in-
dividual, but also to a great extent on the type
of camera in use and on the position in which
it is held. A large, heavy camera can generally
be held steadier than a small, light one ; and it
is safer to hold the camera pressed against the
body than at arm's length or at eye-level. The
type of shutter and its smoothness of working
must also be considered a factor. When all
conditions are favourable, an exposure of a fuU
second should be safely attainable. Another
point that should be constantly borne in mind is
that proper exposure is necessary. It may be
thought that such a consideration does not apply
particularly to hand-camera work. But, un-
fortunately, there is too often an idea that with
a hand camera there is some magic property
enabling much shorter exposures to be given
than if the same camera happened to be set
upon a tripod. Naturally, the exposures given
19
with a hand camera are more or less rapid, but
they are only properly effective when the con-
ditions obtaining demand just those exposures.
An exposure-meter, or some similar guide, is
every whit as essential in work with Uie hand
camera as with the stand camera. A further
aid to successful hand - camera work is the
cultivation of a quick eye. This in itself is but
small gain without the addition of dexterity in
manipulation. It is often imperative that the
camera shall be used quite unobtrusively, and
rapidity and certainty of working thus become
a valuable asset.
The results obtained with a hand camera are
largely employed for the production of either
lantern slides or enlargements. Hence it be-
hoves the hand-camera worker to aim at the
most perfect technical excellence to which he
can attain. He should keep his apparatus free
from dust, pay the most extreme attention to
exposure and development, and strive to pro-
duce a spotlessly perfect negative from every
plate or film exposed. He should absolutely
rid his mind of any idea that good work with a
hand camera can be obtained in a haphazard
and slipshod manner. All the judgment, con-
sideration; and care that are devoted to work
with the stand camera must equally be given to
hand-camera work ; and in addition further
attention must be paid to the added difficulties
arising from the often rapid use of a camera
held in the hand. Only so can a high standard
of excellence be achieved. W. I<. P. W.
HARD NEGATIVES
Negatives in which the gradations are harsh,
irrespective of the total range of contrasts. A
thin negative may be hard, as the gradations
may be very harshly rendered as a result of
shortness of exposure. The term is frequently
applied incorrectly to negatives that are too
strong in contrast with good gradation. If the
gradation is good the negative is not hard
or harsh. Methods of treating hard negatives
are given under the heading " Harmonising
Contrasts."
HARD PRINTS
These naturally result from using hard or
harsh negatives, or those that are too strong in
contrast for the printing process employed, with-
out being harsh. There is no satisfactory
method of treating the prints when once made.
The best course to follow is to modify the nega-
tive by the methods given under the heading
" Harmonising Contrasts," or to modify the print
during its exposure by the methods explained
under the heading " Control in Printing." A
negative may yield a harsh result in one
process and possibly a more satisfactory print
in another one.
HARD WATER (Fr., Eau calcaire ; Ger.,
Haries Wasser)
Water containing carbonates and stUphates of
lime and other earOiy salts. Some of these may
be removed by boiling, allowing to cool, and
then filtering ; and aU water for photographic
purposes should be so treated, although it is
far better to use nothing but distilled water for
all solutions.
Hardeners
290
Hat Camera
HARDENERS
Solutions used for hardening the films of
gelatine negatives and prints with the object of
preventing frilling and blistering. Their use is
not so necessary now as it was in the early days
of gelatine plates and papers, as means of hard-
ening the gelatine during its manufacture are
now employed. As, however, the melting point
of wet gelatine is about 90° P. (about 32° C),
hardening solutions are still necessary in the
tropics, and in colder parts of the world when the
films are to be heated to beyond the normal tem-
perature. Chemicals which possess the property
of hardening gelatine may be mixed with the
" hypo " bath or used separately. Baths which
fix and harden at the same time will be found
under " Fixing-hardening Baths," but fre-
quently it would be fatal to leave the hardening
until fixing, as the harm may be done in develop-
ing or toning. PormaUne, ordinary alum, and
chrome alum are the commonest hardeners,
others being potassium nitrate, aluminium
chloride, and aluminium sulphate. Pormaline is
by far the most satisfactory, i oz. of formaline
being added to 10 oz. of water ; this requires
about five minutes for complete action, but may
be used weaker if desired — say, one part in
twenty — in which case fifteen minutes' immersion
will be necessary. The stronger bath is the less
safe of the two, and may cause the film to become
horn-like, crack, and leave the support. The
formaline solution should be distinctly alkaUne,
inasmuch as acid and neutral solutions have but
very little hardening effect upon gelatine ; also
care should be taken that the hardening action
goes right through the film and not merely half
way.
Chrome alum is next best ; a suitable strength
is i oz. to 15 oz. of water. Its tanning action
is greater than that of ordinary white alum,
and although it has a deep rich colotir, it
does not stain the film. Namias recommends
the following chrome almn mixture, and states
that it has great hardening action : Dissolve
I oz. of chrome alum in ^ pint of cold water,
and add liquor ammonise slowly until a pale
green precipitate is plainly visible. Then add
I pint of a 10 per cent, solution of ordinary alum,
and boil the whole for about three minutes ;
when cool it is ready for use. Immerse negative
or print from ten to twenty minutes. Ordinary
alum (sodium, potassium, or ammonium alum)
was at one time very popular as a film hardener,
but it is not considered to be as safe as forma-
line or chrome alum. The proper strength is
1 oz. to the pint of water. The plate or print
should be immersed for from ten to twenty
minutes. Any of the above hardeners may be
used either before or after developing, toning,
etc., but it is always necessary to wash well
before and after treatment, more particularly
when ordinary alTwn is used after developing
and before fixing ; otherwise, ugly scum-like
markings appear on the negative, and these
cannot be removed. Alum markings are due to
alkaH from the developer remaining in the film,
combining with the alum and precipitating
aluminium hydroxide. When alum hardeners
are used after development the alkali from the
developer can be destroyed by rinsing the
developed plate in a weak solution of citric acid.
In process work, hardening solutions are usefid.
In the Paynetype process the plate is immersed
in a 5 per cent, solution of potassium bichrom-
ate for three minutes, which hardens the gela-
tine image to such an extent that it can be
developed Hke a carbon print. In the enamel
process on zinc it is recommended that, after
developing thoroughly, the plate should be
placed for three minutes in a bath of —
Ammonium bichromate
Chromic acid .
Methylated spirit
Water .
2 oz. 44 g.
5 „ 100 CCS.
50 „ 1,000 „
Wash, dry, and bum in. The image then resists
the acid better. (See also " Pixing-hardening
Baths.")
HARDWICH. T. FREDERICK
Bom at Wells, in 1829; died at Shotton Vicar-
age, Durham, 1890. Author of "Photographic
Chemistry" (published March 12, 1855). Pro-
fessor of Photography at King's College, London.
He made important investigations (from 1854
to 1 861) in the preparation of collodion, and
made many improvements in the optical lantern.
In 1 861 he took holy orders.
HARMONISING CONTRASTS
Harsh contrasts may be softened by chemically
treating the negative or by means of control in
printing As a general principle, when the
contrasts are due to under-exposure, the plate
should be treated with the ammonium per-
sulphate reducer ; but if reduction is carried
too far, the weak shadow detail wiU suffer.
When the contrasts that require harmonising
are due to excessive contrast iu the subject, or
where some portions only are out of harmony
with the greater part of the negative, it is pre-
ferable to adopt the methods described under
" Control in Printing." By chemically reducing
the negative, the contrasts throughout are
softened, and the gradation of every detail is
flattened. By control in printing, the gradation
of the various parts remains unchanged in
strength, and each is printed with full detail.
HARRISON. W. H.
Bom 1 841 ; died August 10, 1897. In 1865
he published his discovery of a bromide emulsion
dry plate and the use of an alkaline developer.
He was for many years editor of the Photo-
graphic News.
HARSH NEGATIVES
For a definition of a harsh negative, see under
the heading " Hard Negatives." Harsh nega-
tives may be improved by the methods given
under the heading " Harmonising Contrasts "
above.
HARTSHORN. SPIRIT OF {See "Ammonia.")
HAT CAMERA (Pr., Le Photo-chapeau ; Ger.,
Hutkamera)
A detective camera, concealed inside a hat.
The lens worked through a small opening in the
side of the hat, norm^y closed by the shutter,
while the exposure was given by pulling a cord
made to resemble a hat-guard.
Head Rest
291
Hellography
HEAD REST {See " Posing Chairs and Head
Rests.")
HEAD SCREEN
A reflector used in portraiture for cutting off
top light or for lighting the side of the face
that is in shadow. Many shapes and styles are
obtainable commercially, but essentially it is a
frame, covered with light-coloured material,
arranged to stand at any suitable angle.
HEATING SOLUTIONS
The important part which the temperature
of photographic solutions plays as regards their
activity cannot be overlooked, and much more
reliable and uniform results will be obtained if
they are always heated to a uniform temperature,
about 65° P. (about 18° C). As a rule, it will
be found quite sufficient to place the stock
bottle or measure full of the solution in any con-
venient outer vessel, which should then be fiUed
up to the level of the hquid in the bottle with
warm water.
HEAVY SPAR (See " Barium Sulphate.")
HECTOGRAM, HECTOLITRE ETC. {See
"Weights and Measures.")
HELIAR LENS
A rapid anastigmatic lens introduced by
Voigtlauder. It consists of two cemented com-
binations, and a central negative lens It is
made in focal lengths from 2 in. to 24 in., all
sizes having an aperture of //4'S.
HELIOCHROME (Pr., HiHochrome ; Ger.,
Farbenphotograph )
A photograph in colours. {See " HeUochromy.")
HELIOCHROMY (Pr., Chromophotographie,
HSliochromie ; Ger., Heliochromie, Farben-
phatographie)
The name given by Niepce de St. Victor to his
method of colour photography, discovered in
1853, but now applied to all such processes.
St. Victor, following Becquerel, used a film of
silver chloride on a silver-coated plate. Various
methods were employed to chlorise the plates,
one being to dip them in a weak solution of
sodium hypochlorite (sp. gr. 1-35) until of a
bright, pinkish hue. The plates were then
covered with a solution of dextrine saturated
with lead chloride, dried, and subsequently
submitted to the action of heat. Rather long
exposures were required in the camera, the plate
being then again heated to render the resiUting
pictures a little less fugitive. Some vivid colour
reproductions were obtained, which unfortun-
ately quickly faded, since no means of fixing
could be found. A slight access of stabihty was
secured by covering the plate with an alcoholic
solution of gum benzoin.
HELIOGRAPH (Pr., miiographe ; Ger., Helio-
graph)
A photograph or engraved plate made by
Niepce's bitumen process {see "Heliography ").
All photographs Were for some time called
heliographs.
By means of the spectrum heliograph mono-
chromatic images of the sun are obtained.
Referring to the illustration, the image of the
sun is formed by the lens c on the slit Sj, and
is projected by the lens 1,1 on the prism p ;
by this it is dispersed and reflected by the
mirror m, and thence brought to a focus by the
lens I,, on the plate F. The whole arrangement
is mounted on the platform a a a a, which is
movable to and fro in the direction of the arrows.
Sj is used to isolate one particular Fraunhofer
line in the spectrum, either the hydrogen f line
A
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Diagram Showing Principle of Spectrum
Heliograph
or H the calcium line. Now the image at Sj
is fixed, but Si itself moves ; therefore successive
portions of the sun's surface are exposed exactly
as though a narrow slit focal plane shutter were
used. As the prism, mirror, and 1,2 are aU fixed,
and Sj is arranged to isolate one line, it is obvious
that by moving the platform we obtain mono-
chromatic images of the sun on the plate F,
which is fixed and does not move with the plat-
form. Some of the most successful photographs
of the sun have been taken in this manner, which
show most conclusively the distribution of
hydrogen or calcium vapour on its surface.
HELIOGRAPHIC PROCESS
A term applied to any method of " sun
printing," as used for copying plans, etc.
HELIOGRAPHY (Pr., miiographie ; Ger.,
Heliographie)
A process discovered in 1826 by Joseph
Nicfephore de Niepce, in which a copper plate
coated with silver ana covered with a film of
bitumen was exposed to light in the camera for
some hours. Those parts of the film affected
by light became more or less insoluble, according
to the extent to which it had acted, whereas
the shadow portions or unexposed parts could
be dissolved away with oil of lavender. Besides
silvered copper, plates of plain copper and other
metals were used. Niepce tried to darken the
bare portions of the silver, where the shadows
should have been, by the application of iodine
and other reagents, and also etched some plates
with acid, for printing in the press. Such pic-
tures, as well as engravings from the etched
plates, were caUed heliographs, the word " heUo-
eraphy " being then used instead of the modem
designation " photography." Niepce's method,
in an improved form, is still in use for printing
banknotes. The term heUography was for some
time employed also in referring to photogravure,
but this usage is practically obsolete. {See also'
" Asphaltum.")
Processes of etching in intaglio on copper by
photographic methods are sometimes referred,
to under the name of hehography, more particu-
larly a process of reproducing maps.
Heliogravure
292
Hill, David Octavius
HELIOGRAVURE
Another name for photogravure {which see).
On the Continent this process is invariably called
heliogravure.
HELIOPHOTOGRAPHY
Solar photography. {See " Sim, Photograph-
ing the.")
HELIOSTAT (Fr. and Ger., Heliostat)
A mirror mounted on a central axis which
rotates at the same rate as the earth, so that
an image of the sun can be reflected to one
constant spot. It is used in photo-micrography
when a powerful light is required, and also in
spectrography.
HELIOTYPE
A modification of the collotype process, in-
vented by Ernest Edwards, of Ivondou. A glass
plate is waxed and coated with a substantial
layer of gelatine and potassium bichromate, con-
taining a small quantity of chrome alum, which
hardens the gelatine and renders it insoluble
without destroying its permeabihty to water.
When dry, the gelatine film is removed from the
glass, and the surface that has been next the
glass is exposed under a reversed negative in
the usual way. Then the film is hardened at
the back by exposure to light, is attached
under water to a metal plate, preferably pewter,
coated with indiarubber, and is then squeegeed
into perfect contact. The bichromate salt is
removed by washing, and the plate is ready
to be printed from in an ordinary typographic
press.
HELLENOTYPE (Pr., Helknotype ; Ger.,
Hellenotypie)
A method of colouring photographs, at one
time popular in America. Two finished prints
were made from the same negative, one rather
Ught and the other strong and vigorous. The
lighter one was rendered transparent by the
application of varnish and was tinted at the
back. It was tiien adjusted over the stronger
print, giving the impression of a photograph
in coloirrs.
A slightly difierent process, known as Hallo-
type, after its inventor, J. B. Hall, of New
York, was patented in 1857. Two similar
prints were used, one being made transparent
by treatment with dammar varnish, and the
other painted With washes of colour. The trans-
parent print was laid over the painted one, and
the two bound together with a glass and back-
ing, in " passe-partout " style.
HENDERSON, ALEXANDER LAMONT
Bom in Scotland, 1838; died at Bad-Nauheim
in Germany, 1907. For many years one of the
best-known figures in photographic circles. He
was a recognised authority on ceramic enamels
and emulsion making ; he was founder of the
London and Provincial Photographic Association
(1882), and private photographer to Her Majesty
Queen Victoria.
There are many " Henderson " formulEe in
use, among the best known being a hydro-
quinone-metol developer and a combined toning
and fixing bath for P.O.P. :—
Hydroquinone-metol Developer,
A. Hydroquinone .
Metol
Sodium sidphite
Water
B. Sodium hydrate
100 grs. ii'5 g.
40 „ 4'S >,
960 „ no „
20 OZ. 1 ,000 CCS.
100 grs. II-5 g.
Potassium carbonate . 120 „ 14 ,,
Water . . .20 oz. 1,000 ccs.
Mix together equal parts of A and B and add
potassium bromide as required. If over-expo-
sure is suspected, begin development with an old
developer and finish with fresh.
Combined Toning and Fixing Bath for P.O.P.
Sodium hyposulphite
I oz. no g.
Lead nitrate .
. 60 grs. 14 „
Chrome alum
. 60 „ 14 „
Sodium formate
. 20 „ 4'5 „
Formic acid .
. 30 drops 6 CCS,
Hot water
. 10 oz. 1,000 „
Dissolve the lead and sodium formate in a small
quantity of water, add the " hypo " in solution
and the formic acid, allow to stand for twenty-
four hours in an open vessel, and add i or 3 grs.
of gold chloride or platinum bichloride.
Henderson's process for the removal of green
fog or reducing a negative was to place it over
a solution of potassium cyanide for several
hours.
HEPWORTH. THOMAS C.
Bom, November 3, 1834; died 1905. A well-
known writer and lecturer on photographic sub-
jects ; for some years proprietor and editor of the
Camera and also editor of the Photographic News.
HERSCHEL, JOHN FREDERICK WILLIAM
Bom at Slough, 1792; died at Collingwood,
1 87 1. A famous scientist, who did much for
photography in its early days. His name will
always be associated with the discovery of the
" hypo " fixing bath and of the " blue print "
process ; he also suggested glass as a support
for sensitive emulsion, and experimented with
many printing processes, most of which, how-
ever, are now obsolete. Knighted, 1831.
HESEKIEL'S PAPER
A platinum paper made by Dr. Hesekiel, of
Berlin, and introduced into England in Novem-
ber, 1893. It differed from the usual platinum
papers chiefly because its surface was granular,
and it gave results resembling those of a half-
tone process block, owing to the " pyramidal
grain."
HIGH LIGHTS
The most brightly illuminated parts of a sub-
ject. If these are represented by considerable
areas of blank paper the effect is " hard " and
unpleasant. High Ughts should not be scat-
tered about the picture when avoidable, as they
draw the eye from one to another, and do not
permit of the attention being concentrated.
Hence the frequent necessity of " toning down "
some of the high Hghts to avoid " spottiness."
HILL, DAVID OCTAVIUS
Bom at Perth, 1802 ; died 1870. A landscape
and portrait painter, and one of the first to apply
Hillotype
293
Hood, Lens
photography to portraiture (on the recommenda-
tion of Sir David Brewster). Many of his calo-
types of eminent men are still in existence.
HILLOTYPE (Pr., Hillotype; Ger., Hillotypie)
An alleged process of photographing in colours
claimed to have been invented by the Rev. Levi
L. HiU, of Westkill, New York State, in 1852.
HOAR FROST PICTURES (See " Snow and
Hoar Frost Photography.")
HOFMANN'S COLOUR PHOTOGRAPHY
A process in which three constituent negatives
were taken and printed on to carbon tissue con-
taining red, yellow, and blue pigments, the
developed prints being subsequently super-
imposed. It was introduced in 1900.
HOLIDAY PHOTOGRAPHY
There are one or two special considerations
that press for attention in the case of photo-
graphic work undertaken during a hoUday.
Frequently the work then done is of special
interest and importance, and any failure is
more serious than in the case of work which
can easily be done over again. In the first
place, it is well to form some idea beforehand
of the kind of subjects to be dealt with in the
place visited, as this to some extent decides
the best form of apparatus to take for the pur-
pose. Whatever camera is used, it should be one
with which the hoKday-maker is already fami-
liar. Many disappointments have arisen from
the use of new and unfamiliar apparatus specially
bought for the occasion. Even the usual brand
of plates should be adhered to, and it is well
to take a full and reHable supply of them rather
than depend on local purchases.
Some workers make a point of developing
their plates from day to day as they are exposed.
This certainly indicates enthusiasm, but it
demands a considerable encroachment on the
hoUday leisure, and, as a rule, the results suffer
on account of the lack of home facilities for the
work. If all the exposures are carefully timed,
with the aid of a meter when necessary, it is
pretty safe to defer development. In that case
the exposed plates may be re-packed, carefully
tied up, in the original boxes. They should be
placed film to film, with cardboard separators or
plain tissue paper (not printed matter) inter-
posed. At the same time it is advisable to make
occasional exposures in duplicate and develop
one of the plates. This can easily be done with
the aid of developers ready prepared in some
small, handy form, "tabloid" or otherwise, its
main object being to ascertain that no unsus-
pected defect has developed in the shutter or
some other part of the apparatus in use. When
roll film is being used it is equally advisable to
develop an occasional strip.
HOME PORTRAITURE (See " Portraiture.")
HOMOCENTRIC LENS
A name applied by Ross to two distinct types
of lens, one being an " air-space " anastigmat,
and the other a cemented lens of the Goerz
double anastigmat type. The former is made
in four intensities— //4-s, //5-6, //6-3, and //8 ;
and the latter in one intensity — ■//6*8. The
chromatic correction of these lenses is excellent,
and they are therefore well adapted for colour
photography.
HOMOCOL (Ft., Homocol : Ger., Homokol)
A sensitising dye of good green sensitiveness,
used for bathing plates or adding to emulsion
for colour work. It is one of the isocyanine
series. Collodion emulsion, sensitised with it,
keeps well, and shows extremely clear working
qualities. It yields an emulsion of only moderate
speed.
HOMOGENEOUS IMMERSION OBJECT-
IVES
These are described under the heading "Ob-
jective."
HONEY PROCESS
Honey was used in one of the methods for
preparing albumen plates, but it Was more widely
used in tiie early days of coUodion plates for the
purpose of keeping them moist. The use of
honey was advocated in 1854 by George Shad-
bolt and Maxwell Lyte, who independentiy dis-
covered its usefulness. The plate was coated
with a solution of honey after sensitising, and
washed off before development ; it kept the
plate moist and prevented the crystaUisation of
silver. Plates prepared with honey needed
double the exposure of wet plates, but they
could be kept several days before sensitising and
exposing, and also between exposing and develop-
ment. The sticky coating was a serious draw-
back, as it attracted dust.
HOOD, LENS (Fr., Parasoleil : Ger., Sonnen-
blende)
The front projecting rim of the lens tube or
mount. A certain degree of such projection is
useful, serving to exclude unnecessary Ught, but
the hood should not be deep enough to cut ofE
any of the image. Thus, in diagram A, the
outer rays p G proceeding from the object
barely clear the hood, and it is evident that if
this were the slightest degree deeper some of
the marginal rays would be stopped. Hand-
Diagrams Showing Principle of Lens Hood
camera lenses now tend to go to the opposite
extreme by having no hood at all, so as to
facilitate portabihty ; in consequence, flare
becomes probable, and the brilhancy of the
image is Ukely to suffer. Collapsible hoods are
manufactured to fit on the lens in hand cameras
and other apparatus. The use of an extended
hood is especially necessary in telephoto work.
Another kind of hood consists of a blackened
wooden or cardboard tube made to fit at the
Hood Shutter
294
Hydrates
front of a studio camera, as illustrated at B.
The partition p, which comes before the lens,
has an opening covered by a hinged shutter,
■which may be raised or lowered by turning the
milled head at the end of the rod Q. Such an
arrangement, besides affording a convenient
means of exposure, greatly adds to the clear-
ness and freedom from fog of the negatives,
by its complete exclusion of all light except
that coming direct from the sitter.
HOOD SHUTTER (Fr., Obturateur avant-
objectif ; Ger., Vor-obfekiiv Verschluss)
Synonym, before-lens shutter. Any shutter
fitting on the hood or front of the lens, as, for
example, the flap shutter and the outside type
of roller-blind shutter. The term is also applied
sometimes to the combination hood and shutter
accessory often used with studio cameras, and
described in the preceding paragraph.
HORIZON (Pr., Horizon ; Ger., Horizont)
When a camera is level, with the lens centrally
opposite the plate, the line of the horizon, if
visible, wiU bisect the picture. This is generally
considered a defect, and it is well to avoid it by
raising or lowering the lens.
HiJBL'S PLATINUM INTENSIFIER
Used for intensifying weak prints on platino-
type paper. The print is immersed for from
ten to thirty minutes in a solution of platinum
perchloride and sodium formate, the platinum
being slowly reduced and deposited upon the
small particles already present. The formula
advised is : —
A. Platinum perchloride . 5 grs. 2" 3 g.
Water . . . J oz. 100 ccS.
B. Sodium formate . 25 grs. 11 '5 g.
Water . . . J oz. 100 ccs.
Add A and B to 30 oz. of water. Immerse the
print, and when sufficiently dense wash well.
Hiibl has further suggested a method (which see,
under heading " Platiuotype Process") of
obtaining tones between a slate grey and a
bright blue.
HUBL'S THREE-COLOUR PROCESS
The ordinary method of tricolour photography
has been dealt with at considerable length,
theoretically and practically, and with great
exactness, by Baron von Hiibl in his work
" Three Colour Photography."
HUGHES, CORNELIUS JABEZ
Bom 1819 ; died 1884. After an extensive
business experience he became (1862) the official
photographer to Queen Victoria. He was an
authority on carbon work. His best known book
is " Principles and Practice of Photography."
HUNT, ROBERT
Bomi8o6; died 1887. The most copious writer
on photography in its earher period. In 1844
he published " Researches on tight," in which
he was assisted by Sir John Herschel ; and, in
1851, "Photography"; in 1850 he compiled
a history of photography for the British Asso-
ciation. In 1844 he discovered the developing
powers of iron protosulphate, and later made
photographic experiments with the salts of
chromium, nickel, lead, manganese, copper, iron,
mercury, gold, silver, and platinum. He was, in
1853, one of the founders of the (now) Royal
Photographic Society and a, member of its first
council.
HUNT'S COLOUR PROCESS
Robert Hunt in 1844 published many interest-
ing experiments on the action of the spectrum
and coloured lights on silver chloride (" Re-
searches on I/ight," 1844; "Researches on
Light in its Chemical Reactions," 1854), thus
following in the footsteps of Seebeck and
Herschel.
HURTER AND DRIFFIELD, OR H. & D.
SYSTEM
A system of determining the sensitiveness or
speed of plates, suggested in 1890 byHurterand
Driffield, and based on the measurement of a
series of densities instead of a single one. (See
"Plate Testing.")
HUSNIK'S PROCESS (See " Leimtype.")
HUYGHENI AN EYEPIECE (See " Eyepiece.")
HYALOGRAPHY (Fr. and Ger., HyalograpUe)
Synonym, hyalophotography. Photographic
etching on glass. Rozsnyay's method (1875) is
much more elaborate than that of Duchochois,
and according to the latter, paper is coated with
a solution of 100 grs. each of sugar, gum arable,
and ammonium bichromate in 2 oz. of water.
The dried plate is exposed under a positive
transparency and dusted with finely-jgowdered
bitumen. The " developed " image is trans-
ferred to a warm glass, which softens the bitu-
men and causes it to adhere. The paper is
soaked off, the glass dried, and etching done
with hydrofluoric acid vapour.
Photo-hyalographs have been used both de-
coratively and for printing from in the press.
HYALOTYPES
The name by which albumen transparency
positive pictures upon glass, in the form of lan-
tern slides, were originally known. They were
introduced into England by Messrs. Langenheim,
of Philadelphia, and they were known in England
as " Crystalotypes " (which see).
HYDRAMINE (Pr. and Ger., Hydramin)
C,H4 (OH), (NHj), CeHj. Molecular weight,
218. Solubilities, i in 500 cold water, i in 20 hot
water, i in 15 hot alcohol, readily dissolved by
caustic alkalis. It occurs as white scales, and
is obtained as the addition product of one
molecule of hydroquinone with one of para-
phenylendiamine. It was introduced by Lumi dre
and Seyewetz as a developer, which works best
with caustic Uthia : —
Hydramine
Sodium sulphite
Caustic lithaa .
• 44 grs.
. 264
• 26 „
5 g-
32 „
3 ,.
Distilled water to
20 oz.
1,000 ccs.
HYDRATES (Pr., Hydrates ; Ger., Hydrate)
Salts in which a metal replaces one of the
atoms of hydrogen in water. (See "Caustic")
Hydrazine
29S
Hydrogen Sulphate
HYDRAZINE (Pr., Hydrazine; Ger., Hydrazin)
Synonym, diamidogen or diamine. NHj NH,.
Molecular weight, 32. This was proved to
consist of a very faint developer in an
alkaline solution, but neither it nor its organic
derivatives are practically used. Some of its
compounds have lately been suggested as an
addition to haloid emxdsions without free silver,
in order to obtain intense, vigorous images.
HYDROBROMIC ACID (Fr., Acide bromhy-
drique ; Ger., Bromwasserstoffsdure)
Synonyms, bromhydric acid, hydrogen bro-
mide. HBr. Molecular weight, 81. It is a dear,
colourless, or faintly yellow liquid, an aqueous
solution of the gas HBr, of which it usually
contains 40 per cent. It is occasionally used in
10 per cent, solution as an addition to emulsions.
HYDROCHLORIC ACID (Fr., Acide chlor-
hydrique ; Ger., Chlorwasserstoffsdure)
Synonyms, chlorhydric or muriatic acid,
hydrogen chloride. HCl. Molecularweight, 36-5.
Miscible in all proportions with alcohol and
water. It is a dear, colourless, fuming liquid,
containing about 37 per cent, of the gas HCl.
Itis very poisonous, the antidotes being magnesia,
alkaline carbonates, albumen and ice. It is also
a painful escharotic ; that is, it burns the skin.
The worker should avoid breathing the fumes.
It is used for addulating the alum bath, for
removing stains, and to remove the soluble iron
salts from platinum prints after development.
The impure add, which is of a strong yellow
colour, is known as spirit of salt, and is not used
photographically except for deaning dishes, etc.,
work which it does excellently.
HYDROFLUORIC ACID (Fr., Acide fluor-
hydrique ; Ger., Fluorwassersioffsdure)
Synonyms, fluoric add, fluorhydric add, and
hydrogen fluoride. HF. Molecular weight, 20.
A very dangerous acid in use, as it attacks glass,
porcelain, cork, wood ; also the nails and skin of
the user. It must be kept in indiarubber bottles.
The commercial acid is an aqueous solution of
the gaseous add. Practically its sole use in
photography is for stripping films from glass
plates ; but on account of its dangerous nature,
the use of potassium fluoride or sodium fluoride
has been recommended instead, inasmuch as
when an acid is added to either of these, hydro-
fluoric add is set free. The negatives should
be soaked in a 2 to 3 per cent, solution of the
fluoride, rinsed, and then immersed in a hydro-
chloric acid solution of similar strength.
HYDROFLUOSILICIC ACID
Synonym, fluosihdc add. H^SiFj. Molecular
wdght, 144. The product obtained by acting
on silicon fluoride with water ; it gives ofi add
fumes. It is used for the surface etching of
aluminium plates in hthography.
HYDROGEN (Fr., Hydrogine ; Ger., Wasser-
stoff)
H. Molecular weight, i. A colourless, odour-
less gas prepared by the action of metals on
water in the presence of adds or alkalis. Its
only photographic use is when mixed or burnt
with oxygen for the limelight. Nascent hydro-
gen— that is, when freshly generated — is an
extremely energetic reducer. It is sometimes
used tjo reduce the silver haloid residues, and is
then formed by addulating with sulphuric acid
and immersing strips of zinc or magnesium,
when metalhc silver is deposited as a grey
powder.
HYDROGEN DIOXIDE (See "Hydrogen
Peroxide.)
HYDROGEN FLUORIDE {See "Hydro-
fluoric Add.")
HYDROGEN LINES
The Fraunhofer lines given out by glowing
or incandescent hydrogen gas gener^y under
reduced pressure in a vacuum tube. They are
frequently used for the calibration of spectro-
meters, to determine the refractive index of
glass and scaling spectrograms. The visible
ones are the first four in the following table : —
Ha
(C)
\6562-i
Orange red.
H/3
(F)
4860-7
Bright blue.
H7
4339-5
Deep blue.
H5
(h)
4IOI-2
Violet.
He
3969-2
HC
3888-1
H„
3834-9
H9
3797-3
Hi
3769-9
Hk
3750-2
Ha
3734-1
Hm
372I-I
Hi/
37II-2
The first column gives the usual sdentific
method of naming the lines — that is, the hydrogen
or H alpha ; (£e second gives Fraunhofer' s
letters, the third the wave-lengths, and the
fourth the colour of the line. A great many
other lines have also recently been discovered
as belonging to hydrogen, particularly in the
ultra-violet.
HYDROGEN PEROXIDE (Fr., Piroxyde
d'hydrog^ne, Eau oxygin&e ; Ger., Wasser-
stoffperoxyd)
Synonyms, hydrogen dioxide, hydroxyl, per-
hydiol. H2O2. Molecular weight, 34. Miscible in
ail proportions with water or alcohol. A colour-
less liquid with slightly add taste, foaming in the
mouth, prepared by the action of dilute sulphuric
add on barium peroxide. The commerdal pre-
parations are 3 per cent., corresponding to ten
volumes of available oxygen, and 30 per cent,
solutions, corresponding to 100 per cent, by
volume. It should be kept cool and in the dark.
It has been suggested as a " hypo "-eliminator ;
when rendered alkaline it is a weak devdoper.
Finely divided sUver and platinum act as cata-
lysts on it and decompose it into water and
oxygen. (See "Catatype.") To hydrogen per-
oxide has been ascribed the peculiar efiect of
wood, resins, etc., on dry plates.
HYDROGEN SODA CARBONATE
"Sodium Bicarbonate.")
(See
HYDROGEN SULPHATE (See "Sulphuric
Add.")
Hydrogen Sulphide
296
Hydroquinone
HYDROGEN SULPHIDE (Fr., HydrogSne
sulfur d : Get., Schwefelwassersto-ff)
Synonym, sulphuretted hydrogen, hydrosul-
phuric acid. HaS. Molecular weight, 34. A
colourless gas, with extremely unpleasant smell ;
it is usually obtained by the action of an acid
on ferrous sulphide. It is occasionally used to
precipitate silver from old fixing baths.
HYDROMETER
An instrument for determining the specific
gravity of a liquid ; used by floating it in the
liquid which is contained in a tall glass cylinder.
Twaddel hydrometers are adjusted for certain
densities, and the degrees (°Tw.) are converted
into specific gravities by multiplying by -005
and adding i. In the Eeaum6 hydrometer
system (°B.), for liqiuds heavier than water,
0° equals a specific gravity of i ; ^° equals
1-007 SP- §>■• ; 2° equal 1-013 ; 3° equal 1-02 ;
and so on. For liquids Ughter than water, 100
equal i sp. gr., and for every rise of i in the
degrees there is a drop in the specific gravity of
about -005.
In, process work, the Beaume hydrometer is
universally used by copper etchers for measiuring
the strength of the ferric perchloride solution.
An instrument reading to 50° is the most con-
venient, as the density of the solution does not
exceed 45°, and is more generally between
30° and 40°. The test is usually made in a tall
and narrow glass jar made for lie purpose.
HYDROQUINONE (Fr., Hydroquinone ; Ger.,
Hydrochinon)
A developer, known also as hydrokinone,
hydrochinone, and quinol. The use of hydro-
quinone was suggested by Sir WiUiam Abney
in 1880, but it was not possible to bring it into
general use at that date owing to its expense.
Since then, however, manufacturers have been
able to produce it very cheaply. It occurs in
greyish-white or yellow prismatic needles, which
darken on exposure to light, and in chemical
composition it is alUed to pyrogallol, which is
trihydroxybenzeue, CjHj (0H)3, whereas hydro-
quinone is dihydroxybenzene, CeHj (0H)2. Its
solubihty is 5-8 per cent, in cold water, and about
10 per cent, in hot water. When used alone,
particularly if bromide is added as a restrainer,
hydroquinone has a tendency to give excessive
contrasts, and although an excellent developer,
it is more generally used with metol (see
"Developers, Mixed"). A solution of hydro-
quinone is affected by temperature more than
is any other developer, and works very slowly
— sometimes not at all — when very cold. Hydro-
quinone may be used in one or two solutions, and
the best results are obtained with a caustic
alkali.
One-solution Developer (Concentrated)
Hydroquinone . . 310 grs. 35-5 g.
Sodium sulphite . 5 oz. 275 „
Potassium carbonate 8 ,, 440 „
Hot water to . .20 „ 1,000 ccs.
The above is a concentrated developer, and for
use requires to be diluted with from four to six
times the quantity of water. Bromide will be
required only in cases of over-exposure. Another
one-solution form, in which sodiiim carbonate is
used, is : —
One-solution Developer (Ready for Use)
Hydroquinone . . 90 grs. 21 g.
Sodium sulphite . 2 oz. 220 „
Sodium carbonate . 2 „ 220 „
Water to . . . 10 „ 1,000 ccs.
Hydroquinone works more quickly with sod-
ium carbonate than with potassium, but the
latter is thought to give better gradation.
Messrs. Ivumiere have recommended the follow-
ing one-solution (ready for use) formiJa. It
gives absolutely clean negatives of great con-
trasts, which makes it specially suitable for the
reproduction of black-and-white and line draw-
ings, or for obtaining more contrasty positives
from thin and weak negatives, care being taken
in all cases to keep the exposure somewhat
short : —
One-solution Developer (Ready for Use)
Hydroquinone . . 40 grs. 18-3 g.
Sodium sulphite . 400 „ 183 ,,
Formaline . -SO drops 20 ccs.
Water . . . 5 oz. 1,000 „
No bromide or alkali is required. Dozens of
other formula have been given, all more or less
based on the above.
Probably the most popular of the two-solution
forms — and some scores have been published — is
the following : —
Two-solution Developer
A.
Hydroquinone
Sodium sulphite .
Citric acid .
Potassium bromide
160 grs.
2 oz.
60 grs.
40 „
18 g.
100 ccs,
7 g-
4^5 ,.
Water .
20 oz.
1,000 ccs.
B.
Sodium hydrate .
Water .
160 grs.
20 oz.
18 g.
1,000 ccs.
For use, mix together i oz of A, i oz. of B, and
2 oz. of water. More or less water may be added
as desired, and the more water used the softer
will be the result. By using A and B in equal
parts without water very hard negatives will be
obtained, such as are wanted when copying
black-and-white work.
Two-solution formulae embodjTng the use of
sodium and potassium carbonates are as
below :—
Two-solution Developer
A. Hydroquinone . ^ oz. 27-5 g.
Sodium sulphite . 2 „ no ,,
Water to . .20 „ 1,000 ccs.
E. Sodium carbonate ij „ 69 g.
Water . . . 20 „ 1,000 ccs.
Take equal parts of each, i oz. of potassium
carbonate may replace the ij oz. of sodium car-
bonate in the B solution.
Prof. Lainer has published many useful con-
centrated two-solution formulas, five of which
are given on the next page, and in order to
economise space the quantities are given in
" parts," but to those unaccustomed to the
" parts " system it may be useful to know that
if the soHds are weighed in grains and the
Mquids in minims (480 to the ounce), the pro-
portions win be about right.
Hydroquinone Intensifier
297
Hygiene in Photography
No. 1
Wo. a
2Vo. 3
Wo. 4
Wo. 5
A. Hydroqumone
10
10
10
10
10
Sodium sulphite .
25
40
30
35
35
Potass, ferricyanide
60
120
90
25
25
Water .
600
900
950
1000
550
B. Potass, hydrate .
50
50
50
Sodium hydrate .
30
60
Water .
100
100
90
550
550
For use, A and B are mixed together in pro-
portions as follow : No. i — i oz. of A, with
24 drops of B ; very rapid in action, but inclined
to fog. No. 2 — I oz. of A, with 48 drops of B ;
a rapid developer, and gives strong contrasts.
No. 3 — I oz. of A, with 96 drops of B ; gives
softer negatives. No. 4 — i oz. of A, with 50 to
70 drops of B ; slow working. No. 5 — Mix in
equal parts ; a good, normal developer, which
works slowly and gives clean negatives.
One drawback to hydroquinone h£is been
understood to be that it cannot be made up in
a highly concentrated form, as, for example, a
10 per cent, solution. J. B. B. Wellington,
however, as long ago as March, 1889, published
the following formula for a 10 per cent,
solution : —
A.
Hydroquinone
I oz.
no g.
Methylated spirit
3i „
350 CCS
Sulphurous acid .
3i „
350 ..
Water to .
10 „
1,000 „
Sodium hydrate .
I oz.
no g.
Sodium sulphite .
I
no ,,
Water to .
10 „
1,000 CCS
For use, add 1 drm. each of A and B to 2^ oz.
of water. In the above formula the methylated
Spirit is used to dissolve the hydroquinone and
the sulphurous acid to prevent oxidation.
Hydroquinone may be used again and again
for several negatives without fear of staining ;
but ultimately it gets into a cdndition in
which it stains badly. It keeps well in solution.
It should always be dissolved after the sodium
sulphite.
In process worh, hydroquinone is regarded as
the most useful developer for dry plates and
collodion emulsion. For the former it is used
either alone or in conjunction with metol.
HYDROQUINONE INTENSIFIER
This was recommended by Br. Eder in 1890.
The following two solutions are made : —
A. Hydroquinone
20 grs.
ii-S g-
Citric add .
12 „
7 „
Water (distilled)
4 oz.
1,000 CCS.
B. Water (distilled)
I oz.
27s g-
Silver nitrate
16 grs.
92 „
Mix 3 oz. of A with I oz. of B, and immerse
the well-fixed and washed negative until dense
enough ; finally wash.
HYDROQUINONE WITH METOL (See
" Developers, Mixed," and " Metol-
hydroquinone.")
HYDROSULPHITES, DEVELOPMENT
WITH
Jules Breton experimented in 1890 with a
rather intense developer, formed of a solution
of sodium hydrosulphite, NaOSjOj, mixed with
double sulphite of sodium and of zinc. There
is some trouble with deposits, but it is possible
to obtain dry plate negatives of a fine black,
if care is taken.
HYDROTYPE
A reversed collotype process chiefly due to
Cros. It has been used in a modified form for
colour printing. A gelatine image is made to
absorb dyes in proportion to the action of light,
so that when paper is brought into contact with
the stained plate whilst damp an image is
obtained from the dye.
HYDROXYL [See "Hydrogen Peroxide.")
HYDROXYL CARBON COMPOUNDS
Carbohydrates containing the hydroxyl group
OH for a hydrogen atom.
HYDROXYLAMINE (See " Hydroxylamine
Hydrochloride ")
HYDROXYLAMINE HYDROCHLORIDE
(Pr., Chlorhydrate d' hydroxylamine ; Ger.,
Salzaures Hydroxylamin)
NHaOHHG. Molecular weight, 69-3. Soluble
in water and alcohol. It takes the form of
colourless crystals, and can be prepared by
reducing ethyl nitrate with tin and hydrochloric
acid and chlorising. Both hydroxylamine and
the hydrochloride are vigorous developers when
rendered alkaline with caustic alkalis, but they
are of no practical value as nitrogen gas is evolved
during development, which either pits the film
all over or strips it from the glass.
HYDROXYTRICARBOXYLIC ACID (See
" Carboxylic Acids.")
HYGIENE IN PHOTOGRAPHY
Photography does not now involve many risks
to health, but it is necessary to remember that
there are still a few chemicals used which injure
the worker's hands if they come in contact with
them, and of which the fumes become dangerous
if inhaled. Should the dark-room be insuffi-
ciently ventilated the atmosphere will become
stuffy and cause headaches ; and, of course, when
strong-smeUing chemicals are used — as ammonia,
sodium sulphide, etc. — good ventilation is all
the more important.
Many users of a red light find that it makes
their eyes ache if employed for any length of
time, and when this happens a weak solution
of boracic acid should be made up (8 grs. to i oz.
of water), and this should be mixed with an
equal volume of hot water and applied to the
eyes with a clean handkerchief or sponge.
When the daguerreotype process is worked by
experimentalists, particular care should be taken
not to inhale the fumes from the mercury, as
they are most dangerous. The fumes from collo-
dion (ether, really) and ammonia involve but
slight risk to the health, but they affect the
eyes. Should ammonia be found to affect the
worker, he should sniff weak acetic acid or
ordinary brown vinegar, and he may sip a Httle
of the latter with helpful results.
The fumes from all acids, particularly hydro-
Hygrometer
298
" Hypo "-alum Toning
fluoric, and from potassium cyaaide are more
troublesome ; when these substances are used,
the dark-room must be well ventilated, other-
wise bad headaches will occur and the mem-
branes of the eyes, nose, and throat be affected.
The best remedy for acid fumes is to sniff weak
ammonia.
Some chemicals injure the skin and the clothes
if they come in contact ; particularly is this the
case with nitric acid, whici. bums severely. The
remedy is to apply a strong solution of common
washing soda or weak ammonia, or, in fact, any
alkali. Potassium bichromate affects the skin
at times, and the subject will be found dealt with
under " Bichromate Disease." Platintmi solu-
tions are not often looked upon as dangerous,
but when using them or large quantities of
platinum paper some workers suffer from a
skin disease and also nasal catarrh. A warm
and weak solution of salt and water sniffed up
the nose occasionally will, as a rule, cure the
catarrh, while the same solution of salt and water
will soothe and possibly quite cure the skin
trouble. Hydroquinone, amidol, and metol
developers (more particularly the last named)
affect some workers, and when they do the
treatment as prescribed under " Bichromate
Disease " may be tried, or the following oint-
ment, which any chemist wiU make up, used : —
Ichthyol .... I part
Lanoline .... 2 parts
White vaseline . . • 3 „
Boric acid . . . . 20 „
All developers are apt to affect the skin more
or less, and, after developing, the hands should
always be well washed with warm water and a
good soap of the carbolic variety. Developer-
stained fingernails may be cleaned by rubbing
with ink eraser ; or in troublesome cases they
may be rubbed with lemon juice or ammonium
persulphate crystals. When using developers
that stain, workers should wear rubber finger-
stalls or gloves. To keep the hands white and
soft they should be rubbed with new milk pre-
vious to developing. Should an irritation be
felt after using a mercury and ammonia intensifier,
the remedy is to wash the hands with warm
water, dab — not rub — dry with a soft towel, and
rub in the following soothing mixture : —
Glycerine . . .4 drms. 17 ccs.
Carbolic acid . . i „ 4 „
Alcohol . . . 5 oz. 1,000 „
HYGROMETER (Fr., Hygromitre ; Ger., Hygro-
meter)
An instrument for measuring the amount of
moisture in the atmosphere, occasionally used
in plate and paper factories and in coUotype
printing rooms.
HYPERFOCAL DISTANCE
Assuming an object at an infinite distance
from a camera to be sharply focused, the
object is next brought nearer to the camera, and
the distance at which the image visibly loses
its sharpness is the hyperfocal distance. Assum-
ing the degree of permissible unsharpness to be
a circle of confusion yj,,- in. in diameter, the
hyperfocal distance in inches for any given lens
at any given aperture is arrived at in the follow-
ing way. Multiply the focal length by itself,
multiply the product by 100, and divide the
result by the / number. The focal length being
5 in. and the aperture //8, 5 x s x 100 ^
2500 °
— g— = 312J m. = about 26 ft. The hyper-
focal distance is sometimes called the " fixed
focus," and it becomes shorter as the aperture
is reduced ; in the case of the 5 -in. lens, it is
about 13 ft. at//i6 and about 6% ft. at//32.
HYPERGON LENS
A wide-angle, double anastigmat lens, con-
sisting of two very thin single semiglobular
lenses. The largest aperture is //22, and the
angle included about 135°, the diagonal of the
plate covered being five times the focal length
of the lens. In order to equaHse the illumina-
tion over this large field, outside the lens is fixed
a revolving star diaphragm, which, during part
of the exposure, is made to revolve by a jet of
air and then dropped out of the way. Ihe
hypergon is uncorrected for chromatic aberration.
HYPERSTEREOSCOPY
The making of stereoscopic views of distant
objects from two separate and widely apart
stations, with ordinary camera and lens.
HYPERTELESTEREOSCOPY
Hyperstereoscopy with telephoto lenses.
" HYPO "
The abbreviated and popular name for sodium
hyposulphite (which see). For " hypo " fixing
baths, see " Fixing," " Acid Fixing Bath," and
" AlkaHne Fixing Bath."
"HYPO" IN DEVELOPER
The addition of very small quantities of
" hypo " to certain developers is sometimes
advised; with the ferrous oxalate it acts as an
" accelerator," because it decomposes the ferric
oxalate formed, which acts as a restrainer.
"HYPO" ELIMINATORS
Various chemicals have been suggested from
time to time for the purpose of curtailing the
washing of negatives and prints by chemically
destroying the last traces of " hypo," such as
hypochlorite of zinc, eau de Javelle, iodides,
alum, lead acetate, hydrogen peroxide, potas-
situn permanganate, etc., and recently several
of the persulphates and percarbonates have been
introduced under fancy names. Many if not all
of these merely convert the hjrposulphite into
tetrathionate. It must not be forgotten that
the hyposulphites of silver have to be dealt with
as weU as the hyposulphite of soda, and these
are not necessarily more soluble. If rapidity
of output regardless of permanency is the result,
then the use of such chemical agents is warranted,
but considering that all possible traces of the
hyposulphites can be removed by an hour's
washing correctly performed, it is an open ques-
tion whether such means are justified.
" HYPO " STAINS (See "Stains, Removing.")
"HYPO "-ALUM TONING (See " Alum-
'hypo' Toning.")
ICELAND MOSS
A moss or lichen found in the Arctic regions.
It forms, when boiled in water, a jelly which
has a few photographic uses, notably as a vehicle
for sensitive salts when sensitising fabrics.
Carrageen (Irish moss) has much the same pro-
perties.
In process work, the gelatinous nature of this
substance has suggested its use as a substitute
for fish-glue in the enamel process of photo-
etching, but it was not found to have any
advantages over fish-glue.
ICHTHYOCOL, OR ICHTHYOCOLLA
Fish-glue or isinglass.
ICHTHYOL
A bituminous substance which emulsifies
quite easUy with water, and can be added
to collotype emulsions, with the object of
strengthening the coating. Dissolved in a
mixture of ether and alcohol, it leaves by
evaporation a granular layer similar to resin
grain or bitumen grain. Dissolved with an
equal weight of water it forms an ink which
has the property of attracting greasy ink and
repelling water, so that it may be used for
lithographic purposes.
ICONOMETER (Fr., Iconomitre: Ger., Ikono-
meter)
A view meter giving a direct image and en-
abling the best standpoint with a given lens to
be ascertained without first setting up the
camera. One form is a rectangular open frame
of watch-spring set upright on a horizontal rod
graduated in centimetres. On placing the eye
at a sight at the zero end of the rod, the exact
view given by the lens with the camera in that
position is seen through the frame. The latter
is movable on the rod by means of a slide, for
use with lenses of different focal lengths. The
rod itself is hollow, and when the instrument is
not in use the frame can be folded up and in-
serted inside it, together with the sight, it
teing then placed in the pocket like a pencil.
ILLUMINANTS, LANTERN {See "Optical
I,antem Tllnminants.")
ILLUMINATION, DARK - ROOM (See
"Dark-room Illumination.")
ILLUMINATION, INTENSITY OF (Pr., In-
tensiti d' illumination ; Ger., Lichtstdrke)
The visual strength or brightness of light. The
intensity of light passing through a lens or pin-
hole is proportional to the area of the opening
through which it is admitted, the opening, in
the case of a lens, being the diaphragm
or stop. It is also inversely proportional to
the distance from the source of light of the
surface receiving it, since the light obviously
spreads out and becomes attenuated. The rule
is, the intensity of illumination is inversely pro-
portional to the square of the distance, but
photographically this rule tends to break down
if carried beyond certain moderate limits. The
intensity is weakened when the hght is made to
cover a larger surface, as, for instance, if it
strikes the plate at an angle instead of perpen-
dicularly, which may happen when using the
swing-back or swing-front. The margins of
the view given by a wide-angle lens are often
not so well lit as the central portion, because the
marginal rays reach the plate at an acute angle.
Printing frames should be placed square to the
light ; if inclined, not only is the light spread
and weakened, but much lost by reflection.
IMAGE, [LATENT OR INVISIBLE (See
" Latent Image.")
IMMERSION LENS (See " ObjecUve.")
IMOGEN SULPHITE (Fr., Imogine sulfite;
Ger., Imogen sulfit)
A developer needing only a saturated solution
of sodium carbonate to make it active. It
occurs in a pinkish white powder which keeps
well, both dry and in solution, owing to there
being combined with it the necessary amount
of preservative ; it yields negatives of a good
warm-black colour. Potassium bromide in small
quantities acts only as a preventive of fog ;
larger quantities have a stronger restraining action
and increase contrast. For correct exposures
no bromide is required, but for over-exposure
a lo per cent, solution may be used. The
Imogen sidphite developer is made up in two
solutions, the makers' instructions being as
follow : —
A. Imogen sulphite i oz., warm water 12 oz.
B. A cold saturated solution of soda carbonate.
For correct exposures take of solution A
2 parts, and B i part. Add water, and use
more of B for under-exposives. For bromide
paper, the above solutions should be diluted
with an equal amount of water, bromide being
added. Fix in an acid fixing-bath.
IMPERIAL
A size of photographic mount which varies
between 6J in. by 10 in. and 7I in. by 95 in.
IMPRESSIONISM
This term is often used vaguely and with great
differences of meaning. The broad idea implied
is that a subject is rendered as it first strikes the
eye ; as it appears at one particxdar time ; or so
as to convey, first and foremost, the general
299
Incandescent Light
300
Indlarubber
mental impression created by its appearance
under certain conditions. Now a hurried impres-
sion would be more or less general, and lacking
in such detail as would be noted after prolonged
or frequent examination. Hence the idea that
impressionism means indistinctness, or involves
" fuzziness." This is not necessarily so. The
impression, or mental effect, might be one of
briUiance, sharpness, and wealth of detail.
To take an example. A photographer's
impression of a church tower might be that it
was one white, gleaming mass, standing out
vividly from all its surroimdings. To convey
this impression he would probably emphasise the
darkness of the sky behind it, and suppress detail
and light everywhere but in the tower itself.
Under other conditions the same tower might
convey the impression of a soUd silhouette stand-
ing forth boldly against a brilliant sky. In
neither case would the tower be rendered with
the realism that an architect would require as a
record of its design. In each case it would be
treated so as to suggest as far as possible the
particular impression it made at the time. This
is, of course, a simple case to take. Carried
farther, the desire for impressionistic renderings
leads to the adoption of all sorts of devices to
modify, control, and emphasise actual photo-
graphic results.
INCANDESCENT LIGHT (See
Light.")
■ Artificial
INCIDENCE, ANGLE OF (Fr., Angle d'inci-
dencB ; Ger., Einfallwinkel)
The angle which a ray of light falling on a flat
surface forms with the perpendicular to that
surface, or to the tangent if the latter is curved.
Thus, if a ray of light c D strikes a plane surface
E F at the point D, as shown by diagram A, the
angle c D G made by the ray C D with D G, a per-
pendicular to E P drawn from the point D, is
the angle of incidence. The line c D is called
the line of incidence. If the plane surface is a
mirror, the light will be reflected from D in the
A. Diagram Illustrating
Angle of Incidence
B. Diagram Illustrating
Line of Incidence
direction D H. The angle H D G, formed by the
perpendicular with the line of departure of the
light, is termed the angle of reflection, and is
always equal to the angle of incidence. When
the line of incidence is itself perpendicular to the
receiving surface, the light is reflected back along
its original course, or in the case of a transparent
body passes straight through without refraction.
When a ray of light strikes a transparent surface
of different density to that in which it was pre-
viously moving it is refracted. Provided the
transparent body has parallel sides, as, for in-
stance, a sheet of glass, the ray will emerge after
refraction in a direction parallel with the line of
incidence, and at the same angle as the angle of
incidence, as shown at B. {See also " Reflection "
and " Refraction.")
INCIDENCE, LINE OF (Pr., Ligne d'inci-
dence ; Ger., Einfall Linie)
The straight line taken by a ray of light pro-
ceeding towards any surface, whether it strike
the latter obliquely or at a right angle. (See
also " Incidence, Angle of.")
INDEX OF REFRACTION (S«e " Refraction.")
INDIA TINT MOUNT
A mount that has pasted down on it a sheet
of thin tinted paper sUghtly larger than the
print which it is to carry. The mounted print
thus shows a narrow margin of one tint with a
wider border of another. A cheap imitation
is made by printing the central tint by litho-
graphy.
INDIAN INK (Fr., Encre de Chine: Ger.,
Tiische)
Indian ink is only so called ; actually it is
Chinese ink, which formerly was available only
in the form of cakes or sticks which had to be
rubbed up with water for use, but which is now
obtainable in the prepared liquid form, water-
proof if desired. It is frequently used for
painting out backgrounds, etc., in negatives,
so that they appear white in the print. It is
inferior to lidian red for this purpose, as it has
a great tendency to crack badly after drying,
and so render the work valueless.
To prevent work done in Indian ink running
when touched with water, a tiny piece of potas-
sium bichromate should be rubbed up with each
saucerful.
Indian ink is not now used so much as formerly
for process drawings, the modem waterproof
inks having largely superseded it.
INDIAN RED
An opaque water colour composed principally
of a natural earth. It is used for painting out
backgrounds or portions of a negative that are
to show as white in the print. The moist form,
in tubes, is preferable, and the pigment should
be applied to the film very thickly. It has no
tendency to crack after drying.
INDI ARUBBER (Fr., Caoutchouc ; Gei., Kaut-
schuk)
Synonyms, caoutchouc, gum elastic, rubber.
Insoluble in water and alcohol, soluble in carbon
disulphide, chloroform, benzene, etc. A natural
product, the coagulated juice of various plants
belonging to the natursd order Euphorbiacece .
It occurs in brownish black cakes, balls or hoUow-
shaped pieces. It is very elastic and of charac-
teristic odour. When heated with 10 per cent,
of sulphur it becomes vulcanised. For photo-
graphic purposes, the pure washed and masti-
cated rubber, not the vulcanised rubber, should
be used. It is employed as an edging for
Indiarubber Cloth
301
Inertia
collodion plates and as a mountant. The most
satisfactory solvent is carbon disnlphide with
S per cent, of absolute alcohol, in which the
rubber, cut in small pieces, should be allowed to
stand with agitation till dissolved. In order to
save the trouble of making, the ordinary cycle
tyre cement may be used and thinned down
with disulphide or chloroform. The great draw-
back to its use as a mountant is that the
rubber perishes in time, and the print leaves
the mount.
In process work, a solution of indiarubber
in benzole of 2 per cent, strength is used in
stripping wet collodion films. The collodion
negative is flowed with the rubber solution, and
when this is dry it is again flowed with stripping
coUodion. The rubber solution prevents the
solvents of the stripping collodion reaching the
original collodion film, and at the same time
increases the flexibiUty and toughness of the
film.
Indiarubber solution is used in the collotype
process for attaching to the negative the tinioil
used for masking.
In aerograph retouching, some workers use
indiarubber solution for stopping-out certain
portions of the print on whic^ the aerograph
spray is not wanted. After the spraying is done
the rubber film easUy peels off by rubbing with
the finger-tip, and carries with it any spray that
has overstepped the boundaries of the stopping-
out medium.
INDIARUBBER CLOTH (Pr., Drap de caout-
chouc : Ger., Kautschukzeug)
Thin sheet vulcanised rubber, or fabric coated
on both sides with a thin film of the latter. India-
rubber focusing cloths are of value in protecting
the camera during bad weather. Cut pieces of
rubber fabric or sheet rubber pads are employed
to lay over prints when squeegeeing, and are
placed at the back of platinotype paper in the
frame when printing, to protect it from damp.
INDIARUBBER MOUNTANT (See
rubber" and "Mountants.")
'India-
INDICATOR {See " Exposure Indicator,"
" Print Indicator," etc.)
INDIGO PRINTING
A process of photographic printing on fabrics
by means of a mixture of indigo white, sodium
bisulphite, soda, water, and gum. The image
is developed in a caustic soda solution.
INDOOR PHOTOGRAPHY
Apart from actual studio work, a good deal of
photography can be done indoors in Smost every
house, and that without any elaborate or unusual
addition to the ordinary outdoor apparatus.
Flashlight work comes under a special category.
A good deal can also be done nowadays with the
ord&nary domestic means of artifid^ illumina-
tion. But stiU more can be done by dayUght.
Flowers, fruit, and all kinds of still-life subjects
can be most effectively and conveniently dealt
with indoors, and portrait and figure studies
provide a wide and varied field of operations.
Except in special cases, the ordinary window
lighting requires some modification before it is
suitable. It is generally necessary not only to
use blinds to shut out part of the light and con-
trol the direction of what is admitted, but to
have a difiuser to soften it and make it even.
This may be white muslin or buttercloth, which
it is generally convenient to stretch on a light
wooden frame. It is also necessary to have a
second screen of more opaque fabric to act as a
reflector on the shadow side. Considerations of
space often compel the use of lenses of some-
what short focus, but every effort should be
made to avoid this, especially in the case of work
from the figure. Ileuses of large aperture are
also an advantage, as they not only facilitate
focusing in what is frequently a subdued light,
but permit of shorter exposures. Suitable back-
groimds must also be considered. Sometimes
the actual surroundings of the room are appro-
priate, but one or two plain backgrounds, both
light and dark in tone, are almost essential. For
still-life studies sheets of paper or cardboard
of various colours are useful as backgrounds, and
as the Ughting is generally from the side it is
easy to avoid cast shadows on them.
INDOTINT (Fr. and Ger., Indotint)
A photo-mechanical process resembling collo-
type, invented by Roche, of New York. A
copper plate roughened by the sand-blast, to
secure adhesion of the sensitised gelatine film,
is used instead of the ordinary thick glass
plate.
INDUCTION COIL (Fr., BoUne ; Ger., Itiduh-
tionsroUe)
Induction coils are almost universally em-
ployed to produce the high potential currents
necessary to excite the vacuum tube in X-ray
work. An induction coil consists of three parts
entirely insulated from one another. In the
centre is the core, a bundle of soft iron wires laid
longitudinally. Roimd this is wound, as on a
reel, two layers of stout insulated copper wire
to carry the primary current from the pubHc
main or accumulators. Round this primary
winding, and well insulated from it, is wound
the secondary, of very thin insulated copper
wire, often many miles in length. Directiy the
current is switched on through the primary the
core becomes magnetised, causing the secondary
coU to give out a current which flows in the
reverse direction. This induced current is only
of momentary duration. A greater though still
momentary effect is produced when the current
is switched off. In order to produce a rapid
and continuous series of shocks or discharges
from the secondary coil with which the tube is
in circuit, the current through the primary must
be interrupted and renewed several hundred
times a minute.
This rapid starting and checking of the flow
of current through the primary winding, technic-
ally known as " making " and " breaking "
contact, is automatically accompUshed by means
of " contact breaks " (which see).
INERTIA (Fr., Inertie ; Ger., Inertia, Trdgheit)
A term adopted by Hurter and Driffield to
measure the slowness of a plate ; the greater the
inertia the slower the plate. (See " Plate Test-
ing.")
Infinite Rays
303
Ink Process
INFINITE RAYS
Rays emerging from an extremely distant
point and consequently practically parallel with
one another.
INFINITY
Photographically, a distance beyond which no
readjustment of focus is necessary to secure a.
sharp image of more distant objects. It in-
creases in proportion to the focal length of the
lens used. It is expressed on focusing scales by
the sign 00, the abbreviation INF, and occasion-
ally tie initial D (distance).
INFLECTION
Synonymous with " difEraction " (which see).
INFRA-RED RAYS (Fr., Rayons infra-rouge ;
Ger., Ultraroten Strahlen)
A vast region of the spectrum lying beyond
the red and to which our eyes are not sensitive,
but which we are conscious of in the form of
heat. Although we cannot see this region we
know that it is traversed by absorption lines
exactly in the same way as the visible spectrum ;
they have been detected not only by direct photo-
graphy by means of a special collodion emulsion
(Abney), but also especially by means of the
bolometer (which see). The absorption lines are
indicated by the letters of the Greek alphabet.
As most glasses are comparatively opaque to the
infra-red rays, spectroscopes for the examination
of this region have to be fitted with rock salt
or sylvin lenses and prisms, or else transmission
diffraction gratings with comparatively wide
spacings, these gratings being in many cases
made of silver or platinum wire.
INITIAL POWER
In photo-micrography, the initial power of a
microscope objective is the magnification which
the lens will give without an eyepiece at a dis-
tance of 10 in. from its back lens ; for example,
if the image of an object thrown by the objective
upon a screen at 10 in. distance magnifies the
object 20 diameters the initial power of the
objective would be 20. The initial power of an
eyepiece or ocular is the magnification given by
the eyepiece itself. The initial power of an
objective multiplied by the initial power of the
eyepiece gives the total magnifying power of
the lenses used.
INK FOR GLASS, PORCELAIN, ETC.
Ink for writing names on glass bottles, porce-
lain dishes, tins, etc., may be made by dissolving
60 grs. of powdered copal in i oz. of oil of laven-
der made warm, and then mixing the solution,
by means of a palette-knife on a stone, with
6 grs. of lampblack and 2 grs. of indigo ; if other
colours are wanted, vermilion, ochre, etc., may
be used. The mixture is appHed with a fine
camel-hair brush. To make the writing stand
out prominently on glass it is advisable first to
pamt a shield or tablet on the glass, using white
ba th enamel for the purpose.
A mixture particularly suitable for lantern
slides may be made by dissolving i dim. of
shellac in -J oz. of methylated spirit ; then dis-
solve J drm. of borax in -J oz. of water. The
solutions should be mixed together very slowly,
and if a precipitate forms the mixture should be
heated rmtil clear. Enough aniline dye of a
smtable colour — methylene blue is generally
used — should be added to coloru: the mixture.
This dries quickly and is permanent.
INK FOR LABELS (See "Labels, Water-
proof Ink for.")
INK PRINTING
Poitevin's pigment process depends upon
three facts : ferric chloride renders gelatine
insoluble, ferrous chloride has not that effect,
and light converts the ferric into the ferrous
chloride. If paper is coated with gelatine and
ferric chloride, printed imder a negative, and
placed in warm water, the shadow portions
(those acted upon by light) are made soluble.
Thus a negative is made from a negative and a
positive from a positive, i oz. of gelatine is
soaked in 1 5 oz. of water, dissolved by heat, and
100 grs. of Indian ink mixed in very thoroughly.
Paper is floated on the still warm mixture for
three minutes, dried quickly, and immersed ia
the following sensitive mixture until limp : —
Iron perchloride
Tartaric acid.
Water .
I oz. no g.
140 grs. 32 „
10 oz. 1,000 ccs.
144 grs. 33 g.
96 „ 22 „
10 oz. 1,000 ccs.
The paper is dried in the dark, printed under a
positive, and developed and fixed simply by
washing gently in warm water.
Anottier method invented by Poitevin is to
float plain paper for three minutes on a sensitive
mixture prepared as follows : —
Iron perchloride
Citric add
Water ...
The paper is dried quickly in the dark, printed
under a positive and developed by immersing
in a weak solution of Indian ink in glycerine.
The ink will affect only those parts that have
not been acted upon by Ught. The developed
print is finally briefly washed and dried.
Most of the photo-lithographic and collotype
processes may be described as iak-printing.
The sensitised bichromate image is rendered
susceptible to printing ink by exposure to light.
The Amphitype process, and the Ordoverax
processes (which see), also show that the iron salts
are capable of being made to take up fatty inks.
INK PROCESS
A method of printing by which photographic
pictures may be obtained in common writing-
iuk, sometimes referred to as the gallate of
iron process. A sheet of white paper is immersed
in a nearly saturated solution of potassium
bichromate and dried, being now of a bright
yeUow colour. It is next placed under a nega-
tive and exposed to sunlight, which acts upon Sie
bichromated surface and gives a pale brown
picture. When all detail can be seen, wash in
plain water for about an hour in order to remove
the yellow and superfluous bichromate. This
washing serves to fix the print, which should be
of a pale yellow colour on a white ground. The
print is given a colour and at the same time
intensified by immersing for a few minutes in n.
solution of 5 grs. of iron protosulphate (ferrous
Ink, Waterproof
303 "Instantaneous" Photography
sulphate) in i oz. of water ; well wash, and place
in a moderately strong solution of tannic acid,
which will cause tannate of iron (writing-ink)
to be deposited, a black image being formed.
The difficulties of the process consist in
thoroughly eliminating the chromium and fer-
rous salts, and in obtaining the writing-ink of a
good blaci colour. There are other methods.
INK, WATERPROOF {See "Labels, Water-
proof Ink for.")
INK, WHITE
White ink is used on black lantern-slide
masks. To prepare it, take a cake of Chiaese
white water-colour, and rub it up with water
by means of a camel-hair brush until of the con-
sistency of ordinary ink. It is put into a pen
with the brush and the title written with the
pen. A white ink that may be stored in a bottle
is made by taking : —
Isinglass
Chinese white
Methylated spirit
Water as required.
i oz.
77 g-
I .. 310 „
I drm. 35 CCS.
Soak the isinglass in i oz. of water until soft,
heat until dissolved, and rub up with the Chinese
white in a hot mortar. Add water until the
mixture is of the consistency of ordinary writing-
ink. Finally add the methylated spirit and bottle
for use. If the ink is to be kept for any length
of time, add 2 drops of carbolic acid as a preser-
vative. A passable white ink is made by rubbing
up zinc white with gum arable solution.
INKING-UP
In photo-mechanical processes this term is
often used. For instance, in photo-lithography
the transfer print after exposure is inked all over
with a thin coating of ink, previous to develop-
ment. The same is done in the case of direct
printing on stone or metal. In line photo-
etching the print on the zinc is inked-up after
exposure by applying all over by means of a
composition roller a thin coating of a special
kind of transfer ink. The image, after it has
been developed on the stone or plate, is often
strengthened by keeping the plate moistened
with gum water and passing over it a roller
charged with lithographic ink, but although this
is often spoken of as inking-up it is more cor-
rectiy called " roUing-up " {which see).
INK-PHOTO PROCESS
A photo-mechanical process worked since
about 1882 by a London firm. It is understood
to be based on a grained image formed in a
similar manner to the collotype process, a transfer
being taken therefrom and put down on stone
for printing in the lithographic manner.
INSECTS. PHOTOGRAPHING
The photographing of insects falls naturally
under two heads — namely, photographing Uving
insects, and photographing dead, set specimens.
Living insects should be photographed in their
natural environment, the caterpillars on their
favourite food-plant, the butterfly or moth upon
the flower, tree-trunk, wall, or other situation
which it most frequents. The most interesting
and valuable results will be obtained by concen-
trating one's efforts upon one insect at a time,
and working to produce a complete set of photo-
graphs which will show every stage in its life-
history from the egg to the perfect insect. The
reflex camera is undoubtedly the best type for
photographing living insects, as it enables one
to follow and focus file subject up to the instant
of making the exposure, and, being fitted with a
focal plane shutter, permits the maximum
amount of light to reati the plate during expo-
sure. A good lens of large aperture and fairly
long focal length should be used, one with a
working aperture of f/4-s or //6, and having, for
a quarter-plate, a focal length of 7 in. Fist
isochromatic plates should always be used.
For photographing dead, set specimens, an
ordinary rigid stand camera, having a long
extension of bellows, will be most useful ; and
for all-round piirposes a half-plate size wiU be
most convenient, because of its greater bellows
extension. The plate-holders can be fitted with
adapters to carry quarter-plates, and the front
of file camera should have two or three extra
lens-panels, so that lenses of varying focal
lengths may be used. By this means it is possible
to obtain photographs direct of life size, and also
of two or three diameters magnification. The
set specimen should not be placed upon a draw-
ing-board or similar support, as the shadows cast
by the body, legs, and wings of the insect will
give a very unpleasant and confusing effect. A
good, clear sheet of glass should be used, and the
insect can then be pinned on to a tiny piece of
cork which will not be large enough to show and
which has been cemented in place. A suitable
coloured background can be placed eight or ten
inches behind the glass, so that no shadow will
be cast by the insect.
A notebook record should be kept of all work
done in the field, and an entry made of each sub-
ject, giving particulars as to the plate used, lens
and stop, exposure, lighting, time of day, day
of month, result obtained, and any notes of
interest concerning the subject itself. F. M-D.
INSENSITIVENESS
Occasionally a plate or film is found to lack
in parts the general sensitiveness. This is almost
always due to the local action of some desensitiser,
generally a metallic impurity, such as iron, etc.
"INSTANTANEOUS" PHOTOGRAPHY
The term " instantaneous " is loosely used in
photography, being generally understood to refer
to exposures of less than one second. The
photographing of ordinary views " instanta-
neously " was vainly attempted by Daguerre in
1 841, and the first authenticated "instanta-
neous " photograph is that of New York harbour,
taken in 1854.
The essential conditions under which " in-
stantaneous " exposures, in order to be succe.ss-
ful, must be made are : A good Hght, an efficient
shutter, a suitable lens working at a large aper-
ture, and a rapid plate. For average street work
■jVth of a second is quite fast enough ; while if
objects are moving to or from the camera direct
and not at right angles, the exposure may be
increased to t'yth of a Second. According to the
Thomton-Pickard Company, the following rule
Instantaneous Shutter
304
Intense Negatives
4V
answers for finding the "instantaneous" expo-
sure for a moving object : — ^The distance of the
object from the camera, measured in inches, is
divided by the number of yards per hour at
which the object is travelling, multiplied by the
focus of the lens in inches. The result Will be
the fraction of a second, which is the longest
allowable exposure that does not show move-
ment in the resulting photograph. Below is
given a table showing the correct exposure for
various moving objects. The table is made out
for a distance from the camera 100 times that
of the focus of the lens : that is, for a 6-inch
focus lens at 50 ft., a 7-in. at 58 ft., etc.
Towards the At right an-
Camera gles to Camera
(sec.) (sec.)
Man walking slowly,
street scenes . .
Cattle grazing . .
Boating ^\ ■ ■ s^o
Man walking, children
playing, etc ^ .. ^
Pony and trap, trot-
ting rhs ■■ -jiir
Cycling, ordinary •• ris •• too
Man running a race,
and jumping . . . . rfo . . ih
Cycle racing . . . . -^ho • • t4tj
Horse galloping .. jjs .. tJtt
K the object is twice the distance, the length of
allowable exposure is doubled, and vice versa.
{See also " Focal Plane Shutter " and " Hand
Camera, Work with.")
INSTANTANEOUS SHUTTER (Fr., Obtura-
teur instantani ; Ger., Moment Vers-
chltiss)
Any shutter which, by pressing a trigger, push,
lever, or pneumatic ball, will give a rapid expo-
sure lasting only the fraction of a second. A
" time and instantaneous shutter " is one that
in addition to giving " instantaneous " exposures
when required, can be set to remain open for
exposures of any length and to close at the will
of the operator by a further pressure of the
release. {See also " Shutters.")
INTAGLIO PRINTING
Any method of printing in which the lines,
dots, grain, or other elements of the engraving
are sunk in the plate, so that the depressions
are filled with ink for printing, as distinguished
from relief plates or blocks where the printing
elements are raised and are inked on their sur-
faces. Thus the old engraving or etching pro-
cesses, such as mezzotint, aquatint, needle-
point etching, copper and steel plate engraving,
and the like are intagho printing processes.
Photogravure and heliogravure are also intagUo
methods. Of late, the term intagUo printing has
come to be applied in a more limited sense to
methods of forming a simk engraving or etching
by means of a ruled screen, and the printing of
the same by mechanical power. For some years
past there have been machines for printing from
flat plates, the sunk image being iiiked and the
siuiace being wiped clean by mechanical arrange-
ments. Such machines have, however, not come
into general use, there being almost insuperable
difiiculties in efSciently wiping the flat surface.
Rotary intaglio printing solves this problem very
successfully, and the method has been success-
fully worked for some years by a Lancaster firm
which was the first to carry out the experiments
and devise suitable machinery for this work.
Their methods are secret, but a number of later
experimenters have proceeded on the assumption
that a photographic carbon print, which has
been also exposed imder a ruled screen, is devel-
oped on a hoUow copper cylinder. The carbon
print forms a resist as in the photogravure pro-
cess, and the image is thereby etched in intaglio.
The spaces between the screen lines form minute
cells which hold the ink, preventing its being
wiped out during the printing operation. The
hollow cylinder is placed on a mandrel and
mounted in a machine similar to that which is
used for wallpaper or calico printing. Under the
engraved cylinder is an inkmg roUer working in
a trough of thin ink, and feeding the ink into
the engraving. Above the engraved cylinder is
an impression roller with an elastic covering of
blanket or rubber. In contact with the engraved
cylinder is a steel knife, called the " doctor,"
which scrapes the surplus ink quite cleanly from
the surface, leaving it in the hoUows of the
engraving. Paper is fed from a reel, and passes
between the impression cyUnder and the engraved
cylinder, thus receiving a print at every revolu-
tion of the latter. Mechanism is provided for
delivering and cutting off the prints. The
method has been found to present considerable
difficulties.
Dr. E. Mertens, of Freiburg, has extended the
process to newspaper printing by coupling up
the intaglio machine to the ordinary rotary
stereo printing machines, so that when the web
of paper emerges from the intagho printing
machine it passes into the newspaper rotary
to receive the impression of the text formes.
The rotary intagUo method has been appUed
to colour printing with very fine results.
INTAGLIOTYPE
A process for obtaining intagho plates,
patented in 1893 by Joseph Hines. A bickrom-
ated gelatine film on a metal plate is exposed
under a negative and developed with heated
sulphate of iron solution until the Hues are clear.
The plate is then mounted and printed from.
INTENSE NEGATIVES
A negative may be very dense from two or
three causes. A plate that is considerably over-
exposed and then developed normally will yield
a very dense negative that takes so long to print
as to be quite useless. If the exposure is cor-
rect, a plate can only be too dense through
excessive or incorrect development. If tie
shadows are strongly veiled, the cause is exces-
sive exposure ; and the best treatment is the
" hypo " and ferricyanide reducer. If the
shadows are moderately clear, the cause is
excessive development, and the ammonium
persulphate reducer should be employed. {See
also " Reducing Negatives.")
A negative may be too intense as the result of
intensification. If mercury has been used for
intensifying, the eflfect can always be reduced
by a weak solution of " hypo."
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Intensification of Negatives 3os Intensification of Negatives
INTENSIFICATION OF NEGATIVES (Ft.,
Renforcement ; Ger., Verstdrkung)
A process whereby density or contrast is in-
creased. Intensification processes in common
use vary in the degree of strengthening rather
than in their character ; with shght exceptions
they do not change the gradation, but strengthen
all parts of the scale in a. uniform ratio. The
exceptions are some of the processes that depend
on bleaching with a mercuric salt as the first
part of the operation. With Monckhoven's
intensifier very thin shadow detail becomes
reduced, and tones with slightly more strength
show no change, while the medium and stronger
tones more than double their printing value. In
bleaching with mercuric bromide or chloride,
exceedingly weak shadow detail is not strength-
ened, but aU other parts of the plate show a
uniform increase in intensity.
A negative to be intensified must have been
thoroughly fixed, as, otherwise, incurable yellow
stains may appear. Thorough washing after
fixing is desirable.
The following methods of working will yield
negatives of a good black colour, free from any
tendency to veiling, staining, or any loss of
quality. And, in addition, the results are quite
permanent. With all mercurial methods, how-
ever, the intensified negative should be varnished,
so as to protect the metallic deposit in the gela-
tine film from atmospheric moisture, otherwise
an iridescence will appear, but this may be
removed by means of methylated spirit {see
"Reducing Negatives by Medianical Means").
A badly stained negative will not become black
by intensification ; and, in addition, when a
negative depends for its printing quality partiy
on silver deposit and partiy on stain, the result of
intensifying wiU always be uncertain. The
intensifier strengthens the silver deposit only,
and either decreases the staining or leaves it
unchanged.
The chief methods of intensification are: —
Chromium. — ^The negative is bleached in an
acidified solution of a bichromate salt, and then
re-developed. The printing value is multiplied
by i\. Mercuric Chloride. — ^The negative is
bleached in a solution of mercuric chloride and
then blackened with sodium sulphite, ferrous
oxalate or by re-development. With sodium
sulphite the printing value is only multipUed
by ItV ; hut with ferrous oxalate by 2. Mer-
curic Bromide. — The working is similar to the
preceding, substituting bromide for the chloride,
and blackening with sodium sulphite or by re-
development ; the printing value is multiplied
by 2. Mercuric Iodide. — ^The negative is strength-
ened in a solution of mercuric iodide, and tiien
re-developed, the printing value being multiplied
by 3. Silver. — Various methods of intensifying
negatives by means of silver have been intro-
duced. Lead, Uranium, Copper Bromide, etc. —
These are treated under their own headings.
A method that has been extensively employed
is bleaching in a solution of mercuric chloride
a,nd then blackening in ammonia. This method
is generally considered to be unsatisfactory, and
the results not permanent.
Of the above, the mercurial processes are the
xnost used and wiU here be described. For the
others, see separate headings.
20
Mercurial Processes. — ^Most of the mercurial
methods are satisfactory, the intensified negative
being a good neutral black or brown-black,
according to the process ; there is no staining or
veiling ; the increase of density is a definite and
known quantity, and the result is permanent.
In all processes of mercurial intensification,
the mercuric solution should be followed by an
acid bath (first suggested by A. Haddon), its
object being to prevent the mercury from com-
bining with the gelatine to the detriment of
permanency. When the plate is removed from
the mercuric solution, it should be washed in
two or three changes of water, and then placed
in a bath consisting of i drm. of hydrochloric acid
in 12 oz. of water, remaining in this solution for
two or three minutes, being then placed in a
second quantity, and finally in a. third. Next
it is washed for fifteen to twenty minutes, when
it is ready for the second part of the treat-
ment.
The following are tne details of the principal
methods of intensifying with mercury : —
First method —
A. Mercuric chloride 120 grs. 25 g.
Hydrochloric add 24 mins. 5 ccs.
Water . . . 10 oz. i,ooo ,,
B. Liquor ammoniae . J- oz. 25 ccs.
Water . . • 5 ,, 500 ,,
Immerse in A until the image is thoroughly
bleached, and then, after treating with acid and
washing as above described, immerse in B until
thoroughly blackened. Wash, and dry. This
method is not recommended.
Second method —
The negative is bleached in solution A (above
given), treated with acid, washed, and then
thoroughly blackened in —
Sodium sulphite
Water .
I oz.
25 g-
250 ccs.
This solution must be used at once, as it will
not keep. The intensified negative is a good
black colour, free from veiUng, and the result is
permanent ; but the increase of density is very
slight.
Third method —
H. Chapman Jones advocates this method.
The plate is bleached in solution A, and then,
after the acid baths and washing, is re-developed
with ferrous oxalate. From the developer the
negative passes to a weak acid bath for two min-
utes, and is then washed. This approximately
doubles the printing value, and may be repeated
as many times as desired, a corresponding
increase of strength resulting each time. Care
must be taken that the ferrous oxalate developer
is freshly prepared and in good condition, or
the negative will be badly stained.
Fovirth method —
Bleach in solution A, and then, after the
add baths and washing, re-develop with amidol
or any dean-working alkaline developer. Pyro
is not suitable. The result is similar to that pro-
duced by the third method. The image is a good
neutral black, there is no tendency to staining
or loss of quality, and the result is permanent.
Intensification of Negatives
306
Intensification of Prints
The increase of density is rather less than that
given by the third method, but the operation
may be repeated with a similar increase of
strength.
Fifth method-
Bleach in
C. Mercuric chloride . 120 grs. 27 g.
Potassium bromide 120 „ 27 „
Water . . .10 oz. 1,000 ccs.
Treat with three acid baths, wash, and then
Immerse in a freshly prepared solution of —
D. Sodium sulphite . i 02. 55 g-
Water . . ■ 5 „ 500 ccs.
until thoroughly blackened. The resulting nega-
tive is a good neutral black without the shghtest
staining or loss of quality, and it is quite per-
manent. The printing value is approximately
doubled, and repeating the process wiU not pro-
duce any increase of strength.
Sixth method —
The working is as in the fifth method, but the
bleached image is blackened in —
E. Sodium sulphite . -J oz. 55 g-
Sodium carbonate. | „ 55 „
Water . . • 5 ,, 500 ccs.
This solution will keep indefinitely. The
result is exactly the same as that produced by
the fifth method.
Seventh method —
Bleach in solution A, and then, after the acid
baths and washing, re-develop in amidol or
other clean-working alkaline developer. The
gain in printing value is slightly less than that
produced by methods 5 and 6, but the strength
may be increased by repeating the operation as
many times as desired.
Eighth method. Monckhoveu's process —
Bleach in solution A, and then, after the usual
washing, etc., blacken in
P. Silver nitrate . . 50 grs. 23 g.
Potass, cyanide (about) 50 „ 23 „
Water . . . 5 oz. 1,000 ccs.
The silver nitrate is dissolved in the water,
and potassium cyanide added, a. little at a time,
until the precipitate that forms is just dis-
solved. The plate must be taken from the
cyanide solution directly it is blackened
through, as a reducing action on the shadow
details begins as soon as the blackening is accom-
plished. If the first washing is not rapid and
effective, there will be a similar reduction. It is
impossible to prevent a slight reduction in the
extreme shadows. The original printing value
is rather more than doubled, excepting in the
shadows, where the strength is actually reduced.
The operation may be repeated if the density is
not sufficient, and a proportionate increase of
strength will result each time.
Ninth method. Mercuric iodide, I<umiere's
method —
G. Sodium sulphite 20 grs. 46 g.
Mercuric iodide . i „ 2-3 „
Water . . . i oz. 1,000 ccs.
The sodium sulphite must be dissolved first,
and then the mercuric iodide, which is insoluble
in water, added ; and the solution well shaken
until the iodide is dissolved. The solution must
be prepared when required, as it will not keep.
Immerse the negative in this solution, rocking
the dish to ensure even action, and a steady gain
in strength will result ; the maximum intensity
is attained in about seven or eight minutes, but
the negative may be withdrawn at any time.
Afterwards the plate is washed, immersed in the
acid baths as already described, washed, and
then re-developed in any alkaline developer.
Pyro or any other developer may be used, the
printing value not being affected by the choice
of developer, but when pyro is used the plate
is not quite so clean as with other developers.
If the plate is not re-developed, the image will
graduafiy bleach. If the action is carried out
fully, repetition will not produce any increase of
strength ; but if a. smaller degree of intensifica-
tion only is attained at the first operation, repe-
tition at any future time will complete the work
and produce the same strength that a full action
would have secured in the first instance. The
intensity is greater than that given by any other
form of mercurial intensification at one oper-
ation, the printing value being multiplied by 3.
In all these methods of mercurial intensifica-
tion, a moderate washing after the final operation
of re-developing or blackening completes the
work.
In aU excepting the ninth method (Ivumiere's
mercuric iodide process), the treatment with
the mercuric solution must be thorough and the
operation must be taken as far as it will go, the
completeness of the work being judged by the
thorough whitening of the image. If this bleach-
ing is not thorough, the intensification will be
irregular, some portions being fully strengthened
and others only partially. It follows, neces-
sarily, that the increase of strength is a fixed
quantity ; one degree of intensification only
can be obtained from any negative, neither more
nor less, excepting in those modifications which
can be repeated, in which cases the result of
repetition is a series of regular steps.
In process work, the negatives have always to
be intensified in order to get the necessary
intensity for photo-mechanical printing. In wet
collodion negatives for Hue work, the lead
intensifier is generally used, followed by ammo-
nium or sodium sulphide for blackening. For
half-tone negatives, the copper bromide intensifier
is more generally used, both with wet collodion
and collodion emulsion, though the lead intensifier
can also be employed. With both intensifiers
the method known as " cutting " is adopted.
This consists in treating the plate with a
solution of potassium iodide and iodine, and
afterwards applying a solution of potassium
cyanide ; this cuts ofi the fringe of the dots
or lines, and so sharpens up the image, at the
same time clearing the transparent spaces. For
dry-plate process negatives the silver cyanide
intensifier is found bestj and " cutting " is
done with potassium ferricyanide and " hypo "
solution.
INTENSIFICATION OF PRINTS
Prints by most processes cannot be intensi-
fied satisfactorily ; and generally intensification
is more trouble than obtaining a new print.
Intensity of Lenses
307
Interiors, Photographing
Intensification is either impossible or undesir-
iable in the carbon, platinotype, and many
silver printing-out methods. Bromide and gas-
light prints can be strengthened by bleaching
with mercuric bromide and then blackening by
means of sodium sulphite, or they may be
bleached in mercuric chloride and then black-
ened by means of ferrous oxalate. Silver
intensification has a tendency to stain the paper
slightly ; and in any method that requires re-
development care must be taken to use a solution
that has no tendency to stain. Another method
of strengthening weak bromide and gasUght
paper prints is given under the heading " Toning
Bromide Prints."
INTENSITY OF LENSES
A term synonymous with angular aperture and
focal aperture, and signifying the ratio of aper-
ture to focal length.
INTENSITY RATIO
The ratio of focal length of a lens to the
aperture.
INTERFERENCE HELIOCHROMY (See
"Lippmann's Process.")
INTERFERENCE IMAGE (S«e "Lippmann's
Process.")
INTERFERENCE OF LIGHT
Ivight is a wave-like motion in the ether, the
waves proceeding in all directions precisely as
when a stone is lirown into the centre of a pond.
In order to grasp the subject of interference,
considerations are here limited to waves pro-
ceeding in one direction only, from left to right.
The transverse or to-and-fro motion of the
ether particles may then be explained as
follows : If a series of waves start from con-
tiguous points their individual crests and troughs
w3l coincide, or, in other words, they wiU be in
the same phase, and the result will be that the
light is intensified, as the resultant light effect
is the sum of tiie individual wave motions. It
is not necessary even for the waves to start
from the same point as long as they are in the
same phase. If, however, the path of the waves
is such that crest falls on trough and trough on
crest, then it is obvious that there must be
equal forces acting in opposite directions. The
result must therefore be no movements, or, in
other words, there is an interference of light,
and consequently darkness. The waves need
not start from the same point; as long as they
start from points half a wave-length apart they
are in opposite phase.
Hitherto, the path of the hght waves has been
considered as being in the same direction ; but
when the direction is changed, as by reflection,
then we have standing or stationary waves, which
are of considerable interest in that they are the
theoretical basis of the Lippmann process.
INTERIORS, PHOTOGRAPHING
Tti addition to the considerations given under
the heading " Architectural Photography," there
are a few special points that should be noted.
The view of an interior of a room, of a church, or
portion of a large building, must necessarily be
taken from within its own limits ; therefore a,
wide-angle lens is necessary. If too wide an
angle is included, there is a risk of the perspective
effect being exaggerated. About three-fourths
of the longer side of the plate, or sUghtly less,
should be the minimum focus employed ; and
a longer focus is preferable when possible. By
care in selecting the point of view the exagger-
ation of the perspective effect may be minimised.
One of the greatest difficulties in interior work
is the presence of windows in front of the
camera, especially if they command a clear view
of the sky, and form an important part of the
lighting of the interior. These windows throw
a glare of strong light upon the lens, rendering
it practically impossible to secure clear negatives
with good gradation and tending to fog the plate.
When these windows are not actually included
in the picture, a " sky-shade " should be fitted
to the camera front ; and if this sky-shade is
adjustable in position it can be made to exclude
all that part of the room where the imdesirable
windows are situated, without obstructing any
part of the subject included on the plate. Another
method of accomplishing the same purpose is to
have a shield of card or thin wood. In either
case, the value of the window in hghting the
interior is fully retained.
Where a window commanding a clear sky
view is included in the picture it should be
covered, whenever practicable, during the greater
part of the exposure. There will be no difficulty
in doing this when there are other windows
which partially light the interior ; should it be
the only window, it will be quite impracticable
to include the whole of it and secure a successful
photograph. If part of the window only is
included, that part only should be covered, while
a shield on the baseboard of the camera pre-
vents the light from the remaining part from
reaching the lens. At times, the sun may be
streaming through a window that is not included
in the picture, but the sunlight may fall on the
floor within the field of view and cause an
undesirable patch of hght or an tmequal lighting
of the interior. A white blind drawn over such
a window, or sheets of white tissue paper attached
over that part on which the sun is shining, will
form a remedy, these not only diffusing the light
but illuminating dark comers in a way that
cannot be attained by other means.
In all interiors the inclusion of a liberal pro-
portion of floor or foreground assists in giving
a sense of space.
When a wide-angle lens is used in a room
which is ten or twelve feet high, or when photo-
graphing a small part of a large interior, the
camera should be placed much lower than when
photographing a large subject with the same
lens. A high or normal point of view wten
including floor very near the camera gives the
impression that the ground is running up-hill,
this effect being quite obviated by lowering
the centre of the lens to about three feet from
the ground.
It may be necessary to work with a small stop,
as some portions of the subject may be very near
the camera, and sufficient depth of focus may not
be possible otherwise.
Precautions against the camera tripod slipping
must certainly be taken. {See "Tripod.") It
Intermittency Error
308
Iodide
is necessary to acquire the art of capping and
uncapping the lens as many times as may be
necessary for casual obstructions — persons walk-
ing across, etc. — without shaking the camera.
Special points in photographing workshops
are treated in the article " Factories, Photo-
graphing in." The subject of exposure in
interior work is considered in detail under the
headings " Exposure " and " i^xposure Tables."
INTERMITTENCY ERROR (Pr., LVrygMj- »»/er-
mittente ; Ger., Intermittierender Fehler)
The failure of a series of iatermittent expo-
sures to produce the same effect as an equivalent
continuous exposure. This is of considerable
importance in sensitometric work, where a
sector wheel or other device is used for testing
plates.
INVERSION, LATERAL (Pr., Inversion
latirale : Ger., Seiten-Umkehrung)
The reversal of right and left, as seen when
objects are viewed in a mirror. A ferrotype
photograph, taken direct on a metal plate, is
laterally inverted, as was also the daguerreotype.
Lateral inversion becomes serious in photo-
graphs of buildings, or where lettering occurs.
A negative on a modem dry plate is laterally
inverted, but the inversion is corrected in print-
ing. In the carbon process {which see), special
precautions are taken to avoid lateral inversion,
either double transfer or a reversed negative
being resorted to. Reversed negatives are also
used in photo-mechanical processes, since if
blocks or plates showed the picture the right
way round it would obviously be inverted in the
printed impressions. Strictly speaking, what is
called a reversed negative is really unreversed ;
it is the ordinary negative which properly
deserves the name. It is the custom, however,
to apply the term to negatives that give reversed
prints. {See also " Reversed Negative.")
INVISIBLE IMAGE {See " Latent Image.")
INVISIBLE RAYS, PHOTOGRAPHING BY
The fact that photography can depict objects
invisible to the eye has long been known. Pox
Talbot referred to the subject in his book, " The
Pencil of Nature," published in 1844, and his
own words are : " Among the many novel ideas
which the discovery of photography has sug-
gested is the following rather curious experiment
or speculations. When a ray of solar light is
refracted by a prism and thrown upon a screen,
it forms there a very beautiful coloured band
known by the name of the solar spectrum. Ex-
perimenters have found that if this spectrum
is thrown upon a sheet of sensitive paper, the
violet end of it produces the principal effect, and,
what is truly remarkable, a similar effect is
produced by certain invisible rays which lie
beyond the violet, and beyond the limits of the
spectrum, and whose existence is only revealed
to us by this action which they exert. Now I
would propose to separate these invisible rays
from the rest by suffering them to pass through
into an adjoining apartment, through an aperture
in a wall or screen. This apartment would thus
become filled (we must not call it illuminated)
with invisible rays, which might be scattered in
all directions by a convex lens placed behind the
aperture. If there were a number of persons in
the room, no one would see the other ; and yet
nevertheless if a camera were so placed as to
point in the direction in which anyone was
standing it would take his portrait." More than
half a century later Edgar Senior, of the Battersea
Polytechnic, took a most successful portrait under
what are practically those conditions. The
source of dark (invisible) rays was an arc lamp,
the visible hght being cut off at the lens by means
of special screens invented by Prof. R. W. Wood ;
the necessary exposure was five minutes. The
" X-rays " discovered by Prof. Rontgen, of
Wurzburg, in 1896 are invisible rays, and the
work they will do is common knowledge.
(For " X-ray " work, see under its own heading.)
The photographic spectrum therefore stretches
out beyond both ends of the visible spectrum,
and measures seven or eight times the length of
the visible spectrum. Thus, not only do ultra-
violet rays give results photographically, but
the infra-red as well, although the latter are, of
course, at the opposite end of the spectrum and
below the visible red.
Prof. Sylvanus Thompson, at the Royal
Institution in 1896, illuminated a piece of
apparently white paper by means of a powerful
arc-lamp. A photograph was then taken of
the white paper, and fjie negative showed an
inscription written thereon. This inscription
had been written upon the paper with an acid
(citric or sulphuric) solution of sulphate of
quinine, which, being like water in appearance,
could not be seen by the eye. The camera
detected it, however, because the chemical
liquid absorbed the ultra-violet rays, and they
were not reflected to the plate, hence they
appeared black. The experiment may be made
by anyone, but it is important that a wet collo-
dion plate be used and not a modem dry plate.
Dr. Gladstone made similar experiments as early
as 1873, and exhibited his results at the Brad-
ford meetitig of the British Association in that
year.
There are many substances that are fluorescent,
or that change the refrangibility of rays of light,
and which have a light action upon a photo-
graphic plate. An unUghted incandescent gas-
mantle gives off sufficient invisible rays to make
an image upon a photographic plate. Among
other substances are radium, mineral uranite,
certain salts of uranium, canary glass, alcohoHc
solution of chlorophyll, eesculin, tincture of
stramonium seeds, and of turmeric.
Prof. Wood, of the Johns Hopkins University
(U.S.A.), has paid particular attention to the
action of the invisible ultra-violet and infra-red
rays, and his lecture before the Royal Photo-
graphic Society on September 27, 1910, should
be referred to for full particulars.
IODIDE (Pr., lodure; Ger., lodid)
A combination of iodine with a metal. All the
iodides — with the exception of a few of the
heavy metals, lead, silver, mercury, etc. — are
soluble in water, and generally of bright colours.
They are formed by treating tie metal in powder
with iodine direct. The alkaline iodides are
prepared in the same way, or by acting on iron
iodide by an alkaUne carbonate. The following
Iodine
309
Iron Printing Processes
table gives the equivalent quantity of the prin-
cipal iodides used in photography and their
corresponding proportion of iodme : —
Iodine
Ammo-
nium
iodide
Potas-
sium
iodide
Sodium
iodide
Cad-
mium
iodide
Zinc
iodide
I-OOO
1-142
1-307
1-181
I -441
1-255
0-876
I-OOO
I -145
1-262
1-262
I -099
0-765
0-874
I -000
I -102
I -1 02
0-960
0-847
0-967
I -107
1-420
1-220
0-630
0-694
0-793
0-907
I -000
I -000
0-871
0-797
0-910
1-042
I -148
1-148
I-OOO
In process work, an iodide solution is used
in the intensifying and " cutting " of line and
half-tone negatives, as described under the head-
ing of " Intensification of Negatives."
IODINE (Pr., lode; Get., lod)
I. Molecular weight, 127. SolubiUties, i in
5,000 water, i in 12 alcohol, i in 3 ether; soluble
in carbon disulphide and solutions of alkaline
iodides. It occurs as gUstening steel-blue-black
plates with pecuUar odour ; and it is obtained
from seaweeds. It is poisonous, the antidotes
being emetics, the use of the stomach pump,
magnesia, starch solution, and " hypo." A solu-
tion of iodine in an aqueous solution of potassium
iodide is used for bleaching bromide prints for
sulphide toning, the formula being : —
Potassium iodide . 200 grs. 20 g.
Distilled water . I oz. 50 ccs.
Dissolve and add —
Iodine . . .10 grs. i g.
and when thoroughly dissolved add —
Distilled Water to 20 oz. i,cxx) ccs.
Immerse the print in this tiU the image is
bleached. The paper becomes stained dark blue,
which may be discharged by a 10 per cent,
solution of sodium sulphite.
Small quantities of iodine are added to collo-
dion to ripen it, and a few drops of a i per cent,
alcoholic solution is recommended as an acceler-
ator with hydroquinone.
In process work, iodine has important uses.
When collodion becomes colourless or lighter in
colour it is apt to give foggy plates. In this
case add i min. of solution of iodine in alcohol
(2 grs. in I dim.) to each ounce of collodion.
lODISER (Fr., lodo-bromure ; Ger., lodirungs-
flUssigkeH)
A solution of metaUic or alkaline iodides and
bromides in alcohol, kept as a separate stock
solution and added to collodion just before use.
(See "Collodion Process (Wet).")
lODO-BROMIDE (Fr., lodo-bromure; Ger.,
Bromiodid)
Applied to emulsions containing bromide of
silver plus a small proportion of iodide.
lODOEOSIN {See " Erythrosine.")
lODOSE
In order to simplify the operation of iodising
collodion, a compound called iodose has been
introduced. A dry mixture of suitable iodising
salts is made in the proper proportions, so that
the compound has only to be dissolved in alcohol
and added to the collodion.
IRIDESCENCE (Fr., Iridescence ; Ger., Schein-
fdrbung)
The play of colours seen in thin films, such
as oil on water, in the opal, mother-of-pearl, etc.,
and due to the interference of light in
extremely thin films. Iridescent colours are
occasionally seen between the cemented com-
binations of lenses, and are then due to partial
separation ; the remedy is to separate and
re-cement them, which is work that is best done
by an optician.
IRIDESCENT HELIOCHROMY (See " tipp-
mann's Process.")
IRIDESCENT MARKINGS
Chemical fog often seen in the form of green
stains at or near the edges of plates and films ;
known also as green or dichroic fog. It may be
due to stale plates, stale sodium sulphite, and
forcing under-exposed plates with the pyro-
ammonia developer. It rarely occurs when soda
or potash is used as an alkali, or with any of the
newer developers. It may be cured by bleach-
ing the plate, after well washing, ia : —
Ferric chloride
. 20 grs.
23 g-
Potassium bromide
. 40 „
46 „
Water .
2 oz.
1,000 ccs
The plate will be reduced slightly in density as
the iridescent fog disappears. It is afterwards
well washed and re-devdoped, in daylight, -with
hydroquinone, metol, or ferrous-oxalate (the
last-mentioned preferred), until of the desired
density, it being finally re-fixed and washed.
In process work, the degree of contact obtained
in the screw-pressure frames between the process
negatives and the metal plates is judged accord-
ing to the iridescent markings visible through
the thick front glass of the frame. These mark-
ings are due to the phenomenon known as
Newton's rings.
IRIDIUM CHLORIDE OR TETRACHLO-
RIDE, IRIDIUM AND POTASSIUM
CHLORIDE, AND IRIDIUM AND
SODIUM CHLORIDE
IrCl,; IrOjaKa; and Ira42Naaa or NajIrCl,
respectively. These are respectively dark brown,
red, and brownish-black crystals which have
been suggested for toning prints, and are occa-
sionally used in ceramic work. Practically,
however, they are of but very slight photogra-
phic interest.
IRIDIUM AND GOLD TONING BATH
(See " Gold and Iridium Bath.")
IRIS DIAPHRAGM (See " Diaphragm.")
IRIS VIGNETTER (See " Vignetter.")
IRON PRINTING PROCESSES
Processes of printing by means of salts of iron
are descaibed under the heading " Ferric Salts,
Printing with."
Irradiation
310
Isochromatic Plates
IRRADIATION (Fr., Irradiation; Ger., Strah-
lenwerfen)
A theory that has beea propounded in regard
to the formation of the dots in half-tone process
negatives, especially in collodion emulsion and
dry plates, accounts for the want of sharpness
by irradiation of light from particle to particle
of the silver forming the image.
ISINGLASS (Fr., IchthyocoUe ; Ger., Hansen-
blase Fischleim)
A gelatine obtained from the swimming
bladder of various species of fish. It occurs in
thin plates or fine white shreds with a yellowish
tinge. It is entirely soluble in boiling water, and
sets to a. jelly on cooling. It is occasionally
used as a substratum and in mountauts.
In process work, isinglass has been used instead
of, or as an addition to, gelatine, especially in
some old methods of collotype and photo-
lithography. Also it has been suggested as a
substitute for fish-glue in the enamel process,
but it has no advantages.
ISOCHROMATIC PHOTOGRAPHY
Photography in which colours are rendered
in a monochrome picture according to their true
visual brightness. Known also as orthochro-
matic photography. It is well known that
yellow or red objects appear very dark in an
ordinary photograph. The ordinary plate is
chiefly affected by violet and blue rays of light,
and is comparatively insensitive to green, yellow,
orange, and red rays. Hence, blue objects
impress the plate far too strongly, comparatively,
the result being that they appear much too light
in the photographic print. This serious fault
is very evident in photographs of vividly coloured
objects, and isochromatic methods are adopted
to overcome it. The plates used (see "Isochro-
matic Plates ") have been treated in a way that
renders them " colour sensitive," but as plates
made sensitive to green, yellow, and orange-red
rays are still too sensitive to blue-violet, a com-
pensating screen is placed in front of the lens,
so that the blue-violet rays are lessened in
intensity. A further function of the screen is
that it entirely absorbs the ultra-violet rays,
which otherwise affect the plate ; and as they are
invisible, it is of course necessary that they play
no part in the formation of the photographic
image.
Vogel and others discovered that by mixing
certain aniline dyes with the silver bromide
emulsion of a plate, the latter becomes sensitive
to the colours absorbed by the dye (or the dyed
silver bromide particles). It is hence possible
to adapt a dyed or " isochromatic " plate and
a screen so that the combination will result
in objects of all colours being represented in
the print in tones of visual brightness corre-
sponding. Yellow-green being the brightest
colour visually, objects of this colour will appear
lightest in the print, and so on. Isochromatic
photography as usually practised is more par-
ticularly a rough compromise, as to give accur-
ate colour records too long exposures would be
necessary, owing to the slowing effect of the
yellow screen. {See also tmder the headings
" Isochromatic Plates," " Isochromatic Screens,"
and "Monochrome, Rendering Colours in.")
ISOCHROMATIC PLATES
Plates specially sensitised for colour, and used
with compensating light filters or isochromatic
screens. They may be roughly grouped into
three classes : (i) those which are sensitised for
green and yellow rays of light, and give an
approximately true colour rendering; (2) those
which are sensitised for the entire spectrum,
often called " panchromatic " (which see) ; and
(3) plates rendered sensitive to orange and red,
but which lack green sensitiveness.
There are a great many varieties of the first
type, but aU possess what is termed a maximimi
of colour sensitiveness in the yellow-green region ;
staining an ordinary plate with certain of the
aniline dyes induces this sensitiveness, and ery-
throsine is characteristic of type i in its action.
Panchromatic plates being discussed under their
own heading, this article will deal only with the
first and third types. The ordinary isochromatic
or orthochromatic plate has a distinct maximum
in every instance in the green-yellow region of
the spectrum, and its sensitiveness generally ends
off abruptly at about the D line (= A 5893)- S^c^
a plate can be prepared by bathing, this process
giving excellent results provided that the plates
bathed are used a day or two after being treated.
Two solutions should be made up as folio vr : —
A. Brythrosine . . 10 grs. i g.
Alcohol . . . 4 oz. 166 CCS.
B. Liquor ammoniae (-880) i drm. 52 „
Water . . .24 oz. 1,000 „
For use, i drm. of A is mixed with 6 oz. of
B a few minutes before use. Great care must
be taken only to bathe clean working dry plates
of medium rapidity, about 150 or 180 H. and D.
(pyro-soda or pyro-metol speed). A " safe "
ruby light must be employed for the illumination
of the dark-room. (See " Colour Screen or
Filter.") Scrupulous cleanliness must be ob-
served, dishes etc., being thoroughly clean in the
strict chemical sense. The quicker the bathed
plates are dried, also, the better, so that a
warm room in which they wiU become dry in
two to three hours should be chosen if possible.
The plates are placed in the dish, and flooded
over with the solution, 2 oz. being allowed to
each haU-plate ; the dish is gently rocked for
three minutes, and the plates are then placed in
another dish and given six rinses in plain water
or left under a running tap for two minutes.
They should be placed in a new wooden rack to
dry, and this rack should not be used for any
other purpose. Dry in complete darkness.
A sensitiser for the green and blue-green rays,
w'hich tends to slow the plates, may be prepared
thus : —
Auracin .
Boiling water
lo oz.
•23 g-
1,000 CCS.
Allow to cOol, then filter the solution, and add
■J drm. of strong ammonia.
Plates of type 3 are difficult to prepare
because, owing to their great red sensitiveness,
the work must be done almost in darkness. A
suitable solution for bathing may be made up
as foUows : —
Cyanine blue (ethyl cyaniue
or pinacyanol)
Alcohol ....
I gr. -28 g.
8 oz. 1,000 ccs.
Isochromatic Screens
3"
Isochromatic Screens
Add -J oz. of this to 6 oz. of distilled water,
add -J drm. of strong ammonia, allow to stand
for twenty minutes, and filter. Two ounces
of solution will suffice as before for one half-
plate.
There has been a tendency of late to produce
plates so highly sensitive to greenish-yellow that
when used without a screen quite satisfactory
colour renderings can be obtained. Such plates
are by no means perfect, but they show a marked
improvement over ordinary plates. A " no-
filter " plate may be prepared by means of the
following solution : —
A. Erythrosine . . i gr. -23 g.
Distilled water . . i oz. 100 ccs.
B. lyiquor ammouise (-880) i„ 55 g.
Distilled water to . 10 ,, 1,000 ccs.
C. Silver nitrate . . 2 gr. '46 g.
Distilled water . . 1 oz. 100 ccs.
Mix equal parts of A, B, and C, and dilute the
mixture with an equal volume of distilled water.
Select slow ordinary plates, bathe them for two
minutes each, rinse them well under the tap,
and put them in the rack to dry. Very intense
green-yellow sensitiveness is thereby produced,
but no such plate will give an accurate colour
rendering, because it is still sensitive to ultra-
violet rays, to extinguish which a yellow filter
is necessary.
Isochromatic plates of commerce are made by
adding carefully selected and purified dyes,
dissolved in alcohol or water, to the liquid
emulsion with which plates are coated. The
sensitive particles of emulsion are thereby
coloured, though often almost imperceptibly,
and their colour absorption altered in conse-
quence, so that rays of light for which the plates
are " sensitised " are absorbed. One of the
earliest descriptions of an isochromatic emulsion
for plates was given in TaiUer and Clayton's
patent specifications of 1882-3.
ISOCHROMATIC SCREENS
Only those rays of light that are visible to the
eye shoiUd be allowed to affect the photographic
plate ; besides the visible rays of the spectrum,
there are two sorts of invisible ones — the ultra-
violet and infra-red — situated respectively before
the violet and after the red rays. The ultra-
violet rays are particularly active photo-
chemically, and are present in daylight and all
the kinds of artificial light usually employed
for photographic work. It is the primary
function of the isochromatic (or orthochromatic)
screen to absorb these rays, and the ordinary
screen is therefore a yellow glass of the requisite
shade, which is placed' in front of or behind the
lens, or immediately in front of the plate, or it
is sometimes fixed in the lens diaphragm between
the two components of a doublet or other com-
pound lens. The next function of the screen is
to cause rays of each colour to act upon the plate
to an extent dependent on their visual bright-
ness. Thus a yellow daffodil photographed
against a dark blue background should appear as
a light grey flower against dark grey ; with an
ordinary plate the dafiodil would appear darker
than the background. The isochromatic screen
is yellow, and therefore " damps down " the
action of the blue rays by partially absorbing
them, so that in the negative the blue background
would come out faint and would therefore appear
dark, as it should be, in the print.
No plate, however carefully colour-sensitised,
is sensitive to all colours in degrees proportionate
to their visual luminosity. The erythrosine type
of plate, for example, is always deficient in the
bluish-green region. The screen must compen-
sate for such deficiencies by absorbing those
colours to which the plate is most sensitive, to
such an extent that the other colours are
adequately recorded. The average " isochro-
matic " plate is not red-sensitive, and only
an approximately correct colour rendering can
therefore be obtained, unless a panchromatic plate
and a properly adapted light filter are employed.
For general working, a very fair " ortho-
chromatic " effect is obtained by using a yellow-
green sensitive plate, and a yellow screen which
cuts out all ultra-violet rays and depresses the
blue-violet, though it is, of course, better to use
one special type of colour-sensitive plate and a
screen adapted accurately to it. The yellow
screen is more usually made by dyeing the film
of a piece of optically flat glass which has been
coated with pure neutral gelatine. The dye
should give as transparent a filter as possible ;
that is, the screen should be pale, and exposure
only increased by a minimum amount. Thus,
while naphthol yellow and tartrazine are good dyes
for the purpose, a screen can be made with filter
yellow K, or rapid filter yellow, which gives equally
good results, while exposure is only increased
perhaps half as much as it is in the former case.
Gelatine-coated glass may be stained with a
I : 500 solution of the yellow dye selected, and
filters of various intensities should be made ;
the best one to use may be found by experimental
exposures on an actual coloured subject.
To adapt a light filter or screen correctly to a
given plate, two methods are available. One is
to test the experimental screens by photographing
the spectrum through them, and varying the
colour until each portion of the spectrum is
recorded in the negative with a density pro-
portionate to its visual intensity ; the other is
to photograph a test chart, which is most con-
veniently made by drawing concentric circles on
a card and dividing each of these circles into
two parts, one painted black, the other coloured ;
blue, green, and orange are the best colours to
use if a panchromatic plate is being tested, or
blue-violet, blue-green, and gamboge if a green-
yellow sensitive plate. The circular card is
attached to a small motor and revolved rapidly,
and the amount of black in each ring is increased
until all the rings appear of equal luminosity.
If a correctly compensating screen be used, then
each ring wiU appear, in a photograph taken of
the disc, of equal density. The screen must be
experimented with imtil this result is obtained.
A liquid filter is very convenient for experi-
mental work, as its colour may be varied at will
by adding concentrated dye solutions. Thus by
adding, say, m ccs. of a i : 100 solution of
filter yellow and n ccs. of a i : 100 solution
of crocein scarlet to water contained in a flat
glass cell of 1 6 sq. cm. area, a liquid screen is
obtained which satisfies the tests for a good
colour rendering. Flat glass can then be coated
with a 5 per cent, solution of gelatine, allowing,
Isocyanines
312
Ivory
for example, i cc. to coat each 10 sq. cjtn.
of surface ; each cc. of the gelatine solution
must therefore contain 4S x or — e.
^' 100 160 ^
of the yellow dye, and— ^ of the orange dye, and
so on. Stained gelatine filters are usually bound
up with a cover glass, the two glasses being
cemented together with Canada balsam.
Pot glass filters (made from glass coloured in
the mass in course of manufacture) are usually
inefficient, requiring prolonged exposures owing
to a considerable percentage of grey in the glass.
The multiplying factor is important in iso-
chromatic photography, as by under- or over-
exposure and attempted correction in develop-
ment, the colour contrasts in monochrome may
be somewhat falsified. All yellow screens
necessitate an increase in exposure of from two
to ten or fifteen times the normal. A screen with
which five times the normal exposure is required
is often designated a X S screen, and so on.
The only satisfactory way to find the multiplying
factor is to photograph a black-and-white
object, giving varying times of exposure, and
judging from the results which is the correct one.
This should be verified then on a landscape.
ISOCYANINES (Pr. and Gr., Isocyanine)
A class of dyes for colour-sensitising plates,
all complex derivatives of cyanine, which they
have superseded. The group includes ortho-
chrome T (introduced in 1903), pinachrome
(1904), pinaverdol, pinacyanol, homocol, and
dicyanine. These are treated under their
respective headings. Pinacyanol is the best
sensitiser for the extreme visible red, while
dicyanine sensitises for the infra-red.
ISOTYPIE
A process of half-tone negative making pro-
posed by Vittorio Turati, and expounded in an
elaborate treatise. The system depends on the
use of variously shaped diaphragms in con-
junction with a suitable screen distance. The
latter is determined by means of what the
inventor termed a " finder " stop, having two
small openings placed at a mathematically deter-
mined distance apart. The image of this stop is
viewed by means of a microscope through the
ruled screen, whilst the latter is moved to and
fro until a. position is found where the images
of the two openings coincide in the focal plane.
The variously shaped diaphragms can be put
in the lens, and different patterns of dot forma-
tion are obtained on the negative, although the
ordinary cross-ruled screen has been used
throughout. The process has not come into
commercial use.
* * IX "
Sir WilHam Abney in his presidential address
before the Royal Photographic Society, in
October, 1896, proposed tie term "It" (the
initials of intensity and time) as an expression
of the imit of exposure. He used the term pro-
visionally only, and suggested that a rmit might
be called " talbot," just as in other branches of
physics the units were named after pioneers, as,
for example, the " watt," the " volt," and the
" amp^e."
IVES' COLOUR PROCESSES
P. E. Ives, of Philadelphia, U.S.A., may be
considered as one of the pioneer workers in
practical three-colour work, as it was mainly by
his efforts that the true theory of the processes
was recognised and of recent years reduced to
practical results. He laid down the principle,
though it had already been enunciated by Clerk-
Maxwell and Ducos du Hauron, that the object
to be reproduced in colours should be photo-
graphed through three separate screens or colour
filters, which should give negatives that repre-
sented by light and shade the degree to which
light coming from different portions of the sub-
ject excites a single primary colour sensation in
the eye ; and that for projection these three
photographs should be projected simultaneously
upon a screen, each by light which excites only
the primary colour sensation which it represents,
and in such manner that the three-coloured
images are superimposed. This involves the
production of one photograph by the joint action
of the red, orange, yellow, and yellow-green
rays, but chiefly by the orange, so as to represent
the effect upon the red sensation ; another by
the joint action of the orange, yellow, yellow-
green, green-blue rays, but chiefly by the
greenish yellow rays so as to represent the
action of the green sensation ; and a third
photograph by the joint action of the blue-green,
blue, and violet rays, but chiefly by the blue
rays to represent the action of the blue sensa-
tion. Positives from negatives were projected,
the first by pure red light, the second by pure
green hght, and the third by blue-violet Ught.
Several cameras of varying types have been
devised by Ives to obtain the negatives, some
in which ihe image formed by one lens was spUt
up by means of mirrors into three images, and
others with three lenses. In his latest type
only one lens is used, and a reflector spUts the
image up into two parts, and one image is received
by one plate, and the other two by a plate and
a celluloid film placed surface to surface with a
colour screen in between.
IVES' HALF-TONE PROCESS
One of the early half-tone processes. It was
invented by P. E. Ives, and patented in
America in 1878. A gelatine relief was cast in
pure white alabaster plaster, and brought into
contact with an indiarubber sheet covered with
pyramidal raised points or Unes which had been
inked. According to the amount of reUef on
the cast the rubber points were more or less
spread out, and thus gave dots of ink of varying
size on the surface of the cast. The hght and
.shade of the image was thus reproduced, and the
cast was then photographed, the negative being
equivalent to the half-tone negative now secured
through the ruled screen.
IVOIRE DUR
The name by which carbon pictures upon
porcelain were once known, owing to their being
an imitation of photographic prints upon ivory.
IVORY (Pr., Ivoire ; Ger., Elfenbein)
The tusks of the elephant ; a very hard white
or creamy white bonehke substance which is
occasionally used as a support for prints.
Ivory, Artificial
313
Juniper Resin
IVORY, ARTIFICIAL
Artificial ivory is either white vulcanite or
white opaque celluloid.
IVORY BLACK (Pr., Noir d'ivoire ; Ger.,
Elfenbeinschwarz)
Calcined ivory scrap, turnings, and powder,
used as a pigment.
IVORY, PHOTOGRAPHS ON
Generally, photographs are printed on ivory
by the carbon transfer process {which see). Other
methods have been advocated, as, for example,
sensitising the ivory and printing by contact
or through a camera, but the carbon process is
the easiest and best. Such pictures are largely
used for the production of coloured miniatures,
the print being made weak to serve as a base
for the colours.
IVORYTYPE
An imitation of prints upon ivory. The
working directions are as follow : Select a print
upon plain salted paper, strong and brilliant ;
prints from flat negatives do not give pleasing
effects. Edge a glass plate with moimtant to
the extent of about J in. ; damp the picture, and
lay it face upwards upon the glass so that it
becomes fastened by the edges. The glass
should be of such a size as to leave about -J- in.
margin round the print. When dry, the print
will be found stretched tight upon the glass.
It is then coloured with bright water-colours
or aniline dyes. A flat slab of soap-stone is now
taken, the glass bearing the print is mounted
upon it, and the whole placed over a gas-stove
or oil-stove until the glass is hot enough to
melt wax. A cake of white (not paraffin) wax
is then rubbed over the warm surface of the
picture. The wax gradually melts and saturates
the print, which at this stage presents a hope-
less appearance, and appears to be ruined. The
print is next cut roimd the edges, so as to detach
it from the glass. A sheet of dean plate glass
is heated in the same manner as the first piece,
and the print, waxed face down, is laid upon it.
The wax soon causes glass and paper to adhere,
and any air-bubbles can be pressed out by using
a piece of wax with a straightedge as a squeegee.
The glass with the print upon it is then allowed
to cool, and the print is next backed up with white
cardboard, and bound at the edges with bind-
ing strips, or the card is attached by means of
wax. Finally, the whole is framed.
Prints produced by the " Ebumeum Process "
{which see) have also been called ivorytypes.
JAFFA'S PAPER
A commercial photo-lithographic transfer
paper, sized with hardened gelatine, which has
to be sensitised in a bath of potassium bichro-
mate. Max Jaffe recommends the addition of
manganese oxysulphate to the bath in summer
time. Two kmds of this paper are made, one
having the natural gelatine surface and the
other being highly glazed. The latter is recom-
mended for half-tone and delicate line work.
JAFFfeTYPE
A half-tone process, invented by Max Jafie,
of Vienna, consisting of printing from an ordinary
continuous tone negative on to a collotype-
prepared plate, with a piece of gauze interposed.
Thus a kind of half-tone print was obtained from
which lithographic transfers were pulled and
put down on metal for etching into relief.
JAUNE BRILLANT
A pigment consisting of a mixture of cadmium
yellow, vermilion, and white-lead, and used
occasionally for colouring photographs.
JAVELLE WATER {See " Eau de JaveUe.")
JENA GLASS {See " Glass.")
JEWS' PITCH {See " Asphaltum.")
JOLY'S COLOUR PROCESS
A screen-plate process of colour photography,
introduced in 1894, in which a glass plate
ruled with parallel lines, about 150 to the inch,
of red, green, and blue-violet, was placed in
front of a panchromatic plate during exposure,
and gave an image in lines corresponding to the
distribution of the colours of the object. From
this a transparency was made in the ordinary
way and bound in contact with a viewing screen
ruled with lines of similar width and adjusted
till the object was seen in its natural colours.
{See " Screen-plate Processes.")
JOSEPH, PAPIER
An extremely soft Japanese tissue paper of
silky texture, used for cleaning glass.
JOUGLA PROCESS {See " Omnicolore Plate.")
JUNIPER RESIN {See "Gum Sandarac"
under the heading " Gums and Resins.")
K
K SCREENS
A commercial name for yellow screens pre-
pared with, filter yellow K.
KACHIN (Pr. and Ger., Kachin)
A developer, possibly identical with and cer-
tainly resembling pyrocatechin. It is soluble in
water (28 in 100) ; keeps well ; does not stain
fingers, plates, or papers ; and gives good black
images. The standard formulae are: —
One-solution Developer
Sodium sulphite . -J- oz. 27-5 g.
Sodium carbonate . i ,, 55 ,,
Kachin . . . 100 grs. 11-5 „
Water . . .20 oz. 1,000 ccs.
The above is ready for use.
Two-solution Developer
A. Kachin . . 160 grs. 18 g.
Sodium sulphite . 2\ oz. 137-5 »
Water - . . 20 ,, 1,000 ccs.
B. Sodium carbonate . 2 oz. 1 10 g.
Water . . . 20 „ 1,000 ccs.
Use equal parts of A and B. Dilute with water
for softer results. Use as a restrainer 10 to 30
drops of a 5 per cent, solution of borax to each
ounce of developer.
Another popular form of a two-solution
developer of a different character is : —
Two-solution Developer
A. Kachin . .192 grs. 22 g.
Sodium sulphite . 2 oz. no „
Water . . . 20 „ 1,000 ccs.
B. Sodium phosphate 3^ oz. 200 g.
Caustic soda. . 192 grs. 22 „
Water . . .20 oz. 1,000 ccs.
For use, mix i part of A, i part of B, and i part
of water. A few drops of a 10 per cent, solution
of potassium bromide per ounce of developer has
very great restraining power, and is of use in
cases of extreme over-exposure. A curious and
valuable property of kadiin is that it gives better
results on very stale plates than any other
developer. Kachin has been advocated for use
in developing and fixing a negative in one
operation. (For f ormulje see " Developing and
Fixing Combined.")
KALEIDOSCOPIC PHOTOGRAPHY
Photography of the multiple images produced
by two mirrors placed at an angle with one
another, as in the kaleidoscope. The sym-
metrical images given by the latter instrument
are often photographed for the use of designers.
[See also " Polyscope.")
KALLITYPE
A printing process invented by Dr. W. J.
Nichol in 1899. Paper, coated with a mixture
of a ferric salt and silver nitrate, gives, on expo-
sure to light behind a negative, an image in
ferrous oxalate and silver oxide which, on the
application of a suitable developer, precipitates
an image in metallic silver. The principle of the
process is old, and was foreshadowed by Hers-
chel's obsolete " Chrysotype " process. The
instructions immediately following are practically
those originally published by Nichol, who at one
time placed the paper ready for use on the market
but withdrew it because he was not satisfied with
the permanency of the results ; his fixer was a
weak solution of ammonia, but later experiments
proved that the use of " hypo " as a fixer gave
more permanent prints.
The paper, preferably after sizing, is sensi-
tised by coating with : —
Ferric oxalate .
Silver nitrate .
Oxalic acid
Distilled water
750 grs. 167-5 g-
300 „ 67 ,,
q.s. q.s.
10 oz. 1,000 ccs.
Place the ferric oxalate in a bottle with the
water, which stand in a saucepan of water, and
gradually heat until the ferric oxalate dissolves.
If there is need, add not more than from 5 to 10
grains of powdered oxalic acid to assist solu-
tion. Filter the hot solution, and add the silver
nitrate to the clear filtrate ; this will keep good
in the dark for several months. The paper is
then coated (in a yellow light) after the manner
described under tiie heading " Blue-print Pro-
cess," dried, and printed upon until of a bluish
brown colour upon a yellow ground. At this
stage the image consists of reduced iron (ferrous)
salt which has the power of reducing the silver
nitrate to a metallic state, which power, however,
is latent until a developer (a solvent of the
ferrous salt) is applied to the paper.
Of the many possible developers, the chief are
sodium tungstate, Rochelle salt, sodium acetate,
and borax.
(i) For Black Tones —
Borax . . . i oz.
Rochelle salt . . |- ,,
Potassium bichromate
(i % solution) .7-9drms. 87-112 ccs.
Water . . .10 oz. 1,000 „
(2) For Sepia Tones —
Rochelle salt . . -J 02.
Potassiimi bichromate
(I % solution) .4-5 drms. 50-62 ccs.
Water . . 10 oz. 1,000 „
(3) For Purple Tones —
Borax ... J oz.
Rochelle salt . . i ,,
Potassium bichromate
(1% solution) .7-9 drms. 87-112 ccs.
Water . . .10 oz. 1,000 „
no g.
82-5 „
55 g-
27-5 g-
no „
314
Kallitype
315
Kallitype
(4) For Maroon Tones —
Rocielle salt . . 1 oz. no g.
Sodium tungstate . ^„ 55 „
Water . . . 10 „ 1,000 ccs.
The print is immersed in the developer and the
dish is rocked for from fifteen to thirty minutes.
Although the image may appear quickly, the
print must remain in the bath some time in order
to render the iron salts completely soluble. The
print is then passed direct, without washing,
into the fixing bath, consisting of —
Sodium hyposulphite i oz. 55 g.
Liquor ammoniae (-880) i„ 12-5 ccs.
Water . . 20 „ 1,000 „
The print is kept on the move in this bath for
about ten minutes, then washed for about
twenty minutes, and finally dried. Some
workers advocate a second immersion in a fresh
fixing bath (as above) in order to be sure of
thorough fixing, which is absolutely necessary
to secure permanent pictures.
A finished kaUitype picture has an image
consisting of metaUic silver, and it may there-
fore be toned with gold, platinum, or by the
sulphide process, if desired.
Modified Kallitype. — Another and more mod-
em paper is that known as " Water-developing
kallitype," which is a good paper for home pro-
duction, but the warm brown results cannot,
as a rule, be said to equal those given by the
proper kallitype process described above. Four
solutions are necessary for sensitising : —
A. Green ferric am-
monio-citrate
1,100 grs.
252 g.
Water .
10 oz.
1,000 ccs
B
Tartaric acid
180 grs.
41 g-
Water .
10 oz.
1,000 ccs
C.
Silver nitrate
460 grs.
106 g.
Water .
10 oz.
1,000 ccs
D
Gelatine
300 grs.
69 g.
Water .
10 oz.
1,000 ccs
The A and C solutions keep well in the dark ;
the B solution keeps for a few days only, owing
to the formation of mould ; while the D solution
should be made just before use, the gelatine
being soaked in the water and dissolved by heat.
Equal parts of the four solutions added together
form the sensitiser ; A and B solutions shoxild
be added to the warm gelatine D, the whole
being kept warm by placing the measure, say a
10 oz. graduate, in hot water. The C solution
is then added very slowly, stirring the combined
mixture with a glass rod the while. The warm
solution is then coated upon the plain paper, and
as soon as the coating has lost its wet appearance
and begins to look duU the paper is hung up in
a warm room and out of the way of actinic light
to dry ; when dry it is ready for printing.
The print needs to be vigorous ; from the
printing frame it passes into plain water for about
two minutes, and in this the image develops up to
a greater strength and of a reddish brown colour.
It is then transferred to a weak "hypo " fixing
bath ("hypo" 50 grs., water 5 oz.,) or to a 10
per cent, sodium sulphite solution, in which the
print becomes a richer brown in colour. Finally,
the print is washed for about half an hour, and
dried.
20 grs.
4-5 g-
200 ,,
45 „
SOO „
II2-S „
10 oz.
1,000 ccs
American KaUitype. — In America much atten-
tion has been paid to kallitype, and many
formulae and improvements have been intro-
duced. The J as. Thomson process needs a
" salting " and a " sensitising " solution : —
Salting Solution
Ferric-ammonio
citrate . . . 200 grs. 45 g.
Ferric oxalate .120 „ 27 „
Potassium oxalate .120 „ 27 ,,
Copper chloride . 60 „ i3'5 „
Oxalic acid . . 40 ,, 9 ,,
Gum arable . . 100 ,, 225 ,,
Distilled water . . 10 oz. 1,000 ccs.
The paper (sized if velvety tones are desired)
is coated with the above, dried, and treated with
the sensitiser : —
Oxahc acid
Citric acid
Silver nitrate .
Water
When surface dry, complete the drying by
gentie heat, but excess of heat will convert the
ferric salt to ferrous. For printing, three or four
minutes in sunhght is generally sufficient. The
image appearing is chestnut brown upon a
yellow ground, and printing should be stopped
before the half-tones appear. The print is
placed direct into clear cold water, where it will
develop fully ; four changes of water, or about
three minutes in running water, will be sufficient.
After washing, fix in a weak " hypo " bath
(50 grs. to 32 oz.) ; a ten-minute immersion is
generally sufficient. Wash in plain water for
about half an hour and dry ; the resultant colour
should be a good brown.
Single-solution Kallitype Sensitiser. — ^The fol-
lowing sensitiser is one of the simplest and most
widely used for menu, note paper and post-
card work. Geo. E. Brown, who has advocated
it, gives the following directions : 55 grs. of
silver nitrate is dissolved in 4 or 5 drms. of
distilled water ; and liquor ammoniae (-880),
diluted with an equal quantity of water, is very
carefully added. As the first drop or two is
added, a copious precipitate of silver oxide is
thrown down in the solution. Addition of more
ammonia solution will re-dissolve this precipi-
tate ; cease to add ammonia on the disappear-
ance of the last traces of the precipitate. Weak
sulphuric acid is next added drop by drop until
the faint odour of ammonia disappears. 40 grs.
of green ferric ammonium citrate dissolved in
6 drms. of water is then added, and the Hquid
is complete. Stored in the dark or in a stone
bottie, it will keep good for several months.
It is applied to paper in the same way as other
kallitype sensitisers, dried, and the paper treated
as before described, namely, with water and
"hypo."
After-treatment. — Kallitype prints may be
toned, reduced, re-developed, and intensified.
For toning, a simple combined bath which works
well is : Water, 8 oz. ; sodium hyposulphite,
I oz. ; gold chloride, i gr. Over-exposed prints
may be reduced by immersing in a weak solution
of hydrobromic acid, a suitable strength being
30 drops of the strong commercial acid to i oz.
of water. One immersion for a minute or two
Keunmatograph
316
Kinemacolor
will usually suffice ; the print is then washed
well. Another method is to immerse the print
in the weak acid for a few seconds only, and then
transfer to a weak fixing hath of " hypo " and
water for a few minutes ; this increases contrasts
considerably, and much can be done in the way
of getting good prints from weak negatives.
As regards intensification, the image consisting
practically of metallic silver, it can be subjected
to the processes advocated for intensifying
negatives and bromide prints, and even the
uranium and sulphide processes of toning and
intensification may be used. The kallitype print,
unlike a bromide print or a negative, can be
easily bleached in a solution of hydrochloric add,
and 10 drops of the acid added to i oz. of water
rapidly removes the image and converts the
silver into silver chloride. If the bleached
picture is then well washed and exposed to a
strong light, it may be developed with any
clean working developer, as hydroquinone-
metol, etc. In this way a strong developer may
be employed to produce a cold tone, or a weaker
developer one 'of a warmer tone, and the tones
can further be modified in a gold or platinum
toning bath.
KAMMATOGRAPH
An apparatus for taking and projecting kine-
matographic pictures, invented by I^eo Kamm.
A circular glass plate, 12 in. in diameter, is
used as a support for the sensitive emulsion, at
its centre being a hole about i^ in. in diameter,
and the mechanism is such that the plate cannot
race past the point at which it is required to
be held momentarily stationary for purposes
of exposure. The circular plate is given an
intermittent rotary motion and also an hori-
zontal displacement, which enables a series of
pictures to be impressed upon it in a spiral
form. The combined camera and projector is
made in two patterns, both of the same size,
but one taking 350 and the other 550 pictures
on the disc. Bach picture of the 550 series
measures J in. by ^V in-, while those of the
350 series are slightly larger.
The apparatus is fireproof, whilst the process
of making the positive records from the nega-
tives involves but little trouble, the printing
of the positive images being done exactly in
the same way as one would make an ordinary
lantern slide — by contact, exposure, and develop
ment in one sheet. There is considerable
novelty in the mechanism, but the principle of
arranging pictures in a spiral form upon a disc
is not new, this having been done by American
and French inventors prior to the inception of
the kammatograph.
Anthony's " spiral " lantern and Nelson's
" spiral " camera may be mentioned here,
although they were limited to a. much smaller
number of pictures in any one series.
KAOLIN (Pr. and Ger., Kaolin)
Synonyms, china clay, white bole. A native
hydrated aluminium silicate which, when pre-
pared, is a white powder that is used for clearing
the silver bath and in the production of matt
surface paper, and is added to emulsions for
the same purpose. It is also employed in the
manufacture of crayons.
KARTALINE
A modification of the crystoleum process in
which the print is attached face downwards to
glass for colouring. When coloured and re-
moved, it is finished by varnishing.
KATA-POSITIVE
An obsolete name for a positive on an opaque
base, as ivory, paper, etc. Positives upon glass,
etc., were known as dia-positives.
RATA TYPE (See "Catatype.")
KEITH'S PAPER PROCESS
A waxed-paper process (which see) introduced
by Dr. Thomas Keith, of Edinburgh, in 1856;
practically the same as Le Page's process.
KENNETT, RICHARD
Died 1896. Patented, November 20, 1873, a
process for using gelatine instead of collodion
combined with salts of silver. A prepared com-
pound was cut into strips, washed to remove
the free salts, and afterwards dried. In this
state the " pellicle," as it was called, could be
stored for use, and when required it was dis-
solved in water and plates coated with it in the
usual way. Advertisements of the period stated
that " R. Kennett is now issuing his patent
sensitised gelatiuo-pellicle, in packets containing
sufficient to make two, four or six ounces of
emulsion, at one, two and three shillings respec-
tively." In March, 1876, he placed "rapid
pellicle plates " all ready for use on the market,
but photographers faUed to appreciate the
extraordinary sensitiveness of the plates, as
compared with the slow wet plates, and they
invariably got fogged pictures, either on account
of over-exposure or unsafe (yellow) dark-room
hghts.
KETONES
A class of substances derived from the secon-
dary alcohols by a removal of two atoms of
hyi:ogen, and distinguished by the divalent
group CO imited with two alkyl radicles, as in
acetone CHaCOCH,, which is practically the
only one of any photographic interest, and
which is described under its own heading.
KEY
A print is said to be in a high key when there
are few gradations of tone, none of which is
very deep ; it is in a low key when the few
tones are all at the dark end of the scale.
KILOGRAMME. KILOLITRE, KILO-
METRE, ETC. (See "Weights and
Measures.")
KINEMACOLOR
A system of producing kinematographic pictures
in colour, devised by Charles Urban and G.
Albert Smith. Only two colour filters are used,
both in taking the negatives and in projecting
the positives, but the projected pictures exhibit
a remarkable range of intermediate tints, due
partly to the fact that the green filter trEmsmits
a considerable amount of blue hght, the pictures
showing blue sky and water, besides black and
■vyhite, and partly to the laws of persistence of
Kinemacolor
317
KinematograpK
vision relative to colour perception. The
camera resembles the ordinary kinematographic
camera except that it is built to run at twice
the speed, Oius taking thirty-two images per
second instead of sixteen, and that it is fitted
with a rotating colour filter in addition to the
ordinary shutter. This filter is an aluminium
skeleton wheel A having four segments, two
open ones, g and h, one fiUed in with red-
dyed gelatine, e f, and the fourth containing
green-dyed gelatine, a b. The machine is so
geared that exposures are made alternately
through the red gelatine and the green gelatine.
The negative is printed from in the ordinary way,
when the desired variations of tone become
evident in the positive. (See a plate accom-
panying this work.) It will be understood that
there is no colour in the film itself, which, in-
deed, resembles at first sight any ordinary
kinematograph film; the filter is the medium
by which the colour is obtained.
The projecting apparatus is shown at B. As
in the camera, the mechanism is designed to
work a*t double ordinary speed, projecting
B. Kinemacolor Projector
thirty-two images per second, sixteen being
projected through the green segment of the
colour filter A, and the other sixteen through
the red segment. G shows the governing balls
communicating with the safety shutter B,
compelling the latter to drop out of tiie path
of the lantern rays as soon as the film is passing
at a safe speed through the apparatus. The
arrow h indicates the direction of the hght rays
from the iUuminant ; c is a light guard, pre-
venting stray light from passing to the screen ;
D the driving pulley, F the film, and E E safety
jpool boxes.
A special feature in the formation of the
colour filter must now be referred to. Supple-
mentary to the green filter a b (in illustration A)
an overlapping segment of green is filled from
C to D with the object of obtaining balance of
colour, since red is more vivid to lie eye than
green. The size of the supplementary segment,
C D, is a matter of great importance if perfect
results are to be obtained. If it is not large
enough, the yellows will have a greenish hue ;
if it is too wide, the green will be too dense and
the red will be in excess, giving to the yellow
an orange hue. If the red and green filters
have been rightly balanced, the revolving disc
will transmit to the screen a neutral white
" colour."
When taking the negative photographs, the
speed of film through the camera must be
maintained at 2 ft. per second, otherwise the
object, when projected, will appear to move
at an unnatural pace. Assuming a uniform
rate of projection, increased speed of taking
will cause an effect of abnormally slow motion
in the projected pictures ; while if the subject
is taken too slowly, the projected images will
show everything moving too fast. In addition
to this, the too quick operation of the camera
tends to under exposures and excessive vividness
of colours, and too slow operating to over-
exposures and dull results.
Turning now to the operation of the pro-
jecting machine, it will be understood that at
the m.oment when a particular filter is opposite
the optical centre, the monotone image belonging
to that colour will be in the gate of the instru-
ment and be projected upon the screen. The
images following in this order at the high speed
of thirty-two images per second, the combined
effect upon the screen will be a picture reflecting
not only red and green, but also their com-
plementary or accidental colours intermixed
with many other hues resultant from the
blending of the red and green proper. Although
the Kinemacolor system cannot be said to be
absolutely perfect, it is the most successful
system of colour projection combined with
animated effects yet evolved. An ideal process
would be that in which the three primary colours
of the solar spectrum were embraced, taking
the negative images through suitable colour
filters and projecting positive images therefrom
through yeilow, blue and red filters ; but at
present tiie chemical, optical, and mechanical
difficulties of doing this in a way that would
meet conditions inseparable from kinemato-
graphy are insurmountable. Not until the
three requisite images are taken simidtaneously
and from a common optical view-point within
the time-limit of persistence of vision, and the
positives projected under sinular conditions, can
fuUy satisfactory results be expected.
KINEMATOGRAPH
A general outline of the whole process or
manner of taking and projecting kinematograph
pictures must be given to render intelligible a
description of the necessary mechanism. Briefly,
the camera consists of a Ught-tight chamber
fitted at the top with a magazine for holding a
long roll of negative film ; a similar magazine
at the bottom of the chamber for the reception of
the film after exposure ; mechanism for drawing
Kinematograph
318
Kinematograph
the unexposed film from the top magazine, passing
it intermittently past the exposure aperture,
and finally winding it up in the lower magazine ;
and an optical system for projecting the image
upon the film. A negative obtained in this camera
is taken under cover to a dark-room with the
usual ruby illmninatiou ; wound on a frame,
and developed in large tanks. After develop-
ment and washing, the negative is woimd on
;f
c
A. Cam Pin
Movement
B. Maltese Cross
Movement
large drums, provided for the purpose, in
hot-air chambers. When dry, it is put through
■a. contact-printing-machine, in which an un-
exposed film (the positive stock) is placed in
contact with the negative film and the two run
together with the celluloid side of the neg-
ative next to the illuminant and the positive
film behind the negative, both in contact,
gelatine to gelatine. The positive, or so-called
print, is treated in the same manner as the
negative, and dried ou drums or on frames.
When dry the films are ready to be exhibited,
for which purpose projecting machines are
required. All projecting machines in general
use are built on the intermittent principle.
The entire apparatus consists of an arc-lamp
(sometimes a high-power limelight jet), lantern
body, film mechanism, and optical system.
Projecting consists in feeding the mechanism
with a positive film from spools designed for
the purpose, and winding it up as used, the
images being projected upon a screen.
In many of the early kinematograph machines
the film travelled through its requisite path
from spool to spool with a continuous movement,
whilst the optical system was made relatively
stationary by following the motion of the film
and being then brought back to its starting
point with a jerk. In practice this was unsatis-
factory, and it has been superseded by what
is known as the " intermittent movement,"
according to which the film comes to a standstill
for a fraction of a second and is held stationary
during exposure. Three distinct methods are
now in general use, namely, the pin movement,
the dog movement, and the Maltese-cross move-
ment.
The three forms of intermittent movement
will now be referred to. The pin movement
mecharisui is illustrated at A. A shaft E, slotted
at D, and carrying a pin at the top, oscillates
on a fixed point c. The lower end of the
shaft B is pivoted at B to a cam A, which, on
rotation in the direction of the arrow, causes
the pin shaft to rise and fall, and at the same
time to make a forward and backward move-
ment. The dotted line at F indicates the edge
of the film, the alternate open spaces indicating
the perforations. The figure shows the pin
about to enter a perforation. On rotating the
cam A, the pin will enter the perforation, and as
the cam continues to revolve, the pin will pull
down the film the distance of one picture space,
being ultimately released as the revolution of
the cam continues and brought into position
for re-engagement with the film perforation.
In practice, the cam A rotates sixteen times
per second ; hence the film will be moved
sixteen times and as often allowed to remain
stationary.
The Maltese-cross movement is shown at
B. A sprocket-wheel F carries teeth which
engage with the film perforations. Fixed to its
side is a Maltese cross D. A disc B, carrying
on its side a second disc A, and a pin at G, is
made to rotate continuously in the direction
of the arrow. During its motion, the pin G
enters the slot E, and at a certain point begins
to turn the Maltese cross ; the points of the
cross pass into the notch H of disc A and thus
allow the sprocket-wheel to make one quarter
revolution ; then it is brought to a standstill
and held steady by the concave edge 1 coming
opposite to the convex plain edge of disc A.
When disc A has made a complete revolution,
the same action takes place, and so on, on each
comer of the cross.
The dog movement, invented by Demeny,
of Prance, and shown at C, has a disc G, centred
at B, and carrying in a slot, so as to be adjustable,
a semi-circular shaped pin a, which, on each
revolution of the disc, comes into contact with
the film F, drawing this down a distance of one
picture space. The slack film is taken up by
the continuously rotating sprocket-wheel D.
A diagrammatic view of the interior of a kine-
matograph camera is shown at D. The casing
T is divided into three compartments : (i) A
front compartment tr, containing a rotating
shutter N, pin mechanism o P, and other parts
not shown ; (2) a compartment v containing
C. Demeny Dog Movement
the film mechanism and magazines ; (3) and a
compartment on the opposite side containing
further mechanism communicating with the
spools in the magazines, with the sprocket-
wheels and with tiie parts in the front com-
partment. The two magazines A B, consisting
of light-tight boxes, fit into the back portion,
and carry bobbins w x, on which the film
is wound. This apparatus works as follows:
The roll of unexposed film 1, passes out of a
small aperture s} at the comer of the top
Kinematograph
319
Kinematograph
magazine a, round guide rollers c d, engages
by its perforations with the sprocket-wheel F,
to which it is kept in contact by the roller E,
is looped up at h'^, and then takes a, downward
course through the guide groove made in the
gate G ; it passes out at the bottom of the
gate, where it forms a second loop H", and then
D. Diagram of Kinematograph Camera
passes between spring-roller i and sprocket
wheel J, under the guide roller K, and enters
at ff* the bottom magazine B, where it is wound
up on the bobbin x. The sprocket-wheels
rotate continuously, drawing the film from the
supply at I, and taking it up at M ; the motion
of the film in the gate G, however, is intermittent.
During the period of rest, a surplus loop of film,
forms at H^, which is then pulled down through
the gate by the action of the pin o engaging
with the perforations. The whole mechanism
is so arranged and geared together that, just
as the film is stationary, an open sector of the
rotating shutter N comes opposite the lens and
film aperture at R. Likewise, just as the film is
making its intermittent move downwards, an
opaque sector of the shutter v comes opposite
the lens, so that being thus under cover, it is
saved from being fogged. Through the centre
of the camera and opposite the lens, a long
tube Y extends, with a detachable cap at s.
This tube forms the sight hole for purposes of
inspecting the image upon the fflm prior to
exposure. The gate G is a kind of hinged door
with an aperture in it, and its function is to
keep the film flat and vertical during exposure,
and also to act as a channel or guide. After
taking a subject, the operator presses a button,
and in so doing punches a hole in the film, at a
point just above the gate, this enabling him
to determine where one subject ends and another
begins.
Each individual photograph requires an
exposure of from •j'ijth to •rlo^ °^ ^ second,
the shorter the exposure the better, provided
there is sufficient light to produce a well-exposed
negative. The lens must give really excellent
definition. A slight lack of sharpness caused
by movement of the object during exposure
will not seriously injure the efiect, but the
stationary surroimdings repeated in the succes-
sive pictures must be sharp. Rapidity in the
lens is also a matter of importance ; //6 or
thereabouts is sufficient for most purposes, and
at times //8 or even f/11 can be used. The
focal length will be short, so that the attendant
defect of great rapidity, namely, lack of depth
of definition, is not of great importance. The
lens that is generally employed has a focal length
varying from i^ in. to 4 in.
The lens that has been employed for taking
the photograph is frequently used for its pro-
jection upon the lantern screen ; this is a
mistake, for a lens with the largest possible
aperture, at least f/4, and better //3, of the
Petzval form should be used for projection,
unless the lens is of more than 4-in. focus, in
which case it is not of so much importance.
Projecting machines vary as regards type and
method of translation of the ISlm, but all of them
work on the intermittent principle. The film
is brought to a dead standstill sixteen times per
second, whilst within the same space of time
it is also moved forward in a vertical direction
downwards sixteen times ; this movement is
accomplished at the moments when the opaque
sector of the rotary shutter is opposite the optical
system. The essential parts of a kinemato-
graph projector are shown at E, the main
support and the gearing mechanism being
omitted. A and B are the two spools to carry
the film before and after passing through the
machine, the top one being the feed-spool and
the bottom one the take-up spool. An upper
and lower sprocket-wheel c and D engage with the
perforations of the film F. The latter passes
from A, between sprocket c and spring pressure
rollers E G, forms a loop at j, passes through
gate K, past the exposure aperture i,, goes under
the dog M, between sprocket-wheel D and
pressure spring rollers H I, and finally to the
take-up spool B. Sprockets c and D work in
E, Diagram of Kinematograph Projector
unison. A surplus loop of film is provided at
J, as in the camera already described. The
top spool A rotates by reason of the pull made
on the film and is free to revolve accordingly.
The lower spool B is turned continuously by
a slip-belt, so that the film is tightly wound
thereon, as it comes from the sprocket d ; the
sUp-belt compensates for the constantly increas-
ing size of the roll of film on b. The gate K
Kinematograph Book Pictures 320
Kinematography
has springs and pressure pads which hold the
film steady after its downward motion ; and
the channel through which it travels is recessed,
contact only obtaining at the edges where the
perforations are. The gate turns on hinges
after the manner of a door, in order to facilitate
insertion and threading of the film, being
fastened by a catch and held by a spring. A
revolving disc With open sector constitutes the
shutter o, which is geared in such a, manner
that the open portion arrives opposite the
exposure aperture and optical system just at
that moment when the film is brought to rest.
Finally, a safety drop shutter p is situated
between the gate and condenser R, its rise and
fall being controlled by the governor Q. The
governor does not allow of the shutter rising
till the mechanism, is ruiming at the rate of
showing sixteen pictures per second, at wliich
speed it is safe to allow the emission of the
lantern rays through the celluloid film. The
objective lens for throwing the image upon the
screen is at s, between the gate and the rotary
shutter. The lantern situated immediately
behind the condensing lenses R contains the
necessary source of illumination, an electric
arc-lamp, the carbon pencils v w of which
create the arc at tj, at which point also a crater
forms exactly in a line with the centre or axis of
the optical system ; or a Hmehght jet can be used.
The film is threaded through the projecting
machine with the gelatine surface turned
towards the condenser, and with the pictures
inverted. If on projection it is found that
the halves of two pictures appear on the screen,
the pressure rollers H i are raised, and the
film lifted forward till the sprocket teeth
engage with two perforations in advance of
its previous position. Another way is to raise
or lower the gate k by means of the pinion
and rackwork provided for the purpose, but
the picture is not then always exactiy opposite
the centre of the optical system. Equally
important, in order to get the picture as steady
and life-like as possible, is that the handle
should be turned with the greatest regularity
and at the rate of two revolutions per second.
{See also " Kammatograph," " Kinemacolor,"
and other headings.)
KINEMATOGRAPH PICTURES IN BOOK
FORM
The fundamental principle of the kinemato-
graph picture is based on the fact that if a series
of complementary images be presented to the
eye in such a manner as to satisfy the laws of
persistence of vision, these images wiU combine
and thus produce the illusion of a single impres-
sion. Fivrther, if each image or picture in such
a series be shghtiy different, according to the
changes presented by a moving object, the com-
plete scene will have the semblance of life.
These conditions are fulfilled in a primitive way
by depicting on successive leaves of a book the
phases of the subject it is intended to present,
and then allowing the leaves to escape rapidly
in succession.
KINEMATOGRAPHY
The art of photographing objects in motion
and projecting the images upon a screen. It
derives its origin from a toy called the " zoe trope "
and depends for its resiUts on what is known
as " persistence of vision." When light is
reflected from a moving object it forms an
image on the retina (or sensitive plate) of the
eye, and creates a nerve current which passes
along every one of the fibres which receive the
image and collectively carry the impression
through the optical nerve to the brain. This
sensation may be divided into four periods :
First, a latent period which is almost instan-
taneous, and during which nothing seems to
happen ; second, a very short period, estimated
at less than yj^th of a second, during which
the sensation reaches the maximum ; third,
a much longer period, ^th to ^th of a second
(varying according to the power of illumination)
during which the sensation slowly diminishes ;
and, fourth, a short period of decline, during
which the efiect dies away. It is found that
in the case of a moving object on which attention
is directed the fourth period remains unnoticed,
owing to the fact that a new image takes up
the place of the old one before that period
begins. Prof. Tindall estimated the time of
persistence of an impression on the retina to
A. Skeleton Drum for
Drying Film
B. Frame for
Negative Film
be T^gth of a second, that is, the impression
remains for ^^th of a second after the source
of excitation is removed. Upon this all kine-
matograph apparatus is based.
The kinematograph camera and projecting
apparatus are described under the heading
" Kinematograph."
The three chief requisites to final success are :
(i) A photographic emulsion suflScieutly sensitive
to receive latent impressions at the rate of
sixteen per second ; (2) optical systems capable
of forming the negative images in the camera and
the positive image upon the lantern screen ;
and (3) mechanical means for suitably trans-
lating the films through the camera and after-
wards through the projector.
The emulsion is supported on celluloid cut
into ribbons if in. wide, and in lengths of about
150 ft. The inner portion of the surface, i in.
in width, is devoted to the pictures, the margins
being used for the perforations by means of
which the film is held in position during its
progress through the camera or projector.
Each image is i in. wide, and f in. high, there
being sixteen pictures to i ft., and four per-
forations on each side per picture. Slightly
thicker celluloid is used for the positive film
than for the negative, the former being sub-
jected to more wear and tear than the latter.
Having decided on the type of camera to be
Kinematography
321
Kinocyanine
employed and the make of negative stock film
to be used, the operator may proceed to work
much in the same way as he might when taking
ordinary snap-shot photographs in an ordinary
magazine film camera. The negative stock
film can be obtained in rolls of 1 50 ft. in length,
ready perforated, and supplied in sealed tins,
in whidi it is wrapped in lead sheets and light-
tight paper. The magazines A B (see D, p. 319)
are detached, and the unexposed film opened in
the dark-room, with ruby light, and placed in
magazine A, the centre of the roll being slipped
over the bobbin w. The starting end of the
film is drawn through the small aperture at the
comer of the magazine, and the hd secured.
The short length of the film projecting at the
comer serves as lead film to facilitate drawing
out, when it is desired to thread through the
camera mechanism just before actual operations.
When about to make the exposures, the side of
the camera is opened and the film threaded as
indicated at D (p. 319), taking care to arrange for
the loop at h^ and at H'. The bobbin x has a
dip wmch holds the end of the film securely.
The Ud of the magazine B is, of course, removed
during these operations, and the length of film
extending from c is imavoidably fogged. The
operating handle of the camera should be
turned a few times in order to make sure that
everything is working properly ; then the lid
of B and the side of the camera may be closed.
It now remains to see that the picture is sharply
focused and, to do this, the handle should again
be turned so as to bring an unexposed portion
of the film opposite the exposure aperture R,
and at the same time cause an open section of
the shutter N to arrive in a. line with the lens.
By removing the cap S from the sight tube Y,
the operator may now have a view of the image
on the film. If a focusing scale is provided
on the lens itself, this operation is, of course,
unnecessary ; a separate view finder is provided
on the camera. See that the cap s is replaced.
The handle must be turned at the requisite
speed, and as the mechanism is generally geared
to make eight exposures for each complete
turn of the handle, two turns should be made
per second. Too fast camera operating will
result in abnormally slow motion of objects in
the projected picture, and vice versa. The
most important point is the question of steadi-
ness, for if the camera has been allowed to
vibrate during the work of turning the handle,
no afterwork can rectify such an error. Manu-
facturers supply very rigid and somewhat heavy
stands for the camera. The screw holding the
camera to the stand should be very tightly fas-
tened. (See also " Theatrical and Kmematograph
Photography.")
Development of kinematograph films is carried
out in precisely the same way as that of ordinary
film negatives ; but some special appliances
are necessary. The frame B is one. The pins
top and bottom serve to hold the film in place,
it being wound in spiral fashion and secured
at each end by clips or drawing-pins. The
emulsion side is turned outwards, so that only
the celluloid surface comes into contact with
the frame. A tank sufficiently large to take the
frame is provided for the developer, another
for the fimng solution, and a third for washing
21
purposes. The latter is furnished with a siphon
overflow so that proper circulation of the water
is secured ; a tap provides a constant supply
of fresh water at one end of the tank, the
overflow siphon being situated at the opposite
end. The washed film is wound on a skeleton
drum A in spiral fashion, and placed in a warm
room free from dust, and kept rotating for
fifteen minutes. When the emulsion is
thoroughly dry, the cleaning process is carried
out, all finger marks being poUshed oflE from
the celluloid side by means of a pad of soft
material fixed to a bench over which the gelatine
surface may pass vnthout injury. A hole cut
in the bench, through which the light of an
incandescent electric lamp is directed upwards,
enables the cleaner to detect smears and other
marks. The film is wound up into coils by
means of special winders.
The positive film is made by contact printing
from the negative. Special machines are pro-
vided for the purpose, in which the action of
the mechanism is approximately the same as
that in the camera. Exposed positive stock
is developed, fixed, washed and cleaned in the
same manner as the negative.
If through accident a subject becomes broken
in the middle, cutting out should be done so
that when the two ends are rejoined, pictirres
follow on consecutively as before the accident.
The ragged part of one end should be cut away
exactly at the juncture of two pictures, and
the end to be joined thereto should have an
|th portion of a picture left on. The gelatine
on this -Jth part should be removed, leaving
the bare celluloid exposed. PUm cement is
then applied with a brush to the scraped-off
portion, and this is quickly laid against the
celluloid backing of the piece to be joined,
firmly pressed, and allowed to dry. The cement
dries within a few seconds after application.
See that the perforations on the overlapping
portions of the film exactly register. The
blank spacing of film subjects is a source of
many troubles if not correctly carried out. There
are four perforations each edge to each picture
and any length of blank film joined between
succeeding subjects should correspond in length
to a. given number of complete pictures ; other-
wise, it will be necessary to make an adjustment
in the machine when projecting.
KINETOSCOPE
Edison's apparatus for exhibiting his " kine-
tographs," pictures on a continuous band of
film h'ghted by an electric lamp behind them.
KINOCYANINE
A developing agent discovered in 1891 by
Noel, a French chemist, whilst preparing kyanol
or bleu de Paris ; so called because of its
similarity to vegetable cyanine and quinone.
CjjHjjCio. It takes the form of an amorphous
powder or ill-defined small crystals of n bluish
violet with grey tinge. The original formula is :
Sodium sulphite
50 parts
Sodium hydrate
I part
Sodium carbonate
. 140 parts
Kinocyanine
. ID „
Water
. 1,000 „
Kite Photography
322
Kruss Camera
KITE PHOTOGRAPHY (Fr., La photographie
par cerf-volant : Ger., Drachenphoto-
graphie)
Photography by means of a camera attached
to, or suspended from, a kite is of frequent use
in obtaining bird's-eye views for military pur-
poses, and as an aid to the surveyor and meteor-
ologist. A. Batut, of Eulaure, Prance, was the
first to devote special attention to this class of
work. In 1887 he employed a large diamond-
shaped kite, as illustrated, having a long tail to
give stability. The camera A was fastened to
the kite by a triangular support, and had a
shutter B of the gmllotine type, working hori-
zontally by means of two rubber bands. The
shutter was held in tension by a thread, which
was burnt through by a slow fuse C, ignited
before flying the kite. In its passage across the
lens the shutter was made to release a paper
streamer, thus announcing that the exposure
had taken place. Flat fflms Were used. To
prevent obstruction of the view by the cord,
this was attached by a kind of double bridle to
Camera attached to Kite
a bar D. A self-registering barometer E indi-
cated the height attained.
E. Wenz, in Germany, used shortly afterwards
a kite of similar shape, but with the camera
fastened to the bridle cords. Since then, kite
cameras of a much more elaborate kind have been
employed. As an example may be mentioned
one made in 1899 by L. Gaumont, of Paris, for
the use of A. I^awrence Rotch, of the Blue Hill
Meteorological Observatory, near Boston, Massa-
chusetts. While primarily intended for photo-
graphing the under surface of clouds, this could
be employed also for obtaining views of the
surrounding country. Clockwork allowed of
successive exposures on a roll of film at pre-
determined intervals. Electric releases and
simple cord releases operated from the ground
have also been used.
The kite employed for photographic purposes
must be steady in the air, the box kite and the
multicellular obHque type being now preferred
to the older pattern. The camera, which should
be as light as possible, and of the fixed-focus
box-form variety, carrying films, is now usually
attached to, or hung from, the cord. A simple
method of making the exposure, suitable for
experimental use, is as follows : A rubber band,
one end of which is fastened to a small staple,
is stretched over the trigger release of the
shutter, and the latter is set back against the
pull of the rubber by a thread tied to another
staple as far away from the lens as possible. A
sufficient length of ordinary wool soaked in a
strong solution of potassium nitrate and dried
is then tied to the further end of the thread,
and ignited when the kite is ready to be flown.
The slowly-burning fuse will eventually sever the
thread, and thus enable the rubber band to work
the trigger release of the shutter.
KLIC PROCESS
The process of photogravure (which see) as
invented by Karl Klic, of Vienna.
KNIFE, RETOUCHING
A small knife of any convenient shape used for
reducing the over-dense parts of a negative by
cutting or scraping, for which purpose the film
must be bone-dry and the hght particularly
good. The work must be done gently.
KNIFE, TRIMMING {See "Trimming Prints.")
KODAK
A trade name which is so familiar that many
suppose it to apply to all hand cameras, although,
as a matter of fact, the Comrts decided in 1903
that it is the registered property of one particular
company.
KOENIG'S COLOUR PROCESS (See " Pina-
chromy.")
KROHNKE'S INTENSIFIER
A method of intensification without mercury,
advocated by Herr Krohnke. The negative is
made yellow in a -3 per cent, solution of iodine
and potassium iodide in water, washed, and made
brown by flooding with a solution of Schlippe's
salt, 15 grs. ; caustic soda (10 per cent, solution),
2 to 3 drops ; and water 3J oz. Finally, the
negative is washed and dried, the process being
claimed to give clear shadows and to remove
entirely any yellow stain.
KROMAZ
The viewing instrument used in connection
with a process of stereoscopic colour photography
invented by Barnard and Gowenlock, in which
different colours were viewed by each eye.
KROMOGRAM
A name given to the transparencies used in
the Ives Kromskop.
KROMSKOP
The name given to two forms of apparatus
invented by Frederick Ives for projecting photo-
graphs in natural colours. Three shdes taken
through certain filters are simultaneously pro-
jected to give the effect of a single picture, there
being for each sUde a colour filter, respectively
red, green, and blue-violet.
KRUSS CAMERA (See "Magic Camera.")
LABARRAQUE'S SOLUTION
Another name for " eau de Javelle " {which see).
LABELLING BOTTLES
Special care is necessary in labelling bottles
that are to contain photographic chemicals.
First make the outside of the bottle per-
fectly clean and dry ; use gummed labels, or
attach by means of liquid gum, and smooth
into close contact. When quite dry, write on
the label with ordinary or waterproof ink, or
even with pencil, which is more permanent than
some inks. Coat, when dry, with size made by
dissolving J oz. of common glue in 2^ oz. of water,
and when this is dry apply a thin coat of oak or
hard carriage varnish. A label varnish much
used in laboratories, etc., is the following : —
Sandarac
2^ oz.
78 ,g.
Mastic .
I „
31 „
Camphor
24 grs.
i'5 „
Oil of lavender
3i drms.
12'25 CCS
Turpentine
2
7 ..
Ether .
3
10-5 ,,
Alcohol .
2^ oz.
8-75 »
Macerate for several weeks, agitating until
dissolved.
A less efficient method is to attach the paper
label in the usual way, warm it, and smear with
wax by rubbing with the end of a candle.
Another plan is to coat the attached label with
celluloid varnish, made by dissolving celluloid
(old films will serve if the gelatine is cleaned off)
in acetone, amyl-acetate, or methylated spirit.
The bottle itself may be written upon, using
one of the inks given under the heading " Ink
for Glass, Porcelain, etc."
There are many special recipes for pastes for
attaching labels to chemical bottles. Caustic
soda and nitric acid are sometimes included with
the object of breaking up the starch granules, and
alum and sugar to increase the adhesive proper-
ties. One of the best of the many formulae is : —
Wheat flour .
Powdered alum
Cold water
Formaline
2 oz. 220 g.
160 grs. 37 „
10 oz. 1,000 CCS.
40 drops 8-5 „
Mix the first three ingredients together, boil
in an enamelled saucepan, and when cold stir in
the formaline.
In America it is common to label flat bottles
in the following way. A strip of glass is cut ^ in.
narrower than the fiat side of the bottle, and the
paper label should be about f in. smaller than
the glass strip. The written side of the label is
pasted to the glass strip, the edges of which are
then smoothed. Both bottle and strip are then
wanned, and the two attached together with a
cement made by melting i part of beeswax with
3 parts of resin.
Names may be etched on bottles and the etch-
ing left plain or fiUed with Brunswick black or
other pigment. Mix up the two following solu-
tions : — (i) Sodium fluoride, 36 grs. ; potassium
sulphate, 7 grs. ; distilled water, 2 oz. (2) Zinc
.chloride, 14 grs. ; hydrochloric acid, 65 drops ;
distilled water, i oz. Mix the two solutions and
write on the bottles with a quill or camel-hair
brush ; leave for about five minutes and then
wash ofi.
LABELLING TINS
It is more difficult to attach paper labels to
tins than to bottles. A plan that is often recom-
mended is to gum the label in the usual way,
but before attaching it to rub the part of the
tin where the label is to go with a piece of freshly
cut onion. Another method is to use a piece of
fixed P.O. P. ; write on the plain side and then
wet the gelatine surface and place in contact
with the tin. It is desirable to use waterproof
ink and to varnish the labels.
LABELS, POLYGLOT
These are a convenience to the travelling photo-
grapher, but hardly a necessity, as English or
French inscriptions are sufficient for the Customs
authorities practically all over the world. The
following is a polyglot label for a box of dry
plates, the only photographic materiEd that there
should be the slightest desire to label in this
way : —
English — Photographic Plates. Sensitive
to light. France and Belgium. — Plaques
Photographiques. Craint la lumi^e. Ger-
many and Austria. — Trockenplatten. Nur
bei rothem I<icht zu offnen. Holland. —
Droge Platen. Slechts in sene donkere kamer
te openen. Denmark. — ^Torreplader. Maa
kun aabnesi morkkammaret. Norway. —
Fotografiplader. Maa kun aabnes vid
rothlys. Sweden. — Torrplatar. Oppnasend-
ast i morktrum. Finland. — Walokuvaus-
levyja. Saapi avata ainoastaan pimeassa
huoueessa. Italy. — Lastre Fotografiche.
Teme la luce. Spain. — Placas Fotograficas.
No abrir sino en el cuarto oscuro. Portugal.
— Chapas Photographicas. So' se deve abrir
n'um quarto escuro.
LABELS, WATERPROOF INK FOR
Dissolve in 2 oz. of hot water i oz. of borax,
add i oz. of shellac, and simmer gently until as
much of it as possible has dissolved. When cool,
decant the clear liquid and mix with Indian ink
or finely powdered lampblack to a suitable con-
sistency.
LAC (See " Gums and Resins.")
LACMUS (See "Litmus.")
323
Lactic Acid
324
Landscape Photography
LACTIC ACID (Pr., Acide lactique : Ger.,
Milchsdure)
CjH.O, or CHsCH(OH)COOH. Molecular
weight, 90. Miscible in all proportions with
water and alcohol. A colourless, thick liquid,
obtained from sugar by the lactic ferment, and
used in the platinum toning bath.
LAMBERTYPE
A carbon print with an enamelled surface.
A glass plate is polished with a solution of 5 grs.
of beeswax in i oz. of benzole and is then coated
with enamel collodion and dried. The exposed
carbon tissue is squeegeed on the plate, developed
in the usual way, and the final support for the
tissue is squeegeed into contact. When quite
dry the collodion-supported image is detached
from the glass.
LAMPLIGHT EFFECTS
Lamplight scenes which do not include
figures present no difficulty, providing a suffi-
ciently long exposure can be given. Out-of-door
lamplight effects are described under the heading
" Night Photography." Indoor lamphght effects,
with figures, may be obtained by concealing a
piece of magnesium wire in the lamp, which is
preferably provided with a globe or shade, or
by having the magnesium in such a position as
to give the effect of the light coming from the
lamp, as described in the article, " Caudle-Hght
Effects."
Daylight can also be used, and the following
is H. Bssenhigh Corke's method. An imitation
or dummy lamp is used. First, a real lamp,
alight, is photographed and the image enlarged
to the same size as the lamp. The enlarge-
ment is mounted on cardboard, which is then
cut to the outline and a strut placed at the
back. The dummy lamp can be placed any-
where in the scene, and in the finished photo-
graph cannot be told from a genuine lamp. The
lamp and sitter are arranged near a window, of
which all except a small space is blocked up in
such a way that a strong light appears to come
from the lamp and fall upon the sitter, the light
tones graduating into darker ones on parts of the
drapery and surroundings. The " lamp," being
of thin cardboard, does not throw a perceptible
shadow ; but a certain amount of hght must fall
upon its face, in order that the details may be
shown. It may be necessary to use reflectors, as in
ordinary portraiture. For lamplight effects it is
more natural to retain almost all the shadow de-
tail, and not, as in firelight effects, regard only the
high lights and half-tones. Exposure will vary,
and must be a matter for experiment. The
prints should be stained with an orange-colouied
dye, such as eosine and methyl-orange aniline
colours, or carbon prints on a suitably coloured
support may be made.
LAMPS, ARC (See "Arc Lamps" and
"Electric Light.")
LAMPS, DARK-ROOM (See "Dark-room
Lamp.")
LAMPS, MAGNESIUM (See "Flash Lamp.")
LAMPS, SPIRIT (See "Spirit Lamps.")
LANDSCAPE, CLOUDS IN
Clouds in landscape photographs not only
fill a space that might otherwise be blank, but
they form an essential element in completing a
picture, in its composition, and its balance of
light and shade. Careful attention must be
given to the depth or general tone of the sky,
and also to the intensity or contrast in the
clouds themselves. Clouds may appear briV
liant to the eye, but it must be recognised that
their scale of tones is short when compared
with that of the landscape. When clouds are
included successfully on the same plate as the
landscape, their depth of tone may be made to
harmonise with the landscape by the methods
given under the headings " Harmonising Con-
trasts " and " Control in Printing." When they
are printed in from a separate negative (see
" Douds, Printing in"), the depth of printing
can be controlled so that they may still ap^ar
to be in harmony with the tones of the landscape.
A common fault is the rendering of clouds much
too strongly, in tones that are too heavy or too
brilliant for the picture. The forms of the clouds
and their grouping are frequently of the greatest
value in completing the composition of a picture,
especially in simple subjects that consist of a
few well-defined masses, and have, in addition,
a large proportion of sky. The masses of cloud
may form a line that wiU balance or harmonise
with the principal hues in the picture, or the
clouds may be so grouped that their principal
points or lights may balance the chief point of
interest in the landscape.
LANDSCAPE, FIGURES IN
in Landscapes.")
(See "Figures
LANDSCAPE LENS (See "Lens.")
LANDSCAPE PHOTOGRAPHY
In modem landscape photography the hand
camera has naturally taken a very prominent
place, but it must be recognised that the best
work in landscape photography results from
studying and arranging the picture on the
focusing screen, this generally involving the use
of a stand. As on many occasions good subjects,
can be obtained when the use of a stand and the
deUberate arrangement of the picture are im-
practicable, a " hand or stand " camera is the
most convenient for landscape work. At times,
a picture may be studied on the focusing screen,
the best point of view selected, and then the
exposure made when all the conditions are
favourable by holding the camera in the hand.
This method is specially applicable to village
scenes, and occasionally to landscapes with
animals.
For general landscape photography the camera
should have a rising front, a swing back, and
should be capable of extending to twice the
length of the plate. In all positions it should
be quite firm and rigid. The tripod should be
firm and capable of adjustment to any height
from 3 to 5 ft. The lens should preferably be a
modem anastigmat with a full aperture of //8 ;
this wiU cover the plate with imiform sharpness
without reducing liie aperture, and at //i i the
rising front may be used to a considerable extent
without loss of definition. The best proportion
Landscape Photography
32s
Lantern Slides
of focal length is about i J times the longer side
of the plate, this giving good perspective effect
■without unduly dwarfing the distance. A lens
of longer focus prevents many subjects from being
composed satisfactorily, owing to various ob-
stacles making it impossible to take a point of
view suffidentiy far from the principal part of
the subject to secure a satisfactory proportion ;
while a lens of short focus has a tendency to
exaggerate the difference between the near and
distant parts of the picture. At times, however,
a wide-angle lens having a focus a little shorter
than the longer side of the plate is very useful,
especially when the subject includes tall trees or
high buildings and the space is limited. The
shutter should be of the " time and instan-
taneous " pattern ; and it is desirable that all
exposures of less than five seconds' duration
should be made by the shutter rather than by
the cap. It is difficult to make a short exposure
by means of the cap in brilliant sunshine with-
out causing slight fog through the sun striking
the photographer's hand, and being reflected
into the lens when removing or replacing the
cap ; with a shutter there is no sudi risk. At
times, too, the wind is very troublesome, and
it is necessary to wait patiently for foliage to
be reasonably still, even for an exposure of one
second. With a shutter provided with a pneu-
matic or an Antinous release, the photographer
can watch the moving foliage carefully, and as
soon as the conditions are favourable for making
the exposure he can press the bulb without
turning or giving any attention to the camera.
By pressing and releasing the bulb of a shutter
set for " time " as quickly as possible, an
exposure of a quarter of a second can be given,
this allowing of photographing figures in the
mid-distance, moving slowly towards the camera,
without showing movement. The plates used
should be rapid, and be backed.
It is in the selection, the arrangement and the
method of treatment of a subject that the
photographer shows his individuality. A feeling
for composition is essential for successful land-
scape photography. The necessity for composi-
tion arises from the fact that the photographer
takes a small portion of the landscape and
encloses that portion in an artificial boundary
composed of four lines forming a. rectangle. It
is essential that the small fragment of the land-
scape should convey the impression that the
photographer desired to express, and one of the
first conditions is that attention should be
drawn from the boundary lines and into the
picture towards the principal part of the subject.
Every picture should consist of foreground,
mid-distance and distance, the principal object
or point of interest being in the near mid-
distance. This wiU naturSly demand primary
attention, but the foreground requires almost
as much. Most landscape photographers pay
too Uttle attention to the foregrounds of their
pictures, thereby sacrificing much of their
quality. In the foreground the gradations of
light and shade are much more strongly rendered
than in any other plane ; and this strength has
very great value in giving the effect of atmos-
phere and in causing the other planes to recede
and take their correct position.
In selecting the point of view, it should be
remembered that the lower the point of sight
the more the foregrotmd is shortened, and small
foreground objects appear more important ;
while a very high point of view wiU frequently
give the impression of the ground running uphill.
Reducing the aperture of the lens becomes
necessary in almost all landscape photography
to secure sufficient sharpness of defmition in the
various planes. The nearer the foreground to
the camera, the smaller will be the stop necessary ;
but the shorter the focus of the lens, the greater
will be the range of distances that can be
rendered sharply with a given value of stop.
Sunshine is very effective in most landscape
work, especially when striJdng shadows break
up an uninteresting foreground, or cause unequal
lighting of the important and unimportant parts
of a subject. pSrequently, an oblique light —
strong sunshine almost at right angles to the
direction of the view — is very impressive.
LANGE'S DEVELOPER
The " washing soda " or " dry pyro " deve-
loper once popular ; recommended by Paul
Lange, of Liverpool, in 1890, for developing
" snapshots " taken on ordinary plates. It is
still a favourite amongst many photographers,
who have no objection to yellowish negatives,
and who prefer to add dry pyro at the time of
use. The formula is : —
Washing soda
2^ OZ.
137-5 g-
Potass, bromide
. 25 grs.
3 ,.
Water (boiling)
. 20 OZ.
1,000 CCS.
For developing a quarter-plate, to f oz. of
above, add i^ oz. water, and 2 to 4 grs. of pyro,
according to density required.
LANTERN
By this term is nearly always meant the
optical or projecting lantern, for which, see
"Enlarging Lantern" and "Optical Lantern."
For the opaque lantern, see " Aphengescope."
Many dark-room lamps are actually lanterns.
LANTERN PLATES
Specially prepared plates used for making
lantern slides, and much slower than those used
for negative work. In their manufacture the
one object in view is their capacity for producing
a clean and sparkling image of good gradation,
with a very transparent character of the deposit
of silver. The British standard size is 3J in.
by 3i in. ; American and Continental, 4 in. by
3J in. But in both cases the slide is usually
masked to give an image not exceeding 3 in.
by 3 in.
There are two distinct kinds of lantern plates :
(i) ordinary, for contact printing by artificial
light and for reduction in the camera by day-
hght or artificial light ; and (2) " gaslight," for
contact printing only. The former must be
manipulated in the dark-room illuminated as for
bromide paper ; the latter may be developed,
etc., in weak white light, the same as gaslight
paper. For details of working, see " Lantern
Shdes."
LANTERN SLIDES
Transparent positives, for projecting by
means of the optical lantern, are made in England
Lantern Slides
326
Lantern Slides
to a standard size of 3J in. square. Specially
prepared slow plates are used, the object being
to secure a fine transparent quality in the image,
combined with good rendering of gradation and
cleanliness in working. A good slide should be
very transparent ; that is, there should be an
absence of any tendency towards clogging or
opaque appearance ; the deepest shadows should
be strong so as to give a ri<i colour when pro-
jected. There should be scarcely any part abso-
lutely white or free from deposit, and the range
of gradation should be as perfect as possible,
with full detail in both light tones and shadows.
Plates of two kinds are used. One corresponds
in speed and character with the papers used for
developing in weak gaslight, while the other is
similar to a slow bromide paper in speed, but
differs materially in character. The first kind
will be considered later. For the second kind a
yellow light is the most satisfactory when deve-
loping, etc., and there is a wide range in speed,
the faster varieties yielding black tones only,
while the slower ones give readily any tone
from warnx brown to black by simple modifica-
tions in exposure and development. These
plates are sufficiently rapid for producing slides
by reduction in the camera by daylight or arti-
ficial light, using a condenser in the latter case ;
or they may be employed with equal facility for
contact printing by artificial light. An ordinary
camera is employed for making slides by re-
duction in daylight.
Any adjustable camera may be used, provided
that it is not smaller than 3j- in. square. There
must be a frame to hold the negative parallel
with the sensitive plate, and at a suitable distance
in front of the lens. In adjusting the distances
of the various parts of the apparatus, the same
proportion of the focal length of the lens will be
required as in enlarging, but with this differ-
ence : the greater distance will be that between
the lens and the negative ; the smaller, the dis-
tance from the lens to the sensitive plate on
which the image is produced. The space be-
tween the lens and the negative must be covered
in so as to exclude as much extraneous light as
possible, or the slides will suffer considerably,
both in gradation and brilliancy. The apparatus
should be pointed towards a window, preferably
one that commands a clear sky view, in the same
manner as in enlarging by daylight.
In making slides by reduction in an artificial
light enlarging apparatus, the only difference in
setting will be the distance from the lens to the
easel and the extension of the camera body, these
distances being the same proportion of the focus
of the lens as in enlarging by daylight. With some
enlarging lanterns in which the source of light
is an incandescent gas mantle there is much
greater risk of an image of the mantle being pro-
jected on to the easel in reducing for sMde making
than in enlarging. This can be entirely pre-
vented by interposing a piece of ground glass
between the condenser and the light.
Definite data for exposures cannot be given.
With the slowest of the plates suitable for camera
reduction, the exposure may range from fifteen
seconds on a clear spring day, using //16, and a
thin negative, when working for black tones, up
to as much as eight times as long for warm
colours. Strong negatives will require much
longer, and some of the more rapid plates will be
fully exposed with one-fourth of these times.
For artificial Ught, as described, these exposures
would be correct if //8 were the lens aperture
used.
For contact printing, magnesium ribbon forms
the best illuminant, especiaUy when warm colours
are desired. The colour and quality of the light
influence the colour produced by development.
For black tones, i in. of ribbon at a distance of
6 ft. will be sufficient for a medium or thin nega-
tive, or 4 in. at 3 ft. will yield a good warm tone.
The colour of the image depends on two
factors, exposure and development. The mini-
mum exposure that will produce a well-graded
image with sufficient strength in the shadows
and full detail without any mass of clear glass
in the high lights is that which must be given
for pure neutral black tones. For a warm black,
the exposure must be doubled, and for various
tones of brown, deep or rich, from four to eight
times the minimum exposure will be necessary.
The exposure may be increased even beyond this
with some plates, very warm brown and red-
brown colours being obtained by increasing
the exposure up to sixteen times the minimum.
For neutral black tones any of the developers
given for bromide printing will give the best
result. For warm black and brown, pyro and
soda win give excellent transparency and
quality. Potassium bromide will be found the
best restrainer. Most of the additions suggested
by some photographers for obtaining warm
tones clog the shadows and produce a semir
opaque deposit that spoils the efEect of a. slide
when projected. Potassiimi bromide added
liberally wUl produce the same degree of warmth
combined with great transparency and fineness
of quality. Other developers may be used in-
stead of pyro by adding potassium bromide in
the same way.
The following are typical formulae, the deve-
loper being prepared from the usual stock solu-
tions : —
For deep brown tones —
Pyro . . 15 grs. 3-5 g.
Potassium bromide 7^ „ 1-75 „
Sodium carbonate 60-120 ,, 14-28 „
Sodium sulphite 60-120 ,, 14-28 ,,
Water . . 10 oz. i,OQO ccs.
For rich brown tones —
Pyro . . 15 grs. 3-5 g.
Potassium bromide 15-30 „ 3'S-7 „
Sodium carbonate 60-120 „ 14-28 „
Sodium sulphite 60-120 ,, 14-28 „
Water . . 10 oz. 1,000 ccs.
Begin with a small quantity of the sodium car-
bonate solution, increasing to the larger amount
if necessary. Development wiU take from six
to twelve minutes. If the development is begun
in the more highly restrained solution, and the
exposure should prove to be insufficient, the plate
may be transferred to the less restrained, and a
good slide should result ; and, if development is
begun with a small quantity of sodium carbonate,
and this should prove insufficient, adding more
will not detract from the quality of the slide, but
will modify the colour. This method of working
allows very great latitude in exposing, as the
Lantern Slides, Diagrammatic 3^7 Lantern Slides, Masking, etc.
development may be modified, duriag its pro-
gress, to suit the exposure.
After development, the plate should be washed
in two or three changes of water and then fixed,
preferably in an acid " hypo " bath containing
I oz. of potassium metabisidphite to i lb. of
" hypo," diluted so that i pint of solution will
contain 3 oz. of " hypo." The plates should
remain in the fixing bath for ten or twelve
minutes. The developer for use with plates
that are developed in weak gaslight is the same
as that given for gaslight papers. Restraining
by means of bromide may be adopted for secur-
ing warm tones. The same pyro developer
may be used, or an equally large proportion of
bromide may be added to an amidol or other
developer. With these plates a longer range of
tones may be secured, a good red and red-brown
being easily obtained by increase of exposure
and restraining. The image produced on these
plates is exceptionally transparent and fine in
grain. Even when strong, the image presents
the appearance of a stain rather than a deposit.
The clearing of lantern sUdes should be
unnecessary, if an acid fixing bath is used;
otherwise proceed as explained for negatives
under the heading "Clearing Solutions."
LANTERN SLIDES, DIAGRAMMATIC
I,antem sUdes of diagrams and other line sub-
jects may be made in many ways, as, for example,
the following : (a) Copying through the camera
and printing the slide by contact from the nega-
tive ; (6) printing from the drawing itself, which
serves as a negative ; and (c) the use of specially
prepared glasses on which the diagrams may be
drawn direct and serve as slides.
(a) The copying of the diagram through a
camera is advisable in most cases, because the
image can be reduced if necessary so as to come
well within the limits of a lantern sUde. Take
care to obtain strong contrasts — the whites
opaque and the Hnes clear. Should it be desired
to show the diagram reversed as regards white
and black — that is, white lines upon a black
ground — the negative itself may be cut down to
3^ in. square and used as a slide, or the diagram
may be copied on a lantern slide direct, through
the camera.
(6) The second method is of particular service
when drawings are to be made specially for lan-
tern sUde work. A piece of white paper, thin
and comparatively grainless, is cut to the size of
a lantern sUde. The drawing is then made on
the paper in black ink, and used as a negative,
a lantern slide being placed in contact with it
and printed in the usual man Tier. The sUde will
show the blacks and whites reversed. Should a
black hne sUde be required, the slide just pre-
pared may be used as a negative and another
shde printed by contact from it.
(c) This is not strictly a photographic process.
Plain glass plates are coated with groimd glass
varnish, made as follows : —
150 grs.
34 g-
150 „
34 „
10 oz.
1,000 CCS.
Sandarac
Gum mastic
Methylated ether
Benzole
100 grs. 23 g.
100 .. 23 „
10 oz. 1,000 CCS.
2 „ 200
When dry it gives a surface which takes the
pencil well, and any drawing or writing may be
made. The slide may then be made transparent
again by flooding with : —
Sandarac
Gum mastic
Methylated ether
which destroys the grain and leaves the drawing
on what appears to be plain glass. Another plan
is to use a special ink (see " fiik for Glass, etc."),
while another is to use the finest ground glass
obtainable, and after making the drawing, to
destroy the grain by coating it with gum dammar
dissolved in benzole. If white lines on a black
ground are wanted, plain glass plates may be
smoked by holding them over burning camphor,
or by coating them with Brunswick black or
other opaque pigment, and then scratching with
a needle-point.
LANTERN SLIDES, MASKING, BINDING,
AND SPOTTING
When a lantern slide is developed, fixed and
washed, it requires finishing in such a manner
that it can be shown efiectively in the lantern,
and handled without injury. The picture requires
masking, that is, the portion of the plate not
required needs to be covered with opaque
paper, so that the picture is isolated on a dark
screen, the edges being sharp and triie as in a
well-trimmed print. I/antem-slide masks are
obtainable with openings of various shapes and
sizes, but a serious worker soon finds it difficult
to adapt them to his requirements. A print
should be trimmed to a nicety, so as to include
the amount of subject desired, and no more.
Using commercial masks is like using untrimmed
paper of a uniform size for prints ; while it
might answer in many cases, it faUs frequently.
A favourite plan with some workers is to cut a
number of shps of thin opaque paper slightly
less than 3 j- ins. long, and varying in width from
J- in. to |- in. Four such slips can be attached
to the film of the slide with a touch of gum at
each comer, they can thus be arranged to cut off
the subject exactly as required. By keeping
these slips true to the edges of the plate, rect-
angularity of the opening is secured.
Before or after binding, the slide requires
spotting. Two prominent spots have to be
appUed for the purpose of indicating to the
lautemist the correct position for inserting the
shde in the lantern. These spots must be at the
two top comers on the face of the sUde, film side
towards the operator.
There are two methods of binding a cover
glass to the face of the slide so as to protect the
film from injury. The first is adopted by those
who make lantern slides commercially on a large
scale. A strip of gummed paper about 15 in
long is moistened and attached to the four edges
of the two plates, the comers being deftly
mitred. The second method is to appl^ four
separate short slips, one for each side, and it is
much easier to bind a sHde neatly and securely
by this method. Short binding sUps for attach-
ing in this manner are obtainable, or binding
slips may be made by the worker. A thin
paper shoidd be used, and gum has to be applied
when ready for using. An advantage of cutting
binding slips is that they may be made wider,
and so hold the plates together more firmly.
Lantern Slides, Two-colour
328
Latent Image
LANTERN SLIDES, TWO-COLOUR
TONING OF
In slides showing floral pictures, Somerville
tones tlie leaves green by means of vanadium,
and the flowers to another colour, say red or
brown, which is given by the copper or sulphide
toner, all the solutions being applied with a
brush. A light or blocked-out background.
LANTERNOSCOPE
A viewing box for lantern slides, fitted with
eyepiece or magnifying lens.
LAPIS INFERNALIS
An old name for silver nitrate (which see)
LATENT IMAGE (Pr., Impression latente ;
Get.,.Latenies Bild)
The acfaon of light upon many sensitive sub-
stances IS at once visible by a change of colour,
as in the darkening of silver or bichromate salts
on paper. This is known as a direct light action.
In other cases there is no visible change, and
the exposed material has to be treated with some
agent, usually termed the developer, which
renders the action of light visible. The action
of light is thus said to produce a latent image,
which is of such a nature that the result of the
light action cannot be quantitatively or chemic-
ally recognised.
The exact natiire of the latent image has been
a subject of much dispute, but the theories may
be divided into two sections, the physical and
the chemical. Advocates of the former consider
that the action of light is to produce some
change in the physical character of the silver
salts, whilst the adherents to the chemical theory
assume that there is an actual chemical change
and the formation of a lower haloid salt, which is
usually called a subhaloid.
Bearing in mind that it has been proved by
Dewar that a photographic plate possesses the
power of forming the latent image at tempera-
tures closely approaching absolute zero, whilst
every other known chemical action ceases at a
much higher temperature, it may be asked why
the photo-sensitive salts of silver should be an
exception. Dr. Bose, a well-known physicist,
would liken the formation of the image to the
strain of the silver salt under the electric force
in the light-wave, a theory known as that of
molecular disturbance or strain theory. Accord^
ing to this, the silver bromide is converted into
an aUotropic form, which is more readily reduced
to the metallic state than the normal silver
haloid, and the function of the sensitiser is then
to retard the recovery from the strain. There
are undoubtedly many parallels between the
strain phenomena in metallic silver and other
substances under the electro-magnetic radiation
of light and the effects of exposure of the photo-
graphic plate. But this theory hardly explains
the various latent images whidi may be formed
on the silver haloids, for instance with silver bro-
mide and iodide. In the former case, so far as
experience goes, the latent image is permanent,
whilst with iodide there is retrogression of the
image or it fades away, and the sensitive salt
returns to its non-developable original state. It is
stated above that the physicist looks upon the
sensitiser as a substance which prevents the
recovery from the strain, and a correlative
action has been found in the case of calcium
oxalate for pure electric response from mechani-
cal and light stimuli. When the action of light
is permanent — that is to say, no matter how
long the exposed sensitive material be kept the
product of the hght action, the latent image, may
be developed. This is then known as an irrever-
sible action ; but if, on the other hand, the latent
image reverts to its original and undevelopable
condition, the action is reversible, and assuming
that the formula for silver subiodide be taken as
Agal, then this may be expressed by the follow-
ing equation : —
In light
SAgI
= 2AgjI -1- AgIs
<
In darkness
That is to say, in light the five molecules of Agl
are spUt up into two molecules of subiodide,
AgjI, and one molecule of silver triiodide, Aglj,
whereas if such a mixture be kept in the dark,
the two molecules of subiodide and one molecule
of triiodide rearrange themselves and reform
five molecules of silver iodide. Now as this action
takes place in the presence of gelatine, but does
not take place in the case of silver bromide, it
seems a somewhat difficult point to explain from
the point of view of the physicist.
Another physical theory is that the silver salts
are charged electrically, and that the action of
Ught is to ionise them or set free the electrons,
and in support of this theory is advanced the
fact that tiie photo^alts of silver are vigorously
electric and in the order of bromide, chloride, and
iodide, which is the same as their order of sen-
sitiveness to ultra-violet light. As considerable
support to this theory is also adduced the fact
that eosine, fuchsine, cyanine, and other dyes
set free electrons under the stimulus of hght,
and that the particular wave-lengths absorbed
by these substances are those which are most
effective in hberating the electrons. In other
words, the photo-electric activity displayed is
dependent upon their colour absorption, and
there is thus an exact parallel with the sen-
sitising power of these dyes for the photo salts
of silver.
The chemical theories assume the decom-
position of the silver bromide, and that bromine
is given off ; and if the formula for silver bro-
mide be written AgiBri, in which x merely repre-
sents a given number of atoms of each dement,
the latent image could be described as K%xSTx—y,
in which y is merely ,a certain number of bromine.
In support of this theory it must be noted that
it is by no means so easy to destroy the latent
image ; nitric acid, potassium cyanide, ferri-
cyanide, and acid bichromate do not entirely
destroy it, and it is possible to fix an exposed
plate, and yet physically develop it afterwards
so as to obtain a good image.
Other chemical theories are that metallic
silver is produced, but this has been proved to
be untenable, as strong nitric acid would dissolve
silver, but does not destroy the latent image.
Another chemical theory is that a subsalt is
formed, but the latter forms a soUd solution with
the silver bromide in varying proportions.
Lateral Inversion
329
Lead Acetate
At present, at any rate, no definite conclusion
as to the nature of the latent image can be
formed, and the position is probably best summed
up in the words of Dr. Joly in his presidential
address to the Photographic Convention in
1905 : " The latent image is built up of ionised
atoms, or molecules, the result of the photo-
electric effect upon the illuminated silver haloid,
and upon these ionised atoms the chemical
effects of the developer are subsequently directed.
It may be that the liberated electrons ionise
molecules not directly affected, or it may be that
in their hberation liey disrupt complex mole-
cules built up in the ripening of the emulsion.
"With the amount that we have to go upon, we
cannot venture to particularise. It will be said
that such an action must be in part of the nature
of a chemical effect."
In connection with this subject it should be
pointed out that Dr. Scheffer, of Berhn, has been
able to obtain photo-micrographs of the image
on silver bromide, and these prove that there is
some sort of thread formation or protrusion of
a filament from an exposed sensitive grain, which
would certainly point to disruption of the com-
plex ; but this might agree with both the phy-
sical and chemical theories, as in the former case
it would represent the disruption of the particle,
and in the latter case the extrusion of the sub-
bromide.
Meldola has assumed the formation of an oxy-
haloidj but the objection to this is that the latent
image can be formed under gases and in the
presence of substances which preclude entirely
free oxygen, which would be necessary for this
formation.
From a series of experiments on development
with the indoxyl compounds, Homolka advances
the theory that the latent image is an equi-
molecular mixture of sub-bromide and per-
bromide of silver, which is formed according to
the equation : —
3AgBr
silver bromide
AgBrj
sub-bromide
-1- AgjjBr
per-bromide
The existence of per-bromide has also been tenta-
tively established by Lumite and Seyewetz, but
further proof is required.
LATERAL INVERSION (See "Inversion,
Lateral.")
LATITUDE OF PLATES AND PAPERS
In negative-making variations may be made
in exposure, within moderate limits, without
any loss of printing qualities. The latitude is,
however, influenced considerably by the subject
and the conditions. A subject with good con-
trast, or exposed in a clear and brilliant light,
will allow more latitude than one deficient in
contrast exposed in a dull hght. With the
latter and in copying, there is practically none
at all.
It must be recognised that it is only in over-
exposure that latitude can really exist. Loss of
quality is inseparable from under-exposure. In
all subjects, however, it is possible to compen-
sate for errors in exposure to a moderate extent,
if the error is known before commencing to
develop. A modified solution may be applied
liiat will have the property of compensating for
the extra exposure given. {See also " Exposure,
Incorrect.")
With regard to papers, in a platinotype print
there is practically no latitude ; in a cold bath
the development may be shortened to save au
over-exposed print, but the result is distinctly
inferior. An over-exposed silver print may be
sUghtly reduced by a long immersion in the com-
bined toning and fixing bath, but the quality
suffers. A carbon print has more latitude than
any other photographic printing process, as
errors can be compensated when the print is
partially developed : that is, the stage at which
the error is discovered. Within moderately wide
Umits, the loss of quality is inappreciable. With
bromide prints a moderate latitude could be
secured by modifying the developer before com-
mencing to develop. After development is com-
menced, compensation can only be made for over-
exposure by shortening the duration, but this
produces results that are so inferior to those pro-
duced by correct exposure and full development,
that it cannot be called true compensation.
LAURUS CAMPHORA
Camphor or, more accurately, the botanical
source from which camphor is obtained.
LAVENDER RAYS
A term (now practically obsolete) applied to
the commencement of the ultra-violet rays just
oeyond the visible violet.
LAVENDER, OIL OF (See "Spike Oil.")
LEA, M. CAREY
Bom at Philadelphia, 1823 ; died at Phila-
delphia, 1897. Experimentalist and writer on
photographic matters, who spent much of his
time in England, and did much valuable work
in photography. One of his early inventions
was a plate-cleaning solution, composed of
potassium bichromate and sulphuric acid, often
referred to as the " Carey Lea " mixture. His
ferrogelatine developer (1865) consisted of a
chemical combination of gelatine with the
ordinary iron developer as used for the wet-
plate process. He published (also in 1865) a
process of intensification by means of Schlippe's
salt. In 1875 he worked out a washed collodion
emulsion, and in June, 1877, published the first
formula for a ferrous-oxalate developer. His
investigations regarding the properties of red
silver chloride are of great interest to the student
of colour photography.
LEAD (Pr., Plomh ; Ger., Blei)
Pb. Molecular weight, 207. A bluish-grey
soft metal obtained from native lead ores by
roasting. It is used for making dishes and smks
owing largely to its acid-resisting properties and
to its softness.
LEAD ACETATE (Fr., Acetate de plomb ;
Ger., Bleiacetat)
Synonyms, sugar of lead, normal plumbic
acetate. Pb. (CHsCOO)a 3H2O. Molecular
weight, 379. Solubilities, 1 in 2-3 water, i in 30
alcohol; insoluble in ether. All lead salts are
poisonous, • the antidotes being emetics and the
use of the stomach pump, and also sodium,
Lead Chromate
330
Leimtype
potassium or magnesium sulphate, milk or white
of egg. Efflorescent colourless crystals or masses
with acetous odour and sweet taste obtained
by dissolving lead carbonate in acetic acid. It
is used in some combined toning and fixing baths.
LEAD CHROMATE (Fr., Chromate de plomb ;
Ger., Chromsaures Blei)
PbCrOi. Molecular weight, 323. Insoluble
in water and alcohol. Poisonous (see " I^ead
Acetate "). A yellowish brown powder obtained
by precipitation from a soluble lead salt and a
chromate. It is used as a pigment, and also
forms the colouring matter of orange fabric —
a dark-room medium. A good orange safe light
may easily be prepared by iriunersing a fixed-out
dry plate for five minutes in 5 per cent, potas-
sium chromate solution, rinsing, and then
immersing in lead nitrate or acetate solution,
washing and drying.
LEAD FERRICYANIDE
This is always prepared in solution by mixing
lead nitrate with potassiimi ferricyanide, and
it is used for intensifying collodion negatives.
LEAD INTENSIFIER
An intensifier used for negatives of line or
black and white subjects in which no half-tones
appear ; it gives great contrasts and is not
recommended for ordinary negatives. Immerse
the well-fixed and washed negative, imtil
thoroughly bleached, in the following : —
Potassium ferri-
cyanide . . 300 grs. 68 g.
I,ead nitrate . 200 ,, 45 „
Nitric or acetic acid 50 mius. 10 ccs.
Water . . 10 oz. 1,000 „
Next rinse in weak nitric or acetic acid
(I in 15), wash thoroughly and blacken with
ammonium sulphide, i part ; water, 10 parts.
Clear again in weak acid and wash thoroughly.
The bleaching and blackening may be repeated
until sufficient density is obtained, if care is
taken always to wash thoroughly, as any trace
of lead remaining in the negative will inevitably
cause fog. Great care is also necessary when
handling the film, as the acid makes the film very
tender.
Other blackening agents besides the ammonium
sulphide given above may be used after bleaching
in the lead solution. The following have been
recommended : —
(a) Water, 20 oz. ; sodium sulphide, i oz.
(b) Water, 20 oz. ; Schlippe's salt, 90 grs. ;
ammonia, j- oz. (c) Water, 20 oz. ; liquor
ammonise, 1 oz. ; potassium bichromate, 2 oz.
In process work the lead intensifier is largely
used for wet collodion negatives for line repro-
duction. It is not so generally used for half-
tone, but has been recommended in collodion
emulsion work. I^ead intensification has been
largely superseded by the copper bromide inten-
sifier in half-tone work ; it survives for line
work because of its cheapness.
LEAD NITRATE (Pr., Azotate de plomb;
Ger., Bleinitrat)
Pb (NGjjj. Molecular weight, 331. Solubili-
ties, I in 1-85 water; almost insoluble in alcohol.
White translucent crystals prepared by the
action of nitric acid on lead or lead carbonate.
Poisonous (see " Lead Acetate "). It is used in
the lead intensifier and in the combined toning
and fixing bath.
LEAD, SUGAR OF (See " Lead Acetate.")
LEAD TONING
Albumen and gelatino-chloride prints may be
toned with lead acetate. The colouring is due
to sulphuration and the residts are not per-
manent. A simple formula is : —
Lead acetate . . ^ oz. 27-5 g.
Sodium hyposulphite . 4 „ 220 „
Water . . . 20 ,, 1,000 ccs.
The above is a " combined " toner and fixer
as well. The tone obtained is due to the forma-
tion of lead sulphide. There are many other
formulse,
Messrs. Lumi^re have found that by employ-
ing salts of lead made from di-, tri-, tetra- and
penta-thionic acids, mixed with a solution of
" hypo," a toning and fixing compound can be
obtained, which, without gold, gives warm tones,
and with gold colder tones.
Lead acetate is often used in conjunction with
gold in many of the combined toning and fixing
baths. The following is typical : —
Sodium hyposulphite.
Citric acid
Lead acetate .
Ammoniiun sulpho-
5 oz.
60 grs.
60 „
275 g-
7 „
7 ,,
cyanide
Gold chloride .
200 „
3 .,
23 ,.
•35 „
Water
20 oz.
1,000 ccs.
Dissolve all but the gold chloride in the order
named in hot water, boil, filter, and then add
the gold chloride.
LEATHER, PHOTOGRAPHS UPON
White leather was used by Wedgwood, Reade,
and others in the early days of photography as
a support for the sensitive silver salts. In the
wet plate days collodion positives were some-
times made on black patent leather, the image
appearing, of course, of a white or cream colour,
hke a modem ferrotype picture. Modem
photographs upon leather are usually produced
by the carbon transfer process, or by sensitising
the leather with a suitable bromide or other
emulsion.
Unless special precautions are taken emul-
sions will soon decompose when ordinary leather
is prepared direct with a sensitive emulsion ;
in the same way the gold of toning baths decom-
poses, and the prints soon become spotty
because of the chemical action of substances
contained in the leather. To overcome this,
it has been recommended that the leather be
given a substratum of collodion of ^ to i
per cent, strength. After twenty-four hours
the leather may be coated with any sensitive
emulsion and then treated in the same way
as plates and papers.
LEIMTYPE
A process commonly associated with the
name of J. Husnik, of Prague, who took out a
Lengthening Camera
331
Lens
patent in 1887, but a very similar process was
patented in Boston, U.S.A., in 1871, by W. H.
Mummler. The object is to obtain images in
high relief for direct typographic printing. A
thick layer of bichromatised gelatine is exposed
under a line negative, next attached by means
of guttapercha to zinc or wood, and then
developed with a solvent such as a saturated
solution of an alkaline bichromate. This not
only dissolves those parts acted on by light,
but also strengthens the relief parts. After
development, the plate is dried, and the hollow
parts are filled with an opaque printer's ink
by means of a camel-hair brush. The plate is
then exposed for a second time to the action
of light, by which it is hardened and strength-
ened in the lines.
LENGTHENING CAMERA
For copjring, and in photographing small
objects at close quarters, Uie bellows extension
of an ordinary camera sometimes proves
insufficient. The professional photographer in
such a case makes use of a wooden tube or cone,
fitting on the front of the camera and carrying
the lens at the outer end, as illustrated. But
'Wooden Extension to Camera
a. good modem studio camera will usually have
an extension adequate for any probable require-
ments. For smaller cameras, extension acces-
sories of various kinds are obtainable, some
being made to fit the front and others the back
of the camera. (See also " Extension, Camera.")
LENS (Pr., Lentille, Loupe, Objectif; Ger.,
Ohjectiv, Linse)
Photographically, a lens is a combination of
two or more glasses capable of producing an
A. Landscape
Lens
B. Zeiss Rapid
Anastigmat
Combination
C. Chevalier's
Achromatic
Meniscus
image. Simple or " spectacle " lenses, con-
sisting of one piece of glass, are occasionally
used to obtain special effecte, but the single
achromatic combination may be taken as the
starting point in the evolution of the modem
photographic objective. The elementary forms
of lenses, as illustrated under the headings
"Concave Lens" and "Convex Lens," made
in a great variety of glasses and with widely
diflfering curves, are used in combination to
D. Principle of the Pinhole
build up the more or less complex objectives
now in use. The simplest combination of these
elements is found io the single " landscape
lens " A, which is composed of a double convex
lens of crown glass cemented to a plano-concave
of flint glasSj thus securing achromatism (see
"Chromatic Aberration"); while the latest
and most complex combination is found in the
Zeiss anastigmat B, composed of four elements
cemented together, two of such combinations
iorming the " Series Vila Rapid Anastigmat."
It will be convenient to deal with the principal
types of lenses in groups, showing their gradual
development, as improvements in the various
forms have been and are proceeding simul-
taneously.
The action of a photographic lens may be
better understood by considering what happens
when a small bevelled opening is made in the
shutter of -a darkened room, as at D. Rays of
light from all parts of any object outside — say,
a church — are admitted by the aperture, cross
each other, and proceed in straight lines to form
an inverted, image on the wall opposite. Photo-
graphs can, in fact, be made with a pinhole
instead of a lens. Except with a very small
opening, however, which means a long exposure,
the image is blurred. By using a convex lens,
as at E, which has the property of converging
light rays and bringing them to a focus, a much
larger aperture becomes possible, together with
improved definition.
Single or Landscape Lenses. — ^In its primitive
form, the single combination was nothing more
E. Principle of the Lens
than the object lens of a field glass. The first
lens made specially for photography was of
this model, and was issued by Chevalier, of
Paris. This maker soon issued an improved
model, now generally known as an achrcSmatic
meniscus C, which had a much wider field
of definition and greater rapidity than its
Lens
332
Lens
predecessor. This was followed by Grubb's aplan-
atic P which departed from the telescope lens
construction, being composed of two meniscus
elements ; in this lens ttie relative positions of
the crown and flint glasses were reversed,
greater covering power and rapidity being thus
concave flint. Both these early forms of portrait
lenses were comparatively slow in action, and
were superseded by the Petzval portrait lens K
(introduced by Voigtlander in 1840), which,
with little modification, is the standard lens for
studio work at the present day. It gives greater
F. Grubb's G. J. H. DaU- H. T. R. Dall-
Aplanatic meyer's Wide- meyer's Rapid
Lens angle Lens Landscape
Lens
obtained as well as portability. The next
forward step was made when J. H. Dallmeyer
constructed a wide-angle landscape lens of
three elements {see G), a concave flint being
between two crown meniscus glasses. This
covered the widest angle ever attained by any
single lens, the longest side of the plate being
equal to the focal length of the lens, while the
curvilinear distortion was reduced to a minimum.
By the use of different glasses, T. R. Ijallmeyer
constructed a. lens on the same lines, covering
a narrower angle, but working at the large
aperture of //lo. This was known as the
Rapid Landscape lens (see H) and was recom-
mended for distant views, large heads, and
subjects where pleasing perspective was pre-
ferable to wideness of angle. Still later, the
same optician produced a non-distorting
" single " lens, the " Rectilinear Landscape" I,
which, although fitted with an outside diaphragm,
was absolutely rectilinear. Its comparatively
small aperture (//14) prevented its general
adoption, the rapid rectifinear with an intensity
of //8 being preferred. There is an internal
air-space in this lens. A somewhat similar
lens was produced by J. T. Goddard, but did
not appear on the market.
Portrait Lenses. — At a very early period in
the practice of the art the necessity for a rapid
T. R. Dallmeyer's
Rectilinear Land-
scape Lens
J. Ross (CoUen)
Portrait Lens
lens was felt by portrait photographers ; and
in :84i, Andrew Ross constructed a double
combination lens J for Henry CoUen. This
consisted of two cemented combinations, one
being placed at each end of a tube to which
central diaphragms were fitted. In the same
year Thomas Davidson produced a symmetrical
lens for portraiture, this being composed of
two similar combinations, each composed of a
plano-convex crown cemented to a plano-
K.
Petzval Portrait
Lens
J. H. Dallmeyer's
Portrait Lens
flatness of field, and the presence of an air space
between the flint and crown elements of the
back combination, gives perfect correction for
spherical aberration. The only important modi-
fication in the design of the portrait lens was
patented by J. H. Dallmeyer in 1886, improved
covering power being obtained together with
less liability to flare. This lens is shown in
diagram L. In the Dallmeyer lens the position
of the crown and flint elements is reversed,
the crown element being a meniscus instead of
a " crossed " double convex lens. These lenses
are fitted in an adjustable cell so that the
distance between them can be varied at will ;
when placed closely together, sharp definition)'
is obtained, while by separating them more or
less " softness " results. The front combination
of both types of portrait lens is frequently
used alone, either for landscapes or for portraits,
especially large heads. Small lenses of this
form were used for rapid landscape work in the
earlier days of the art, but at the present time /
they are rarely used except by naturalists and
for night photography.
Doublet Lenses. — The want of rapidity and
rectihnearity of the single lens and the bulk and
cost of the portrait lens, caused attention to be
directed to the production of lenses for copying,
outdoor work, etc., which should be free from
these defects. One of the earliest of these was
the Orthoscope or Orthographic lens of Petzval
JL Ross Doublet
N. Rapid Recti-
linear Lens
(made by Voigtlander in 1859). For this lens
great claims as to flatness of field, rectilinearity
and other virtues were made, although actually
it possessed but little advantage over the single
landscape lens. It had a greater equivalent
focal length than the distance between any part
of the lens and the focusing screen, or, in other
words, it was to a certain extent a telephoto
lens, the back combination being of the negative
form. The orthoscope was succeeded, in 1864,
by several doublets of various rapidities, but all
Lens
333
Lenses, Brasswork of
some-wliat similar in type, designed by Thomas
Ross {see M), and these enjoyed considerable
popularity for many years, some being still in
use. The next great stride towards perfecting
the photographic lens was made in 1866 when
Dallmeyer, in London, and Steinheil, in Mimich,
almost simultaneously issued lenses of the type
which is so well known imder the name of Rapid
Rectilinear {see N), the original uncorrected
form of Steinheil being designed for wide-angle
work only. This lens, worHng at an intensity
of //8 or more, gave perfectly rectilinear images,
having a fairly flat field and being free from
flare or " ghost," and achieved immediate
success. Lenses on similar lines, but slower in
action, were constructed for wide-angle work,
and no considerable improvement was made
until the Zeiss and Goerz anastigmats appeared
on the field in the early nineties of the nineteenth
century. Rectilinear lenses were made by J. H.
Dallmeyer with an intensity as high as f/$,
while other forms, known as the " euryscope,"
"extra rapid rectilinears " or "universal sym-
metrical " had intensities of about //6. The
wide-angle rectilinears or portable symmetricals
usually had a maximum aperture of //16. An
"actinic doublet" was achromatised for actinic
effect; but modem doublets are achromatised
for both the visual and actinic effects.
Anastigmatic Lenses. — Lenses of greatly
improved design were introduced in 1890 by
Carl Zeiss, of Jena, the first model being an
apochromatic triplet, this being followed by a
double combination which was greatiy superior
to all lenses then existing. Improvements have
followed in rapid succession. The Series VII
{see B) may be considered as being the most
useful type of the Zeiss anastigmats, being
truly luuversal in its character. The single
lenses are perfectiy corrected for astigmatism,
spherical aberration and curvature of field, and
are practically rectilinear. Their intensity is
f/i2-$. Used in combination to form doublets
they retain all their good qualities with the
adition of greatly increased covering power,
angles of 80° to 90° being obtained, while the
intensity varies from //6-3 to //8, according to
whether lenses of siniilar or dissimilar focEil
lengths are combined. In 1893 an excellent
series of double anastigmats was introduced by
Goerz with an intensity of f/yy afterwards
increased to //6-8. Each combination is com-
posed of three glasses cemented together. The
single combinations may be used for landscapes,
but do not work at the same large aperture as
the Zeiss lenses. The Goerz " Pantar " lens,
recently introduced, corresponds in rapidity to
the Zeiss Series Vila. Other opticians have
placed on the market lenses corresponding to
the Goerz model under various names.
The foregoing may be considered as the
principal grojips of lens types, but many other
forms are described under separate headings.
In process work, it is essential that the lens
should give perfect definition uniformly all over
the plate, that it should be free from distortion
and astigmatism, and give even illumination ;
and that it should be colour-corrected. For
line reproduction it is not necessary to work
with a large aperture, and therefore by stopping
down extreme sharpness is obtained. In half
tone large apertures are not permissible on
account of the action of the ruled screen. For
the same reason the focus must not be too
short ; an equivalent focus of about 1 8 inches
is usually considered best for a 15-inch by
12-inch plate. In colour reproduction without
the ruled screen interposed large apertures are
desirable to counteract the considerable length-
ening of exposure due to the action of the
colour filters. Process lenses have to be fitted
with Waterhouse diaphragm slot in order to
permit of variously shaped stops being used.
LENS ADAPTERS
Threaded brass rings which enable a lens to
be screwed into other flanges than those for
which it was originally screwed. In cases
where the screw-threads on the lens and flange
do not agree, and in the absence of an adapter,
it is necessary to have for each lens a detachable
front {which see).
LENS, POSITION OF STOPS IN
With the majority of lenses the position of
the stop or diaphragm is determined by the
maker, and in many modern lenses there is
only just sufficient room to allow the iris to
be fitted. In the case of a compound lens
having front and back components of equal
focal length, the diaphragm should be placed
equally distant from each, but in the case of
components of im.equal focal length the dia-
phragm should be placed at a distance propor-
tionate to the focal length from each lens — that
is to say, a littie nearer to the lens of shorter
focal length — otherwise, the combination will
not give rectilinear images. The diaphragms
of single lenses are usually placed at a. distance
equal to the diameter of the lens, but this
distance may be varied at discretion, a flatter
field with a reduced circle of illumination being
obtained when the diaphragm is placed farther
from the lens. Flare spot is often due to an
incorrect position of the diaphragm. Portrait
lenses usually have the diaphragm midway
between the glasses ; but for outdoor work,
the tendency to flare is greatiy reduced by placing
the diaphragm slightiy in front of the lens, this
somewhat reducing the size of the field covered.
LENSES. BRASSWORK OF
The term " brasswork " is applied generally
to the metal cell which holds in place the
various glasses of which a modem lens is com-
posed, although both aluminium and brass are
used for the purpose. The production of the
brasswork demands the application of highly-
trained skill and the use of machines which
work with scientific precision. The screw
threading must be efficient, and it is a matter
for regret that all lenses are not threaded
uniformly to one system. The Royal Photo-
graphic Society has recommended certain
measurements and standards, which will be
found under the heading " Mounts, Lens." It
is necessary that the inside surfaces of the
brasswork should be blackened to avoid pro-
ducing cross reflections, which would seriously
interfere with the efficiency of the lens. (For a
method of blackening camera brasswork, see
" Blackening Apparatus.")
Lenses, Cementing
334
Lettering Negatives, etc.
LENSES, CEMENTING AND UNCEMENT-
ING
I<ens glasses are cemented together with
Canada balsam, which needs to be specially
prepared for the purpose. The balsam as
bought should be put in a saucer and baked in
an oven until, when cold, it will be hard. The
hard balsam needs to be broken up, placed in
a bottle and covered with benzene, allowed to
stand for about twenty-four hours, and then
gently heated over a water-bath imtil fluid.
The lens glasses, having been cleaned with
extreme care, should be gently warmed, and a
drop of the warm balsam placed in the centre
of the concave glass. Next the convex glass
is pressed down into the concavity until the
balsam has spread and oozed out at the edges.
The lens is left for the balsam to harden, or
this process may be hastened by gently heating
in an oven of which the door is open. At the
end of a few days any surplus balsam on the
edges may be removed with a rag moistened
with benzene.
A safe method of uncementing a lens is to
place it (minus its mount) in a glass vessel, and
to pour warm water upon it ; the water is kept
warm, by means of a spirit lamp or Bunsen
burner, until the glasses can be slid apart.
Should this fail, soak in turpentine.
LENSES, CLASSIFICATION OF
In the past, when photographic lenses were
more limited in their capabilities, it was usual
to designate them accordmg to the class of work
for which they were best adapted. Thus there
were view lenses which were not adapted for
architecture ; portrait lenses of great rapidity
but limited covering power ; group lenses
which were usually portrait lenses of a slower
variety ; copying lenses which were rectilinear
but still slower in action, etc., etc. Under
modem conditions the necessity for such classi-
fication has almost disappeared, as a good
anastigmat will answer for practically any class
of work, subject only to the angle which it is
capable of embracing. Lenses for copying still
form a class by themselves, as slight modifica-
tions in design are necessary to obtain the best
possible covering power when the back and
front conjugate foci are equal or nearly so.
LENSES, CLEANING
Careless cleaning must always be guarded
against, and such a thing as vigorous rubbing
with a harsh duster most strictly avoided. The
proper methods of cleaning lenses are explained
under the heading " Cleaning I<enses."
LENSES, CONDENSATION ON
In a damp atmosphere, moisture rapidly
condenses upon a lens which is colder than the
atmosphere itself. The trouble is especially
likely to occur in early morning and towards
evening, and in photographing in certain kinds
of factories, underground wor^ngs, and at great
heights where the atmosphere is highly charged
with moisture. It is not a bad plan to carry
the lens, enclosed in a wash-leather or other casej
in a pocket of one's clothes to ensure its tem-
perature being higher than that of the atmos-
phere. But in addition to this precaution,
which may not always answer, it is necessary
to watch for the condensation and, should it
form, to remove it at once. The presence of
condensed moisture on a lens makes photo-
graphy hopeless.
■ The lantemist has especially to guard against
moisture condensing upon either objective or
condenser ; and he should make it a rule to
examine the lenses immediately before beginning
an exhibition. A lantern brought from the
cold street straight into a hall where people
are congregated is sure to need attention.
LENTICULAR STEREOSCOPE {See
" Stereoscope.")
LERMANTOFF'S STEREOSCOPE {See
" Stereoscope.")
LETTERING NEGATIVES AND PRINTS
The advantage of lettering a negative rather
than a print is that the work requires to be
done but once, and then any number of prints
can be made, each with the lettering printed
upon it. The usual way of writing on a negative
to produce white letters on the print is to write
the title backwards on the film side with opaque
pigment, such as red water-colour or Indian
ink, applied with a finely pointed camel-hair
pencil, in this way obtaining effective titles upon
the shadow (clear) portions of the negative. The
backward writing needs some httle practice, and
it may be found helpful to write the title pro-
perly upon the glass side, and then to foUow the
outline of the letters on the film side ; while
another plan is to write the title properly upon
a piece of glass, lay the titled glass, inscription
side downwards, upon white paper and use as
a guide for the eye. Many methods of trans-
ferring the title to the film have been recom-
mended ; a good one is to write the title pro-
perly upon white paper with a fine pen and an
mk made by dissolving either methyl-violet or
eosine in water. When the ink is dry, the paper
and the wet or damp film are brought into
contact by pressing with the finger ; the paper is
then pulled away and the reversed lettering will
be found on the film ; it may easily be strength-
ened if necessary. A copying-ink pencil has
been recommended in place of the dyes.
A transfer paper can be made by coating
smooth paper with a thin solution of rubber in
benzol, allowing to dry, coating with a thin
solution of gelatine, and again drying. The
title is written upon the gelatine surface with
waterproof ink, and is transferred by trimming
the paper to the proper size, and soaking it for
a minute in cold water. It is then pressed on
the film side of the negative, the superfluous
water being removed with clean blotting-paper.
The transfer paper is allowed to dry upon the
negative, and is then moistened at the back
with benzol, which dissolves the film of rubber,
enabling the paper to be stripped off, leaving
the thin gelatine film with the title beneath it
upon the negative. Another method is to write
the title upon a thin film of celluloid or tracing
paper, and to stick it face downwards upon the
fihn with a transparent adhesive.
To letter a negative so as to produce a black
title upon the print, it does not suffice to scratch
Lettering Negatives, etc.
335
Lichtkupferdruck
the film witli a sharp point, as this causes ragged
lines ; it is better to use a bleaching solution
made by adding equal quantities of glycerine
and Uquid gum to tincture of iodine ; the fluid
should flow evenly from a quill pen. The title
Numbering Negatives with the Pantograph
is -written in the reverse way with this solution,
which must be used with care and not allowed
to spread. Immediately the lettering appears
white right through the gelatine, wash the
negative quickly in water to stop the bleaching
action and immerse in a "hypo" fixing bath,
which dissolves out the bleached letters and
leaves clear glass ; finally, wash and dry.
Numbering is not so difficult as lettering, and
is, of course, done in the same way. The illus-
tration shows how the well-known pantograph
can be appUed to the work. In a frame the
negative is laid film upwards. At the lower end
is placed a strip of metal on which is engraved a
set of numerals reversed. The lower end of the
pantograph is made to follow the outline of
the desired numeral, this being reproduced on
a small scale at the upper end by a pencil,
stylus, or needle-point.
The following method may be adopted where
the titles are required in neat type characters :
Set up the titles in type and get a good proof on
enamel paper. Photograph this impression,
using a wet plate for preference. Then from
this negative make a transparency. When this
is dry, strip the film and attach it to the nega-
tive with an adhesive. This wiU give white
lettering on dark ground. Black lettering on a
light groimd can be obtained by printing from
a separate negative on to the paper or plate,
using register marks to ensure exact position.
Titles on prints may be written in waterproof
ink, black or white, each print being done
separately, of course. The sensitive paper may
be written on before printing, using Indian ink,
red water-Golour, etc., which, when toning and
fixing, becomes washed away, leaving white lines.
Finished prints may be written upon with the
following chemical ink : —
Potassium iodide
Iodine
Gum arable
Distilled water
170 grs. 40 g.
17 ,, 4 „
17 ,. 4 „
I OZ. 1,000 CCS.
This written upon the dark part of a silver
print discharges the colour and appears white.
Or, if preferred, a white pigment ink may be used.
Black letters upon finished prints are made with
black waterproof ink or by letterpress printing.
LEVEL, CAMERA (See "Camera Level.")
LEVELLING SLAB (Pr., Dalle d niveler :
Ger., Nivellierplatte)
A flat, smooth plate of glass, slate, marble,
or other material, either attached to a frame-
work that may be levelled accurately by means
Levelling Slab
of screws at the comers, as illustrated, or
intended for use on a levelling tripod (which
see). Employed as a support for plates to be
coated with emulsion, or for other purposes
where a perfectly even distribution is indis-
pensable.
LEVELLING TRIPOD (Fr., Support A niveler :
Ger., Nivelliergestell)
A stand in the shape of a tripod, with screws
at the feet for accurate levelling, as illustrated.
It may be either large enough to support a
LeveUing Tripod
levelling slab (which see), or sufficiently small to
hold single plates, and is used to ensure a film
of even thickness when coating plates with
emulsions, etc.
LICHTDRUCK (Ger.)
An early name for the collotype process (which
see).
LICHTKUPFERDRUCK
A photogravure process invented by J. B.
Obemetter, of Munich, about 1886. From the
original a negative was made and converted into
a silver chloride positive, which was then placed
in contact with a perfectly flat copper plate.
The quantity of silver chloride thus deposited
on the metal corresponds exactly to the inten-
sities of the original ; thus, in the darker parts
there is a denser, and in the lighter parts a less
deposit. By a simple galvanic process, the
silver chloride is decomposed and is replaced
by a soluble chloride and metallic silver.
Light
33^ Light Intensities, Difference in
The copper is by this means etched out, the
depths correspondiug to the amount of silver
chloride in the different tones. The hollows of
the plate are filled with ink for printing in the
usual copper-plate manner.
LIGHT (Fr., LumUre ; Ger., Licht)
Light is generally considered to be due to
minute undulatory waves in the ether that
pervades all space. The molecules of any
luminous body are in a state of rapid vibration,
this movement being communicated to the
adjacent ether particles and transmitted by
a wave-like motion to the eye, the impact of
the waves on the retina giving the sensation
of light. In free space light moves with the
velocity of 1 86,000 miles per second. It travels
invariably in a straight line, in a medium of
uniform density. I/ight falling on a mirror or
other polished surface is either wholly or partially
reflected, at an angle equal to that at which
it strikes the reflecting surface. (See " Reflec-
tion.") White light is not homogeneous, but
a mixture of various colours, of different wave-
lengths. The colours of objects in Nature are
not inherent in themselves, but due simply to
their absorbing certain rays and transmitting
others. (See " Colour.") If a beam of light
is caused to pass through a small opening or
slit and to fall upon a prism, it is separated into
its constituent colours. (See " Dispersion.")
Besides the visible rays of the spectrum so
obtained there are others that are invisible.
Those beyond the violet end of the spectrum
are known as the viltra-violet rays, and are of
great actinic power ; at the opposite end are
the infra-red rays. If a prismatic spectrum is
thrown on a sheet of white paper in a darkened
room, and the region beyond the violet is
painted with a solution of quinine sulphate, it
will at once be illuminated with a violet Ught.
It is thus seen that certain substances have
the power of reflecting or emitting rays quite
different from any that are originally thrown
upon them. (See "Fluorescence.") When a
ray of light passes obliquely from one trans-
parent mediixm into another of different density
it is bent aside from its course. (See " Refrac-
tion.") If light falls at an angle on a very thin
film or plate it is partly reflected at the first
surface, while part passes through, imdergoes
refraction, and is reflected back from the second
surface in a direction parallel to the portion
first reflected. The two sets of light waves will
interfere with each other at certain points, in
such a manner that the waves appertaining to
one or more of the colours will be extinguished,
so that the reflected light appears of a colour
complementary to the missing rays. The
particular rays extinguished will vary according
to the obUquity of the incident ray and the
thickness of the film or plate, so that if the
film is of varying thickness a number of colours
will be seen. It is in this way that the play of
colour in a soap-bubble is caused, as also the
phenomenon known as Newton's rings, which is
turned to account in testing the figuring of lenses.
(See " Interference of Light.") Wjben light
from a bright point or slit passes through a
minute aperture it emerges as a series of coloured
bands ; the same effect occurs when Ught is
reflected from a surface covered with a number
of very fine indentations or scratches. (See
" Diffraction.") Certain crystals, such as
Iceland spar, have the property of dividing a
ray of light into two distinct refracted parts,
one obeying the ordinary law of refraction,
while the other has a peculiar law of its own.
(See " Polarisation.") Many substances continue
to give out light in darkness after removal from
the exciting source of light, a phenomenon known
as phosphorescence (which see). (See also
"Absorption" and "Spectrum.")
LIGHT, ABSORPTION AND REFLECTION
OF
Absorption is dealt with under its own
heading ; but, in one sense, it may be regarded
as iuvolvictg the obstruction of light. Thus, for
example, a glass window absorbs the hght falling
upon it in the following percentages : —
Plain glass, clean . 7 to 10 per cent.
Plain glass, dirty . 40 per cent, and upwards
Ribbed glass . . 15 to 30 per cent.
OpaUue glass . . 15 „ 40 ,,
Ground glass . 30 ,, 60 ,,
The following table gives the
percentage of
light reflected by various mediums.
In
nearly
all cases the figures are merely a
jproximate : —
per cent.
Mirror ....
95
White blotting-paper
82
White cartridge paper
80
Ordinary foolscap .
70
Newspapers
50
to 70
Planed deal (clean)
40
to 50
Yellow wall paper (clean)
40
White tracing cloth.
35
Blue paper
25
Planed deal (dirty) .
20
Yellow wall paper (dirty)
20
Brown paper .
13
Macadam road
8
Chocolate paper
4
Black surface .
I
To obtain the same density for the various
colours on an ordinary plate as that given by
white or blue hght, the following approximately
lative exposures mus
t be given :—
Violet .
2
Green
4
Greenish-yellow
YeUow
30
36
Orange
Red
120
1,600
LIGHT, CONTINUING ACTION OF (See
" Continuing Action of Light.")
LIGHT, DIFFRACTION OF (See "Diffrac-
tion.")
LIGHT FILTER (See "Colour Screen or
Filter." )
LIGHT FOG (See " Fog.")
LIGHT INTENSITIES, DIFFERENCE IN
Daylight varies in intensity according to the
time of day and year, and also according to the
PORTRAIT
BV H. ESSENHIGH CORKE, F.K.P.S.
A phutujirttpVi in rmturul' colours, taken n
by the tour-cdUi
the Thames plate, lind reproduced
r process,
Light Rays, Colours of
337
Ughtning, Photographing
latitude. Further, the freedom or otherwise of
the sky from douds has an important influence.
As the exposure of a sensitive plate is dependent
on the intensity of light, it is important tiiat this
should be determined, and numerous tables have
been published giving the variations, but of
recent years the plan of actually testing the
actinic power of ttie light by exposure meters
has come into general use, thus doing away with
the personal equation in the estimation as to
whether the hght is " bright," etc.
LIGHT RAYS, COLOURS OF
Every ray of the spectrum has its own par-
ticular colour, although the human eye is not
sufficiently sensitive to differentiate between
rays that are closely contiguous. {See " Spec-
trum.")
LIGHT, REFRACTION OF (See "Refrac-
tion.")
LIGHT STANDARDS (Pr., ttalons de la
lumiire ; Ger., Licht-einheiten)
Various imits have at different times been
adopted or recommended for comparing light
intaisities, such as the standard sperm candle,
the amyl-acetate lamp, the Carcel lamp, the
Methven screen, the pentane lamp, etc. These
are dealt with under their respective headings.
Acetylene has also been suggested for use.
The British imit, the sperm candle (i c.-p.), is
subject to slight variations from different causes,
and scientific workers now commonly prefer
to use the pentane lamp. The Methven screen
and the pentane lamp are each equal to i c.-p.
and are eqtiivalent to I-I4 Hefner-Kerze, or
" H. P." (amyl-acetate lamp) ; while the Carcel
lamp gives a light equal to about 9-5 standard
candles. (See also " Sensitometry " and "Unit
of Light.")
LIGHT, UNIT OF (5ea "Unit of Light.")
LIGHTING OF LANDSCAPES
An astonishing variety of effects may be
obtained from the same landscape, due entirely
to differences in its lighting. Some views are
most effective as seen under a soft grey light,
whereas in other cases a strong lighting gives
the best result. In a bright light the most un-
satisfactory position for securing the view is
with the light directly behind the camera, and,
therefore, full on the subject, as the shadows are
concealed by the objects casting them. A side
lighting is far more satisfactory as giving more
relief and allowing the shadows to play their part
in the arrangement of the picture. It is often
possible to secure a striking and pleasing effect
by photographing "against the light" — that is,
with the sun more or less opposite the camera —
but it is necessary to protect the lens from the
direct rays of Ught. Another opportunity for
variation in effects comes when there are clouds
through which the sun breaks at intervals in
such a manner as to light up this or that portion
of the view, while the rest remains in shadow.
Such a play of hght and shade on a landscape
must be accounted for in the print by a sky that
corresponds; so that, if it is not possible to
record the sky on the same plate as the land-
scape, a second plate should immediately be used
to secure the sky with a. shorter exposure. Not
only are the amount and the direction of the
hght important considerations in landscape
work, but also the condition of the atmosphere.
A certain amoimt of haze or mist veiling the
distance is often of the greatest value in the
pictorial effectiveness of the result. There is
much educative value in taking a series of views
of the same landscape under as many different
conditions of Ughting as possible and carefully
studying the results.
LIGHTING OF SITTERS (See "Portrait-
ure," and other headings.)
LIGHTNING, PHOTOGRAPHING
The first successful photograph of a lightning
flash was taken on a dry plate on September 2,
1882. Lightning cannot be photographed during
the daytime, as, however dark Qie sky is, the
sun is behind it and actinic enough to have an
action upon the dry plate, and make the flash
invisible. At night the sky may be black and
have no action upon the photographic plate, the
flash appearing to stand out prominently. It is
not advisable to photograph hghtning through
a closed window. Coming storms exhibit the
best flashes, although at the seaside good flashes
may often be obtained from storms disappearing
seawards. The finest lightning photographs
have been taken looking seawards, there being
no obstructions between camera and horizon.
The latter should always be included in the
picture, as when taking clouds ; otherwise, in
the photographs, it may not be easy to tell the
top from the bottom of the flash. The camera
must be supported, either by a stand or other
means ; if it is of fixed focus, there will, of
course, be no focusing necessary, but if of the
focusing pattern, the lens should be racked out
to the position it would occupy if a distant view
were being photographed. It is desirable to
focus during the day and to make a mark on
the baseboard, so that the focus may be
instantly ascertained at night, when accurate
focusing is impossible. Having made all ready
and fixed the camera with the lens pointing in
the direction of the flashes, the dark-slide is
inserted, the shutter drawn, the plate exposed,
and the flash waited for ; when it does appear,
providing that it is within the range of the lens,
it photographs itself ; the lens is then capped and
the plate changed. It is advisable to use wide-
angle lenses so as to include as much of the
sky as possible, as forked lightning has a way
of disappearing from a narrow field of view.
The largest possible stop should be used, and a
rapid plate, well backed so as to prevent hala-
tion. Detail is not so much wanted as contrast
in the negative, and development should there-
fore not be continued long enough to produce
fog, as a flash showing but faintly on a negative
may easUy be intensified, preferably with mer-
cury and ammonia. One developer is as good
as another for negatives of this class, but hydro-
quinone and a mixture of hydroquinone and
metol appear to be the favourites. The plate
should be changed after every flash photographed,
no matter of what kind ; one may be unfortunate
enough to expose a dozen or more plates on weak
Light-struck
338
Limelight
sheet flashes, which are useless photographically,
while, on the other hand, one may be fortunate
in securing a forked flash every time. Sheet
lightning will fog a plate and make it quite use-
less.
UGHT-STRUCK
A term applied to sensitive plates or papers
that have been fogged by exposure to actinic
light. The term is sometimes appHed to dark
foggy streaks upon the negative caused by the
dark-shde not being perfectly light-tight. {See
also " Fogged Dry Plates, Restoring.")
LIGHT-TRAP FOR DARK-ROOMS (Pr.,
Trappe-lumiire ; Ger., Lichtfalle)
A ventilator admitting air to the dark-room
while excluding Ught. A common form is that
illustrated. A row of holes is bored at the
bottom or top of the door, or in any other
suitable place, and a three-sided case of wood A
Light-trap
is made having a similar series of holes. In
the middle of the case is a partition B reaching
nearly across. The case, blackened inside, is
attached to the door by screws or angle-pieces
and the two ends are boxed-in. Since light
can only travel in a straight line it is effectually
blocked, whereas the air proceeds uninter-
ruptedly into the room, as shown by the arrows.
It is usually necessary to have at least two
light-traps, one at the bottom to admit fresh
air and another at the top for the exit of foul
air. (See also " Dark-room Ventilation.")
LIGNIN (Fr. and Ger., Lignin)
Woody fibre. Formed from the cellulose of
plants by incrustation with other compoimds,
probably aromatic, during the change into
wood. It was at one time believed to be identical
with celliilose (CgHijOj) in chemical composition,
but later research has shown that this is not so,
the true formula being approximately CjaHijOj.
It is decomposed by sulphuric acid, forming
dextrine.
LIME, CARBONATE OF {See "Calcium
Carbonate.")
LIME, CHLORIDE OF {See " Calcium Hypo-
chlorite.")
LIME, CHLORINATED {See " Calcium Hypo-
chlorite.")
LIME IN WATER
The presence of lime in the washing water
sometimes causes a scum to appear on the dried
negative ; and although the deposit is of but
htUe importance in itself, it may interfere more
or less with the proper working of an intensifler
or reducer. Lime scum appears mostly when the
ferrous oxalate developer is used, and is due to
precipitation of lime oxalate. It may be
removed by placing the negative before drying
in a weak solution of hydrochloric acid (4 drops
of acid to I oz. of water). Some workers use
alum water, as it dissolves the lime without
softening the gelatine. When the presence of
lime is suspected, the negative should be wiped
with a pad of wet cotton-wool before drying.
Water may be tested for Hme by adding to it
a solution of ammonium (or potassium) oxalate ;
a milkiness or white precipitate indicates the
presence of a calcium salt.
LIME WATER
Known also as liquor calcis, and prepared by
shaking up pure slacked hme in distilled water
and decanting. Commercial lime water con-
tains haU a grain of calcium oxide (quickhme,
CaO) per ounce.
LIMELIGHT
An illuminant for use in optical lanterns, etc.,
in which a spot on the surface of a cylinder of
lime is heated to incandescence by a gas flame
fed with oxygen under pressure. Oxyhydrogen
limehght has a photometric value of i6-6, as
compared with that of a multiple-wick lamp i,
and of a 50-ampere arc lamp 160. When an
ordinary flame, as of hydrogen, coal-gas, alcohol,
etc., plays upon a piece of hme, the latter
becomes dull red-hot, but when the combustion
is forced and made more complete by means of
a supply of oxygen under pressure, the heat of
the flame is increased to such an extent that
a small part is raised to such a high temperature
that it emits a blinding white light. In the
past, the combustible gas for UmeUght has been
suppUed in a number of different ways. The
best known of these, hydrogen, was made by
acting with dilute sulphuric acid on scrap zinc ;
the gas was stored in a collapsible bag which,
when required, was connected to the UmeUght
jet. By other systems, special forms of jets
were necessary ; for example, in one was a
simple spirit lamp through the flame of which
a jet of oxygen was forced ; in another was a
vessel containing ether, through which was
passed a current of oxygen, which thereby
became laden or saturated with particles of the
ether and was then burnt at a nipple. All such
arrangements are, or should be, obsolete, as by
the modem system of supplying gases in sted
cylinders {see " Compressed Gas ") a convenient
and safe supply of a combustible gas is easily
secured. These cylinders are periodicaUy tested
and annealed, and their use is attended by a
minimum of risk, which is not the case in the
oxy-alcohol and oxy-ether systems, especially
the latter.
Limelight jets are of two main kinds — the
blow-through and the mixed. In the former, A,
the gases do not mingle until they reach the
point of combustion ; in the latter, B, the gases
mingle in a mixing chamber at the base of the
actual jet. The more intimately the gases
mingle, the greater is the heat of the flame
Limelight
339
Lines in Composition
produced, and therefore the high-power jet is
always of the mixed type, the blow-through
jet being practically restricted to the use of
the beginner. The jet is supported on a vert-
ical pin projecting from a sheet-metal tray
which slides into the lantern body from the
back. One nozzle H is connected by rubber
tubing to the hydrogen supply, whici in the
case of a mixed jet is a cyhnder, and in the
case of a blow-through jet either a cylinder
or an ordiaary gas bracket. The other nozzle o
is connected to the oxygen supply, which,
nowadays, is always a cylinder. In the case
of the blow-through jet, the nozzles are con-
nected to the gas suppUes in such a way that
the oxygen issues in a stream from the central
nipple, whilst the cone of burning hydrogen
surrounds it. The taps are generally stamped
with either " O " or " H," indicating the proper
connections. The lime cylinder {see dotted lines
C) is supported on a pin at an adjustable distance
from the nipple, there being provision for
rotating the lime by means of the rod d, so as
Blow-through and Mixed
Limelight Jets
to obviate the formation of deep pits in the
lime while the jet is in use. When a flame
plays upon a deeply-pitted Ume, there is a
risk of the lime cracking or of the flame being
deflected upon the condenser. The distance
of the lime from the nipple is a matter for
experiment and varies with the dass of jet ;
it has a great influence upon the quaKty of the
light. Simple jets are here illustrated, but very
elaborate appUances are obtainable, these being
fitted with screw-down adjustment valves and
various mechanical devices for regulating the
light as regards its height, distance from con-
denser, distance of lime from nipple, etc.
The following matters should receive attention
when managing a limelight exhibition. An
automatic regulator or screw-down adjustment
valve regulator must be screwed into the valve
of each cylinder (see " Cylinders, Gas "), it
being necessary to reduce or check the pressure
of the gas as it issues from the cylinder. High
quality rubber tubing connections should be
used, and if an automatic pressure regulator
is not used, these tubes should not be tied on,
in which case, also, the taps on the jets should
be opened wide, and the whole of the adjust-
ment done from the cylinder valves. A Ume
(see " Cyhnders, Lime") is put in place, a small
flame allowed to play upon it, and the lime
turned occasionally so that it gets warm
right through, the object being to prevent
cracking when the oxyhydrogen flame is turned
on. Then the hydrogen flame is increased
slightly, and the oxygen gently turned on,
adjusting the two taps and the distance of lime
from nipple until the best efiect is observed
upon the screen. Push in the jet or withdraw
it from the condenser until there is an even field
of Ught ; if the jet is not central, there will be
coloration or a shadow somewhere on the screen
and the jet should be moved in the opposite
direction to the defect imtil this is removed.
Three minutes' experimenting will teach all that
it is necessary to know in this matter. The
adjustment of the light should preferably take
place after a slide has been roughly focused
and withdrawn. Always, when tiiming ofi the
light, cut ofE the oxygen first, as otherwise there
■vnU be a slight pop in the hydrogen tube of a
mixed jet.
It is advisable to retain a key on the valve
stem of each cylinder so that in the case of a
biirst rubber tube or other similar accident the
gas can be cut ofi immediately.
LIMES (See "Cylinders, Lime," and "Lime
light.")
LINE DRAWINGS {See "Copying," "Copy-
ing Illustrations for Translation into Line
Drawings," " Copying Stand," " Drawings
Made from Photographs," and " Engrav-
ings, Copying.")
LINE NEGATIVES
Negatives of line drawings. Commercially,
they were usually produced by the wet-plate
process, but photo-mechanical gelatine dry
plates are now widely used. A good test for a
line negative is to lay it film side down on a sheet
of white paper, and note whether all the lines and
blacks on the original appear quite transparent.
Veiled lines are sure to give trouble later. Every
endeavoiir should be made also to secure nega-
tives free from yellow stain, as this will retard
the printing and make it difficult to obtain the
correct exposure, so that the lines will wash away
in the development of the prints, or if sufficient
exposure is given to retain the lines there will
be a difficulty in clearing the groimd.
LINEN, MOUNTING PRINTS ON
In this work it is desirable to strain the fabric
on a frame, and the prints need to be rubbed into
close contact, as explained under the heading
" Canvas, Mounting Prints on."
LINEN, PHOTOGRAPHS ON {See "Fabrics,
Printing on.")
LINES IN COMPOSITION
What are spoken of as lines in the composition
or arrangement of a photograph may not exist
as actual lines at all. For instance, the tops of a
row of trees woidd not be connected by a line,
but they woidd none the less suggest one. Simi-
larly, various masses suggest boundary lines
which roughly enclose them, while detached
objects, which carry the eye along from one to
another, also suggest a line of direction. More
Lines, Fraunhofer
340
Lippmann's Process
or less clearly defined lines may also be actually
present — the horizon, the banks of a river, the
edge of a path, tree trunks, hill-sides, roofs, and
so on. The principal lines, present or sug-
gested, are generally most evident when the print
is viewed from such a distance that minor de-
tails do not obtrude themselves. The position,
arrangement, and direction of these lines decide
whether the general composition is satisfactory
or otherwise. Even the points where certain
lines reach the margins play an important part.
A good arrangement generally results when the
lines indicating the masses of the principal object,
or objects, are grouped somewhere near the
middle of the picture space, with the other
principal lines radiating therefrom. The lines
are unsatisfactory when they tend monotonously
in one direction ; when they are too symmetrical ;
when they lead the eye out of the picture towards
the edges ; or when they lead the eye to a part
of the picture that does not contain the main
objects.
Although no very definite rules can be laid
down on this question of the lines of a subject,
it is a good plan to make analyses of pictures
in this way from time to time. No skill in
draughtsmanship is required for the purpose.
It is sufficient to mark out a space proportionate
to the print under study, and mark, in their
relative positions, the general (not detailed)
outlines of the principal masses, and to add any
lines that attract the eye, whether those lines
are actually indicated or only suggested. The
sort of pattern thus formed should then be
studied, noting the way in which the eye is
attracted to, or led to, certain points, and the
effect that the lines have in suggesting harmony,
monotony, contrast, stability and so on. By
degrees a sort of instinctive perception of the
principal lines of a subject will be acquired.
(See also " Pictorial Composition.")
LINES, FRAUNHOFER (See "Fraunhofer
iines.")
LINING BEVELLER
A machine made by Royle, of Paterson, N.J.,
for bevelling half-tone plates, and forming ruled
lines round them. The bevelling is done by
means of a rotating head carrying two cutters,
one of which makes the flat of the bevel, and
the other parts off the waste margin of the
metal. Another cutter, shaped like a graver, is
arranged to work parallel to the bevel, and
mechanical adjustments permit of the tool being
placed at any distance from the bevel. Thus
several lines can be made one after the other
to form a border.
"LINKED RING," THE
The managing committee of the original
Photographic Salon. The first Salon was held at
the Dudley Gallery, London, in October, 1893,
and there were annual exhibitions in that place
until 1904 ; in 1905-9 the exhibition was
held at the gallery of the Royal Society of
Painters in Water-colours, I<ondon.
LINOTYPE
An early and now almost obsolete name for
photographs on linen and other fabrics.
LIPPMANN'S PROCESS
A process of colour photography in which the
phenomenon of stationary or standing waves is
utilised. The process consists in exposing a
transparent emulsion in contact with a reflecting
surface, such as mercury. Prof. Gabriel Lipp-
mann first used Taupenot's albumen process, and
Krone, who has been extremely successful with
this process, gives the following method : —
Albumen from whites
of 6 eggs . . . 4 oz. 130 CCS.
Pot. bromide (10 % sol.) 51 mins. 4-3 „
Liq. ammonise (strongest) 51 ,, 4-3 ,,
Beat to a froth, and allow to stand for twelve
hours to liquefy, and then carefully decant or
filter through some glass-wool. Unused glass
plates should be thoroughly cleaned with
alcohol, and then evenly coated with the above
and drained, allowing them to dry in a hori-
zontal position. When thoroughly dry they
should be heated to 140° P. for two minutes,
and then allowed to cool down to normal temper-
atiure and sensitised by bathing for two minutes
in a 10 per cent, solution of silver nitrate acidu-
lated with 10 per cent, of glacial acetic acid.
The plates should next be washed for ten min-
utes and rinsed with distilled water, well orained,
and colour-sensitised in one of the following
baths : —
A. Chinoline red sol.
(I : 500) . . 27 mins. 1-6 ccs.
Cyaninesol. (i : 500) 7 „ -4 cc.
AJnmonia (2 % sol.) 50 ,, 3 ccs.
Distilled water to . 7 oz. 200 „
B. Erythrosine sol.
(i : 500) . . 17 mins. 1 cc.
Cyaninesol. (i : 500) 17 „ i „
Ammonia sol. (2 %) 51 „ 3 ccs.
Distilled water to 7 oz. 200 „
C. ChinoUne red sol.
(i : 500) . . 25 mins. 1-5 ccs.
Malachite green sol.
(I : 500) . ■ &i „ -5 cc.
Ammonia sol. (2 %) 51 „ 3 ccs.
Distilled water to 7 oz. 200 „
D. Erythrosine sol.
(i : 500) . . 17 mins. i cc.
Malachite green sol.
(I : 500) . . 17 „ I „
Ammonia sol. (2 %) 51 „ 3 ccs.
Distilled water to 7 oz. 200 „
The plates should be bathed for three minutes
m absolute darkness, allowed to drain for a
minute or two, and then dried at 140° P. (60° C).
For normal work A is to be preferred, but with
decreasing height of the sun E or D is better.
The developer recommended is —
A. 10 per cent, alcoholic solution of pyro.
B. Ammon. carbonate 772 grs. 50 g.
Distilled water to 10 oz. 268 mins. 300 ccs.
C. 10 per cent, solution potassium bromide.
For a 7 X 5 (13 X 18 cm.) plate, mix
freshly of —
A . . . . 128 mins. 7*5 ccs.
B . . . . 338 „ 20 „
C . . . .15 drops 15 drops
Distilled water i oz. 27 mins. 30 ccs.
Lippmann's Process
341
Lippmann's Process
When developed, wash and fix in a i -J solution
of "hypo," and if the plate appears too thin,
intensify with acid pyro and silver intensifier.
Valenta was the first to publish a gelatine
emulsion formula : —
A. Distilled water 10 oz. 268 mins. 300 ccs.
Gelatine . .154 grs. 10 g.
Silver nitrate . 93 „ 6 »
B. Distilled water 10 oz. 268 mins. 300 ccs.
Gelatine . . 309 grs. 20 g.
Potassium bromide tj „ 5 „
Heat both solutions to 95° P. (35° C.) and add
A slowly to B with vigorous agitation. Valenta
recommends pouring the emulsion immediately
into 35 oz. or i litre of alcohol, stirring well with
a glass rod and then washing for a short time
in running water the precipitated emulsion, next
placing in a vessel and aading enough water
to make 21 oz. or 600 ccs., mdting at
as low a temperature as possible, filtering and
coating the emulsion. Later be suggested coat-
ing the plates without washing the emulsion,
and waslung the plates when the emulsion had
set. The sensitiser used was : —
Cyam'ne sol. (i : 500) 68 mins. 4 ccs.
aythrosinesol. (i : 500) 34 „ 2 „
and I to 2 parts of this were added to every 100
parts of the emulsion. Increase of sensitiveness
was obtained by bathing the plates just before
use in: —
Silver nitrate .
Glacial acetic add
Alcohol
48 grs. s g.
48 mins. 5 ccs.
20 oz. 1,000 „
Valenta also stated that the addition of 31 grs.
or 2 g. of sodium sulphite to the above quantity
of emulsion, and digestion for a short time, in-
creased the sensitiveness without increasing the
size of the grain.
Messrs. I<umi&e in 1893 published their
method of making the emulsion, and valuable
contributions also came from Valenta, Neu-
hauss, and Senior. The last named specially
recommends the following : —
A. Nelson's No. i gela-
tine . . 77-15 grs. s g.
Distilled water . 7 oz. 7 drms. 2'i „
Potassium bromide 32-4 grs. 225 ccs.
B. Nelson's No. i gela-
tine . . 77-15 grs. 5 g.
Silver nitrate (re-
cryst ) . . 46-29 „ 3 „
Distilled water 7 oz. 7 drms. 225 ccs.
Bring each solution to 95° F. (35° C), and add
B to A with continual stirring.
I^ippmann's later formula is as follows : —
Potassium bromide . 8-1 grs. -53 g.
Gelatine . . . 62 „ 4 „
Distilled water . . 3^ oz. 100 ccs.
For colour sensitising add : —
Alcoholic solution cyan-
ine (i : 500) . . 90 mins. 6 ccs.
Alcoholic solution chino-
line red (i : 500) .45,. 3 »
Idiz the above at 95° F. and add : —
Silver nitrate (dry) . iif grs. 75 g.
and stir until dissolved. Filter through glass-
wool and coat the plates, allow to set, place each
plate in alcohol, then wash for half an hour,
drain, and dry. The plates will keep a long time.
Senior increases the general sensitiveness of
the emulsion by adding to every 3J oz. or 100
ccs., 3 grs. or -2 g. of silver eoside.
For fixing all plates a 15 per cent, solution of
" hypo " may be used, or a 5 per cent, solution
of potassium cyanide, but the latter must only be
allowed to act for 15 to 20 seconds.
The heliochromes may be intensified with
dilute mercuric chloride followed by amidol and
sulphite, or the latter alone, and they may be
reduced by a very weak " hypo " and ferricyanide
bath.
One of the most exhaustive researches of the
Lippmann process has been undertaken by
H. E. Ives, whose conclusions will be found in
the British Journal of Photography (1908).
As already stated, the sensitive film must be
in contact with a reflecting surface such as mer-
cury, and special dark-slides can be obtained
commercially for this process. These have
usually a hard rubber rebate in the front of the
slide, against which the glass is pressed, and
behind the film is another washer which clips
the plate all round the edges so as to form, with
the recessed back, a shallow trough into which
the mercury is allowed to flow from a reservoir
bottle connected With the slide by a rubber tube.
Nothing but chemically pure mercury must
be used, but even this is liable to oxidation, and
this causes streaks and marks on the film on
development. It is advisable, therefore, either
occasionally to treat the mercury with siilphuric
acid, which dissolves the oxide, or, better still,
to form a bag of fine chamois leather by gathering
together the ends and then shake the mercury
to and fro in this, the leather having been
thoroughly freed from grease by washing with
soap and water and petroleum ether. In all
cases it is advisable to rub gently the gelatine
film of the plate after removing it from the dark-
slide with a tuft of cotton-wool, to remove any
adherent globule of mercury. In filling the slide
with mercury great care should be taken to
obtain an even flow of the latter, as stoppage
in the flow will generally show as a line across
the plate.
A finished heliochrome, when examined by
looking through it, generally appears as a more
or less dense negative of a brownish or brownish
black hue, and it is only when looking at the
film at a particular angle that the colours can be
seen. As a rule they appear very pale, and they
are actually diluted with white light reflected
from the front surface of the film. For pre-
liminary examination of the results the helio-
chrome may be immersed at an angle in a vessel
containing benzole, but for permanent examin-
ation it is advisable to cement to the film (with
Canada balsam or gum styra) a prism of glass
of about 10° angle.
The pictures must be viewed by parallel light,
and all side light cut off ; this may be effected
by cutting a hole in a window shutter and stand-
ing with the back to the hole with the helio-
chrome held in the hand at arm's length and
shifted till it reflects the sky light. Obviously,
somewhat similar results can be obtained by
Liq. Ammon. Fort.
342
Local Development
enclosing the heliochrome in a box and reflecting
sky light on to it by a mirror.
For projection on to a screen by means of a
lantern the aphengescope may be used.
LIQ. AMMON. FORT. {See " Ammonia.")
LIQUID GLUE {See " Pish-glue.")
LIQUID LENS {See " Fluid Lens.")
LIQUOR AMMONI/E {See "Ammonia.")
LITHIA, CAUSTIC {See " Lithium Hydrate.")
LITHIUM BROMIDE (Pr., Bromure de lithium ;
Ger., Bromlithium)
LiBr. Molecular weight, 87. Solubilities,
I in -6 water ; very soluble in alcohol and ether.
A white granular powder obtained by dissolving
lithium carbonate in hydrobromic acid. It is
very deliquescent, and must be kept in well-
stoppered bottles. On accoimt of its great
solubility in alcohol and ether it is used in
collodion emulsion making.
LITHIUM CARBONATE (Pr., Cavbonate de
lithium; Ger., Lithiumcarbonat, Kohlen-
saures Lithium)
LijCOa. Molecular weight, 74. Solubilities,
I in 75 water ; insoluble in alcohol. A hght,
white granular powder, occasionally used in
coUodio-chloride emulsion making, and to form
the other lithium salts.
LITHIUM CHLORIDE (Pr., Chlorure de
lithium ; Ger., Chlorlithium)
LiCl. Molecular weight, 42- 5. The hydra ted
salt has the formtda, LiCl aHjO. Molecular
weight, 78-5. Solubilities, i in 2-5 water; very
soluble in alcohol and ether. Colourless granular
crystals obtained by dissolving lithium carbonate
in hydrochloric acid. Used in coUodio-chloride
print-out emulsions.
LITHIUM HYDRATE (Pr., Lithium caustique ;
Ger., Aetzlithium)
LiOH. Molecular weight, 24. Soluble in
water and slightly in alcohol. A caustic white
powder, whidi readily absorbs carbonic acid
from the air, and must, therefore, be kept well
stoppered. Suggested by Lumi^e as the alkali
for use with hydramine.
LITHIUM IODIDE (Pr., lodure de lithium;
Ger., lodlithium)
Lil. Molecular weight, 134. Solubilities,
I in -61 water ; very soluble in alcohol and
ether. A white coarse powder occasionally used
in collodion emulsions. Very dehquescent.
LITHIUM TONER
A toning bath for gelatino-chloride paper
(P.O. P.) but Uttle used. The formula is : —
I/ithium carbonate . 2 J drms. 17 g.
Gold chloride . . 5 grs. -6 „
Water . . .20 oz. 1,000 ccs.
The bath is ready for use as soon as made.
Prints should be washed before and after toning
and fixed as usual.
LITHOGRAPHIC PHOTOGRAVURE
A photo-mechanical printing process, invented
by Carl Eckstein, of The Hague. A polished
lithographic stone is covered with an etching
ground, and is then ruled with very fine lines,
about -04 in. apart, scratched through the
ground with a diamond point, operated by an
engraving machine. The lines are then etched
and fiUed with ink. A photo-lithographic transfer
is next laid down over the lines, thus forming
a kind of half-tone effect, and the stone is rolled
up and printed from by the ordinary process of
lithography.
LITHOGRAPHY {See " Photo-hthography.")
LITMUS
Synonym, lacmus. A colouring matter yielded
by a process of fermentation from various lichens,
and is obtainable in soluble violet-coloured
lumps, a decoction of which is used to stain
sheets of absorbent paper, which paper is cut
up into strips and made up into little books.
Litmus papers are used for testing the acidity and
alkalinity of solutions, and those known in
photography are of a blue or red colour, the
blue for acids and the red for alkabs. Should
red htmus paper be turned blue by a solution,
this is proof that the solution is alkaUne and not
acid ; but if it remains red the solution is either
acid or neutral, to ascertain which blue litmus
paper is introduced, this turning red if the
solution is acid, but remaining imchanged if
neutral. Although litmus paper is suitable for
photographic purposes, it is a fact that some
acids do not affect it.
Litmus paper should be kept in a tightly
corked bottle, so as to exclude the air, and
should the blue paper become red by exposure
to air, as it sometimes does, the colour may be
restored by holding it over the fumes of am-
monia. Litmus is also made up in the form of
a pencU, which is used for making a mark on a
scrap of paper, which is then used in the same
way as htmus paper.
LITRE
A standard measure of capacity in the metric
system, equivalent to 1,000 cubic centimetres
(ccs.), I-7S98 British pints, or 2-113 American
pints. {See also "Weights and Measures.")
LIVER OF SULPHUR {See " Potassa Sul-
phurata.")
LOCAL DEVELOPMENT
The development of some portions of a
negative to a greater extent than others. There
are two methods of working, opposite in their
character and effect. The first, which is more
correctly termed " local development," consists
in applying to certain parts of the negative a
stronger solution than that in the dish, this
being kept weak — that is, either dilute or
containing but little alkah. The plate is taken
from the dish, and some strong solution, kept
separately in a measure, is applied by means
of a soft camel-hair brush to the parts that
are to be strengthened, taking care to prevent
the strong solution from spreading or running ;
tilting the plate may sometimes help in tfis
Local Intensification
343
Lubricant
connection. The negative must not be kept
out of the developer for more than a minute
at a time, and preferably less, there being always
the risk of the solution settling in patdies and
of the developer in the film oxidising and causing
stains. Therefore, it is best to brush the strong
solution on the parts of the negative for about
thirty or forty seconds, rinse the plate under
the tap for a few moments, and return to the
developing dish. After about a minute, the
local work may be repeated, observing the same
precautions, and then again repeated as many
times as desired.
The second method consists in developing
the plate in a normal solution and then, from
time to time, appljdng a lo per cent, solution
of potassium bromide to those parts that need
to be held back, taking all necessary care as
explained in the preceding paragraph. This
method is frequently employed for holding
back the sky part of a negative, so that clouds
may retain their printing value.
A serious objection to these methods is that
the plate has to be exposed freely to the dark-
room Ught, and it is almost impossible to avoid
fogging. The photographer may decide, there-
fore, to adopt, instead, the methods given under
the headings " Control in Printing," " Har-
monising Contrasts," or even to adopt local
intensification or local reduction, although the
local application of chemicals to negatives is
not advised if the desired results can be
obtained by other means.
LOCAL INTENSIFICATION
Intensification of parts of a negative only,
performed by appljnng solutions by means of
a brush. It is desirable to select well-marked
outlines at which the intensification should begin
and end, and then to work carefully in a good
light. The solution used must be one that can
be applied perfectly evenly, or one in which
slight unevenness will not show appreciably in
the finished result. Intensification by means
of mercuric bromide is suitable ; first brush on
the bleaching solution until the uneven markings
caused by the brush disappear in an even
bleaching. Then wash for a minute under the
tap, next in a dish, and then immerse in the
blackening solution in the usual manner. For
strengthening only small parts of a negative
the bleaching solution should be brushed on
without previously wetting the plate. For
larger parts, the plate should be soaked in water
for half an hour before beginning to intensify.
{See also "Intensification of Negatives.")
Local intensification is delicate work, and
difficult to carry out successfully ; while if it
is unsuccessful the negative is ruined. In
general, and if the photographer is not highly
skilled, it is better to avoid local chemical
treatment ; similar results can often be secured
without running risks by the methods that
are described under the heading " Control in
Printing."
LOCAL REDUCTION
Reduction of parts of a negative only, per-
formed by brushing on solutions, as in the case
of local intensification. For treating small
parts only, work with the negative dry, and
contmue to apply the solution with the brush
until the reduction is sufficient. Great care
must be exercised in keeping exactly to the
outlines of the parts under treatment. On a
large surface even working is easier after the
plate has been soaked in water for half an hour.
Compared with local intensification, the work
is more easily controlled, and the solutions are
less liable to deteriorate or produce erratic
results by acting unevenly. The Howard
Farmer reducer — " hypo " and potassium ferri-
cyanide — ^is the most suitable for local treat-
ment. As soon as the desired result is attained,
the negative should be washed in two or three
changes of water, and then placed in an add
"hypo" fixing bath for about ten minutes,
fin^y washing as usual. Many of the notes
on local intensification apply equally to local
reduction.
LOCOMOTIVES, PHOTOGRAPHY OF
The general principles that govern the photo-
graphy of machinery apply equally to such
subjects as locomotives. (See " Engineering
Photography.") Although, at times, a flat side
view is required by engineers as a record of the
elevation or outline of the engine, an oblique
view will always make a more interesting
photograph, taking it from the front end of
the engine and showing the front buffer-beam
very much foreshortened. For such a position
a lens should be used having a focus at least
one-third longer than the long side of the plate ;
and one of still longer focus wUl be preferable.
Modem locomotives are so long that the far
end is dwarfed considerably if a lens too short
in focal length is used. The subject is long in
proportion to its height, and unless the print
is made very long and narrow there will be a
wide expanse of foreground ; but this assists
in giving the impression of size and dignity.
In order to give it its fullest value, a posi-
tion should be chosen, whenever possible, in
which this foreground consists of rails forming
other lines in front of the engine photographed.
A man standing near the cab of the locomotive
will assist in conveying an idea of size, and an
engine-driver or fireman in working cdothes is
the only suitable figure. The camera should
not be more than s ft. from the ground, and a
little less is generally preferable. A higher
point of view dwarfs the engine.
LOGWOOD
A dye-wood obtained from the heart-wood
of the logwood tree, Hamatoxylon cam-
peachianum. The extracted dye is of a red
colour, and known as " haematein." Under
certain conditions a decoction of logwood will
precipitate gelatine. It was used for experi-
mental piurposes in the early days of photo-
graphy.
LORRAINE MIRROR (See " Qaude Lorraine
Glass.")
LUBRICANT
A mixture of Castile soap and alcohol is used
as a lubricant when burnishing prints with a
bar burnisher ; and a solution composed of
equal parts of linseed oil, liquor ammonise and
Lu-meter
344
Lumiere Colour Processes
water has also been recommended. Encaustic
pastes are sometimes referred to as lubricants.
French chalk and blacklead are used for lubri-
cating apparatus.
LU-METER
An instrument invented (1911) by J. S. Dow
and V. H. Mackinney for the purpose of esti-
mating the surface brightness of an object com-
pared with the light of a standard candle, and
for determining the necessary exposure required
for such object.
LUMIEIRE. ANTOINE
Bom 1839; died in Paris, 1911. Founder of
the famous photographic firm of A. Lumi^e
et ses Pils, which, with his two sons, Auguste and
Louis, he established at Lyons in 1883.
LUMli:RE COLOUR PROCESSES
Reference is made elsewhere to the starch
grain process {see " Autochrome Process " and
" Screen-plate Colour Photography "), but the
brothers Lumiere had worked out various
processes before this. In the bleach-out process
they suggested (1894) the use of cyanine, quino-
line red and turmeric, and also a partial fixation
of the results by means of metallic salts. In
1895, they exhibited prints produced from
negatives taken through the usual set of red,
green and violet screens, the positives being
printed on bichromated films of gelatine or
glue, soluble in cold water, which also contained
some silver bromide or other inert insoluble
matter, which increased the relief of the images.
After development of the print, the silver bromide
was dissolved out and the rehefs stained up and
superimposed.
The process above described was introduced
commercially, thin celluloid films being coated
with the gelatine so that the printing could be
done through the celluloid, thus obviating the
necessity of double transfer or lateral inversion
of the pictures.
In 1900, the brothers Lumi&:e exhibited a
series of fine prints produced by the super-
position of bichromated reliefs on collodion
supports, the following being an outline of the
process : The screens for taking the negatives
can be prepared by coating plate glass with
a 10 per cent, solution of gelatine. When the
gelatine is quite dry the plates should be
immersed in the following baths, which should
be at a temperature of 68° P. (20° C), for about
five minutes, then rinsed and dried. Two
glasses of each colour should be cemented
together with Canada balsam to form the
screen : —
Green Bath
Methylene blue N
(•5% sol.) . 20Z. 4iimins. 143 ccs.
Auramine G ("S^ sol.) to 20 oz. 1,000 „
Blue-violet Bath
Methylene blue N
(■5 % sol.) . . 10 oz. 500 ccs.
Distilled water to . 20 „ 1,000 „
Orange Bath
Erythrosine J (-5 % sol.) gi oz. 474 ccs.
Metanil yellow (sat. sol.) to 20 „ 1,000 „
The dish should be well rocked whilst staining
up the gelatine. The above colours are obtain-
able, methylene blue from Casella, auramine G
and erythrosine J from the Badische Anilin und
Sodafabrik, and the metanil yellow from Hepp
and Oehler. The papers are prepared as follows :
Plate glass should be well cleaned, dusted with
French chalk, edged with rubber solution, and
then coated with an enamel collodion of the
following composition : —
Alcohol
,
9 oz.
444 ccs.
Ether
•
11 „
556 „
Pyroxyline
•
105 grs.
II g-
Castor oil .
.
24 mins.
2-5 ccs.
When the collodion is dry, the plate should be
immersed in a 7 per cent, solution of gelatine
at 110° P., and a sheet of baryta paper cut
to the same size also placed in the gelatine.
The baryta side of the paper should be brought
into contact with the collodionised plate, and
the two thoroughly squeezed together and then
dried. When dry, the back of the paper should
be varnished with Soehnee's white varnish A,
diluted with an equal quantity of alcohol.
After twelve hours drying the paper should
be coated with the following mixture : —
Emulsion gelatine . . 2|^ oz. 1 20 g.
Hard glue (Coignet) . 2^ „ 120 „
Ammonium bichromate ij „ 60 „
Potassium citrate, neutral
(25 % sol.) . .384 mins. 40 ccs.
Cochineal red . . 9J grs. i g.
Alcohol . . . 4 oz. 200 ccs.
Water . . . 20 ,, 1,000 „
Soak the gelatine £md glue in the water and
dissolve at 120° P., allow to cool down to
95° P., and then add the other ingredients,
and finally the alcohol in small quantities.
Filter the mixture and coat the paper, whilst
on the glass, with the mixture, allowing
about 90 mins. or 2 ccs. for every 100 sq. in. or
100 qcm. The paper is then thoroughly dried
exactly as in the carbon process, stripped from
the glass, and exposed beneath the three nega-
tives, an actinometer being used to determine
the duration of insolation. After exposure
the print should be squeegeed into contact with
a sheet of glass which has been previously
collodionised with the above-mentioned collodion,
and then coated with a -75 P^^ cent, solution
of rubber in benzole. The coated glass and
the exposed print should be immersed in a dish
of cold water, squeegeed into contact and placed
under pressure for five minutes, then soaked
in cold water for two hours so as to allow of
complete expansion of the gelatine and paper.
Development should be effected in water at
100° P., and the print allowed to soak for about
half an hour, when the paper can be readily
detached and the print developed as in the
carbon process, and finally washed in cold
water and immersed in alcohol for five minutes
and dried. The reUef prints thus obtained
are dyed respectively red, yellow and blue, the
necessary baths being as follows : —
Red Bath
Erythrosine J (3 % sol.) ^ oz. 25 ccs.
Water to . . . 20 „ i.ooo „
Luminiferous Ether
34S
Lysol
Yellow Bath
Chrysophenine G
Water
32 grs. 3-3 g.
i6|- oz. 833 CCS.
Dissolve at 160° P. and add —
Alcohol
3J oz. 167 CCS.
Blue Bath
Diamine blue P, pure
(3 % sol.) . . 432 mins. 45 cos.
Hard glue (15 % sol.) . ij oz. 63 „
Water to . . . 20 „ 1,000 „
The relief prints should be left in these baths
for about twelve hours, then rinsed, and the
red and blue impressions immersed in a 5 per
cent, solution of cupric sulphate and then
rinsed and dried. The yellow print must not
be treated to the copper bath. It is possible
to superimpose temporarily the images whilst
on the glass supports and see if they are suflSciently
stained; corrections can then be made by
deeper staining, or washing out some of the dye.
The dyed impressions should be coated with a
1-5 per cent, solution of rubber in benzole, then
collodionised with a i per cent, collodion, and
the yellow print transferred to paper by means
of a warm 15 per cent, solution of gelatine,
the paper being stripped when dry and the red
and blue impressions superimposed on this also.
In a later process MM. Lumi^e suggested the
making of tiie blue impression by conversion
of the image of a bromide print by bleaching
with potassium ferricyanide followed by ferric
chloride, then coating this blue print with
collodion containing tetrazotolylsulphite or
tetrazoanisidinesulphite of soda and tiie chlor-
hydrate of 3-naphthylamine-ether. Exposing
imder the red printing negative and the action
of light produces t&e red image. Another
coating with collodion containing diazo-ortho-
toluidine sodium sulphite with metamidophenol
or resordn gave the yellow image. MM. I/Umi^e
have also paid considerable attention to Ivipp-
mann's process
LUMINIFEROUS ETHER
An extremely elastic and subtle medium
generally assumed to pervade all space and
permeate aU matter, the undulations of which,
communicated to the eye, give rise to the
sensation of light. Information of value in this
connection is given under the headings "Light"
and "Natural Colours, Photography in."
LUMINOUS PHOTOGRAPHS
Photographs which appear luminous or phos-
phorescent at night. They may be prepared in
several ways. The simplest is that of making a
positive transparency — as, for example, a lantern
slide — varnishing the film side, and coating with
luminous (Balmain's) paint. When dry, the
transparency is backed with thin wood or
cardboard, with a ring for hanging, and the
whole bound together with strips of gummed
paper or cloth. If exposed to hght during the
day the picture will appear luminous at night.
Another plan is to spread a thin coating of glue
upon cardboard and sprinkle with powdered
barium or calcium sulphide, or to coat with
Balmain's paint. A print is then made upon
thin sensitive paper which, after finishing in
the usual way, is made transparent with castor
oil, the excess blotted off, and the print attached
to the treated cardboard with thin glue or
strong paste, and dried by heat.
A method popular in Germany is to coat
a piece of thin transparent celluloid with the
following : —
Gelatine . . . 436 grs. 100 g.
Potas. bichromate . 48 ,, 11 „
Calcium sulphide . i oz. 55 „
Water . . . 10 „ 1,000 ccs.
The gelatine is soaked in the water, melted
by heat, the other ingredients added and dis-
solved, and the mixture filtered through cotton-
wool. When dry, the coated celluloid may be
printed upon from a positive through the
celluloid film, and the image developed in
warm water in the same way as in the carbon
process, a print being obtained which shows
as a negative by transmitted hght. This needs
to be backed with black velvet or black paper,
when it will appear as an ordinary black-and-
wlute positive by daylight, and as a luminous
or phosphorescent picture by night.
LUNAR CAUSTIC
A synonym for silver nitrate (which see).
LUNAR CORNEA
Latin for " Horn Silver." A form of silver
chloride occurring naturally in an almost
colourless mass, somewhat resembling horn, for
which reason it received the name of lunar
cornea from the old alchemists. It was first
described by Pabridus (d. 1S71), director of
the college at Meissen, in a book on metals,
pubUshed in 1556. It is often stated that
Pabricius was the first to notice that horn
silver became suddenly black on exposure to
hght, but, according to Major-General Water-
house, none of his writings bears out this
statement and, as a matter of fact, horn silver
does not blacken suddenly, the change being
gradual. (See also "Silver Chloride.")
LUNAR PHOTOGRAPHY (See "Moon,
Photographing the.")
LUXOTYPE
A half-tone process patented in 1883 by
Brown, Barnes and BeU, a Liverpool firm of
photographers. A photographic print was
pressed against a metal plate engraved with
a stipple in reUef, it thus becoming embossed
with a stipple. It was then strongly hghted
from one side so that the stipple could be photo-
graphed, and a negative suitable for making a
half-tone block was thus obtained. A modi-
fication of the process was to rub in the sunk
parts of the embossed surface of the print
with a pigment, so that it could be copied by
direct lighting.
LYSOL (Pr. and Ger., Lysol)
A mixture of alkaUne compounds of the
higher phenols obtained by boiling a mixture of
heavy tar oils, fat, and resin with alkalis. It is
used chiefly as a disinfectant, and is soluble in
water and alcohol.
M
MACHINERY, PHOTOGRAPHY OF {See
" Engineering Photography.")
MACKENZIE-WISHART SLIDE
This is a special form of slide which makes
possible dayUght changing (which see). The
plates are enclosed in light-tight envelopes.
MACROPHOTOGRAPHY (Pr., Macrophoiogra-
phie, Agrandissement ; Ger., Makropho-
iographie, Vergrosserungs-verfahrung)
A term applied to enlarging with the solar
camera ; now synonymous with enlarging gener-
ally. The opposite of microphotography
MADDOX, RICHARD LEACH
Bom at Bath, 1816; died at Southampton,
1902. He became well known for his work in
photo-micrography, and was the originator of
the gelatino-bromide plate. His experiments
with gelatino-bromide of silver emulsion were
published on September 8, 1871, and a modi-
fication of his process is in use to-day. The
original plates were slow because the emulsion
was not washed, and the lack of density was
due to the absence of a restrainer and the
presence of ammonia in the developer.
MAGAZINE CAMERA (Pr., Chambre magasin ;
Ger., Magazinkamera)
A camera carrjong a number of plates or flat
films in metal sheaths. With provision for ex-
posing these successively. Magazine boxes and
cameras for stand work were known as early as
1 861, but such cameras are now mostly of the
hand type. Many different changing systems
are in use, the simplest being that having a
Magazine Camera
leather changing bag attached to the camera ;
this, although reUable, is somewhat slow in use,
and automatic arrangements are now commonly
preferred. The illustration shows the interior
of a typical modem magazine camera, A being
an exposed plate in its sheath, falling into the
bottom of the apparatus, B the next plate in
position ready for exposure, and C the changing
lever. (See also "Hand Camera.")
MAGDALA RED (Pr., Magdala rouge: Ger.,
Magdalaroih)
Synonyms, naphthalene red, naphthalene rose;
naphthalene scarlet, Sudan red, rose naphthyl-
amine. A mixture of naphthylnaphthoros-
induline and naphthyldinaphthosaframine hydro-
chlorides. It is a dark brown powder, soluble
in alcohol and slightly soluble in boiling water.
It has been used as a sensitiser for gelatine
emulsions and gives a strongly marked maximum
at the D lines, but the gap in the blue-green is
wider than with erythrosine.
MAGIC CAMERA
An aphengescope, known also as the magic
camera, named after the inventor, Kruss, of
Hamburg. The original instrument was a tin
' B
D
Diagram of ICruss Magic Camera
box divided into two compartments, A and B.
In the division A was a lamp whose Ught was
concentrated by a condenser c upon the object
at D, an image of which was projected by the
focusing lens E upon a screen.
MAGIC LANTERN (See " Optical Lantem.")
MAGIC PHOTOGRAPHS
Bleached photographs that suddenly appear
on contact with a reagent. Of the possible
processes, the easiest is to make a print on
albumen paper, fix without toning, and to
bleach in a solution of mercuric chloride. Soak
pieces of blotting-paper in an ordinary fixing
bath (a "h3rpo" solution), and, on placing
the photograph between them and pressing
together in the hands, the original image will
once more appear.
MAGIC VIGNETTES (S«e "Black Vignettes.")
MAGILP (See "Megilp.")
MAGNALIUM (Pr. and Ger., Magnalium)
An alloy of magnesium, 15 to 20 parts, and
aluminium, 100 parts, which is harder than
aluminium, but not much heavier. It is easier
to work, and has, therefore, been used for lens
mounts, etc., instead of the pure aluminium.
346
Magnesium
347 Magnesium Ribbon or Wire
MAGNESIUM (Pr., MagnSsium ; Ger., Mag-
nesium)
Mg. Molecular weight, 24. A lustrous, silvery
white metal, which is used in the form of powder
and of ribbon for flashlight, etc. The light
emitted by burning magnesium is extremely rich
in actinic rays, and is the nearest in spectral com-
position to daylight of any artificial light ; one-
sixty louxth of a grain of magnesium burnt in air
gives as much photographically active light as
300 standard candles burning for one second,
assuming that the light has to pass through
the glass of a negative as in printing. (For in-
formation on using magnesium, see under the
headings "Flash Lamp," "Flashlight Photo-
graphy," etc.)
MAGNESIUM BEADS
Beads of dried paste, made with magnesium
powder and distilled water, at one time used
in an oxyhydrogen flame in much the same
way as a Ume to produce a powerful white
light. They are not deteriorated by the atmo-
sphere, as in the case of limes.
MAGNESIUM BROMIDE (Fr., Bromure de
magnisium ; Ger., Brommagnesium)
MgBrj 6H,0. Molecular weight, 291. Solu-
bilities, I in I water ; sUghtly soluble in alcohol.
It is in the form of colourless crystals, obtained
by dissolving magnesium carbonate in hydro-
bromic acid, and crystallising ; it is very
deUquesceut, and must be kept in well-stoppered
bottles. Occasionally used in collodion emulsion
making.
MAGNESIUM CARBONATE (Pr., Carbonate
de magnesium : Ger., Kohlensaures Mag-
nesium)
MgCOj. Molecular weight, 84. It is of small
photographic interest, but, known as calcined
magnesia, it is used in compressed blocks by
photo-engravers for rubbing into the hollows
of an etched plate, so that the state of the
work may be seen. Also, in the form of a fine
powder, it is used for the dry enamel process.
MAGNESIUM CHLORIDE (Pr., Chlorure de
magnisium ; Ger., Chlormagnesium)
MgOj or MgCla 6H2O. Molecular weight, 94
or 202. Solubilities, i in -6 water, i in 5 alcohol.
Colourless, bitter crystals or deliquescent mass
obtained by dissolving magnesium carbonate in
hydrochloric acid and evaporating ; it is very
deliquescent and must be kept in well-stoppered
bottles. A 15 per cent, solution was suggested
by Liesegang as a fixing agent, but it is not so
powerful as " hypo." It is also occasionally
used in collodion-emulsion making
MAGNESIUM FLASHLIGHT MIXTURES
Mixtures of magnesium powder and other
chemicals, particulars of which are given under
the heading " Flashlight Powders."
MAGNESIUM IODIDE (Pr., lodure de mag-
nesium ; Ger., lodmagnesium)
Mgl2 8H20. Molecular weight, 421. Soluble
in water and alcohol. A deliquescent white
crystalline powder that has been used in collodion-
emulsion making.
MAGNESIUM LAMPS (See " Plash Lamp.")
MAGNESIUM LIGHT
The light emitted when burning magnesium
(which see).
MAGNESIUM POWDER
Metallic magnesium in the form of a silvery
white powder. It keeps indefinitely, and
should be stored in a well-corked bottle. For
the methods of burning it see "Plash Lamp."
It should be dried before use, as otherwise it
will not fire properly. The impurities often
present in it do not generally afiect the value
of the hght, but they cause more smoke. Pure
powder shoidd feel soft and not gritty when
passed between the fingers, and should not
leave a dirty mark when rubbed on white
paper.
MAGNESIUM RIBBON OR WIRE
Metallic magnesium in the form of ribbon
or wire. Lamps are supplied for holding the
ribbon, but it is sufficient to cut or break off
the length required, hold in pincers or in any
other way, and apply a Ught. The ribbon will
give slightly more Hght, weight for weight,
than the pure powder, imless the latter is burned
in a form of lamp insuring complete combustion.
When using magnesium ribbon for printing by
contact, I in. of ribbon may be considered equal
to four minutes' exposure to an ordinary flat
gas flame at the same distance. The average
weight of magnesium ribbon is t gr. per 5 in.,
or about -5 g. per 100 cm. Ribbon burned in
oxygen gives a remarkably powerful hght;
a lamp for burning ribbon in this way was
devised by McLellan in 1882, and an improved
form was placed on the market by the Platino-
type Co. m 1899. Ribbon tarnishes and, con-
sequently, deteriorates quickly, and shoiild be
kept in an air-tight vessel ; the tarnish can be
removed by drawing the ribbon between smooth
folded glasspaper. The ribbon gives off a
considerable amount of smoke. Sometimes a
pad of damp cotton-wool lint is supported over
it, this absorbing most of the products of com-
bustion.
Woven Magnesium Ribbon
A method of making ribbon into a net of
coarse mesh has been recommended for con
venience when burning a large quantity and to
produce more even illumination, particularly
when enlarging. Two L-shaped pieces of tin-
plate or copper are cut, and the ends of the
strips of ribbon are then fastened on one of the
L-shaped pieces by pasting on a strip of paper.
When the mesh is complete, the other piece is
clamped on top. The lower, free corner of the
network may then be hghted, and the whole
bums rapidly.
Magnesium Sulphate
348
Manganese Sulphate
MAGNESIUM SULPHATE (Pr., SulfcUe de
magnesium ; Ger., Schwefehaures Mag-
nesium, Bittersalz)
Synonyms, Epsom salts, bitter salts.
MgSOj 7H2O. Molecular weight, 246. Solu-
bilities, I in 1-5 water, insoluble in alcohol.
It takes the form of small, colourless prisms or
needles, obtained from sea Water and certain
springs, or by dissolving magnesium carbonate
in sulphuric acid. It is used in making barium
sulphate, and has an extraordinary hardening
action on gelatine.
MAGNETOGRAPH (Pr., Magnitographe ;
Ger., Magnetograph)
An apparatus employed by meteorologists to
give a photographic record of the oscillations of
a magnetic needle.
Also the name applied to an image obtained
on a photographic surface by means of a magnet,
as explained in the next article.
MAGNETS, PHOTOGRAPHIC ACTION OF
The fact that magnets are capable of affecting
a photographic (daguerreotype) plate was first
asserted by Baron Karl von Reichenbach, about
1850. William Brooks, in 1877, placed a horse-
shoe magnet, poles upwards, in a light-tight box,
a blackened perforated card being supported
f in. above the poles, and a sensitive emulsion
plate \ in. above the card. After leaving the
plate for from 3 to 15 minutes, an image of the
perforations on the card could be developed.
Braham and others have also experimented in
this direction.
MAGNIFICATION (Pr., Amplification: Ger.,
V ergrosserung)
Degree of enlargement. A term used princi-
pally in photomicrbgraphy and telephotography.
The diameter of the enlarged image divided by
the diameter of the original equals magnification ;
or, in telephotography, the Unear measurement of
any object in the picture divided by the measure-
ment of the same object as rendered by the
positive lens alone. (See also " Photomicro-
graphy" and "Telephotography.")
MAGNIFIER (Pr., Verre grossissant ; Ger.,
Vergrosserungsglas )
A supplementary lens which increases or
diminishes the focal length of the lens with
which it is employed. The arrangement has
advantages from the points of view of economy
and convenience, as further explained under
the heading " Supplementary I,enses."
MAGNIFIER, FOCUSING (See "Pocusing
Magnifier.")
MAHOGANYTYPE
A facetious term indicating the result of
inserting an empty dark-slide into a camera,
and going through the operations of drawing
the shutter, making the " exposure," etc.
MALACHITE GREEN (Pr., Vert Malachite ;
Ger., Malachiigriin)
Synonyms, benzaldehyde, new, Victoria, fast,
diamond B, soUd O, benzoyl or benzal green.
Soluble in water and alcohol. It is a complex
aniline dye occurring in yellowish crystals with
bluish-green reflection, or as a brown powder.
It has been used as a sensitiser, and also for
filters.
MALT PROCESS
Malt was one of the many preservatives
recommended in the days of collodion plates.
A mixture of 7 oz. of malt with 24 oz. of water
was kept at a temperature of 156° P. (69° C.)
for half an hour, allowed to cool, was then
filtered, and finally applied to the plates.
MANGANESE DIOXIDE (Pr., Piroxyde de
manganese ; Ger., Manganperoxyd, Braun-
stein)
Synonyms, manganese peroxide or binoxide,
blade oxide of manganese. MnOj. Molecular
weight, 87. Insoluble in water and alcohol.
Occurs native. It is a heavy, black powdei
or in steel-grey lumps containing about 90 per
cent. MnOjj, used for flashlight powders and
preparing oxygen.
MANGANESE PEROXIDE (See "Mangan-
ese Dioxide.")
MANGANESE, PRINTING WITH: MAN-
GANIC LACTATE PRINTING
A novel printing process worked out by the
Brothers Lumi^re in 1895. Por the sensitising
solution, 100 grs. of potassium permanganate
are dissolved in 2 oz. of water, the measure
being placed in cold water so as to keep the
solution as cool as possible ; 4J drms. of lactic
acid are then added, a drop or so at a time,
and the solution swirled roimd after each
addition ; these precautions will prevent the
solution from becoming hot and frothing over.
AUow to stand until all efiervescence has ceased,
and a thick brownish-black liquid results. Add
a solution (cool) of i drm. of glucose or grape
sugar in -J- oz. of hot water, and filter through
cotton-wool. The paper should be gelatine-
coated, and fresh P.O.P., fixed and well washed,
answers the purpose ; it is prepared by appljmig
the solution with a broad camel-hair brush and,
after half a minute, blotting off the excess and
drying in the dark. The paper must be evenly
coated, and none of the solution allowed to
reach the back. It yields a negative image
from a negative, and, therefore, a good positive
or lantern slide should be printed from ; print
in daylight. Develop by immersing the print
in a saturated solution of aniline sulphate in
water, to obtain a green colour ; add a few drops
of liquor ammoniae for a violet colour. By
using orthotoluidine sulphate solution, rendered
sUghtly add with hydrochloric acid, a deep
blue image results ; or, if the acid is replaced
by liquor ammoniae, a violet one. Faramido-
phenol develops an image something like an
ordinary silver print. Mi the solutions used
for developing should be as strong as possible.
Development is complete in about thirty seconds,
the prints being finished by washing in water.
MANGANESE SULPHATE (Pr., Sulfate de
manganise ; Ger., Schwefehaures Mangan)
S3monym, manganous sulphate. MnSO^ 4HsO.
Molecular weight, 223. Solubilities, i in -8
Marble Markings
349
Masks and Masking
water, insoluble in alcohol. It is in the fonn of
transparent rose-red efflorescent crystals,obtained
by dissolving manganese dioxide in sulphuric
acid. It has been suggested as an addition to
the bichromate sensitiser for carbon tissue, etc.
MARBLE MARKINGS
Stains that sometimes appear on wet collo-
dion negatives, due to the film becoming par-
tially dry before or during exposure.
MARBLE, PHOTOGRAPHS ON
Many methods have been advocated for
reproducing photographs upon marble, but the
best and simplest is by the carbon process
(which see). Processes for sensitising marble
and printing thereon direct have been worked,
but with these there is the difficulty of examining
the progress of printing.
MARi:CHAL'S COLLOTYPE PROCESS
The earhest collotype process worked out
after Poitevin's experiments in Paris, 1856, was
that of Tessie du Motay and Ch. R. Margchal,
in Metz, in 1865. Their method was similar
in principle to that in use at the present day.
MAREY'S GUN (See "Gun and Revolver
Cameras.")
MARINE PHOTOGRAPHY
The first supposed successful instantaneous
photograph is of a marine subject — New York
Harbour, taken in the 'fifties. In the same year
Baron Gros, of Athens, made some daguerreo-
types of breaking waves on the shores of Greece
— ^in Phalerum Bay. Marine work in general
resembles other hand camera work, but the
exposures are short owing to the usually
excessive brightness of the sea and sky. Backed
plates should be used, and there is no necessity
to have extra rapid plates ; the consensus of
opinion is in favour of isochromatic plates and
the use of a pale yellow screen, but many workers
prefer ordinary plates. The isochromatic plate
should have the advantage on a bright day,
and in the case of a blue sky. Should clouds
be present (and these often make a seascape a
success) there should be no difficulty in photo-
graphing them, inasmuch as sea and sky require
about t£e same exposure, whereas in landscape
work the foreground requires much longer
exposure than the sky. Breaking waves, and
seascapes with rocky or other dark foregrounds,
are more difficult subjects because of the great
differences in the correct exposures for the dark
foreground and comparatively brilliant sea and
sky. A foreground shutter — that is, -a. shutter
allowing of the foreground receiving a longer
exposure than the sky — should be an ideal
accessory for such work ; but when photo-
graphing breaking waves, the operator may
not know whether the rocks in the foreground
will remain in their natural state or be covered
with a seething mass of White foam, a. foam
which would be whiter, and require less exposure
than any other part of the picture. The shutter
should work at such a speed as to give a
naturalistic effect to the sea and waves. If a
shutter works too fast the water will appear
too sharp and have a frozen appearance, whereas
an exposure that is too long will show movement
and the sea will be blurred. One-himdredth of
a second is a good average speed, and if this
is found to be correct the exposures may be
otherwise corrected with larger or smaller stops.
FI16 is a good average stop, and With a medium
plate and good diffused light (not bright sun)
the exposure above mentioned will be about
right. In brighter weather a smaller stop may
be used and vice versa, and if the waves are
comparatively quiet a longer exposure may be
given.
Hand cameras of any kind are best for this
work, and a good view-finder is essential ; stand
cameras are next to useless. Sea air affects
leather and metal fittings considerably, and
the camera should be protected as much as
possible, especially from sea spray. Seascapes,
particularly those with dark foregrounds, need
careful development because of the great con-
trasts in the subject. A soft working and well-
diluted developer should be used ; adurol is
good, while metol, with or without a little hydro-
quinone, has its advocates. If the dark parts
lag behind, local development may be resorted to
or the lagging parts helped by breathing upon
them.
MARION'S GUM PROCESS
A modified form of carbon printing, now
obsolete, similar to the modem " Ozotype,"
introduced by A. Marion, in 1873. Transfer
paper coated with bichromated gelatine was
exposed under a negative, and a visible image
printed. The unsensitised carbon tissue and
print were then immersed in a 2 per cent, solution
of potassium or ammonium bichromate and
squeezed together ; after remaining under
pressure for several hours, or until nearly dry,
the carbon tissue was developed in the usual
way. The reduced chromium compounds were
absorbed by the tissue and produced a develop-
able image exactly the same as though the tissue
itself had been sensitised and printed. The
advantage was that the printing on the paper
could be watched and no transfer, as generally
understood, was needed.
MARIOTYPE
A gum print produced by Marion's gum
process.
MARS BROWN, MARS ORANGE, ETC.
Brown, orange, red and yellow pigments
prepared from natural earths. The colouring pro-
perty is chiefly due to iron oxide. They are
occasionally used for colouring photographs.
MARTIUS YELLOW (Fr., Jaune de Martius :
Ger., Martiusgelb)
Synonyms, Manchester yellow, naphthalene
yellow, jaune d'or. Solubilities, soluble in water
and alcohol. The sodium salt of dinitro-a-
naphthol, which was used for making yellow
screens.
MASKS AND MASKING
Masks, in the form of pieces of thin opaque
paper pierced with openings, have various uses.
In lantern slides a mask is used to shut off those
parts of the image not required. It consists of
Mastic (Mastich)
350
Measures, Graduated
a square of thin paper the same size as the plate
pierced with an opening corresponding with the
amoimt of picture desired. (See " Lantern Slides,
Masking, Binding, and Spotting.")
In printing, a similar mask is frequently
applied to a negative, especially when printing
a small picture with a broad white margin.
Masks of somewhat different character are
very useful in combination printing, adding
clouds to landscapes, etc.
MASTIC (MASTICH) (See "Gums and
Resins.")
MATT PAPERS
Papers with a matt surface are made for
almost all kinds of photographic printing,
silver printing-out papers for daylight, and
bromide and gaslight for working by artificial
light. Carbon prints always have a slight
effect of gloss in the shadows, even when
developed on a rough surfaced paper. Platino-
type prints, though devoid of gloss, are not
absolutely matt ; the print presents the actual
surface of the paper without any film or coating
to give the lifeless quaUty that distinguishes
the true matt surface.
MATT SURFACE
A matt surface is one that is quite dull, not
simply devoid of gloss like the natural surface
of a good paper, but dead and smooth. It is
considered by many to be more artistic than
a glossy surface, but it possesses a serious
disadvantage. The shadows of a print on matt
paper are always devoid of depUi and trans-
parency, the darker details being all lost in one
mass of uniform dark grey, and the dark masses
of tone appearing dead or lifeless. The shadow
details are visible while the print is wet, but
they disappear as it dries. A very slight sus-
picion of gloss is sufficient to give depth and
transparency to the shadows of a print, and to
render the dark details in their true value.
MATT VARNISH
Generally used on the backs of negatives for
softening lie light, particularly in the shadows.
A common practice is to coat the whole of the
back of the negative with matt varnish, to
scrape it away over the high lights, and either
to paint on the varnish over the shadows with
carmine water colour or to rub a soft lead pencil
on the varnish. The two following formulae
will be found satisfactory, and the coarseness
of the grain is dependent on the quantity of
benzole added, so that it is advisable to add a
small quantity first and test the grain : —
I. Gum sandarac ij oz. 70 g.
Gum mastic . 144 grs. 15 „
Ether . , 15 oz. 750 ccs.
Dissolve and add —
Benzole to . 20 oz. 1,000 ccs.
If the ether is anhydrous, add to it —
Water
f oz.
50 ccs.
When dissolved, add —
Alcohol . . 10-50 mins. 1-5 ccs.
Benzole to . 20 oz. 1,000 „
This makes a softer varnish than No. i, and
the alcohol gives a very fine grain. These
varnishes are coloured yellow by adding to every
200 parts I part of aurantia or chrysoidine.
Asphaltum gives a brown colour.
MAXWELL {See "Clerk-Maxwell.")
McDONOUGH'S COLOUR PROCESS
A process of screen - plate photography
patented by McDonough, of Chicago, in 1892,
and introduced for a brief period in 1897.
Sheets of glass were ruled with alternate lines
of red, green, and blue-violet, and placed in
front of a panchromatic plate during exposure.
The exposed plate was then developed in the
ordinary manner, and positives made there-
from which were bound up with similarly nded
viewing screens. In consequence of the some-
what coarse ruling of the Unes, they were rather
obtrusive, and owing to the want of absolute
contact between the viewing screen and the
photographic positive parallax existed, so that
the colour of an object changed with the angle
at which the pictiire was viewed.
MEALINESS
Albumen paper that has been sensitised in
a bath weak in silver has a mealy appearance
when printed, and density and brilliancy are
lacking. Very rarely a badly made toning
bath and one weak in gold Will cause mealiness.
Improperly kept platinum paper also gives
mealy effects.
MEASLES
A peculiar defect met with in all kinds of
printing-out papers, but usually with albumen
paper. The prints have a mottled appearance,
and on being viewed by transmitted light the
interior of the paper appears to be covered with
opaque blotches, which, if allowed to remain,
will afterwards discolour. The cause is gener-
ally a weak " hypo " fixing bath, or insufficient
or acid fixing, but sometimes it is fixing in a
strong light. The measle spots cannot be cured
when once they appear, but they may be pre-
vented by fixing thoroughly, and the use of an
alkaJine bath.
MEASURES. GRADUATED (Pr., Mesure
graduie. Vase gradui ; Ger., Mensur, Mess-
glas)
Vessels of glass, opal or celluloid of various
OliWlT \
-I \
PINT?
Fn
"' /
\J
A \
f
^
}
. Gum sandarac
I oz.
SO g.
Gum dammar
144 grs.
15 ,.
Ether .
12^ oz.
625 ccs
Graduated Measures
Measuring Jug
shapes, used for measuring solutions. They are
graduated either in ounces and drams, as at A,
Measures, Weights and
3S1
Mercuric Chloride
or in cubic centimetres, a combination form B
containing both scales being also made. Those
of white glass with black graduations are most
visible in the dark-room. Measuring jugs C
are convenient for large quantities. {See also
" Burette," " Dropping Bottle," etc.)
MEASURES, WEIGHTS AND {See "Weights
and Measures.")
MEDALLIONS. ETC. (S«fi " Bas-reliefs " and
"Coins and Medals, Photographing.")
MEDICAL PHOTOGRAPHY
Every year sees the wider application of
photography to medical science. At the present
day photomicrography and radiography are of
the very greatest importance, the first making
it possible to obtain a permanent and exact
record of the normal and abnormal appearance
of the tissues, of the blood corpuscles, and of
those blood-parasites and bacteria which are
the cause of various diseases ; while the second
assists in the diagnosing of fractures of the
bones, the presence of foreign bodies within the
thoracic and abdominal regions, and calculi in
the kidney, etc., etc. Radiography is fuUy
treated under the heading of " X-Ray Photo-
graphy," but the application of photomicro-
graphy to medical research calls for some
consideration here. The microscope must have
a centring sub-stage, and should also have a
good mechanical stage fitted with vernier
scales which act as " finders." The most
useful objectives will be, for medium and high-
power work, a ^th, ith, and ^th in. oil immer-
sion ; while for large sections and low-power work
generally, a 2 in., i in., and ^ in. The selection
of eyepieces will be governed by the type and
quaUty of the objectives. It is most important
that both eyepieces and objectives be kept
perfectly dean and free from dust, dust on the
lenses of the eyepiece giving rise to the appear-
ance of out-of-focus marks on the negative.
The sub-stage condenser must also be carefully
cleaned from time to time. As it is important
to bring out as much detail as possible in the
resulting negative, and all pathological and
bacteriological preparations are stained with
one or more stains, it is absolutely necessary
not only to use carefully and thickly backed
orthochromatic plates, but also suitable com-
pensating filters, that the maximum amount of
detail, coupled with sufficient contrast, may be
obtained. While visual observation of the
subject, with the compensating filter placed
immediately behind the sub-stage condenser,
will serve as a rough guide to i±.e amount of
detail and contrast likely to be obtained, unless
the dyes used for the filter are spectroscopically
true, and the photographic plate properly
orthochromatised, the photographic result will
not be as satisfactory as the visual examination
promised. Long experience has shown that the
most satisfactory results, as regards both the
quality and resolution of the image, are to be
obtained with a camera extension of 10 in. from
the eyepiece of the microscope to the focusing
screen of the camera. In photographing such
subjects as skin eruptions and rashes, careful
attention must be paid to the colour of the
eruption. For instance, a pink, yellow, or red
rash will show up much better if photographed
with an ordinary plate of medium speed, than
with an orthochromatic plate, for the simple
reason that the ordinary plate being less sensitive
to these colours, they will be rendered darker,
and, therefore, more conspicuous, than if
photographed on an orthochromatic plate. To
photograph culture tubes of bacteria that have
been inoculated by " stab " or " streak," place
the tube in a large water bath or lantern alum
trough filled with water. This will be found
to do away with the unpleasant, bright, vertical
reflections down the front and sides of the
culture tube, and to facilitate the successful
photographing of the growth within the tube.
MEDIUMS
The composition of mediums for colouring,
retouching, and spotting are given under separ-
ate headings.
MEGASCOPE {See " Aphengescope.")
MEGATYPE (Pr., Migatype ; Ger., Megatypie)
A term at one time applied to a process of
enlarging, and to the resulting enlargements.
MEGILP
Synonyms, M'Guilp, magilp, and magilph. A
mixture of linseed oil and mastic varnish, used
as a medium for oil colours and occasionally for
rubbing upon platinotype and bromide prints
for the purpose of increasing the depth and rich-
ness of the shadows.
MEISENBACH PROCESS
The earhest half-tone process commercially
exploited. By the method patented in Germany
in May, 1882, by Josef Ritter von Schmaedel
and G. Meisenbach, a single-Une screen was made
from the proof of an engraved plate ruled with
Unes, and the screen was placed in front of a
photographic positive of tiie picture and the
two photographed together. Half-way through
the exposure the screen was turned so that the
lines crossed. A half-tone negative was thus
obtained from which a zinc block was made.
Afterwards the process was modified by placing
the screen in front of the sensitive plate and
photographing direct from the original print, the
screen being turned half-way as before.
MELAINOTYPE
An early name for the ferrotype process.
MENISCUS LENS (Fr., MSnisque; Ger.,
Menishus)
The concavo-convex lens. (See " Concave
Lens " and " Convex Lens.")
MERCURIAL INTENSIFICATION {See "In-
tensification of Negatives.")
MERCURIC BICHLORIDE {See "Mercuric
Chloride.")
MERCURIC CHLORIDE (Fr., Bichlorure de
mercure ; Ger., Quecksilberchlorid)
Synonyms, perchloride or bichloride of mer-
cury, corrosive sublimate. Hg CI 2. Molecular
Mercuric Iodide
3S2
Mercury Thermo Regulator
weight, 271. Solubilities, i in 16 water, i in 3
alcohol, I in 12-14 ether. White crystalline
masses or small crystals prepared by dissolving
calomel in hydrochloric acid. Very poisonous,
the antidote being white of egg, followed by an
emetic. Its solution" is decomposed by light,
and should therefore be kept in the dark. It is
used as the bleaching agent in mercurial intensi-
fication.
MERCURIC IODIDE (Fr., lodure de mercure ;
Ger., Quecksilberiodid)
Synonym, red iodide of mercury, biniodide of
mercury. Hg Ij. Molecular weight, 454. Solu-
bilities, insoluble in water, i in 116 alcohol, i in
85 ether, very soluble in potassium iodide
solution. A heavy scarlet red amorphous
powder precipitated from mercuric chloride
solution by potassium iodide. Poisonous {see
" Mercuric Chloride " for antidotes). It is used
in intensification, and is then usually prepared
direct as follows : —
Mercuric chloride
Potassium iodide
54 grs.
33 „
6 g.
4 „
Dissolve each in a little water, mix, and add —
Sodium sulphite . 4 oz. 220 g.
Water to . . . 20 „ 1,000 ccs.
Mercuric and Potassium Iodide, Hglj 2KI,
is sometimes used instead of the above, and can
be made by adding 2 parts of potassium iodide
to 1 part of mercuric iodide in dry powder, or
it can be made in solution by adding 99 parts
of potassium iodide to 54 parts of mercuric
chloride.
MERCURIC PERCHLORIDE (See " Mercuric
Chloride.")
MERCURIC AND POTASSIUM IODIDE
This is described under the heading " Mer-
curic Iodide," above.
MERCUROGRAPHY
Many lithographic processes have been based
on the fact that if those parts of a zinc plate
which are not covered with ink are treated with
mercury or a mercuric salt, the amalgam formed
has the property of repelling ink.
MERCURO-URANOTYPE
A printing process (practically obsolete) in
which uranic salts are employed, they being
sensitive to light. Two saturated solutions, of
uranium chloride and mercuric chloride respec-
tively, are required ; i oz. of the first is mixed
with I dram of the second and appHed to paper,
which is next dried in the dark. After printing,
the paper is toned by floating on a very weak
solution of gold chloride or potassium chloro-
platinite, immersed in very dilute hydrochloric
add, and finally washed in plain water. {See
also " Uranium Printing.")
MERCUROUS CHLORIDE
Synonym, calomel. HgjCl^. Molecular weight,
471. Prepared by precipitating a solution of
mercurous nitrate with a solution of sodium
chloride, and of but the slightest photographic
interest.
MERCURY (Pr., Mercure ; Ger., Quecksilber)
Synonym, quicksilver. Hg. Molecular weight,
200. Solubilities, insoluble in alcohol and water,
soluble in nitric acid and hot sulphuric acid. A
heavy, silvery liquid element found native or
obtained by roasting its ore, cinnabar. It was
used as the developer in the daguerreotype
process, and is also used in the I,ippmann
process.
MERCURY BATH
A dark box in which daguerreotypes were
developed by mercury fumes. The mercuric
chloride solution used for intensifying gelatine
negatives is also known by this term.
MERCURY INTENSIFICATION (See "In-
tensification of Negatives.")
MERCURY PRINTING
By this process of printing (now obsolete)
pure mercury is covered with nitric acid, and
in the course of a few days the thick crust of
moist crystals which wiU form should be removed
and dried, as much as possible, on blotting-paper.
Dissolve 230 grs. of these crystals in 5 oz. of
water, and add nitric acid to dissolve any pre-
cipitate. Coat plain paper with starch paste,
d^ it, and in a very Weak light float it on the
above solution. Dry quickly and keep until
required in a calcium tube. Print for two or
three minutes and develop in : —
Ferric sulphate
. 65 grs.
IS g-
Tartaric acid .
• 65 „
15 „
Water
. 10 oz.
1,000 CCS.
Fix for five minutes in a solution of 90 grs. of
sodium chloride in 4 oz. of water, and tone the
greyish image to a black one in : —
Potassium chloropla-
tinite .
3 grs.
1 g-
Tartaric add
60 „
20 „
Water
7 oz.
1,000 CCS.
MERCURY SULPHOCYANIDE (Ft., Sulfo-
cyanure de mercure ; Ger., Rhodanqueck-
silber)
Synonyms, mercuric sulphocyanate and rhod-
anide. Hg (SCNjj. Molecular weight, 316. Solu-
biUties, slightly soluble in water, soluble in
alcohol and solutions of alkaline dilorides and
sulphocyanides. Poisonous {see " Mercuric
Chloride"). It is a white powder, but is easily
prepared in solution as follows : —
Mercuric chloride . 2 oz. 100 g.
Potassium sulpho-
cyanide. . . 768 grs. 80 „
Distilled water to . 22 oz. 1,000 ccs.
For use dilute i part of the above with 10 parts
of water. It is used as an intensifier for nega-
tives, and gives a good black image, but it is
preferable to apply a developer afterwards
MERCURY THERMO REGULATOR
For collotype ovens and drying boxes heated
by gas a heat regulator, which depends on the
expansion of mercury, is sometimes used. The
simplest form consists of a U-shaped tube con-
taining mercury A. Branch B is attached by a
THE MOON
Photographed at the Paris Ouservatory
CELESTIAL PHOTOGRAPHY
Mercury Vapour Lamp
353
Metal, Photographs on
rubber tube to a glass bulb C inside the drying
box. Branch D is connected to the burners. E F
are rubber stoppers, a glass tube G passing
through P to the gas supply, whilst its end inside
Mercury Thermo Regulator
the U-tube is ground ofE at an angle. As the
mercury expands through the heating of the bulb
inside the box, the sloping end of the tube G is
more or less closed, thus regulating the gas supply.
MERCURY VAPOUR LAMP (Pr., Lam-pe d
vapeur de mercure ; Ger., Quecksilber-
lampe, Quecksilberdampflampe)
A lamp in which the vapour of mercury in
a vacuum tube is raised to incandescence by
the passage of an electric current. The illus-
tration shows the Cooper-Hewitt lamp. In
this, four tubes are supported in a frame on an
upright stand, the mercury being contained in
the large bulbs, which form the negative ends
Mercury Vapour Lamp
or cathodes. When the switch has been closed
the tubes are reversed, so that the mercury
runs to the opposite end. This short-circuits
the two electrodes and the tubes immediately
light up, being then returned gradually to their
previous position. The lamp must not be
left with the bulbs uppermost; and the tubes
must be connected up to the right polarity, or
they will be destroyed in a few minutes. The
light obtained is, highly actinic, being rich in
violet rays, and excdlent for copying, printing,
and enlarging. Owing to its great difiusion
and coolness it is well suited for portraiture,
the sole objection being the ghastly colour of
the light. This effect is visuS only, and does
not appear in the photograph ; since it is due
23
to the absence of red rays, it is easily rectified
by using a few ruby or light-red incandescent
lamps in addition. {See also "Electric Light.")
Jn process work, this lamp has been used for
process copying and printing, but the liability
of the tubes to break down rendered its general
employment impracticable, and, on the point of
economy, tests showed that whilst the lamps
only took one-fourth of the current of " enclosed ' '
arcs the exposure was four times longer, so that
there was actually no gain. An advantage of the
mercury lamps was, however, that in photo-
graphing wash drawings in which Chinese white
had been used the reproduction was much more
faithful than that obtained with arc lamps. For
printing purposes with bichromate 0ms the
exposures were not more rapid than with the
enclosed arc on account of the absorption of
much of the actinic intensity of the light by
the yellow stain of the bichromate.
MERCURY-SILVER PRINTING
A process of French origin (1892). Paper is
floated on a solution of J oz. of mercuric chloride
in 6i- oz. of distilled water. It is washed, dried,
and sensitised on a bath of 48 grs. of silver nitrate
in I oz. of distilled water. The paper, when dry, is
printed under a negative iof about a minute, and
developed with the following, after which it is
Washed, fixed in " hypo," and again washed : —
Acetic add . . -J oz. 37 g-
Ferrous sulphate • I „ 37 „
Water . . . 15 „ 1,000 ccs.
METAFORMALDEHYDE
methylene.")
(See " Trioxy-
METAGELATINE (Pr., Metagilatine : Ger.,
Metagelatin)
A name given by Lyte, in 1857, to a solution
of gelatine boiled with dilute acid, usually sul-
phuric, so that it has entirely lost its setting
power. The acid was subsequently neutralised
with chalk, and the solution filtered and used
as a preservative in the old collodion dry process.
Many vain attempts have been made to sub-
stitute metagelatine for fish glue in the enamel
photo-engraving process.
METAL DISHES (Fr., Cuvettes mitcUUques:
Ger., Metallplatten)
Enamelled iron or steel dishes are used for
heating the alum-" hypo " toning bath, and for
hot-bath platinotype, as well as for other pur-
poses. Compared with porcelain dishes of
similar size, they are light, unbreakable, and
readily cleaned. The only danger is the chipping
of the enamel, in which event the solutions act
on, and are affected by, the iron beneath.
Enamelled dishes will, however, last a long time
without this happening, with ordinary care. If
the fault is suspected, a little dilute sulphuric
add may be poured in the dish, when small
bubbles of hydrogen gas will arise from any
part where the metal is exposed. Leaden dishes
are sometimes used for stripping solutions con-
taining hydrofluoric add.
METAL. PHOTOGRAPHS ON
Photographs may be obtained on metal by the
bitumen process (see " Heliography " and " As-
Metallic Films, Flexible
354
Methylpyrocalechin
phaltum "), or on silver plates by the daguerreo-
type process. Ferrotypes — collodjon photographs
on enamelled sheet-iron — are another familiar
instance. Carbon prints may be developed on
metal plates as a final support, giving very
effective results.
METALLIC FILMS, FLEXIBLE
A process invented in 1892 by Brandweiner
and I,autensall, of Vienna. A photographic
image is obtained on a highly polished copper or
brass plate, which is then etched, the protecting
film removed, and a poUshed image is seen on a
matt ground. A deposit of some metal is now
electrically produced, a sheet of paper, linen, etc.,
is made to adhere, and both sheet and thin metal
deposit stripped off, leaving the plate ready for
making another duplicate.
METALLIC SPOTS {See " Black Spots.")
METAMORPH PRINTS
Distorted or trick photographs produced either
by warming the wet film and partially melting
it, taking the film off the plate and stretching it,
or by the use of curved mirrors. (See also
" Anamorphoscope.")
METEOR PHOTOGRAPHY
The photographic delineation of meteors or
shooting-stars forms one of the most fascinating
brandies of astronomical study. The fact that
one of these visitors from outside space may
flash through our atmosphere at any moment
lends additional zest to the attempts made to
portray them ; the only help one has to prepare
for them is that past experience has shown that
they occur in families, as it were, at certain fixed
times of the year, and more or less concentrated
in definite regions of the sky. Thus we have the
Perseids in August, radiating in all directions
from the constellation Perseus, and the I,eonids
in November, radiating from tiie sickle-like con-
stellation of I/eo. Apart from this help as to
probable time and location, one must trust to
patience and an ever-ready camera. The camera
must be directed to the sky with the lens open,
and immediately a meteor is seen to cross the
field, the lens is capped and the plate developed.
No special apparatus or plates are necessary ;
the most rapid plates and a wide-angle lens of
as large an aperture as possible are to be recom-
mended. If the observer is fortunate, he may
chance to photograph a fireball, that is, a
meteorite in the act of exploding owing to the
heat developed by friction with ttie atmosphere.
METEOROLOGICAL PHOTOGRAPHY (Fr.,
La photographie mdUorologique ; .- Ger.,
Meteorologische Photographie)
Photography is of great service to the meteor-
ologist in connection with automatic recording
instruments, among which may be mentioned
the photo-barograph, or barometrograph, which
registers the fluctuations of the barometer ; the
thermograph for recording changes of tempera-
ture ; the psychrometer, a measurer of the
amoimt of watery vapour in the air; and the
magnetograph,,for indicating the oscillations of
the magnetic needle. Photography is also em-
ployed to record the positions and forms of
clouds, in making observations of the solar
spectrum, etc.
METER (See " Actinometer," "Exposure
Meter," " Opacity Meter," etc.)
METHOL
An early name for the metol developer.
METHVEN SCREEN
A sheet of metal pierced with an aperture
placed in front of a standard light to Umit the
effective portion to the part which burns the
most steadily, this usually being at the centre
METHYL ALCOHOL (See "Alcohol.")
METHYL ORANGE (Fr., miianthine : Ger.,
Methylorange)
Synonyms, dimethylaniline orange, gold
orange, tropseoline D, orange III., helianthine,
Poitrier's orange 3 P. Soluble in water. Sodium
or ammonium dimethylaminoazobenzenesul-
phonate. A yellowish powder giving an orange-
coloured solution, which is not affected by car-
bonic acid, turned bright red by mineral acids
and yellow by alkaUs. It has been suggested
for making ydlow screens. It is also the mother
substance from which eikonogen is prepared.
METHYL VIOLET (Fr., Violet de nUthyU :
Ger., Methylviolet)
Many dyes are known under this name, and
they are istinguished from one another by the
suffix 5B, 4B, etc., R, 2 R, 3R, B meaning that
the dye has a more or less bluish shade which is
shown by the figure af&xed to the B ; whilst R
means red, the increase in red being shown by
the figures. They are essentially mixtures of
the hydrochlorides of pentamethykosauiline and
hexamethylpararosaniUne. They generally occur
in greenish glistening crystals or lumps, very
soluble in Water and alcohol. Used for making
three-colour screens.
In process work, methyl violet is used for dye-
ing the print in the fish-glue enamel process, so
that the progress of development may be seen.
METHYLATED ETHER (See "Ether.")
METHYLATED SPIRIT (See " Alcohol.")
METHYLCATECHOL (See " Guaiacol.")
METHYLENE BLUE (Fr., Bleu mMhyline: Ger.,
Methylenblau)
Synonyms, methylthionine or tetramethyl-
thionine hydrochloride. Soluble in water. A dark-
green crystalline powder used for making the blue
screen, and also the blue positive print, in three-
colour work. Various shades of die dye are dis-
tinguished by the suffixes, B, BB, R, RR, etc.,
as with methyl violet.
METHYLEOSINE
The "BN" or "Scarlet B" variety of eosine,
giving with water a scarlet solution.
METHYLIC ALDEHYDE (See " Formaline.")
METHYLPYROCATECHIN
A synonym for guaiacoL
Metol
3SS
Metol-hydroquinone
METOL (Fr. and Ger., Metol)
A salt, genetally the sulphate, of methyl-
paramidophenol C, H, (OH)(KH CH,) according
to Andresen, and of methylparamidometa-
cresol C, Hs(OH)(CH,)(NH CHj) according to
HaufE. It is a white, greyish or pinkish-white
powder easily soluble in water. When mixed
with an alksJi it forms an energetic developer.
bromide) is often advisable. Sodium hypo-
sulphite may be used with caution in any metol
developer, and Eder recommends the addition
of from 2 to 4 per cent, of a lo per cent, solution
for obtaining great contrasts and preventing fog.
Metol is largely used in combination with
pyrogallic acid, hydroqtiinone, glycine and other
developers, and formulae for these combined
METOL.
METOL— HYDROQUINONE.
1.
Andresen
One-
solution.
2.
Hauff
One-
solution.
8.
Average
One-
solution.
4.
One-solution
for
Winter Use.
6.
One-solution
Bromide Paper.
6.
One-solutioft
Gaslight Papers.
Metol
Sodium sul-
phite
Potassium
bromide ...
Potassium
carbonate ...
Hydroquinone
Sodium car-
bonate
Sodium
hydrate ...
Water
For use
l8o grs. 20 g.
3i oz. 195 „
22 grs. 2'5 „
6oo „ 70 „
20 oz. 1,000 CCS.
Mix I part with
3 parts of water.
130 grs. 15 g.
30Z.70 „ 173 „
8J „ . „
550 „ 63 „
20 oz. 1,000 CCS.
Mix 1 part with i
to 2 parts of water.
15 grs. i'7 g.
I oz. 55 „
5 grs. '6 „
lioz. 82-5 „
60 grs. 7 „
20 oz. r,ooo CCS.
Ready for use
for negatives.
75 grs. 8-5 g.
li oz. 70 „
10 grs. ra „
38 grs. 4'4 g.
rso grs. 17 g.
20 oz. 1,000 CCS.
Ready for use.
50 grs. 6 g.
I oz. 55 „
10 grs. i'2 „
25 grs. 3 g.
I oz. 55 „
20 oz. 1,000 CCS.
Ready for use ;
may be diluted.
20 grs. 2'2 g.
700 „ 80 „
7 ,. -8 „
50 grs. 6 g.
700 „ 80 „
20 oz. 1,000 CCS.
Ready for use ;
do not dilute.
On account of the rapid appearance of the
image there is a risk of taking the negative
from the developer too soon. In accordance
with the factorial system of development a
negative developed with metol must be allowed
to remain in the developer about thirty times
as long as the image takes to appear, and density
will then be assured. The table given above
includes formulae for one-solution developers,
and the formulae here given are for two-solution
developers : —
Two-solution Developers
(Andresen)
A. Metol . . .180 grs.
Sodium siUphite . 3 J oz.
Water . . . 20 „
B. Sodium carbonate 560 grs.
g-
20
19s „
1,000 CCS.
64 g.
1,000 CCS.
Water .
For use, take i part of A and 3 parts of B.
(Hauff)
A. Metol . . 130 grs. 15 g.
Sodium sulphite 3 oz. 70 grs. 173 „
Water . . .20 oz. 1,000 ccs.
B. Sodium carbonate 3 oz. 70 grs. 173 g.
Potassium bromide 14 grs. i-6 „
Water . . .20 oz. 1,000 ccs.
With regard to HaufE's two-solution de-
veloper above, for normal exposures and quick
and vigorous development, take equal parts of
A and B ; but for slow development take
equal parts of A, B, and water, and add to
each si oz. of mixed developer, 5 to 10 drops
of either a 10 per cent, solution of potassium
bromide, or of a 10 per cent, solution of sodium
hyposulphite. When using this modified
developer density and detail (surface and
depth) develop approximately simultaneously.
The addition of a few drops of citric add (which
is a more powerful restrainer than potassium
mixtures will be foimd imder the heading
" Developers, Mixed," as well as, in the case
of metol-hydroquinone, in the table which is
given above.
Metol has an irritating efiect upon some
skins, and it is, therefore, wise not to wet the
fingers with the developer more than is necessary.
The irritation is sometimes felt when metol is
used for the first time, but generally it is not
experienced until metol has been used frequently
over a long period. It is wise to discard metol
immediately the trouble occurs, as the pain
and inconvenience are likely to increase every
time the metol is used. The hands should
always be washed With warm water and soap,
preferably carbolic, after using metol, and
wiped with a dry, soft towel. Many remedies
for the disease have been recommended, such as
rubbing the fingers with lemon juice, vaseline,
cold cream, etc., when the itching is first felt.
Aa ointment (to be made up by a chemist)
specially recommended is : —
Mercuric nitrate
. 60 grs.
60 g.
Carbolic acid .
. 10 nuns.
10 ccs
Zinc oxide
. 30 grs.
30 g.
I,anoline
I oz.
480 „
The fingers should be smeared with the above
at night, and an old pair of kid gloves worn.
Coal-tar ointment is also recommended.
METOL-HYDROQUINONE (METOL.
QUINOL)
A mixture of metol and hydroquinone is a
popular developer, being clean in working and
smtable for most kinds of plates and bromide
and gasUght papers. It is sometimes known
as metol-quinol, quinol being another name
for hydroquinone. Scores of one, two, and even
three solution formulae have been given, but
Metol-silver Intenslfier
356
Mica
there is very little difEerence between them.
Taking a dozen of the best known formulae, the
average one-solution developer is as No. 3 in
the table given in the preceding artide, this
developer being ready for use and of the correct
strength for negatives, lantern plates and
gaslight papers, but when used for bromide
papers an equaJ amount of water is required.
The hydroquinone and metol are not in equal
proportions, but msmy prefer to have the hydro-
quiuone in excess, lie metol being the more
expensive of the two. The proportions may be
altered to suit the temperature, it being advisable
to have more metol Uian hydroquinone in cold
Weather, because hydroquinone is apt to work
very slowly in winter, especially when sodium
carbonate is used, and, moreover, is apt to
crystallise from its solution. Formulae for two-
and three-solution developers are given below : —
Two-solution
A. Metol . . .40 grs. 4'6 g.
Sodium sulphite . 120 „ 14 „
Potassium bromide. 10 „ i-2 „
Hydroquinone . 50 „ 6 „
Water . . .20 oz. 1,000 ccs.
B. Potassium hydrate 40 grs. 4-6 g.
Water . . .20 oz. 1,000 ccs.
For use, take equal parts of each.
Three-solution
A. Metol .
Sodium sulphite
Water .
B. Hydroquinone
Citric acid
Water .
C. Potass, carbonate
Water .
loo grs. ii'S g.
300 „ 34-5 ,.
20 oz. 1,000 ccs.
100 grs. 11-5 g.
25 „ 3 „
20 oz. 1,000 ccs.
I oz. 55 g.
20 ,, 1,000 ccs.
Normally, use i part each of A and B and
2 parts of C ; in cases of over-exposure, add
potassium bromide, and for under-exposure
increase the proportion of C.
When making up solutions of metol, sodium
sulphite, and hydroquinone, always dissolve
the chemicals in the order given.
METOL-SILVER INTENSIFIER
An intensifier specially suitable for wet or
dry collodion negatives, either before or after
fixing. Dr. Eder's formula is : —
B.
The well-Washed negative is dipped in A and
then covered with a mixture of 10 parts of A
and I part of B. Density increases rapidly.
The opaque portions of the negative will appear
blue by transmitted light when wet, and brown
after drying.
METOL-SULPHITE
A commercial form of the metol developer
to which alkali does not need to be added. For
use, it is mixed with water, i oz. dissolved in
40 oz. of water makes a good stand developer.
Metol .
72 grs.
i6-s g.
Citric acid
48 „
II „
Water (distilled)
10 oz.
1,000 ccs
Silver nitrate
48 grs.
II g-
Water (distilled)
I oz.
100 ccs
METOQUINONE
Under this name Messrs. Lumi&re introduced
into England, iu 1903, a metol-hydroquinone
developer, but in the same year the name was
altered to " Quinomet " {which see). In other
countries, metoquinone still refers to the Lumi^e
preparation.
METOTYPE (Fr., MMotype ; Ger., Metotype)
A paper or card coated with gold, silver,
copper or bronze powder, beneath the sensitive
emulsion, so that finished prints appear as if
on a metallic surface. A similar result is obtained
by coating ordinary stout gold or silver paper
with celluloid varnish to isolate the metal, and
allowing to dry thoroughly. Any P.O. P. emul-
sion may then be applied.
METRE
A metric measure of length equal to 39-370113
in. (about 39^ in.).
METRIC SYSTEM {See "Weights and
Measures.")
METZOGRAPH SCREEN
A screen placed in front of the sensitive plate
for breaking up the image into a grain in order
to reproduce the image on a printing block,
both screen and process being the invention of
James Wheeler. In making the screen the
surface of a sheet of plate glass is covered with
a fine reticulated resinous grain as a result of
burning pyrobetulin and holding the glass over
the vapour. This grain forms a resist to hydro-
fluoric acid, so that the plate can be etched,
after which the resinous grain is cleaned ofi
and the granulations on the glass stand up in
relief. Each grain point then acts as a tiny
prism or lens deflecting the light and causing
a grain effect to be imparted to the plate.
MEZZOCHROME
A process of intaglio printing in colours
worked on the basis of the Rembrandt photo-
gravure process.
MEZZO-RELIEVO
A term used principally in photo-sculpture.
When the figures project in relief more than
half their true proportions, the effect is termed
alto-relievo ; when exactly one-half the term
used is mezzo-relievo; and if less than half,
basso-relievo (English, bas-relief).
MEZZOTINTO
A process of colouring engravings, etc., and the
prototype of the crystoleum process (which see).
MEZZOTINTOGRAVURE
A name given by Bruckmann, of Munich,
to his process of rotary intaglio photogravure
printing, which is supposed to be done after
the style of the Rembrandt process.
MICA (Pr., Mica; Ger., Glimmer)
Various double siHcates of alumina and
alkalis, occurring natiirally in blocks which
split up into transparent sheets, each composed
of laminae. Mica has been used as a support
for gelatine emulsions, etc.
Micrometry
3S7
Microscope
MICROMETRY
The measurement of minute divisions of space.
The best known device for obtaining micro-
metrical measurements in microscopy and
photomicrography is the stage micrometer
ruled into lines to ^^ or i^ in., or ^ and
iliy mm. A fairly accurate estimation of the
size of an object can be made by focusing
the ruled lines of this micrometer on the stage
and carefully noting the space in the field taken
up by a certain number of lines. The object
to be measured is then substituted for the
micrometer sUp and focused with, of course,
the same objective, eyepiece, and length of
draw-tube. The approximate size of the object
can then be gauged by comparing the diameter
of the specimen with the space previously taken
by the ruled lines. For accurate work a micro-
meter eyepiece is necessary to measure off the
rulings of the stage micrometer. In the micro-
meter eyepiece a small plate of equidistant
ruled lines is fixed in the focus of the eye lens
of the eyepiece, the lines being then visible
when the microscope is in use. The stage
micrometer is focused in the usual way, and the
number of its lines which take up the same space
as a certain number of the eyepiece divisions
is noted. The stage micrometer is then replaced
by the specimen, and the diameter of the latter
is compared with the previously noted eyepiece
divisions. It is not necessary to have fixed
numbers of lines per inch in the eyepiece
rulings ; in fact, two points in the focus of the
eye lens are all that is required. Two small
ink marks on a cover slip wiU answer the purpose.
The cover slip is dropped on to the stop of the
eyepiece and the number of rulings of the stage
micrometer which fill the space between the
ink spots noted ; the size of the object can then
be calculated.
For extreme accuracy the mechanical - screw
eyepiece micrometer is necessary. In this
eyepiece are two wires, one of which is fixed
while the other, worked by a traveUing screw
turned by a milled head, traverses the field.
Across the field is fixed a plate provided with
minute teeth, and each revolvftion of the milled
head moves Oie wire from one tooth to the next.
By this means the stage rulings can be compared
with the distance between lie two wires with
extreme accuracy.
In photomicrography the magnification of an
object is easily found without the aid of a ruled
eyepiece. The object is first focused on the
ground glass of the camera, and its diameter
marked by ink spots. The stage micrometer
then replaces the object and, after focusing, the
number of lines between the ink spots is read ofi.
This gives the size of the object, and the magni-
fication is then easily calculated by measuring
the distance between the two ink marks.
MICROPHOTOGRAPHY
The production of photographs of micro-
scopic size by means of the microscope. Micro-
photographs Were at one time produced in large
numbers for inserting into penholders, etc.,
but since the introduction of dry plates micro-
photography has become practically obsolete.
The wet collodion process is essential for this
work owing to the structureless nature of the
collodion film, and the extremely fime grain of
the silver deposit. An objective of i in. or
i^ in. focal length is the most suitable lens. A
camera is not required, as the prepared plate can
be fixed to the microscope stage and exposed in
that position. The operation must, of course,
be carried on at night time, or in the dark-room.
A clean, bright negative of the object is first
made on an ordinary dry plate. The micro-
scope, with the eyepiece removed and the
objective in place, is put into a horizontal
position, and Ihe negative is placed at a distance
of about 2 ft. from the lens. The open end of the
microscope tube faces the negative. The most
convenient arrangement for staging and illumi-
nating the negative is a large box with one
hole, slightly smaller than the negative, cut in
the side, and another in the top, to serve as a
chimney. The negative is secured in front of
the hole by drawing-pins with a piece of ground
glass or tissue paper behind it to diffuse the
hght. A lamp is placed behind the difiuser
to illuminate the negative. The image of the
negative given by the objective is now roughly
focused on a piece of white card placed on the
stage of the microscope, which is moved to
and fro until the image is of the required size.
The centre of a glass slip is coated With collodion
and sensitised and transferred to the nilcroscope
stage. A sheet of cardboard is placed over the
negative while the sensitised slip is being placed
in position. The card is removed, and the
image carefully refocused on the sensitised
collodion, which makes an excellent focusing
screen. As a small portion of the filtn wiU be
fogged during focusing, before the exposure is
made the card is replaced, and the slide moved
slightly to replace the fogged part of the film
by a fresh piece. Several trial exposures of
varying length are made on different portions
of ttie film, and the sUde is then developed and
fixed. Pyro and acetic acid should be used
for development, as the deposit given by this
reducer is of finer grain than that produced by
an iron developer. The microphotograph, of
course, requires the microscope or magnifying
lens to resolve its details. The amount of
reduction which the process will allow is limited
by the size of the granules of the silver deposit,
but the details of a half-plate negative are easily
visible in a micro-photograph having as small
a diameter as -/j in.
MICROSCOPE (Fr., Microscope; Ger., Mi-
kroshop)
The simple microscope, which was the earliest
type of instrument, consists of a stand provided
with a single lens or combination of lenses
known as tiie objective, which is focused by
mechanical means. This type of microscope is
still used in laboratories for dissecting work.
The compound microscope is fitted with an
arrangement by which the image given by the
objective is st&l further magnified by another
lens or combination of lenses known as the
eyepiece or ocular. A compound microscope is
usually provided with a coarse and fine adjust-
ment for focusing, the former being used for
low magnifications and the latter for high
magnifications. The illustration shows a typical
instrument. The foot or base is usually of
Microscope, Photography with 35S
Mines, Photography in
either horseshoe or tripod form. The " limb "
carries the focusing apparatus and the body-
tube with objectives and eyepiece. The draw-
tube, a smaller tube, sliding or moving by rack
and pinion, inside the body-tube, receives the
eyepiece or ocular, and enables the separation
of objective and eyepiece to be varied at will.
The draw-tube is also useful for objectives of
very low power which require a longer working
distance than the coarse adjustment will allow,
the lower end of the tube being provided with
a thread to receive the objective. The stage,
which supports the object, is provided with
dips to secure the glass slides, and is sometimes
fitted with mechanical movements to enable the
object under the lens to be accurately adjusted.
The sub-stage condenser, for use with high
powers, is fiied beneath the stage and focuses
the light upon the object which is being
examined. Di the stage is an aperture in order
Compound Microscope
that transparent specimens may be illuminated
by light reflected from the mirror beneath the
stage. To facilitate the operation of changing
the objective for one of another power, a swivel
lens holder, known as a nosepiece, and allowing
of the use of several objectives of various powers,
can be screwed into the lower end of the micro-
scope tube, and high or low power objectives
can be brought into use by merely turning the
nosepiece on the pivot. Most microscopes are
inclinable ; that is, the instrument can be
brought over to a horizontal position for photo-
micrography.
MICROSCOPE, PHOTOGRAHY WITH
{See " Photomicrography.")
MICROSCOPE SLIDES FOR SPECIMENS
Glass slips measuring 3 in. by 1 in., on which
sections intended for microscopic examination
are mounted. Such objects and transparent
sections are mounted in Canada balsam or
glycerine. Opaque substances are mounted in
ceils. {See " Cells for Microscopical Specimens.")
MICROTOME
An instrument designed for cutting extremely
thin sections of any tissue which is to be
examined or photographed through the micro-
scope. Two types of microtomes are used.
One form merely holds, and pays out, the
preparation, the actual cutting being done by
hand. The other includes a razor which auto-
matically cuts sections to the required thickness.
Some kind of support is necessary to hold the
material in the microtome. The method
generally adopted is known as " imbedding " ;
the specimen is placed in melted parafiSn wax
till the tissues are permeated. The wax is
allowed to set and, with the contained specimen,
is then transferred to the microtome for cutting.
The wax is subsequently dissolved from the
tissues with turpentine. Another method of
supporting the tissue is by placing the material
to be cut in gum water on the stage of a micro-
tome and freezing the mucilage by means of
ether vapours.
MID-ANGLElLENS
A lens having a field of view of about 50°, or
having a focal length equal to the longest side
of the plate. The term is, however, very elastic.
MIDDLE ANGLE LENS {See "Mid-angle
Lens.")
MIDDLE DISTANCE
That part of a picture intermediate between
the foreground and the distance.
MILK PROCESS
Milk was one of the many substances used
for preserving collodion plates. Twenty grains
of condensed milk were mixed with each ounce
of water, filtered, and flowed over the coUo-
dionised plate.
MILLIMETRE, MILLIGRAMME, MILLI-
LITRE, ETC. {See " Weights and Mea-
sures.")
MINERAL PAPER
Synonym, papier mineral. A translucent
paper which is pasted upon the glass side of
negatives for the purpose of working upon in
pencil or crayon.
MINES, PHOTOGRAPHY IN
With the advent of the dry plate, the modem
lens and the actinic flash powders, photography
in mines has become much more easy. The
bunch of magnesium ribbon, lime-Hght apparatus
and portable lamps have all been superseded.
In gassy mines, the use of flashlight mixtures
is inadmissible, but it answers well, for example,
in the tin mines of Cornwall, which are deep,
hot, smoky, wet and dirty, with grease, mud,
and slime in abundance, in some places stagnant
air in which the tallow candles will not bum,
in others a draught so strong that naked candles
cannot be kept alight. The hanging walls
from ■yfhich Water drips from every jagged point
of rock, the slippery footwalls, open stopes,
deep gunnies, perpendicular ladders with iron
staves, the low, narrow levels, etc., etc., present
the most unpromising conditions for successful
Mines, Photography in
359
Mirror Camera
photography. The miners work by the light of
tallow candles stuck in a lump of day which
adheres to the hard hat they wear, or against
the rock on arriving at the scene of their
operations. These candles give out Uttle
illumination, but plenty of smoke. The angular
rocks of a dull brown, non-actinic colour require
powerful illuminants to bring out their structure.
The mine photographer should be something of
a mining engineer so as to grasp intelligently
the idea Which the photograph is intended to
illustrate. In Cornwall he becomes famiUar
with mineral lodes and cross-courses, shafts,
levels and winzes, air currents and ventilation.
The principal features of mining, or the natural
position of the miner at his work, must not be
sacrificed in order to compose an artistic or
sensational picture. Neither must he be
fastidious about his dress, hands or apparatus,
nor object to crawl on his hands and knees over
the rough rocks, through narrow openings, and
oftentimes dangerous places. The camera must
be strong and well made, capable of enduring
without serious damage the inevitable contact
with points of rock. Double dark-sUdes filled
with plates sufBicient for the day's use should
be taken. Plates could be changed underground
as absolute darkness e:dsts when the candles
are extinguished, and it is quite easy to feel to
do this work, but other conditions are not
favourable to this course. It rarely happens
that more than six plates can be exposed in
one " shift," and as a rule only one exposure
can be made in one place by reason of the
smoke caused by the combustion of magnesium.
At least three lenses are necessary, respectively
of lo in., 7 in., and S in. focal lengths. The
greatest trouble with lenses is caused by moisture
condensing on their cold surfaces, and in order
to avoid this as much as possible they should
be carried in the inner pocket of the flannel
shirt next the skin. As soon as the cap is put
on after focusing, condensation immediately
covers the front of the lens, and this can scarcely
be wondered at in a temperature exceeding
ioo° P. (about 38° C), with steam rising
from the water which runs at one's feet, or
dropping from the jagged points of rock above
the camera. A piece of soft silk kept in the
trousers pocket should be used to wipe the
lenses, 'bi some places, where the heat is almost
unbearable, drawers are the only garments
worn by the miners at work.
In the past magnesium ribbon and the oxy-
hydrogen light were used ; now, after repeated
experiments, triple flash lamps of great power
have been found to give the best results. Prom
two to four of these lamps are generally sufficient,
with an exposure of about three or four seconds.
By a judicious use of lamps some unique lighting
effects can be obtained, but special attention
must be given to air currents, which, if possible,
should be upward, or else towards the camera.
When it is not possible to photograph a gunnies
(a large chamber) from one standpoint, it often
answers to move the camera to the other end ;
this is probably due to the admission of good
air at one end driving the foul air to the other,
which, although not perceptible to the eye, is
revealed by the lens and produces a foggy
effect. Flash candles are useful when placed
behind a rock so as not to produce a glare in
the lens.
The most sensitive plates are not the best for
the purpose, because of their tendency to fog
in forced development ; there is usually more
than enough of fog surrounding the object itself.
A plate of medium speed, say 100 H. and D.,
backed, has been found to possess all the qualities
necessary.
For photographing coal mines, the general
arrangements are the same as in tin mining,
but naked lights can only be used in those few
collieries that are free from gas ; otherwise,
the difficulties are not so great, the mines are
drier, the coal surfaces reflect the light, and
very little trouble is experienced with coal dust.
Tn the slate mines of North Wales and other
places, where there are vast excavated chambers
a hundred fathoms from the surface, the con-
ditions are easier stiU, the air is good, and it is a
question only of sufficient lamps to Ught up the
dark caverns.
The subsequent printing from the negative
is a matter of ordinary practice, but the picture
should represent as clearly as possible the colour
of the rock or material photographed. By the
carbon process, for instance, bluish tones
representing slate can easily be obtained, or
brown tints will depict the darker rocks in
Cornish mines, and blue-black the coal deposits.
J. C. B.
MINIATURE (Pr., Miniature; Ger., Miniatur)
A term loosely applied to any small portrait.
The best photographic miniatures are usually
carbon prints of a suitable depth transferred
to ivory and then coloured. The commoner
forms of miniatures are prints upon ordinary
P.O.P., coloured by means of anUine dyes.
MINIM
The one-sixtieth part of a dram, and the
one-four hundred and eightieth part of an ounce.
The idea that drops and minims are the same is
erroneous, although when drops are mentioned
minims are often meant. (See " Drops.")
MIRROR. BLACK (See "Black Mirror"
and " Claude Lorraine Glass ")
MIRROR BOX (See " Mirror, Reversing.")
MIRROR CAMERA (Pr., Chambre miroir :
Ger., Spiegelkamera)
A camera devised by J. W. Draper in the early
daguerreotype days, in which a large concave
Mirror Camera
mirror was used instead of a lens, the plate a
(see illustration) being placed in a small box
facing the mirror, and receiving an image by
Mirror Photography
360
Mogul Varnish
reflection. The advantage gained was the possi-
bility of shorter exposures than were feasible
with small aperture lenses, and the absence of
chromatic aberration ; but it is difficult to avoid
a certain amount of stray Ught, and the mirror
has to be large to compensate for the obstruc-
tion of illumination caused by the plate and its
support.
Concave mirrors are of value in stellar photo-
graphy, where any stray hght met with is but
feeble.
MIRROR PHOTOGRAPHY
The art of photographing objects reflected
in a mirror, enabling one at times to obtain
photographs which would otherwise be impossible
owing to confined space or the use of a long
focus lens. For exam.ple, and as shown at A,
in a small room and using a long focus lens,
the only way of photographing a sitter would
be to place a mirror at a suitable angle opposite
the sitter, and to arrange the camera so as to
photograph the reflection. In convenience, the
distance of camera from sitter is doubled,
whereas in fact the camera is nearer the model
but pointing in another direction, namely, that
of the mirror. The law of regular reflection is
that the angle of reflection is equal to the angle
of incidence, as can be proved by a minute's
experimenting. A mirror placed as shown at
B would reflect o at d, c at c, B at 6, and so on.
D is at the same angle with E E as is d, and the
being placed at the side of the box, at a right-
angle with the focusing screen or plate. The
A. Arrangement for
Mirror Photography
B. Diagram showing Prin-
ciple of Mirror Photo-
graphy
same holds good with regard to C and c and
B and b. Therefore, to photograph an object at,
say, C, the camera should be placed on the line
c, but not necessarily at the same distance from
the mirror as the object photographed. Much
depends upon the size of the mirror. As is
wdl known, a mirror reverses the objects as
regards left and right, and therefore to secure
a correct image in the print the negative must
be reversed, either by stripping the film or by
inserting the plate into the dark-sUde glass
surface outwards, care being taken that the
glass is perfectly clean.
MIRROR. REVERSING (Fr., Miroir de ren-
versement ; Ger., Umkehrspiegel)
A surface-silvered plane mirror is frequently
used, at an angle of 45°, in front of or behind
the lens when reversed negatives are required.
Behind the lens is the best position, as the
mirror is then better protected from air and
dust, and one lens can be changed for another
without disturbing the mirror. The mirror is
usually enclosed in a box, as illustrated, the open
side fitting on the camera front and the lens
Mirror Box
copy or object is arranged sideways to the camera.
(See also " Prism.")
MIRRORS, DISTORTING
The use of distorting mirrors is described
under the headings " Anamorphoscope " and
" Caricature."
MISCHEWSKI'S REDUCER
A cerium reducer introduced in 1900, and con-
sisting of a solution of i oz. of cerium sulphite
and 3 drms. of sulphuric acid in 10 oz. of water ;
to be kept in the dark. One part of this stock
solution is diluted with 3 parts of water for use.
It works rapidly, and does not alter the colour
of the negative.
MIXTOL
A " mixed " developer of Continental origin
(1892), and containing hydroquinone and
eikonogen as the developing agents proper.
(For formula, see "Developers, Mixed.")
MODELLING
A term used to indicate that the play of
light and shade has been so rendered as to
suggest accurately the contours and surfaces
of tiie subject.
MODELS (Fr., Modules; Ger., Modelle)
The professional artist's model frequently has
objections to posing for the photographer,
especially if the photographs are intended to
be reproduced commercially in large numbers,
for which purpose the model's permission in
writing should always be secured, even when
the photographer undoubtedly owns the copy-
right of ttie pictures in which the model is
shown. A professional model, whose especial
business is to pose, will thoroughly enter into the
spirit of the business and will frequently, as the
result of experience, be able to offer valuable
suggestions. The amateur model is often
somewhat prone to look camera-conscious.
There has been a general feeUng that actors
make but poor models, but the development of
the art of kinematography has brought into be-
ing a special class of motion picture actors who,
generally speaking, are excellent in every way.
MOGUL VARNISH
A waterproof and acid-resisting varnish of
American origin, used by process workers. It
is believed to be a bituminous by-product from
petroleimi wells, and is dissolved or thinned
Moisture
361
Monochrome, Rendering in
■with coal-tar naphtha. Spread on glass and
etched through with a needle-point, it is the
means of making excellent lantern slides of
diagrams, etc. It may be used for coating
trays of wood, metal, or cardboard for develop-
ing and other purposes.
MOISTURE {See " Damp, Precautions against.")
MOLECULAR DISTURBANCE AND
STRAIN THEORY (See "Latent
Image.")
MOLYBDENUM PRINTING
Several of the molybdennm salts, such as the
chloride and ammonium molybdate, are sensitive
to Ught, and give faint images, usually of a
bluish tinge, which can be developed or toned
to various colours with ferricyanide, chloride
of gold, etc. The processes are, however, of
purely theoretical interest.
MONCKHOVEN'S INTENSIFIER
An intensifier by means of which the image is
bleached with mercury and blackened wiQi a
solution of silver nitrate and potassium cyanide.
It intensifies the hghts to a greater extent than
the shadows, and is best suited to an over-
exposed and under-developed negative. The
formula is : —
A.
Mercuric chloride
10 grs.
2 g-
Potass, bromide .
10 „
2 .,
Water
I oz.
100 CCS.
B.
Silver nitrate
Potass, cyanide
10 grs.
2 g.
(about) .
10 „
2 „
Water (distilled) .
I oz.
100 CCS.
In making up B the water should be halved
and the cyanide dissolved in one half and the
silver in the other. The cyanide is then poured
into the silver solution and the mixture shaken.
A white precipitate will be formed, and will
gradually become almost but not wholly dis-
solved. If it should be quite dissolved, add a
drop or so of silver nitrate solution until a
slight precipitate remains. The mixture is next
filtered, or the clear portion (actually somewhat
discoloured) poured off for use. The negative
is immersed in A until bleached, washed for
about fifteen minutes, blackened in B, and
finally washed. The process may be repeated
it necessary, but the negative must not be left
in the cyanide-silver mixture too long, or a
gradual reduction will take place. The colour
of the intensified image is a good black or brown
black, no matter what the original colour may
have been.
MONO-CARBOXYLIC ACIDS (See " Carb-
oxylic Adds.")
MONOCHROMATIC LIGHT
Literally, this means a light of the colour of
one ray of the spectrum, but in the general
sense it is applied to light of one colour, though
this may comprise a fairly wide band in lie
spectrum. It has been very usual to speak of
the monochromatic sodium light, though this
actually comprises several blue and violet rays
as well as the two f amiUar d lines in the orange
yellow. It is possible to obtain pure mono-
chromatic light by isolating one individual
Pratmhofer line in the spectrum of a metal
or gas, such as thallium, which gives a single
isolated line at A 5348, or the hydrogen P Ime
A. 4861. These lines may be isolated either
by means of a prismatic spectrum and metal
screens so pierced as to allow only the one ray
to pass, or by colour filters which absorb all but
a narrow band in the spectrum coincident with
the line in question.
MONOCHROMATIC SCREEN
A term applied to colour filters usually
prepared with aniline dyes so that they pass
fight of one colour, but not strictly mono-
chromatic if reference is made to the spectrum.
As a rule, such screens pass a band comprising
about ten wave-lengths, but the eye is not suffi-
cientiy sensitive to distinguish them, and they,
therefore, appear monodiromatic, or of one
colour. They are used in photomicrography,
and for special spectroscopic and astronomical
work.
MONOCHROME (Pr., Monochrome ; Ger.,
Einfarbige Gemdlde)
Literally, one tint or colour. Practically all
photographs are in monochrome ; that is to
say, the image is black, brown, red, green, etc.,
according to the process employed. The excep-
tions are prints made by the three-colour
processes, by multiple gum printing, or by
the oil-pigment process. Photographs in colour
on glass plates are, of course, in a different
category.
MONOCHROME, RENDERING COLOURS
IN
The ordinary photograph is limited in the
sense that the various colours of the original
are all recorded by different shades of grey or
monochrome. Should a yellow daffodil be
placed in front of a violet screen, the yellow of
the flower and the violet of the screen both being
equally bright, the eye would at once differentiate
them owing to the colour contrast. A fully
iso- or ortho-chromatic plate would record
them in the negative as of exactly equal tone.
An ordinary plate would render the violet screen
almost white, the yellow daffodil almost black.
Both results would be wrong.
The ordinary photograph is all of one colour,
hence the rendering is in monochrome, and we are
dependent on monochrome contrasts to repre-
sent both light and shade, and colour contrasts.
How a correct rendering in monochrome of a
coloured subject can be effected wiU be seen
by a reference to a plate accompanying this
work : " Various Renderings of Daffodils in a
Blue Vase." The left-hand top picture shows
an absolutely incorrect rendering, as is inevitable
when using an ordinary plate which is practically
insensitive to ydlow, hence the flowers appeal
nearly black. The blue of the vase is intensely
actinic, and in consequence appears white. In
the top right-hand picture is shown the same
subject recorded orthochromatically, the vase
appearing dark and the flowers light grey. By
sfightly overdoing the colour correction a
picture is obtained (bottom right-hand figure)
Monocle
362
Moonlight Effects
which gives an excellent contrast between
flowers and vase. It will thus be seen that by
intentional wrong rendering in monochrome it
is possible to suggest to the eye the colour
contrasts that it would see in the original
subject.
In the spectrum, the brightest colour, to the
eye, is the greenish-yellow ; apple green and
orange are the next brightest ; blue-green and
orange-red less bright ; and violet and ruby
least bright. When a perfectly correct colour
rendering is required, the plate and the screen
must be so combined that on photographing
the spectrum the various pure colours woiUd be
recorded in monochrome in the order given,
greenish-yellow (lightest), green and orange,
blue and red, violet and ruby.
The monochrome gradation is again altered
according to the colour of the print. An
ordinary subject, such as a cottage or house,
appears very " flat " in a yellow carbon print,
and much brighter or more contrasty if printed
in pink, green or blue. The tone values in
each print, relatively to each other, would be
the same, but the apparent contrasts to the
eye would vary greatly. Where subtle contrasts
require emphasis, a warm colour such as sepia
should not be employed for the print, but
either a bright grey, such as would be given
by a gaslight print, or a blue tone.
MONOCLE (Fr., Monocle; Ger., Monohel)
A single or " spectacle " lens used as an
adjunct to an ordinary lens, either to lengthen
or shorten its focal length, or to serve as a
telephoto attachment.
Also a graphoscope for viewing pictures, the
lens being too smaU to allow both eyes to be
used.
MONOCULAR (Fr., Monoculairs : Ger., Ein-
dugig)
Literally, one-eyed. Monocular vision is vision
with one eye, as distinct from binociJar vision,
which is vision with two eyes. {See also " Stereo-
scopic Photography.")
MONOL
A trade developer containing a dark red
auUine or other colouring matter allowing of
plates being developed therein in daylight.
MONOMETHYLPARAMIDOPHENOL
The original name for what is now known as
metol {which see).
MONUMENTAL WORK, PHOTOGRAPH.
ING
The diflJculty in this branch of photography
is common to all subjects that are either
uniformly light or uniformly dark in colour.
Sunshine is not desirable ; it is rarely successful
in small subjects photographed from a near
point of view ; and there is a risk of an entire
absence of good light and shade if too uniform
a lighting be adopted. The best results will be
obtained by selecting a time of day when the
principal side is in strong light, and then making
the exposure while the sun is temporarily
obscured by a light cloud. {See also " Sculpture,
Photographing." )
MOON, PHOTOGRAPHING THE (Pr.
Photographie de la lune ; Ger., Mond-
photographie)
The photographer who wishes to apply his
art to astronomical matters cannot do better
than begin with the portrayal of the features
of the moon, which, as is well known, is
our nearest celestial neighbour. Creditable
work may be done with the ordinary hand
or stand camera, but it will be understood
that with lenses of short focal length it is im-
possible to obtain images of the exquisite detail
which is known to be present on the moon's
surface. To obtain such images, a large equiva-
lent focal length is indispensable, but it is im-
material whether this is attained by a long-focus
objective or by a telephoto combination. Excel-
lent images showing aU the main features of the
craters, etc., may be taken with an equivalent
focal length of about 10 ft., giving an image of
the moon about i in. in diameter. Many of the
standard photographs obtained for charting pur-
poses, however, have been taken with equivalent
focal lengths of as much as 300 ft. For minute
study, enlargements can, of course, be employed,
but they have the disadvantage of showing up
the grain of the original negative, so that if a
large scale picture is desired, it is best to use an
amplifying lens in the camera. The first success-
ful photographs of the moon were made by
Rutherfurd. Later pictures have been produced
by Common, Barnard at the Lick Observatory,
Ritchey at the Yerkes Observatory, and Loewy
and Puiseux at Paris.
Except when working with instruments of very
large aperture, rapid plates should be employed,
so that the minimum exposure may be given,
thereby minimising the risk of failure on account
of movement of the image. Backed plates are
essential. The range of contrast between the
bright limb and the craters near the moon's
terminator is considerable, and development
should be so arranged that the gradation is kept
without having to force out detail. As the
exposures will, in general, be of minimum dura-
tion, a soft developer will be most likely to give
greatest satisfaction.
Quite recently, a new field of research on the
moon has been opened by the discovery by
R. W. Wood that certain regions of the lunar
surface exercise considerable selective absorp-
tion. This is especially noticeable when the
photographs are taken through screens which
only pass ultra-violet hght. If a quartz lens is
coated With a very thin film of pure silver, it wiU
allow the ultra-violet components of light to pass
uninterrupted, but all the visible light rays will
be absorbed. Under such circumstances he has
found that certain portions of the moon's surface
appear darker than when photographed in
ordinary white light, and thus it may be inferred
that such parts of the moon are composed of
some substance which absorbs ultra-violet radia-
tions.
MOONLIGHT EFFECTS
Real moonlight views are possible in very
favourable drcumstances, but most of the
so-called moonlight photographs are taken in
daylight, the usual method employed being to
take the photograph with the sim facing the
Moonlight Effects
363
Motional Perspective
lens, but not included in the view. A cloudy
day should be chosen and the exposure made
when the sun is just disappearing behind a
doud, or re-appearing therefrom. Should the
sun be included it will appear as a reversed
(black) spot and the plate will probably be
fogged. A very brief exposure should be
given (the plate must, in fact, be under-esniosed)
and the developer should be restrained with
potassium bromide in order to give great
density to the bright edges of the clouds and
other high lights, without permitting detail to
be over-pronounced in the shadows. The
object is to emphasise the high lights, more
particularly those in the sky and at other
reflecting points.
The task of photographing a view illuminated
by moonlight is not difficult if long enough
exposure is given, but it is not easy to include
the moon itself. The fastest of isochromatic
plates, backed, should be used. As a rule,
the best time is one or two evenings before the
moon is full, as it then rises early enough to
allow of the photographer making use of the
diffused light of the after-glow to shorten the
exposure, and if the moon is to be included
the slight flattening of the disc will be hardly
noticeable. In marine work, in harbours, or
tidal rivers, where vessels are shown at a wharf
or the water-line along a flat shore is included
(such subjects and winter scenes make the best
pictures), it is better, if possible, to make the
exposure either at full or low tide, as then
objects will not be blurred by a change of
water level during exposure. An average
subject, using //8 and a rapid isochromatic
plate, will need from ten to thirty minutes'
exposure on a clear night. Do not under-
expose ; rather give double or even treble the
exposures named.
W. S. Davis, of the United States, advocates
two ways in which the moon may be included
in the photograph without showing movement.
One method is to wait until the moon is high
enough to be out of the field of view included
by tbe lens ; focus and expose for the fore-
ground as usual, remove the plate, then tilt the
camera and raise the front until the moon comes
where it is wanted in the composition, replace
the plate and give a short exposure for the
moon itself — ^from ten to thirty seconds will be
ample with the lens at fuU aperture. The moon
and the foreground are thus obtained upon
one plate. For early moonrise efEects, W. S.
Davis exposes a separate plate on the moon,
and puts it at the back of the foreground when
printing. The first-named method is to be
preferred, but care must be taken to locate the
moon exactly where it is Wanted. To do this
properly take some gummed black paper and,
before moving the camera for the second part of
the exposure, decide upon the spot on the
focusing screen it is to occupy, and attach a
piece of gummed paper, in which a small hole
has been made, so (iiat when arranging for the
exposure for the moon, the latter can be seen
through the opening.
If wide-angle or medium-angle lenses are
used, the image of the moon in the photograph
will not appear so large, in proportion, as it
does to the eye, and for this reason it is often
advisable to use a longer focus lens for the moon
than for the rest of the view ; otherwise the
moon may be made to appear larger by having
it a little out of focus.
Moonlight photographs are usually printed
on sea-green or blue carbon, or bromide prints
are made and then toned to those colours.
Prints on P.O.P. may be stained by means of
an aniline dye.
MORENO'S DEVELOPER
A pyro-soda developer which aroused con-
siderable interest in 1894, when it was published
in America. Moreno advocated the use of
saturated solutions, with which he developed
batch after batch of plates in the same
bath ; on one occasion, it is said, he developed
100 half -plates in 16 oz. of solution. Two
pint bottles are filled respectively with saturated
solutions of sodium carbonate and sodium
sulphite ; in a third, say a 5 oz. bottle, is placed
4 oz. of the sulphite solution, and to this
is added pyrogallic acid so long as it dissolves
readily — in most cases i oz. will be the
correct quantity. The three stock solutions
may be thus represented in the orthodox way : —
A. Sodium sulphite (saturated solution.)
B. Sodium carbonate „ „
C. Solution A . 4 oz. 100 ccs.
Pyrogallic acid . i „ 25 „
To make up a developer ready for use, mix
together i oz. of A, -J oz. of B, and i oz. of C ;
do not add water.
MORPHIA PROCESS
An old dry collodion process. The plate
was sensitised with bromo-iodised collodion,
washed and placed in acetate of morphia
IS grs.. Water 17 oz. Having been dried, it
was exposed twice as long as a wet plate, and
developed with pyrogallic acid.
MOSSTYPE (Pr., Mosstype : Ger., Mossdrtich)
A method of making half-tone blocks invented
by J. C. Moss, of New York. Plate glass was
coated with bichromated gelatine, dried, exposed
under a dense half-tone negative and soaked in
water, which was absorbed only by the parts
that had been protected from light, these
swelling and forming a half-tone relief. Prom
this was taken a plaster or wax cast, and from
the cast a plaster mould, which was used to
make a stereotype.
MOTAY'S COLLOTYPE PROCESS (See
" Marfechal's Collotype Process.")
MOTIF
This French form of the word motive is
generally used to denote the idea, phase, or
particular presentment which the photographer
intended to convey by his picture.
MOTION (See " Action.")
MOTION PICTURES (See " Chrono-photo-
graphy" and " Kinematography.")
MOTIONAL PERSPECTIVE (See "Stereo-
scopic Photography.")
Mottling
364
Mountants
MOTTLING
A defect seen occasionally upon the dense
portions of a negative. Unless tie developer is
kept moving in a gentle wave backwards and
forwards over the plate mottling is abnost sure
to occur.
MOULDING (Pr., Moulure; Ger., Kehlung)
This is the name given to lengths of wood
used for making into frames. Such mouldings
are generally sold With the wood in its natural
state ; that is, neither stained nor polished.
Some mouldings are faced with composition —
a kind of hard plaster — and these, of course,
are sold in their finished state ; there is some
danger of this surface chipping. In selecting
wood mouldings for photograph frames, it is
generally wise to confine the choice to the
simpler patterns, rather than those that are
elaborate or ornate. The wood should be
sound and well-seasoned, and the mouldings
sharply cut, without roughness or irregularity.
{See also "Frame" and "Framing.")
MOUNT (Fr., Monture ; Ger., Einrahmung,
Einfassung)
Mounts may be broadly classified as paste-
on or sUp-in, and both kinds may be obtained
commercially in large variety ; although some
patterns are everything that a photographic
mount shoiild not be, there are many that are
quite tasteful and suitable. The serious objec-
tion to any ready-made mount is that it
necessitates the dimensions of the print being
kept to one of the standard sizes. As the great
majority of properly trimmed prints vary more
or less from any stock size, it is advisable to
resort very frequently to a mount specially
made. Fortunately, excellent papers and boards
for this purpose are readily obtainable, and it
is well to have these in reserve for use when
the ready-made mount is not quite satisfactory.
Both trade mounts and mounting papers should
be of good quality, and specially prepared for
photographic purposes, so that they may be
free from anything deleterious to the print.
Oxford line, plate-sunk, India-tint, circular
and oval mounts are all made in endless variety,
as are also the usual stock mounts for carte-
de-visite, cabinet, and other standard sizes
for portrait work. There are also embossed
and fancy mounts, with and without inscriptions.
All of these have their uses ; but, as in the
case of frames, it is necessary to bear in mind
that the print itself is the thing, and that its
surroundings should be such as to display it
to the best advantage, and neither to minimise
its effect nor distract attention from it. (See
also " Multiple Mounting.")
MOUNTANTS (Fr., Colles : Ger., KUisters)
The adhesive by means of which a print is
attached to its mount. Of the very many
mountants available, starch is by far the most
widely used, yet it keeps badly and is unsuitable
for glazed prints. A glazed P.O. P. print
mounted with plain starch may lose its glaze
and show markings, whereas if an alcohoHc
solution were used the print would be rmaffected.
Arrowroot. — ^This is an excellent moimtant
when -a. httle gelatine is added : —
Bermuda arrowroot 2 oz. 122 g.
Gelatine . . 90 grs. 11-5 „
Water . . i8 oz. 1,000 ccs.
Soak the gelatine in some of the water for an
hour or two, and melt by heat. Mix the arrow-
root into a cream with a little water, and add
to the gelatine, stirring all the time. Boil the
whole in an enamelled saucepan or in a water-
bath till a clear jelly forms, and add slowly 2 oz.
of methylated spirit and 6 drops of carbolic acid.
Allow to cool, and keep as airtight as possible.
Dextrine. — This is a good mountant of a
white, creamy character ; it keeps Well. A
formula is : —
Best white dextrine 25 oz. 900 g.
Alum . . I „ 36 „
Sugar . . 4 „ 144 „
"Water . . 30 „ 1,000 ccs.
Carbolic acid (10 %) i J „ 54 g-
Mix the dextrine with the water, boil for five
minutes, add the sugar and the acid, and finally
the alum dissolved in about 2 oz. of hot water.
The alum may be left out if desired, as it may
injure some prints, particularly those on coUodio-
cUoride paper. Inferior dextrine is likely tc
remain sticky and not dry properly.
Another and a more simple dextrine formula
which wiU meet all requirements is to rub up
I lb. of best white dextrine with enough
cold water to make a stiff paste and add 10 oz.
of water, and 60 drops of oil of winter-green.
Bring the whole to a boil, when it should be
like dear gum. Pour into pots or jars, and in
about twenty-four hours it should set in the
form of a good white creamy paste. Use cold.
Dextrine and Gum. — ^This has no advantages
over dextrine alone. The best formula is : —
Gum arable (best
white)
1 oz.
70 g-
Dextrine
2i „
315 .,
Liquor ammoniae .
2 mins.
■5 ccs.
Carbolic acid
60 „
IS „
Water
8 oz.
1,000 „
Powder the gum and mix thoroughly with the
dry dextrine, and rub up with 2 oz. of the
water to make a smooth paste. Add the re-
maining 6 oz. of water and boil for ten minutes ;
when cool, stir in the ammonia and carboUc
acid. This wiU keep for months.
Gelatine. — Most gelatine mountants have to be
heated before use. A standard formula is : —
Gelatine . . i oz. no g.
Glycerine . . i „ 50 ccs.
Alcohol . . li „ 150 „
CarboHc acid . 20 mins. 4 „
Water (about) . i oz. 100 „
Cover the gelatine with the cold water and
allow to soai for twenty hours or more. Pour
off any excess of water, place the gelatine in a
jar stood in a saucepan, and heat tiU melted ;
then add the glycerine, alcohol and acid with
constant stirring. If too stiff, add water.
A Uquid gelatine mountant, and one always
ready for use, is made by soaking i oz. of gelatine
in 3 oz. of water for twenty-four hours, melting
by heat, and adding ^ oz. of chloral hydrate,
afterwards heating for half an hour and adding
sufficient washing soda to render the gelatine
mixture neutral to Htmus.
Mountants
365
Mounting
Gum. — Ordinary office and commercial
mixtures of gum are likely to cause fading
because of tiie chemicals used to preserve
such mixtures. A suitable formula for a photo-
graphic mountant is : —
Best gum arable . 5 oz. 275 g.
Glycerine . . ij- „ 69 „
Alcohol . . 4 „ 220 „
Water . 12-20 „ 600-1,000 ccs.
Dissolve the gum in the water, add the glycerine
and finally the alcohol.
Indiarubber. — Indiarubber solution (see " India-
rubber ") is useful for mounting glazed and dried
prints without cockling. Cut a piece of paper
\ in. smaller than the print in both dimensions,
place it centrally upon the back of the dry
print, coat the exposed margin with the solution,
remove the paper, and press the print down on
the mount. In course of time, the rubber
perishes and the print leaves the mount.
Shellac. — A good shellac mountant is made
by mixing 4 parts of shellac with i part of
mastic, powdered, and dissolving in from 10 to
1 5 parts of spirit of wine. It must be put in a
warm place, and after a few days the gums will
be dissolved. If too thick, add more alcohol.
The print must be quite dry, and the back
brushed over with the mountant, imme-
diately placed on the mount, and allowed to dry.
A thin print can be thus mounted without
cockling.
Starch. — Rub up i part of good white starch
with 2 or 3 parts of cold water into a per-
fectly smooth cream-like paste, and then with
constant stirring pour this into from 6 to 8
parts of boiling water and continue the
heat for five minutes, stirring constantly.
AUow to cool, and if not free from lumps
squeeze it through muslin. Another plan is
to rub the starch into a paste, as above, and
to pour boiling water upon it, stirring constantly
until it jellifies. All starch mountants should
be allowed to cool and the top skin be taken ofi
before use. Such pastes keep good for two
or three days only, but the addition of a few
drops of oil of cloves or carbolic acid will preserve
them for a longer period.
Starch and Gelatine. — ^This is a stiff, smooth
paste which does not cause cockling when
properly applied. Take 2 parts of wheat
starch and i part of rice starch, and mix
thoroughly. Soak 60 grs. of gelatine in 10 oz. of
water and heat tiU dissolved. When the latter
has cooled to about 70° P. (21° C), add the
mixed starches in small quantities, stirring all
the time untU the mixture is of the consistency
of thin cream. Heat slowly, in a jar placed
in a saucepan of water, until tiie starch thickens ;
and continue the heat until about one-fifth of
the water has evaporated. Then add slowly,
with constant stirring, i oz. of alcohol and
about 45 drops of oil of cloves.
Starch and Gum. — A suitable formula is : —
Gum arable
Rice starch .
White sugar
Water
I oz.
I ..
4 „
q.S.
100 g.
100 „
400 „
q.S.
starch, which nas been rubbed up into a cream
with water, and boil the mixture until the
starch is jellified.
Adhesive Prints and Mounts. — Adhesive mounts
are made by spreading a thick solution of gum
tragacanth upon them and allowing to dry.
When the damp print is pressed into contact
with the gummed surface, there is immediate
adhesion. Similarly, glazed prints, while still
on the glass or ferrotype plate, may be coated
with : —
A. Bleached shellac .
Alcohol
B. Borax
Curd soap powder
Water
2 oz. 200 g.
4 „ 400 CCS.
24 grs. 5 g.
24 „ 5 „
100 mins. 20 ccs.
Dissolve the gum in as small a quantity of
water as possible, add the sugar, stir in the
Allow A to stand for a week and agitate
frequently ; then add B, thoroughly shake, and
use the clear part, or filter. After the prints
have been coated and allowed to dry, they are
stripped from the support, pressed into contact
with the mount, and attached by passing a hot
iron over them, interposing a piece of blotting-
paper between iron and print.
MOUNTING (Fr., Montage: Ger., Einfassung)
There are many ways of sticking down a
print smoothly on a support or mount, but all
of them are not necessarUy suitable in the case
of photographs, where the image is often of
such a character as to be readily and seriously
affected by substances harmful to it. For
example, glue, gum, and paste, that may be
proper for certain uses, may have disastrous
effects when used as photographic mountants.
In the case of glazed prints, whose surface
would be affected by moisture, indiarubber
solution is sometimes used. Gelatine, which
had to be warmed for use, was once fairly
popular. The favourite professional mountant
was, and to some extent still is, starch paste.
If this is used it should be made freshly every
day and used cold. The prints are generally
mounted while still wet, the starch being applied
to the back, the print placed in position and
rubbed down, and the surface gone over with a
wet sponge. This is a clean and effective
method of mounting, but there is the serious
drawback that the contraction of the print on
drying warps or curls the mount considerably
unless precautions are taken against it, and such
precautions mean additional time and trouble.
Specially prepared mountants can be obtained
that not only contain very little moisture, but
will keep in good condition for a long time.
If such a mountant is used with dry prints the
risk of cockling and warping is reduced to a
minimum. The mountant should be well
rubbed over the back of the print with a stiff
brush, using as little of the paste as can be
made to cover the surface perfectly. If the
print is then applied quickly to its position
(previously marked) on ttie mount, it can be at
once brought into perfect contact by the use
of^a roller squeegee. With care there should
be no trace of mountant on the face of the
print, especially if a sheet of thin paper be
placed over it to protect it from possible traces
of paste on the roller. This method of mounting
is probably the best for the beginner, especially
Mounts, Lens
366
Multi-colour Printing
as the mountant is always ready when an
occasional print has to be dealt with. When
large prints are being treated it is generally
advisable to thin the paste very slightly by
dipping the brush into water before rubbing
up the paste with it, but for small prints simple
rubbing up with the brush is sufiSdent.
Another method of mounting photographs,
and one which has distinct advantages, is " dry
mounting" {which see). Multiple mounting is
described under its own heading.
In process work, the term " mounting " is
also applied to fixing the etched zinc or copper
plates on to a wood or other mount for the
purpose of bringing the plates up to type-
height. It also applies to the various operations
of trimming and squaring up the plate or block.
In America the equivalent term is " blocking."
MOUNTS. LENS
Photographic lenses are usually mounted in
brass, but m certain cases, especially with tele-
photo combinations, the lighter metals, alumin-
ium or magnalium, may be used. The iris dia-
phragm should be made of metal, especially in
a lens for use in an enlarging lantern, as the heat
is liable to distort, and even to destroy, iris
leaves constructed of vulcanite or ebonite.
Lenses should always be fitted with the standard
threads of the Royal Photographic Society, and
in the case of Continental makes it is convenient
to have a fixed adapter made to the next larger
standard thread. The lens hood may be con-
sidered a part of the mount ; unfortunately, it
has now fallen into disuse, but in these days of
large apertures and rapid plates it is more than
ever necessary ; however, it is obtainable as a
separate accessory, which may be made to serve
for several lenses.
The following are the measurements and
standards recommended by the Royal Photo-
graphic Society. The recommendations are : —
( 1 ) That the equivalent focal length of a lens
be engraved upon its moimt.
(2) That the following series of screws for
photographic lens flange fittings be adopted, it
being understood that, in order to secure free
interchangeability, every male screw should be
made at least as small as these sizes and every
female screw at least as large : —
Diameter No. of threads Core diameter
in inches. per inch, in inches.
1 * 24 -9466
125 24 I-I966
If 24 1-3216
1-5 24 1-4466
l| 24 1-5716
I -75 24 1-6966
ij 24 1-8216
2 24 1-9466
2-25 24 2-1966
2-5 24 2-4466
3 24 2-9466
3-5 12 3-3933
4 12 3-8933
5 12 4-8933
And upwards, 12
advancing by
inches
* For screws less than i inch in diameter, the Royal Micro-
scopical Society's Standard screw should be adopted.
The form of thread is that known as Whit-
worth's angular thread, and is designed as
follows : — Two parallel lines, at a distance apart
equal to -96 of the screw pitch, are intersected
by lines inclined to each other at fifty-five
degrees, as shown in the figure at A. One-
sixth of the vertical height of the Mangular
spaces so obtained is rounded off both at the
top and bottom, leaving the form of the screw
thread as at b. The depth of this thread is
-64 of the screw pitch. This is the theoretical
form of the Whitworth thread, but for the
purpose of securing real interchangeability it is
A B
Whitworth's Angular Thread for Lens Mounts
generally found necessary to use chasers or
other threading tools which have additional
prominence upon those points which come first
into operation and are subject to most wear.
For this purpose an addition may be made
to the amount of one- tenth (^"11) of the theoretical
depth of thread or to any less amount that may
be sufficient.
(3) That every flange and adapter have a
mark upon its front to indicate the position of
the diaphragm slot or index of any lens when
screwed home. The mark on any adapter
should coincide with the mark upon any flange
into which it is screwed. This mark should be
placed at the point at which the thread becomes
complete at the shoulder of the flange or adapter.
"M.Q."
The meto-hydroquinone developer (which see)
" M " indicating metol, and " Q " hydroquinone
(quinol).
MUCILAGE (See " Mountants.")
MULTI-COLOUR OR MULTIPLE GUM
PRINTING
An elaborate and somewhat complicated form
of gum-bichromate printing. It consists in coat-
ing paper with the sensitive pigment, printing
and developing, and then, when dry, re-coating,
printing, and developing again, repeating the
process as many times as is considered necessary.
In this way the image is built up and parts
brought out more prominently. It is a common
practice not to recoat with the pigment used
the first time on the paper, but to use a different
colour for each coatmg and so obtain a print
in colours. Lighter colours are used at first
and the shadows built up with deeper colours.
By varying the thickness of coating and depth of
printing, masking during printing, and develop-
ing with a brush, highly efiective results become
possible. Considerable practice and artistic skill
are required to produce a satisfactory print.
One of the greatest difficulties is in registering
the various printings ; some workers prefer
stout card to paper, as the registering is easier,
while others use special frames. The process
opens up a wide field for the display of in-
dividuality.
Multiple Mounting
367
Mutoscope
MULTIPLE MOUNTING
In the simplest form of this style of mounting
a trimmed print is mounted on a sheet of paper,
which is then trimmed so as to show a narrow
margin all round the print. 1*1118 in its turn is
mounted on another sheet of paper, preferably
already laid down on a piece of stout board.
The margins then being measured off and
trimmed, the print will be found to be efEectively
mounted, provided the mounting papers har-
monise with each other and with the print.
There is the obvious advantage that the mount
is made to fit the print, and not the print
trimmed to fit the mount, as in the case of ready-
made mounts.
A simple and efiective mounting may be
secured by laying down a warm print on a brown
paper, which may be called No. i, and trimming
to show a fairly wide edge. This is now laid down
on another sheet. No. 2, either lighter or darker
than No. I, and trimmed to give a narrow edge.
The whole is then finally mounted on a sheet of
No. I. A few experiments of this kind will soon
give an idea of the wide possibilities of this style
of mounting when it is carried out with restraint
and good taste. When several sheets of paper
are superimposed it is frequently the practice to
attach them by their top edges only, but as it is
then impossible to keep all Qie sheets in perfect
contact, there is an inevitable irregularity in the
various margins that considerably detracts from
the beauty of the result. A good stock of suit-
able papers is required for the work, together
with faolities for accurate trimming and perfect
mounting. The " passe-partout " style of framing
is often the most suitable finish for this class of
mounting, but if a frame is used the moulding
should generally be very narrow and simple.
MULTIPLE PHOTOGRAPHY (Pr., La photo-
graphie multiple ; Ger., Vielfachephoto-
graphie)
Under this heading are included many methods
whereby a number of photographs, whether alike
or in different positions, are obtained on a single
graphs "), or in succession with a repeating back.
A method at one time popular in America, and
stiU used in Prance for photographing criminals,
is to place the sitter in front of two large upright
mirrors joining at an angle of 72°, the result
being that five different positions are secured.
The camera is set in line with the junction of
the mirrors, a screen being adjusted at each side
of the lens to prevent reflections from objects
behind the operator. The arrangement of the
apparatus, and the method in which the mulitple
reflections are formed, is shown in the diagram,
N being the camera, o p the mirrors, S the
sitter, and T tr the screens. With sufBciently
long mirrors, full-length photographs are obtain-
able.
MULTIPLE-COATED PLATES
Plates coated with two or more layers of
emulsion of different degrees of sensitiveness,
introduced in 1891, to prevent halation. The
topmost film was a rapid emulsion, the second
of medium sensitiveness and more opaque,
whilst the third was a lantern emulsion of very
slow speed and very opaque, so that on exposure
in a camera the light from a briUiantly-Ut object
would penetrate the first and second films and
possibly partly through the third, but would not
reach right through to the back of the glass, so
that it could not be thence reflected to give rise
to halation. The shadows and less brilliantly
illuminated parts would be recorded on the top
and second films only.
MURIATES {See "Chlorides," "Ammonium
Chloride," "Mercuric Chloride," etc.)
MURIATIC ACID (See " Hydrochloric Acid.")
MUTOGRAPH
Casler's camera for obtaining pictures for
his biograph {which see).
MUTOSCOPE
Casler's " Mutoscope," here shown, consists
of a receptacle having an opening in its face,
under which a set of pictures, made on bromide
paper, is made to pass. The pictures radiate
Arrangement for Multiple Photography
plate. A nimiber of similar photographs may be
made at once by means of a camera with a
battery of lenses {see " Postage Stamp Photo-
Coin-in-the-Slot Form of Mutoscope
from a common centre, on which they turn on
an axis. A coin-freed mechanism is fitted to
the apparatus, which is operated by turning
a handle. There are other forms.
N
NAKAHARA'S PROCESS
A Japanese " black line " process.
NAMIAS' REDUCER
Tlie permanganate reducer, which, under cer-
tain conditions, has a similar action to that of
the ammonium persulphate reducer.
Sulphuric acid {20% sol.) 40 mins. 8 ccs.
^ permanganate
Potass.
(20% sol.)
Water
.80 „
.10 oz.
16
It gives even reduction when applied to u wet
negative, whereas a dry negative immersed in
the solution, is reduced more in the high lights.
Greater softness is obtained by treating the dried
negative quickly with the reducer, washing, dry-
ing and re-immersing. Red or brown stains are
caused by insufficient sulphuric acid, and may
be removed with a 10 per cent, solution of
sodium sulphate containing 2 per cent, of oxalic
acid. The use of impure permanganate causes
irregular action.
NAPHTHA (Pr., Naphte ; Ger., Naphtha)
Mineral naphtha is known as petroleum ether
or benzine (see " Benzine "). Coal-tar naphtha is
chiefly benzole (see " Benzene "). Wood naphtha
is impiire methyl alcohol (see " Alcohol ").
NAPHTHALENE RED
(See "Magdala Red.")
(Pr., Vert naphthol :
NAPHTHOL GREEN
Ger., Naphtholgriin)
The ferrosodium salt of nitrosobetanaphthol-
sulphonic acid, used for making colour screens.
It is soluble in water, with yellowish-green
colour. It is especially useful as it is about
the only green aniline dye which satisfactorily
absorbs the extreme red of the spectrum. There
are various kinds, naphthol green 2-6 being the
most satisfactory.
NAPHTHOL YELLOW S (Pr., Jaune de
naphthol S ; Ger., Naphtholgelb S)
Synonyms, citronine A, sulphur yeUow S,
acid yellow S. Several aniline dyes are sold
under the generic name of naphthol yellow.
Naphthol yellow S is the potassium salt of
dinitroalphanaphtholsulphonic acid, and is used
for making colour screens.
NAPLES YELLOW
A mixed pigment used in colouring photo-
graphs. Commercial Naples yellow is made by
mixing zinc white with cadmium yellow, by
mixing white lead, cadmium yellow and yellow
ochre, and in other ways. The true Naples
yellow is a basic lead antimoniate, which has
the disadvantage, when used as a water-colour,
of|soon being afiected by foiil gases.
NARROW-ANGLE LENS
A lens having a focal length at least twice
that of the longest side of the plate.
NATROL
A solution, German in origin, used instead of
a preliminary washing for P.O. P. prints ; sup-
posed to assist the gold in giving rich tones and
to prevent spots. The formula is : —
Sodium chloride (salt) . 2f oz. 150 g.
Fused sodium acetate or
sodium bicarbonate . 2 „ no „
Water
20
1,000 ccs.
Dilute I oz. with 15 oz. of water. Immerse
the prints for about five minutes, wash, and
tone as usual.
NATURAL COLOURS, PHOTOGRAPHY IN
This subject is of such vast extent and is
divided into so many branches, which are treated
of individually, that a mere sketchy outline of
the whole subject can be given here. The subject
may be divided into four main heads : (a) direct
heliochromy, (b) interference heliochromy, (c) the
bleach-out process, and (d) three-colour work.
Direct heliochromy and interference heliochromy.
— Senebier, in 1785, had pointed out that when
a spectrum was thrown on to silver chloride,
violet and blue were reproduced, but he carried
the experiments no further. However, in 18 10,
Seebeck, the great German physicist, sent to
the poet Goethe a treatise of the action of
coloured iUumination (" Wirkung farbiger Be-
leuchtung") which is printed in Goethe's
Geschichte der Farbenlehre, Vol. II., p. 716.
Seebeck details the effect of allowing " the
spectrum from a perfect prism to fall for 15 to
20 minutes on white damp silver chloride spread
on paper and kept by a special device in the
same place. I foimd the silver chloride to be
altered in the following manner : in the violet
it became reddish-brown (sometimes more
violet, sometimes more blue), and even beyond
the previously marked limits of the violet this
coloration extended, but it was no stronger
than in the violet ; in the blue of the spectrum
the silver chloride had become pure blue, and
this colour extended, increasing and becoming
brighter right into the green ; in the yellow I
found the silver chloride frequently unchanged,
but occasionally it happened to be more yellow
than at other times ; in the red, on the other
hand, and frequently beyond the red, it had
assumed rose-red." Seebeck then describes the
efiect of two spectral lights — fed and violet — and
also tests with coloured glasses. The importance
of this work must not be overlooked, for it was
thirty years before the discovery of the daguerreo-
type, and the results were photographs on paper.
But little notice seems to have been taken of
368
Natural Colour Photography 369 Natural Colour Photography
this work, though this was probably due to its
being published in Goethe's book, which is very
poor in facts but rich in arguments. Seebeck's
work also confirmed Ritter's statement (1801)
that there Were invisible radiations at both ends
of the spectrum.
John Herschel, the son of the renowned
astronomer, was the next to discover anew the
curious property of silver chloride of reproducing
colours ("Philosoph. Transactions," 1840, p. 28,
Athentsum, 261), and followed Pox Talbot's
suggestion of using alternate baths of silver
nitrate and sal ammoniac, but Herschel pre-
ferred to sensitise his paper just before use, and
pressed it in the camera obscura against a glass
plate, which prevented any wrinkling of the
paper.
He did not succeed in fixing these colours ;
yet they were half fixed by merely washing with
water, and could then be examined by diffused
daylight or lamplight without deteriorating.
Herschel also discovered that silver bromide gave
the same colours as, though less distinct &an,
the chloride, whilst silver iodide gave the com-
plementary colours. Robert Hunt, in his Re-
searches on Light, details numerous experiments
both on silver and other substances, and records
the occurrence of colours ; but the next investi-
gator to warrant attention was Edmond Bec-
querel, and to his papers {Annales de Chimie
et de Physique, third series, Vols. XXII., XXV.,
XLII., 1849 — 1855) we are indebted for the real
foundation of successful heliochromy ; his re-
searches are collected into two volumes : La
Lumiire et ses Effets. He exposed to the
spectrum silver plates coated with silver chloride
which gave a fairly satisfactory rendering, but
the uneven film of chloride caused unevenness
of colouring ; ultimately, he found it better to
obtain an electrolytic deposit of chloride. He
also used a solution of cupric chloride (copper
sulphate i part, salt 3 parts, water 10 parts),
and in this the silver plates assumed a violet-
white coloration, and gave, on subsequent ex-
posure, not only the spectral colours, but white
also. He says : "I ^hitiV that the substance
formed on the surface of the metaUic silver is
a special chlorine compound, perhaps violet
silver subchloride or a mixture of wMte silver
chloride and subchloride."
Niepce de Saint Victor carried on similar
experiments to those of Becquerel ; Eder states
that one of his heUochiomes in his possession
stUl shows brilliant colours, forty years after its
preparation. Niepce started with the theory
that those chlorides that gave a definite colour
to a Bunsen flame were the best for reproducing
the colour when used for chlorising the silver
plate. He not only obtained the spectrum, but
also copied objects in the camera and obtained
excellent reproductions of the shimmer of glass
and poUshed metal objects, and also reproduced
black, which in many cases reflects tie ultra-
violet or infra-red or both. He used a varnish
of dextrine and fused lead chloride, which was
a great protection, and this was further in-
creased by subsequently coating the plate with
tincture of Siam benzoin, and heating till some
of the benzoic add was driven ofi ; his results
are recorded in the Comptes Rendits, 1851 —
1859, etc.
24
In 1851, an Amencan clergyman named Hill
claimed to have discovered photography in
colours, but eventually the process was proved
to be useless. In 1855 and 1856, Testud de
Beauregard brought forward the view that a
silver photograph without colour possessed a
latent power for colour; but no one has ever
been able to produce colours by his process —
save the discoverer.
Poitevin (Comptes Rendus, 1865, p. 1,111)
describes his process for obtaining colours on
paper, and the following is his final method :
" I form upon non-albumenised paper a film of
ordinary silver chloride by floating one side of
the paper on a 10 per cent, solution of salt;
when dry, I float this on an 8 per cent, solution
of silver nitrate, or the back of the paper is
painted with a mixture of equal volumes of a
saturated solution of potassium chromate, and
a 10 per cent, solution of cupric sulphate, dried
in the dark, and then floated on the silver bath.
Chromate of silver is now formed ; I wash with
plenty of water in ordter to remove excess of the
nitrate salt and add to the last washing water a
few drops of ordinary hydrochloric acid till the
red chromate salt is converted into white silver
chloride. iBoth these methods of preparing the
silver chloride film are equally good. Now, in
order to obtain the violet subchloride, I pour
into the dish, which contains the paper soaked
in water, a small quantity of 5 per cent, stannous
chloride solution ; about 20 ccs. (about |- oz. )
are required for a whole sheet. Now I expose the
sheet, without taking it out of the bath, to the
action of light, and preferably in the shade than
in the sun ; its surface quickly discolours and
after five or six minutes, has assumed the desired
dark violet colour. It is not advisable to allow
the Ught to act still longer, otherwise a greyish
black tone would be obtained, which is not suit-
able for heliochromy. After the action of light,
I wash the sheet in several changes of water, and
then allow it to dry in the dark. In this condi-
tion it is very little sensitive to light, and can be
kept for a long time." Poitevin used water
acidulated with sulphuric add, or a very dilute
solution of mercuric chloride diluted with sul-
phuric add for fixing, and subsequently glazed
the pictures with albumen.
Wharton Simpson followed with a suggestion
to the use of an emulsion of silver chloride in
collodion (1867). Saint Florent (Bull. Soc.
Franf., 1874) also suggested a method of using
collodio-chloride paper, which was exposed to
sunlight for 80 to 100 seconds, or till reddish-
black ; immersed in a bath of alcohol 100 ccs.
(3J0Z.), glycerine 7 ccs. (126 mins.), i per cent,
tincture of iodine 7 ccs. (126 mins.), and am-
monia 6 drops, for 10 minutes ; dried in a dark
place ; exposed under a coloured transparency
for about one hour in sunshine ; fixed in a 10
per cent, solution of " hypo " ; washed and
dried in sunshine. In the fixing bath the
colours disappear, but reappear when exposed
to the sun, or ironed with a hot iron.
Veress, in 1890, followed up on Poitevin's lines,
and in the following year Kopp, of Miinster,
certainly made some advances, which promised
well. The best report of his work is found in
Valenta's work, Die Photographie in NatUr-
lichen Farhen, 1894.
Natural Colour Photography 370 Natural Colour Photography
He floated raw paper on salt solution, then on
silver nitrate and again on salt solution, thus
obviating any excess of silver nitrate, which both
Becquerel and Poitevin had pointed out as pre-
judicial to the purity of the colours ; the paper
was then well washed and exposed, under an
acidulated -i per cent, solution of zinc chloride,
to diffused daylight till it had assumed a blue-
grey colour. The paper is washed and dried, and
made sensitive to all colours, as weU as white
and black, by treating with a solution made as
follows : —
Potassium bichromate
Cupric sulphate
Distilled water to .
. 1,940 grs. 150 g.
.1,940 „ 150 „
20 OZ. 1,000 CCS.
Dissolve by the aid of heat, and when boiling, add
Merciiric nitrate . .1,940 grs. 150 g.
dissolved in as small a quantity of water as pos-
sible, and acidulated with nitric acid. A red
precipitate forms, which should be filtered out
when the solution cools down ; then make the
filtrate measure 20 oz. or 1,000 ccs. by adding
water. This solution will keep well in well-
closed bottles. The blue-green paper should be
immersed in this for half a minute till completely
decolorised, drained and immersed in a 3 per
cent, solution of zinc chloride tiU it again becomes
blue, then well washed in running water, super-
ficially dried between blotting-paper, and exposed
Whilst stUl damp. The yellow and green of the
spectrum appear at once — that is, with about
30 minutes' exposure — and the picture should
then be coated as to these colours with a shellac
or celluloid varnish, well heated, immersed in a
2 per cent, solution of sulphuric acid till all the
colours appear, thoroughly washed and dried
between blotting-paper ; fixed in the above-given
mercury bath, in which the colours disappear,
and finally immersed in a sulphuric acid bath
and coated with a solution of gum arable con-
taining 5 per cent, of sulphuric acid. Valenta's
improvement was the use of -5 — i per cent,
solution of sodium nitrite instead of the zinc
chloride solution, and excellent results are
attainable.
The above process is also applicable to many
of the commercial printing-out papers, both
gelatine and coUodion, if they are immersed in
a solution of acidulated zinc chloride, are then
well washed and treated with a. 10 per cent,
solution of hydroquinone.
Krone {Darstellung der Natiirlichen Farben)
has confirmed Valenta's statements, and also
Poitevin's and Eecquerel's.
So far, merely the practical side of the question
has been considered. Schule assumed that the
dark silver subchloride was oxidised on exposure
to yellow silver chloride, and this chemical view
was supported by many chemists, though physi-
cists considered that the colours were due to
thin films, as in Newton's rings, and this was
confirmed by the very thin films obtained by
Becquerel in the electrolytic chlorising of his
plates. The true explanation was first pro-
pounded by Wilhelm Zenker in his Lehrbuch
der Photochromie (1868), and this has been
purposely disregarded till this particular stage,
because it forms a fitting connection to the next
process to be here considered.
Zenker examines the various methods which,
up to 1868, had been suggested, and in most
cases gives his criticisms of the processes founded
on actual experiments ; his book (reprinted,
1900), therefore, is extremely valuable. Zenker
states : " When different coloured rays pene-
trate a light-sensitive substance with equal
intensity, they must act on the same in abso-
lutely equal manner ; every ray, no matter what
its vibration may be, must act on all the particles
of the substance which lie in its path, set them
in motion, and thus chemically alter them.
Tlius, there may be a general darkening, colora-
tion or bleaching ; these must be under one
colour the same as under the other ; a difference
of colour is not conceivable. The facts are, how-
ever, quite different when the incident rays meet
again outgoing rays of the same phase, that is
to say, if we consider that with all these photo-
graphic processes the incident rays are again
reflected. This takes place most strongly with
the daguerreotype, but also with sensitive sur-
faces lying on other supports, and one can
convince oneself of the quantity of reflected light
by merely looking at it. Now, if two waves of
the same phase meet they give rise to the
phenomenon which is called, in the case of water,
' stationary or standing waves.' "
The formation of these waves is shown in
diagram A, in which the incident rays are shown
in continuous lines, and the returning rays in
A, Stationary or Standing Waves
dotted lines. In E it is assumed that the ray
is reflected from a substance with higher refrac-
tive index, and in F with a lower refractive
index, than G, the sensitive surface. At the
points 6 6 the reflected ray augments the inci-
dent, whilst at a a the pifll on the ether particles
is in contrary directions ; consequently there is
no movement, and therefore no Ught. As a
matter of fact, in standing waves, the ether par-
ticles rise and fall, but there is no propagation of
light. Now, it is obvious that if G is a film
of sensitive substance, the action of Ught will be
to cause a deposit of silver at the intemodal
planes 6 b, as shown by the hatched Unes, and
this deposit is exactly half a wave-length of the
incident Hght apart ; therefore, it can only
reflect Ught of tiiat colour which has a wave
length of double the distance 6 b.
The truth of this theory was disputed by
Schultz - SeUack (Annalen d. Phys. u. Chem.,
1871, p. 449), following which further doubt was
created by Carey Lea's production of the photo-
salts, as he was able to prepare the coloured
Natural Colour Photography 37i Natural Colour Photography
substances, produced by the action of coloured
Ugkt on silver chloride already exposed, by purely
chemical means in the dark. Otto Wiener
(Wiedeman's Annalen d. Phys. u. Chem., 1890,
p. 203) was able to prove experimentally the
formation of Zenker's standing waves, and the
following is a. brief summary of his work : With
homogeneous illumination, there is formed in
front of a reflecting surface a series of standing
waves parallel to the reflecting plane. This is
shown at B, in which r r is the reflecting sur-
face, and the planes of equal phase are shown
in section, the nodal points in dotted lines, and
the waves in maximum action in continuous
lines. Now, if a hght-sensitive film be coated-
on the glass, the metallic silver resulting from the
light action must be - apart, but as this distance,
one half wave-length for red light, would be about
•3 n, it is obvious that it woiild be invisible
to the naked eye. Wiener, therefore, coated
his sensitive film, a 6, at an acute angle with
the reflecting surface, and it will be at once seen
that the distance of the sUver laminse is increased,
for if - is the distance between two maximum
2
wave planes, the separation, b, of the silver
laminae would be : 6 = - sin a. Wiener used
2
coUodio-chloride of silver emulsion thinned down
with about 15 to 20 parts of solvent, and thus
obtaiaed a colourless, transparent emulsion in
which the silver laminae were distinctly visible.
Later, he was able to confirm this with silvered
glass plates fumed with iodine.
In 1895, Wiener (Annalen d. Phys. u. Chem.,
1895, P- 225) examined the question of the See-
beck and Poitevin processes on paper, to deter-
mine whether the colours were apparent or body
colours — that is to say, whether they were pro-
duced by interference or absorption. To deter-
mine this question, he used a right-angle prism
of highly refractive glass, ii = i-y^ for D, with
its hypotenuse on the colour pictures, the
intervening air space being filled with benzole
so as to prevent total reflection, and thus securing
for Ught rays entering normal to the side surfaces
an angle of incidence of 45°, so that the ray
entering the silver chloride must form a consider-
able angle with the normal to the surface. The
difference in path of the interfering Ught Waves
will, in comparison with vertical incidence, be
greatly changed, and according as the colours
are thus altered or not they are interference or
body colours. The prism was so placed upon
one half of the photographed spectrum that the
Une between the hypotenuse and the side face 1
(diagram C) cut similar colour lines at right
angles. The eye of the observer was placed in
the prolongation of the same surface i (the
arrow indicates the hne of vision) so that a line,
S, drawn before the experiment, in the direction
of a single colour — as, for example, the yellow —
appeared straight when viewed through the air
and prism. D shows another arrangement, in
which the spectrum reproduction was cut in half
perpendicularly to the reference mark after draw-
ing the latter in the yellow. One of the parts
was placed upon the side of an auxihary prism,
I I, fastened to a level glass plate, upon which
the other half of the sheet was so placed that the
marks came together. Finally, prism I, with the
high refractive index, was set upon the second
half, benzene poured between, and the eye
placed in line with the reference mark and with
the surface of the principal prism. Wiener thus
sums up his conclusions drawn from the above
experiments: In the Seebeck and Poitevin pro-
cesses there is no change of colour under the
above conditions, and they are, therefore, body
colours ; this is also confirmed by the fact that
these pictures show the same colours by trans-
mitted as by reflected light. The colours of the
Becquerel pictures, produced on an underlying
silver mirror, were chiefly produced by inter-
ference. Carey Lea and Krone proved that the
substances present in the Seebeck and Poitevin
processes were capable of yielding compounds
which embrace almost all the spectral colours,
if not aE their tones, and the reason why they
B. Standing Waves
parallel to Re-
flecting Plane
C and D. Use of
Prism to detect
Interference or
Body Colours
agreed in hue with the illumination-produdng
decomposition is that of all the coloured sub-
stances capable of being produced, only those
will be stable which agree in colour most nearly
with the incident hght, since these will best
reflect and least absorb it, and can, therefore,
be least changed. Decomposition products of
other colours, on the other hand, absorb this
hght, and will be again decomposed. Proof of
this was found when a spectrum was thrown at
right angles on a colour photograph of the
spectrum. It was then found that a correctly-
reproducible illuminating colour was capable of
decomposing all colours differing from it, but
similar colours remained unchanged. It is,
therefore, fundamentally possible 1±at coloured
illumination shall, in suitable substances, produce
similar body colours, and such substances Wiener
termed " colour receptive."
In 1891, Prof. Gabriel Lippmann, lecturing at
the Acadfemie des Sciences (Comptes Rendus, 1891,
p. 274), explained at length the theory of inter-
ference, and exhibited actual photographs in
colours produced by his method, which is essen-
tially that of Wiener, and theoretically described
by Zenker. He used a transparent gelatine
emulsion of silver bromide with the sensitive
Natural Colour Photography 372 Natural Colour Photography
film in contact with a film of mercury and the
glass of the plate presented to the lens. From
what has already been said, it wiU at once be
seen that here was the ideal method of recording,
if possible, the formation of standing waves, and
if formed they would naturally reflect the
colours of the incident light.
Lippmann's own description (Phot. Journ.,
1897) is by far the easiest to grasp, and he says :
" Now, how is it that we see the colour ? The
photographic operations are the same as in
ordinary photography, the result of the opera-
tions is the same, a similar deposit of reduced
silver is obtained, and the materials of which
the image is composed are the same as those in
a colourless plate. The difference is that the
plate has acquired such a structure that it
decomposes the light by which it is illumined,
and sends back to the eye of the observer
elements of white hght, which together make
the natural colours of the object. In the same
manner the colourless drops form the rainbow.
A soap bubble appears coloured, although
consisting of a colourless solution, and mother
of pearl appears coloured although made of
colourless carbonate of lime. It is a phenomenon
of interference due to the structure which the
deposit has acquired ; if you were to use a
plate without a mirror you would get an ordinary
negative, but the presence of the mirror changes
everything, and this is how it is done : You
know that light is made up of vibrations, just
as sound is ; these vibrations give rise to light
waves that rush through the ether and the
plate with a velocity of 300,000 kilometres per
second ; therefore, they impress the plate more
or less strongly, and thus leave a design of
difierent intensities of the image, but as they
rush through the plate they leave no record of
their form. And this is what I mean by their
own form : EJach ray of Hght of a certain colour
has a certain structure ; it is made up of waves
which have a certain wave-length ; you know
a wave-length is the distance between the crests
of two succeeding waves ; red has a. com-
paratively great wave-length, blue has a much
smaller one, and the intermediate colours have
each a distinct and intermediate length of wave.
If you put no mirror, each train of waves rushes
through the plate and wipes off every record
of its own form by reason of its velocity ; you
cannot expect a thing which moves with a
velocity of 300,000 kilometres in a second to
give a photograph of itself. If you put a
mercury mirror behind the plate, then the
following phenomena occur : The hght is
reflected back on itself ; the hght rushes in
with a velocity of light and rushes out again
with the same velocity ; the entering and
issuing rays interfere, and the effect of the inter-
ference is that vibration takes place, but the
effects of propagation are stopped, and instead
of having propagated Waves we get stationary
waves — that is, the Waves now rise and fall,
each in its own place ; they pose, therefore, in
the interior of the film and impress their form
upon it, the largest movement giving the
strongest impression, and where the move-
ment is naught the impression is naught. So
that you have the form of the vibration impressed
in the interior of the film by the photographic
process, and the photographic film has really
now acquired the structure of the incident rays,
because they have become stationary, and
impressed their form upon it. The result is,
that if you look through the film you see nothing
special ; it looks like an ordinary negative ;
but if you look at it by reflection, then you
see it coloured. And this for the following
reason : Suppose at one place the plate has
been impressed by red hght, the red Hght has
impressed its structure on that part of the plate,
and that part of the plate is now able to reflect
back to our eyes only the red part of the white
rays — only the red element which is a com-
ponent part of white hght, and similarly with
every part of the spectrum ; it is a mere me-
chanical adaptation of the form of the deposit
to the form of the hght vibrations."
Now, if the capability of one of the Lippmann
hehochromes to reflect the colour of the original
incident ray back to our eyes is dependent on
the distance of the laminae of silver one from
the other, it is obvious that if we could increase
this distance the colours should change. This
is precisely what takes place. It is only neces-
sary to expose a heUochrome to steam or
aqueous vapour, which is absorbed by the
gelatine ; this swells, and the distance between
the laminae is increased. Now, assuming that
this distance of separation for the extreme
violet be half one wave-length, 4,000 ten-
milUonths of a millimetre, that is, 8,000, and
we steam it so as to increase the distance by
one-fourth, then our 8,000 becomes 10,000, and
one-half of this would be 5,000, which is the
wave-length of the bright blue ; therefore, this
would be the colour reflected to the eye. This
change of colour with steaming or absorption
of aqueous vapour can be proved with any
heliodirome. It is obvious that there might
Well be hehochromic effects produced on
daguerreotypes, with which a poUshed silver
plate with a sensitive film is used, and such
coloured results have actually been observed
(J. Nicephore Niepce).
Bleach-out Process. — A. Vogel {Schweigger's
Journal, 1813, pp. 229-236) recorded the fact
that under coloured glasses the colours of
tinctures of certain flower petals were bleached,
but that under glasses of the same colour as
the tinctures there was no change. This
subject was studied by Herschel (Philos. Trans.,
1842) and Robert Hunt (Researches on Light,
1844, p. 170), and the former propounded the
law that dyes Were bleached when exposed
under their complementary colours, but were
not bleached when exposed to hght of the same
colour. In 1889, R. E. Liesegang (Phot. Archiv.,
No. 633, p. 328) recommended the admixture
of three fundamental colours — red, yellow and
blue — and in 1891 (Phot. Almanach, 1891) he
stated that the bleaching took place more
rapidly in oxygen. Two years later (Phot.
Archiv., 1893, Nos. 729, 730) he also pubhshed
a series of experiments on the increase of rapidity
of bleaching aniline dyes by the addition of
certain sensitisers, sudi as stannous chloride,
oxalic acid, hydroxylamine, ammonium sulpho-
cyanide, etc.
Wiener, in his already cited paper (Annalen d.
Phys. u. Chem., 1895, p. 225), includes a special
Natural Colour Photography 373 Natural Colour Photography
chapter on " the theoretical basis of a method
of colour photography with body colours," and
says : "In order that a substance sensitive to
light can be chemically changed by the action
of any kind of light, it must absorb it." The
converse proposition is not general. The
absorbed light can, for example, be exclusively
formed into heat. A distinction is, therefore,
made between thermal and chemical absorption
of light. For the sake of simplicity of expression
I shall designate as a regularly absorbing Ught-
sensitive substance one which is sensitive to all
colours which it absorbs, and is affected by each
colour in proportion to the capacity for absorp-
tion. That there are such substances, at least
to a considerable degree of approximation, is
known. Upon their existence is based the
important law of optical sensitisers established
by H. W. Vogel. It is conceivable that the
regularly absorbing light-sensitive substance may
be decompased by Uhe action of light to form
coloured substances also regularly absorbing and
light-sensitive. I will designate as a colour-
receptive substance a black regularly absorbing
light-sensitive substance whose products of
decomposition consist only of monochromatic
regularly absorbing light-sensitive substances of
at least three radically difierent colours, and,
besides these, of a white substance which,
however, is the least readily formed. These
colours must be radically difierent in order that
by their mixture with one another and with
white all compound colours may be possible.
In distinction from these compound colours
the unmixed colours will be called ground
colours. The monochromatic substances reflect
only one colour well. They must absorb the
others the more completely they difier from
them. With these preliminaries it may be
shown that a colour-receptive substance repro-
duces the colour of the illumination correctly.
First, let the colour of the illumination agree
with a ground colour. It will be absorbed by
the black body and produces a decomposition
substance which, by hypothesis, is regularly
absorbing and light-sensitive. In this decom-
position difierent coloured substances are formed.
Those not agreeing in colour with the incident
light absorb it, since, by the hypothesis, they
are monochromatic, and must absorb all
illumination different from their colour. Since
these are regularly absorbing Ught-sensitive
substances, they are also decomposed by the
light which they absorb. On the other hand,
the substance of the same colour as the incident
light is not decomposed, since it does not absorb.
In the end, therefore, it alone can remain in
company with the white substance. The amount
of the latter is, by hypothesis, very sUght, and
its effect upon the colour is, therefore, noticeable
only under strong illumination. Where the
colour of the illumination differs from that of
a ground colour, but is intermediate between
two groimd colours — as would, for example, be
the case with green, and if yellow and blue were
ground colours — the coloured substances would
suffer least decomposition which reflect green
best — that is, the yellow and blue. A green
mixture would thus arise besides the small
quantity of white. In white light all the
colour substances would be decomposed, leaving
White alone. In the absence of illumination
the substance would remain black."
Incited by Wiener's theorising, Vallot (Mon.
d. la Phot., 1895, p. 318) used aniline purple
(red), Victoria blue and turmeric on paper and
exposed for three or four days to sunlight and
obtained coloured results. The subject was
followed up by Worel, who published (Auz.
K.K. Ahad. Wissent. Wien, 1902) details of
his process, though he had shown results at
the end of 1901, and he used anethol as a
sensitiser. Neuhauss followed up the subject
(Phot. Rund., Jan., 1902, and Eder's Jahrhuch,
1902-3-4), using oxidising substances, such
as hydrogen peroxide and the persulphates,
as sensitisers. Szczepanik (Phot. Korr., 1902),
instead of mixing the dyes, coated them in
three superimposed layers, and in 1906 a com-
mercial paper, " Uto," was placed on the
market by Smith and Co., of Zitrich. Prom a
practical point of view all these preparations
leave much to be desired, but such a paper
with reasonable sensitiveness would be of great
practical interest.
Three-colour Processes. — ^These are dealt with
separately (see " Three-colour Photography "
and " Screen-plate Colour Photography"). The
only other process with which it is necessary
to deal is the —
Prismatic Dispersion Process, which practically
splits up the Ught reflected from any object
into its spectrum, and allows this to act on the
sensitive surface, and then reconstitutes the
image. In this process no dyes or filters are
used, and it may be considered to be nothing
more than a method of optical synthesis, in
which the whole spectrum and not three colours
are used. The first suggestion for the process
was made in an EngUsh patent. No. 16,548 of
1895, taken out by P. W. Lanchester. The
essentials of the process are as follow : A
grating of black lines With clear interspaces is
arranged between the object and the camera,
a prism is arranged behmd the lens with its
axis parallel to the bars of the grating, the
dispersion of the grating being such that when
the lens is focused on the grating the images
of the clear interspaces form a series of spectra
on the plate, whidi are broken up by the light
reflected from the object so that the image
consists of lines of shaded intensities. Prom
this negative a transparency is taken on an
ordinary lantern plate and placed in the position
occupied by the original dry plate, and the
coloured picture is then reconstituted by placing
a Ught behind the grating and viewing the
picture at the distance of normal vision. In
the British Journal of Photography for Jan., 1904,
Dr. Rheinberg suggested a similar process, and
it has since been taken up by Cheron, Bruignac
and Raymond, and the latter seems to have
obtained the most practical arrangement. The
following description is taken from " Colour
Photography," the supplement to the British
Journal of Photography for Mar. i, 1907 : To
an ordinary camera is fitted a diaphragm behind
the lens, and this diaphragm should preferably
be a narrow rectangle. In front of the plate
is fitted an ordinary cross-line screen, with
preferably opaque lines wider than the inter-
spaces ; behind the screen is placed a prism of
Natural History Photography 374
Negative Numberer
from 3 to 8 degrees, and then the plate. The
exposure is made in the usual way, and a positive
from a negative made and placed in the position
of the negative. At present the process is but
in its iofancy, but it promises well, the only
disadvantages being the prolonged exposures
required, and the difficulty of exhibiting the
pictures to more than one person at a time.
NATURAL HISTORY PHOTOGRAPHY
The equipment of the naturalist photographer
largely depends upon the subjects to which he
intends to devote attention. (For example,
the reader w'ill find further useful and suggestive
hints under such headings as " Insects,"
" Pish," " Birds," etc.) For much natural
history photography a good reflex camera is
essential. For photographing very shy birds
and beasts, the improved type of telephoto
lens, having an aperture of //7 or //lo, and
requiring only a comparatively short extension
of camera to obtain on a small plate a large
image of an object at a considerable distance,
will be found of the greatest service. AU
cameras and tripods used should be strongly
made and not have any bright metal fittings
or highly polished surfaces to reflect the light
and attract attention. The tripod may with
advantage be painted a duU, dark green, and
the camera and fittings dead black. A good,
deep, easily-fitted hood for the front of the
lens is desirable to cut off strong reflections on
the front surfaces of the lens, which are often
responsible for general flatness or hazy definition.
The whole of the apparatus should pack into
thoroughly water-proof cases, for the naturalist
photographer may frequently have to face
inclement weather. A well-made Alpine ruck-
sack is a convenient receptacle for parts of the
outfit when long distances have to be covered
on foot. In selecting apparatus, weight must
be considered, but for the sake of lightness
and portability, strength and rigidity must not
be sacrificed. The use of aluminium for any
parts of photographic apparatus to be used in
the field for natujral history is a questionable
advantage. If one is working within reach of
the salt spray of the waves, or where sea water
is likely to come in contact with the outfit,
there will soon be trouble with any aluminium
fittings. The tripod should be of well matured
wood, and of the three-fold type, closing to a
small space, and capable of considerable adjust-
ment for varying heights and inequaUties of the
groimd. As it is important to obtain as faithful
a monochrome rendering of the colours of the
original subject as possible, isochromatic plates
should always be used if there is sufficient light
to obtain a good exposure. Prints should be
made upon platinotype for preference, or
bromide paper, so as to obtain all possible
detail and gradation.
" NATURALISTIC PHOTOGRAPHY "
Under this title a book was published by
Dr. P. H. Emerson, in i888. Its efiect was to
lead to the production of a class of photographic
work which had hitherto received little attention.
The hollow artificiality of much of the photo-
graphic work that had been accepted with
approval was reaUsed, and a school of workers
sprang up who gave their attention to the
beauties of Nature. Many strikingly fine land-
scape subjects were produced which demon-
strated that photography was fully capable of
taking its stand firmly as a graphic art of no
mean capacity. Pictorial photography in the
true sense sprang into being. Less and less
reliance was placed on the theatrical accessories
of the studio, and photographers went direct
to Nature for their subjects and effects.
NATURE PRINTING
Printing on paper prepared with flower juices
(see "Anthotype") and upon fruit; for the
latter purpose, flexible stencil plates are attached
to the green fruit, chiefly apples and peaches,
the Sim then printing the pattern as the fruit
ripens over a period of several weeks. Film
negatives may be used, but they must possess
extreme contrasts.
NEBUL/E, PHOTOGRAPHY OF (See
"Stars, Photographing.")
NEEDLEHOLE (See " Pinhole.")
NEGATIVE (Fr., NSgatif ; Ger., Negativ)
An image in which the lights and shades are
reversed ; a term first used by Sir John Herschel,
in 1840, to describe Talbot's pictures upon
calotype paper. The first negatives were upon
paper made translucent by waxing, but glass and
celluloid have now almost whoUy replaced paper.
NEGATIVE ABERRATION
The opposite of ordinary (positive) aberration
in a lens. A concave lens showing negative
spherical aberration can be used to correct
positive aberration in a convex lens.
NEGATIVE BOX (See " Box, Negative.")
NEGATIVE CARRIERS AND HOLDERS
(See " Enlarging Camera," " Plate
Holder," etc.)
NEGATIVE COLLODION PROCESS (See
"Collodion Process (Wet).")
NEGATIVE ENVELOPE (Fr., Enveloppe aux
cUchSs ; Ger., Negativ-kouvert)
Thin paper envelopes used for storing nega-
tives. Particulars of the subject, date of expo-
sure, and other details may be written outside.
(See also " Negative Storing.")
NEGATIVE LENS
A concave (diminishing) lens, which cannot
focus rays upon a screen to produce an image.
NEGATIVE NUMBERER (Fr., NumSrateur
aux clichis ; Ger., Negaiivenzdhler)
There have been several devices for number-
ing negatives. In one, a small stencil which
changes automatically to a higher number at
each exposure is fitted to the camera or dark-
slide, so that it comes against a comer of the
plate, the number therefore appearing on
development. The sheaths of some hand
cameras have notches indicating their respec-
tive numbers, which show at Qie edge when
Negative, Paper
375
Nephograph
developed; this, of course, only indicates the order
in which each dozen plates are exposed. Some
studio operators have a set of separate printed
numbers, to slip in a small grooved frame, after
the principle of a church hymn-board. This is
laid near ttie sitter so as to come at the margin
of the plate, and is changed at each exposure.
NEGATIVE, PAPER (See "Paper Negatives.")
NEGATIVE, PERFECT
The term " perfect negative " is frequently
met -with in photographic literature ; but a
negative that is perfect for one printing process
may be quite unsuitable for another one. A
nice-looking, clean negative, say, one developed
■with hydroquinone, will often give a print far
inferior to one sometimes obtained from a
yellow-stained pyro-develbped negative. Of the
good average negative, R. Child Bayley says
that, placed film side down, upon a sheet of
white paper, and looked at from above, the
edges on which the light did not fall in the
camera ought to be almost clear ; a slight trace
of greyness is unavoidable, unless a backed
plate is used. There must be an appreciable
quantity of greyness in the very deepest of the
shadows, or the plate has not had sufficient
exposure ; if there is too much the plate has
been over-exposed. The highest lights, the
most opaque portions, are tested by placing
the film in contact with printed matter ; the
print must be considerably darkened as compared
with the lighter parts of the negative, but it
should be possible to read it through even the
most opaque portions without difficulty ; other-
wise, whether the plate was over-exposed,
correctly exposed, or under-exposed, it has been
over-developed.
At one time the wet-collodion negative was
thought to give the effect to be aimed at in
the dry plate ; but at the present time the
Hurter and Driffield dictum, that the negative
should be judged by its printing qualities alone,
is generally accepted.
In process work, various classes of negatives
are used. They may be in " half- tone," " grain,"
or in " continuous tone." The last-named
resembles an ordinary negative, with gradated
tones, not broken up into dot or grain, but
must be of very good quality, with full range
from almost clean glass in the shadows to perfect
opacity in the Ughts. Such a negative for
photogravure or collotype should not be hard,
but somewhat thin and full of detail, with a
uniform gradation throughout.
NEGATIVE, REVERSED
A negative from which is produced a print
that represents the object reversed as regards
left and right. It is easily produced by placing
the plate in the camera glass side towards the
lens. Photo-mechanical workers use, as the
daguerreotype workers did, a reversing mirror
or prism fitted to the front of the lens and
throwing a reversed image direct upon the
plate. Negatives already made may be reversed
by stripping the film and replacing it in a reversed
position. Reversed negatives are largely used
for carbon and collotype work. (See also " In-
version, I^ateral.")
NEGATIVE STORING (Pr., Magasinage des
clichis ; Ger., Negativenlagern)
Negatives are best stored in wooden or metal
boxes. (See " Box, Negative.") Grooved boxes
and drawers are favoured by some, others pre-
ferring boxes without grooves and placing each
negative instead in an envelope bearing the
number, title, and other particulars. This takes
up much less room, but the negatives caimot be
inspected without removal from the envelopes,
unless these are transparent. Films are prefer-
ably stored in albums with stout leaves, in
which slits are cut to hold the four comers ;
envelope albums are also made.
NEGATIVES, OWNERSHIP OF
Questions as to the ownership of the copyright
in negatives and the ownership of the negatives
themselves constantly arise in professional
work. Taking the ordinary case in which a
photographer makes, to the order of a customer,
a negative and supplies prints from it, the
copyright is the customer's, but the negative
itself is the property of the photographer, and
the latter is free to retain it, destroy it, or
apparently do anything with it short of printing
from it, enlarging from it, or copying it imless
ordered to do so by the customer. (The term
" customer " is here synonymous with " sitter,"
except in cases where the person who remunerates
the photographer is not the person who is
photographed.) This applies also to aU the
superfluous and rejected negatives made by the
photographer in the course of producing a
satisfactory photograph. When such negatives
are sold, the buyer acquires the rights held by
their maker ; that is, he can do with the
negatives as he pleases short of infringing
copyright ; in this connection, though, it is of
interest to read the article under the heading
" Copyright." Naturally, the buyer does not
buy the right to reproduce the negatives, because
that right was not possessed by the maker of
the photographs ; and no greater title in any
property can be conveyed to a second party
than was possessed by the first party. The
English law has always upheld the photographer
in retaining the negatives of photographs
suppUed ; in one case, for example, the High
Court decided that duplicate negatives made
by a photographer for the purpose of executing
an order for prints, the dupUcate negatives being
charged to the customer, must remain the
property of the photographer.
NEOMONOSCOPE (Pr., Niomonoscope ; Ger.,
Neomonoskop )
Bean's viewing apparatus for photographs,
invented about 1862, and consisting of a conical
box, with a lens or lenses at the upper end and
a portion of one side removed to admit light.
The bottom could be withdrawn for the inspec-
tion of transparent objects.
NEPHOGRAPH (Pr., Niphographe ; Ger., Ne-
phograph)
An apparatus used by meteorologists for photo-
graphically registering the height and position
of clouds. It is furnished with a camera, having
an electrically-operated shutter, which may be
Nernst Lamp
376
Niepce, Joseph Nicephore
worked from a distance. Two or more of the
instruments are placed at different stations,
sometimes far apart, the separation and exact
relative position of which have been accurately
ascertained, and exposures are made simul-
taneously from each. The resulting negatives
or prints enable the required data to be calcu-
lated by photogrammetric methods.
NERNST LAMP (¥1., Lampe Nernst ; Ger.,
Nernst-Licht)
A lamp in which a stout filament composed
of magnesia and the oxides of rare earths is
rendered incandescent by the electric current.
It was invented by Walther Nernst, in 1897.
This illuminant is excellent for enlarging,
optical projection, and cinematography with a
Nernst Lamp
small disc. It is very economical of current,
carries its own resistance, and is usually furnished
with a short length of flexible wire and a con-
nection that m.erely requires insertion in the
bayonet catch of an ordinary incandescent glow
lamp from which the bulb has been removed
(see illustration). The filaments when broken
are readily replaced with fresh ones. Various
useful modifications by R. W. Paul and others
have rendered the lamp still more adaptable for
photographic and projection purposes.
NESSLER'S SOLUTION
Used for testing certain chemicals — the
ammonium, salts, for example, with which it
gives a coloration or brownish precipitate. It
is made by dissolving 30 grs. of potassium iodide
in if drms. of distilled water, and boiling with
successive portions of solid mercuric iodide
until some of the latter remains undissolved.
The liquid is then added to if oz. of distilled
water, filtered, and the filtrate mixed with
120 grs. of caustic potash dissolved in 4 drms.
of water, and the whole again filtered. There
are other formulae.
NEUHAUSS'S BLEACH-OUT PROCESS
Dr. Neuhauss, of Berlin, has paid particular
attention to the bleachiug-out process, and
gives the following instructions for working the
same : —
Soft emulsion gela-
tine . . . 2 oz. no g.
BistiUed water to . 20 „ 1,000 ccs.
Allow to soak in the water, melt by the aid of
a water-bath, and add with constant stirring —
Methylene blue BB
(Bayer) (-2% sol.) 528 mins. 60 ccs.
Auramine, concen-
trated (Bayer) (-2%
alcohol sol.). . 132 „ IS »
Erythrosine (Schuc-
hardt)(-5%sol.) . 264 „ 3° .,
Then filter and heat for four or five hours to
104° P. (40° C.) before coating. When dry, the
plates must be bathed in —
Hydrogen peroxide
(30% sol.) . . 660 mins. 75 ccsi
Ether to . .20 oz. 1,000 „
for at least five minutes. Instead of the ether
solution, the following may be used, and gives
greater sensitiveness : — ■
Chloral . . .176 grs. 20 g.
Caustic soda (10% sol.) 5 mins. -S ccs.
Instead of bathing the plate in the peroxide
solution, the latter may be added to the gelatine;
and then the following formula should be
used : —
Methylene blue BB
(as above) . . 480 mins. 50 ccs.
Auramine (as above) 192 „ 20 „
Erythrosine „ 384 .. 40 „
Add these to the gelatine solution at as low a
temperature as possible, and add 10 per cent,
of the total quantity of 30 per cent, solution of
hydrogen peroxide, and immediately coat the
plates.
NEUTRAL OXALATE {See "Potassium
Oxalate.")
NICKEL (Fr. and Ger., Nickel)
The electro-deposition of nickel has lately
come into considerable use in the graphic arts.
Zinc etchings are often nickelled to prevent
corrosion. Stereotype plates are nickd faced
to make them wear and print better. Nickel
and nickel steel electrotypes are being produced
by direct deposition on the wax mould.
NICOL PRISM
Used in microscopy for polarising Ught, and
consisting of a small block of Iceland spar one
of the edges of which is cut to an angle of 68°
to the long axis. The prism is divided to form
two prisms, which are cemented together by
Canada balsam. A ray of Ught passing through
the cemented surfaces is spht up into two
portions ; one, known as the ordinary ray, passes
out at the side and is lost, whereas the other,
the extraordinary ray, emerges from the end of
the Nicol prism and through the object which
is being examined into the microscopic objective.
The prism is mounted in a revolving cell under
the stage of the microscope. (See also " Polarised
Light.")
NIEPCE, JOSEPH NICtPHORE
Bom at Chalons-sur-Saone, 1765 ; died 1833.
A French chemist who began his photographic
experiments about the year 18 14. In 1824 he
obtained Ught impressions on bitumen spread
upon plates of metal. Six to eight hours'
exposure was necessary, when the parts acted
Niepceotype
377
Night Photography
npon by light became hardened and were rendered
insoluble, while the rest could be dissolved
away. The exposed portions of the metal were
then etched and used as printing plates. On
December 5, 1829, he entered into an arrange-
ment with Daguerre to exchange with one
another information regarding all tieir attempts
to fix the pictures obtained by the camera
obscura. Niepce and Daguerre worked together
until the former's death, when his son Isidore
took his place.
NIEPCEOTYPE
One of the earliest photographic processes,
and called by the above name after its dis-
coverer, Niepce. He found that bitumen
became insoluble by the action of light {see
" Asphaltum"). Pewter plates were coated
with bitumen and exposed to Ught under a
print. Afterwards, efiorts were made to expose
the plates in the camera, but the necessary
exposure was found to be excessive, so that
the process had only a limited appUcation.
Niepce at first only endeavoured to get a picture
on the plate in the bitumen varnish, but after-
wards he etched the plates to make printing
blocks, and thus was the first to make photo-
engravings. The earliest photo-engraving by
Niepce is a portrait of Cardinal d'Amboise, now
preserved in the museum of Ch^ons. It was
copied by contact from a print.
NIEVSKY'S PROCESS
A ferrotype process in which ferrotype dry
plates are used instead of wet collodion. Intro-
duced by L. Nievsky in 1891.
NIGHT EFFECTS
These, both artificial and real, will be foimd
described under various headings ; for example,
"Night Photography," "Moonlight Effects,"
" Candle-Ught Effects," " PireUght Effects," etc.
NIGHT PHOTOGRAPHY
Photography by the aid of the artificial light
of towns or by that of the moon. The practice
of producing "night photographs" by what is
known as a double exposure — a very short one
by day and then by leaving the camera in
position and giving a long exposure at night —
does not give true night pictures. The exposure
necessary for true night photography is not so
protracted as might be supposed, and it is
possible nowadays to take snapshots " in
well lighted streets at night, the camera being
held in the hand, and a very large aperture and
the very fastest plates being required. Ordinary
night work can be done easily with an ordinary
camera and lens, and the fast plate used for
dayhght work. With a lens working at f/S,
a plate of a speed of about 250 H. and D. and
the time about one hour after sunset, the
exposure required for different classes of subjects
will work out somewhat at follows : Illuminated
shop windows, decorations, etc., two minutes ;
the same subjects, not including the Ughts
themselves, but only the effects of lights on the
objects, five minutes. Open subjects, such as
streets and squares in towns well lighted, ten
minutes; the same subjects, when heavy dark
obiects have to be registered with a certain
amount of detail, 20 minutes. The country-side
on a bright moonhght night, 30 minutes ; but
this subject is very variable in character and
conditions, so that this estimate is only approxi-
mate. These exposures are given only as bases
to start from, and each worker must find out
his own exposure data. If snow is on the
ground the exposure, as a rule, can be halved.
Ji the ground is wet with rain water (not merely
greasy), one-third can be taken off the exposure.
Moonlight or its absence makes a great difierence
in the duration of exposure, and at least one
third can be taken off when strong moonlight
is present. On the country-side, where there
is httie artificial light available, tiie absence of
moonlight will make night work, when there is
no snow on the ground, almost impossible.
The nature of the subject again will greatiy
influence the time of exposure. If night
exposures are to be accurately and quickly
determined, one must be able to consult his
record of exposures, each of which must be kept
with the time, place, state of the weather,
plate, aperture of lens, etc., all recorded for
future reference. If instead of using the lens
at f/S it is possible to expose at f/3, as in the
case of certain modem but expensive lenses,
the exposure will be reduced to at least one-
eighth of those before given ; and by using a.
plate working at 400 H. and D., then the exposure
can again be halved. To be able in 2^ minutes
to take a subject which under the former con-
ditions required 40 minutes makes a wonderful
difference to the photographer's comfort on a
cold and inclement night ; to reduce i^ minutes
to 5 seconds is to be able to get figures showing
Utile movement; while to give one-third of a
second instead of a minute is to take " snap-
shots " in the streets with the camera held in
the hand.
It is now a matter of common practice in
I/Ondon and other well-Ughted towns to take
moving figure subjects by the light of the street
lamps. There is much difference of opinion as
to whether isochromatic plates give better
results than the non-colour-sensitive. The
photographer should experiment with the fastest
plates obtainable, including Extra Speedy (not
the press variety, which are designed to give too
mudi contrast) and the Super Speed Ortho. The
developing of negatives of night subjects is as
difficult as the exposing. Plenty of water
should be used. Perhaps the plan most favoured
is to begin development with a developer of
ordinary strength (without any bromide), and
after detail is fairly out to pour off the developer
and, after rinsing the plate, cover it with water
and leave it to progress by itself. Many get
excellent results by diluting the developer with
three to four times the usual amount of water
and letting the development proceed very
slowly. Anyway, a night negative will look a
poor, weak thing to a day worker. Some night
workers find that the warming of the developer
tends to reduce halation, and to soften the
hard results caused by fog. Taking the normal
temperature of the developer to be about
65° P. (18° C), it may witii many plates be
gradually raised to 80° P. (27° C.) without the
film leaving the glass, but great care must be
taken la handling the film in its softened con-
Nitre
378
Numerical Aperture
dition. As to developers, metol alone, pyto soda,
rodinal, etc., are used. When a negative shows
bad hsilation, it should be bleached with the
ordinary mercury bath, and then "surface de-
veloped" only with some quick-acting developer,
whipping out the plate before the developer has
time to work through to the halated parts.
NITRE {See " Saltpetre.")
NITRIC ACID (Fr., Acide nitrique ; Ger.
Salpetersdure)
Synonyms, aqua fortis, hydrogen nitrate.
HNO3. A colourless, fuming Uquid when pure
which strongly attacks the skin, causing painful
burns, or with short contact a brown stain.
It is prepared by distillation from saltpetre
and sulphuric acid. Used as a preservative in
the pyro developer. The add shoidd always
be kept in a glass-stoppered bottle. Should
the add be spilled upon the dothes or skin,
apply chalk, lime, or magnesia.
In process work, nitric add is the universally-
used mordant for etching zinc. Prom 5 to
20 per cent, is the range of baths employed.
NITROCELLULOSE (Pr., Cellulose nitrie :
Ger., Nitrocellulose)
Formed by the action of nitric acid on cellulose,
and important as forming the basis of all
collodions and celluloid. (See " Pyroxyline.")
NITROGEN IODIDE
A black, extremely explosive powder. NHIj.
It is of purely theoretical interest as being very
light-sensitive.
NITRO-HYDROCHLORIC ACID (Fr., Eau
rSgale ; Ger., Konigswasser)
Synonyms, aqua re^a, nitro-muriatic, diloro-
nitrous or chloroazotic add. Misdble in all
proportions with water and alcohol. A fuming
yellowish liquid made by mixing i part of
pure nitric and 3 parts pure hydrochloric add.
It is used to dissolve gold and platinum, and
should be kept cool and in the dark. The fumes
cause intense irritation to the mucous membrane.
NODAL POINTS, OR GAUSS POINTS
A ray of light falling obliquely upon a plate
of glass or other transparent medium does not
pass through in a straight line, but is refracted
and emerges in a direction parallel to its original
A«I6
Diagram showing Nodal Points
path. The same thing occurs when a ray falls
obliquely upon the surface of a lens, as shown
in the diagram. A ray of light proceeding
from A enters tne lens at b, is refracted and
leaves it at C, proceeding to d in a parallel direc-
tion. A B and C D extended to the prindpal
axis of the lens give the two nodal points n n.
That nearest the object is called the "node
of admission," and that nearest the image the
" node of emergence," or " node of emission."
It is from the latter that the focal length of a
lens or combination of lenses is measured, and
at this point a lens for use in a panoramic camera
must be pivoted. The nodal points are not
necessarily situated within the lens. They may
be before or behind it, and they may be crossed ;
that is to say, the node of emergence may be
farther from the plate than the node of admission.
With many modem anastigmats the nodes are
so far outside the lens that considerable difference
in the camera extension is necessary, according
to whether the convex or concave side is turned
to the object.
NORRIS'S COLLODION PLATES
One of the earliest forms of collodion dry plates,
introduced by Dr. HiU Norris, of Birmingham, in
May, 1855.
NORWICH FILM (See " Pihn.")
NUDE, PHOTOGRAPHY OF THE
The nude figure, male and female, is exten
sively and successfully treated by painters and
draughtsmen. To photographers, however, this
particular dass of work ofEers less opportunity
for successful effects. In some hands results
have been secured that are quite pleasing and
satisfactory, but in the ordinary way the chances
of complete success are remote. The great
difficulty Ues in the fact that the photographer
does not possess the unhmited fadlities of the
artist for ideahsing, for combining, modifying,
emphasising, and suppressing, to secure the
final satisfactory result. For purposes of figure
study, good photographs of the nude have a
real value and use. The introduction of nude
figures into landscapes has also been success-
fully accomplished in some cases. But the
treatment of the single nude figure for pictorial
purposes is sddom satisfactory in the photo-
grapher's hands, although this is not because
photography is not eminently capable of render-
ing the beautiful contours, texhire, and deUcate
light and shade of the human body. The
difficulty lies rather in first securing the perfectly
artistic model, and then rendering it by photo-
graphic means with that ideal perfection and
purity which should characterise all renderings
of the nude figure. Too often the result is
mere nakedness, which is a different thing
altogether. On the whole, therefore, this dass
of work is better left alone by the ordinary
photographer.
NUMERICAL APERTURE
Usually written N.A. The present system,
almost universally adopted, of describing the
aperture of microscopic objectives and substage
condensers was devised by Abb§, in 1873. The
numerical aperture of an objective is the sine
of half the angle of aperture multiplied by the
refractive index of the medium in which the
objective works (air in dry lenses, water, oil,
etc., in immersion lenses).
o
OBERNETTER'S PAPERS
A collodio-chloride paper, introduced in 1868,
and a gelatino-chloride paper, in 1884, both by
J. B. Obemetter, of Munich.
OBERNETTER'S PROCESSES
A photogravure process (see " Lichtkupfer-
druck") and a printing process (see "Ferric
Salts, Printing with").
OBJECT GLASS
Abbreviation, O.G. The image-forming lens
of a telescope or microscope. (See " Objective.")
OBJECTIVE
The lens in any optical system — such as a
telescope, microscope, or photographic camera —
which forms or projects an image either for
examination by means of an eyepiece or for
reception by a sensitised surface. The objectives
of ordinary telescopes and microscopes are
usually corrected for visual use only, and require
a small allowance to be made when used for
photography, so as to bring the surface of the
plate into the position of sharpest focus. Supple-
mentary lenses for efEecting this correction are
sometimes fitted to telescopic objectives, and
compensating eyepieces, or oculars, to micro-
scopic objectives. Many objectives of both
classes are now made especially for photography.
The projecting lens of an optical lantern or
cinematograph is usually called the objective.
The focal lengths of the microscope objectives
in general use range from 3 in. to i^ in., but
lenses of both lower and higher powers are manu-
factured. These figures refer to the equivalent
focal lengths and not to the distance of the lens
from the object when the latter is in focus.
Objectives of less than \ in. focus are almost
invariably immersion lenses ; that is, a medium,
generally oil, fills the space between the front
lens of the objective and the cover slip over
the object ; by using in this way a medium of
higher refractive index than air, a higher
numerical aperture, and consequently increased
definition, can be obtained. In some older
types of lenses water was the immersion medium,
but cedar oil is now almost universally used,
as it is of practically the same refractive index
as crown glass. The depth of focus given by
microscope objectives, which is of more import-
ance for photographic than visual work, is
extremely limited, especially with high powers.
The penetration or depth of focus of a lens
is approximately -^-^ of its focal length ; thus
the penetration of an objective of ^ in. focal
lengUi would be about ^i^ in. In photo-
micrography the depth of focus would be con-
siderably less than this, but stops can be placed
in low-power microscope objectives to increase
the depth of focus, and when thick sections
or specimens are photographed, this plan is
often necessary.
In microscopy the magnifying power of a
lens refers to the number of diameters by which
the image given by the objective at a distance
of 10 in. from the back lens magnifies the object ;
this is easily estimated when the focal length
is known, as an objective of i in. focal length
gives a magnification of ten diameters at a
distance of 10 in. from the lens ; therefore, a
^ in. objective would magnify 60 diameters at
the same distance. These figures represent the
magnifying power of the objectives without the
eyepiece, and are termed tiie initial power of
the lens. When an eyepiece is used, the initial
power of the objective multiplied by the magni-
fying power of the eyepiece, gives the total
magnification of the lenses.
The resolving power of an objective — that is,
the number of lines per inch which the lens
will separate or resolve — does not depend upon
its magnification, but upon the numerical
aperture (which see), and a lens with a high
N.A. will give better definition than a lens of
higher magnifying power with a lower N.A.
Objectives with high N.A. have a small
working distance between object and lens, and
consequenUy less depth of focus. In photo-
micrography a good working distance and depth
of definition are often extremely useful, and on
this account an objective of high N.A. is not
always desirable.
The best type of objective is known as the
apochromat, which is expensive, and in practical
work but littie superior to first-class achromats,
especially when colour filters are used. AU
modem objectives are fitted with the R.M.S.
screw, that is, the worm at the back of the
lens which is screwed into the body tube always
has the same number of threads per inch, and
any objective can be used with any microscope
OIL LAMPS (See "Dark-room Lamp.")
OIL TESTER (See " Aerometer " and
" Oleometer.")
OIL OF VITRIOL (See "Sulphuric Acid.")
OILED NEGATIVES (See "Paper Negatives.")
OILrOZOBROME (See " Ozobrome, Oil.")
OIL-PAINTINGS, PHOTOGRAPHING (See
"Paintings, Photographing.")
OIL-PIGMENT PROCESS
A method of producing prints in pigment or
ink applied with a brush. As contact printing
is an essential part of the process it follows
that an enlarged negative must be made before
379
Oleometer
380
Opacity
such a print can be obtained of a subject
originally taken on a small plate. It was to
obviate this that the bromoil process was
evolved. The steps preceding the actual pig-
menting are few and simple. Special paper
made for the ptirpose may be obtained, but a
variety that is perfectly satisfactory is that
supplied for the final support in the double-
transfer carbon process. In any case it is
simply a paper coated with gelatine. This has
to be sensitised. It should then be stored in
a calciimi tube, but it is preferable to use it the
next day if possible, so that it is best only to
sensitise sudi quantities as are wanted for
immediate use.
A 10 per cent, solution of potassium bichromate
is an effective serisitiser. It should be applied
by means of a Blanchard brush {see " Brushes").
Equal quantities of potassium bichromate
solution and of methylated spirit are placed in
a clean porcelain dish, which is tilted so that
the solution lies at one end. One ounce of each is
more than sufficient for half a dozen 12 in. by
10 in. sheets. A piece of the paper is laid face
upwards on a pad of folded newspaper, and the
brush is charged with solution and drawn across
the paper first in one direction and then at
right angles to it. Only enough solution should
be taken to cover the surface. The stroking
action in two directions is continued until the
streaks on the surface practically disappear as
the gelatine absorbs the seusitiser. The sheet
is then pinned up, by one corner only, to dry,
and the other sheete treated similarly. The
sensitising should be done by a yellow hght that
would be fairly safe for bromide work, and
the drying completed in the dark-room. When
dry, the sheets may be placed in a box or tube,
and should be protected from actinic light with
the same care as in the case of platinotype paper.
In fact, the paper resembles platinotype in its
sensitiveness to light, and in the character of
the image that prints out under the negative.
Printing is continued until all that is required
in the finished print is visible.
The prints are now washed in several changes
of water. The yellow bichromate stain first
disappears, but washing should be continued
utttU there is practically no trace of colour even
in the darkest shadows. In cold weather the
temperature of the later washing waters should
be raised to 60° or 65° P. (15-5° or 18° C).
The paper finally shows the subject as a gelatine
relief, the high lights appearing considerably
raised. Pigmenting may be proceeded with at
once, or the prints may be dried and stored
away for future treatment. In the latter case
it is only necessary to re-soak the prints until the
relief is again evident. For the method of
finishing the print, see the outline of procedure
given under the heading " Pigmenting."
OLEOMETER (Pr., OUomHre; Ger., Oleometer)
Another name for the aerometer, a form of
hydrometer specially graduated for testing the
specific gravity of oils.
OMNICOLORE PLATE
This is a screen colour plate of Prench
manufacture, the patent of Ducos du Hauron
and De Bercegorol. By means of a printing
machine two lines in greasy ink are printed on
gelatinised glass at right angles to one another,
thus leaving Uttle rectangles between the lines
of gelatine, which is alone permeable to aqueous
dye solutions. A compensating yellow screen or
filter is used with the plates, and this and the
filter elements reduce the speed of the emulsion
to about 2^^ Watkins, 1-7 H. and D., or 27 Wynne.
It is advisable to manipulate the plates in
the dark, and they must be placed with the
glass towards the lens and a piece of opaque
card in contact with the film to prevent it from
being injured. The compensating filter should
be placed behind the lens and the ground glass
reversed, or with fixed-focus cameras the insertion
of the screen behind the lens sufficiently lengthens
the focus for ordinai<y purposes. The developer
recommended is : —
Metol . . .36 grs. 4 g.
Sodium sulphite
(anhydrous) . . i oz. 50 „
Hydroquinone . .18 grs. 2 „
Potass, carbonate (dry) 264 „ 30 „
Potassium bromine . 8§ „ i „
"Hypo" sol. (i : 1000) 145 mins. 15 ccs.
Distilled water to . 20 oz. 1,000 „
Development should be continued for five
minutes, the plate washed for 15 to 20 seconds,
and then immersed in the reversing bath of —
Potassium or sodium
bichromate . . 70 grs. 8 g.
Sulphuric acid . .114 mins. 12 ccs.
Distilled water to . 20 oz. 1,000 „
In which it should be left for about two minutes
with gentle rocking. If a negative is required,
naturally the plate is fixed after the first develop-
ment and not reversed. If a positive is required,
then the plate in the bichromate bath should
be taken out into daylight for three or foiir
minutes, or for five or six minutes to artificial
light, and as soon as the whole of the image is
dissolved, immersed in a 5 per cent, solution of
bisulphite lye or metabisulphite, or 20 per cent,
solution of sodium sulphite. The plate should
then be re-immersed in the developer for five or
six minutes, and when sufficiently dense, washed
for about 30 seconds and fixed in —
Sodium hyposulphite 2,^ oz. 125 g.
Sodium metabisul-
phite . . . 265 grs. ■ 25 „
Water to . . 20 oz. 1,000 ccs.
Next wash for 20 to 30 minutes in running
water, dry, and varnish with a 15 per cent,
solution of mastic or dammar in benzole.
Under-exposed or too dense pictures may be
improved by reducing in a "hypo" and ferri-
cyanide reducer; or weak pictures may be
intensified with mercuric chloride followed by
sulphite.
OPACITY (Pr., OpacitS; Ger., Schwarzung)
The optical property of a substance, such as
silver, to impede the passage of hght through
it. In sensitometry it is termed —
_ _ lo Intensity of incident hght
~~ I ~ Intensity of transmitted hght
Thus, if we assume the intensity of the incident
Opacity Balance
381
Opera-glass Camera
to be I and that of the transmitted light i,
obviously 1=4, which is the opacity of silver
that reduces the light to one-fourth.
OPACITY BALANCE
An instrument devised by Chapman Jones
for measuring the opacities of bromide prints
and other surfaces.
OPACITY METER
There are various instruments for measuring
the opacities of negatives, etc., such as spectro-
photometers, polarisation photometers, the
modified Bunsen photometer of Hurter and
Driffield, and the Chapman Jones opacity
meter. In the last named {see the diagram) an
D/ .r- XDl
/•
;\
6a
Opacity Meter
incandescent gas light shines through aperture b
upon an Abney screen c, a beam also being carried
round the velvet-Uned tube (by means of the
mirrors D) to illumine the translucent part of
the screen to which a negative is clipped. As a
rule, in practical sensitometry {which see), the
logarithms of the opacities are termed " densi-
ties " and are plotted.
OPALINES
Photographs mounted under glass and then
upon plush or other supports. The glasses
and aU other necessary materials are supplied
by dealers. A print, preferably P.O.P., is
mounted, while wet, face downwards upon the
cleansed bevelled glass; it may or may not
have been treated with formaline or other
hardening solution. For mounting, use i oz.
of gelatine in 5 oz. of water, allowing this to
stand for a time, and then melting by gentle
heat. Strain the warm gelatine solution through
muslin into a flat dish, and while stiU warm
soak each print in it bodily for about a minute
and transfer, face downwards, to the glass,
avoiding air bubbles. Should bubbles form,
slide the wet print nearly off the glass and then
back again over the edge, or roll the print with
a rubber squeegee, fi the original gelatine
of the print is soft, no additional gelatine
mountant may be necessary. The edges of
the print should be flush with those of the
glass, but when there is a gilt border, the print
may be a trifle smaller. If desired, an ungilt,
plain, bevelled glass may be used, the print
being of such size as to leave a margin of clear
glass all round ; a backing of white or coloured
paper can then be applied.
OPALS, OR OPALOTYPES (Pr., Opales ;
Ger., Opals)
Photographs may be transferred to opal
glass by the carbon process, or the opals sen-
sitised (or bought ready prepared) and printed
upon direct, exactly as when using bromide
paper. To ensure a perfectly clean and even
border, use a printing frame a size larger than
the opal, and prepare a suitable mask having
a clean-cut opening. Place a piece of cleaned
glass in the frame and upon it the negative.
Then, in a good light, place the mask in a
suitable position on the film side of the negative,
being careful not to move it when it is once in
position. By the light of the ruby lamp, place
the sensitive opal over the mask in such a way
that the image, as seen through the mask, is
in the centre, and that the margin of the opal,
covered by the mask, is even. Put on the back
of the frame, expose, develop, and finish.
For vignetted opals, use artificial light, and
place an ordinary vignetter about -J in. in front
of the frame ; then expose to a weak light,
such as that of a match or a candle, moving
the light so as to soften the vignetting effect.
To assist in securing clean margins, use fresh
developer ; but if stains or markings appear,
clean them off with the iodine-cyanide reducer.
After fixing and drying, coat with crystal varnish.
OPAQUE. OR OPAQUE PIGMENT
A blocking-out material for use on negatives,
and consisting of any mixture sufficiently
opaque to prevent the light acting through
the covered parts of the negative. Brunswick
black and red water-colour paint, such as
Indian red, are largely used, the latter when
working on the film side of the negative, because
of the ease with which it may be washed off
with water. For the glass side, use Brunswick
black, or the following : —
Turpentine . . zj oz. 250 ccs.
Asphaltum . . i „ 28 g.
Beeswax . . 40 grs. 9 „
Carbon black . . 20 „ 4-5 „
Mix well and apply with a brush.
OPEN APERTURE (See "Aperture.")
OPEN LANDSCAPE
A view in which there is no near foreground ;
for example, that seen from an elevated spot.
OPERA-GLASS CAMERA (Fr., Chamhre
lorgnette ; Ger., Opernglas-kamera)
A camera resembling an opera- or field-glass,
and so designed that it may be worked while
A B
Opera-glass Camera
held close to the eye. A illustrates a modern
pattern of stereoscopic binocular, which permits
Ophthalchromat Lens
382
Optical Lemtem
the pictures to be taken at a right angle to the
direction in which the glass is ostensibly pointed.
The two concealed lenses of the camera are at
I, and M, while one eyeglass, N, acts as a finder
by means of a mirror inclined at an angle of 45°,
as shown at B, a sectional view of the apparatus.
The camera takes a dozen plates in a magazine.
OPHTHALCHROMAT LENS
A biconvex fluid lens patented in 1905 in
Germany. It worked at //p.
OPTICAL AXIS
A straight line joining the centres of curvature
of a spherical lens is called the principal optical
axis. In the case of a lens having one plane
surface, the principal axis passes through the
centre of curvature of the spherical face and is
perpendicular to the plane face. It is, of course,
highly necessary in combining glasses to form
a photographic lens that the principal optical
axes should be absolutely coincident.
A straight line passing through the optical
centre of a lens, and making with the principal
axis a more or less large angle, is called the
" secondary axis."
OPTICAL CENTRE
The point at which rays passing through a
lens cross each other. It is only in the case
of a symmetrical lens that the mechanical and
optical centres coincide. According to the
form of the lens and the position in which it
is placed, the optical centre may be within
the lens, or considerably befpre or behind it.
It IS often stated that the focal length of a
lens should be measured from its optical centre,
but this is not correct ; the point measured
from should be the node of emission.
OPTICAL CONTACT
The condition existing when the surfaces of
two pieces of glass, or those of a piece of glass
and another substance, are in such intimate
contact that aU air is excluded. Under these
conditions the surface of the glass that is in
optical contact with the other substance, or
the two glass surfaces that are in contact, cease
to reflect light. But Ught is reflected by an
opaque substance in optical contact with glass.
Backing on a dry plate must be ia optical con-
tact if it is to be efficient; hence a piece of
black velvet or paper at the back of a plate,
sometimes advocated as a substitute for backing,
is of small efficiency. The various glasses
which form the combinations of a lens are
cemented together in optical contact by means
of Canada balsam. Prints are sometimes
moimted in optical contact with glass, producing
a very brilliant result. Priuts on album enised
paper and on collodion emulsion paper, do not
require preparation ; but those on gelatine
printing-out or on bromide or gaslight papers
should be hardened in a bath of formaUne i part
and water 10 parts. The glass that is to receive
the print must be thoroughly clean and, after
slightly warming, should have a solution of
gelatine (about 1 5 grs. per i oz. of water) poured
upon it. A print is laid face down on the
gelatine, and squeegeed into contact so as to
expel most of the gelatine and all the air.
OPTICAL GLASS (See "Glass.")
OPTICAL INTENSIFICATION
A process for obtaining an intensified negative
without the emplo3mient of chemical intensi-
fication. The details of a thin negative may
be more plainly seen if the negative is laid film
side downwards upon white paper, the light
being reflected through the negative and giving
the same effect as if two identical negatives
were superimposed and held up to the Ught.
A thin negative so backed is copied in the
camera and the resultant positive is, in turn,
copied (backed up with white paper as before),
or ix negative is made from the positive by
direct contact. Lord Rayleigh, in 1897, recom-
mended backing up a thin negative with mercury,
or with a flat, polished reflector, and iUuminatiug
ia a special way, but the process first named
above gives as good results.
OPTICAL LANTERN
An appliance, popularly known as the " magic
lantern," by means of which transparencies
are optically projected by artificial light upon
a screen, the diameter of the image being thereby
increased by from 24 to 1 50 times. The enlarging
lantern {which see) is an optical lantern, but the
increase in the size of the image rarely exceeds
from 20 to 30 times, and is generally m.uch less.
An optical lantern comprises a body, an
illuminant, an optical system, and means for
holding the transparency (slide) in the path of
the hght. The body may be of wood or metal,
the former (generally mahogany) being the
stronger, and the latter being the lighter, and
therefore having advantages from the point
of view of portability. A typical high-dass
lantern having a wooden body is here illustrated.
There should be a door on one or both sides,
and a close-fitting cowl or crinkle as light-tight
as possible. When an oil-lamp is the source
of hght, the chimney projects at the top. The
Optical Lantern -with 'Wooden Body
illuminant {see the next article) is supported
by the body in line with the optical axis of the
lenses, and the lamp or jet is mounted on a
metal plate or in a metal tray, which slides in
grooves formed in the lantern body, it being
necessary to provide for adjusting the distance
between the condenser and the illuminant.
The condenser, consisting in its commonest
Opticed Lantern
383
Optical Sensitisers
form of two plano-convex lenses mounted in
a brass cell with, the convex surfaces facing
each other {see "Condenser"), collects the
light rays and causes them to illuminate the
transparency evenly ; thence the rays pass to
the objective lens, which projects them upon
the screen. (For a diagram explaining the
optical principle involved, see " Condenser.")
The objective is a lens of the Petzval portrait
type (see " Lens "), but it is not wise to use it
for photography, as its visual focus may not
coincide with the actinic focus. The draw-tubes
in the front of the lantern, and the rack and
pinion on the jacket of the objective tube, allow
of proper focusing. Frequently, in front of the
lens mount is a " flasher," consisting of a
hinged or pivoted disc serving as a lens cap.
The transparency, carried in a wooden slide
carrier having a to-and-fro movement, is
inserted into the stage of the lantern imme-
diately in front of the condenser, the carrier
being held in place by a spring plate.
To shield the audience from stray light rays,
it is usual to fit a heavy curtain to the back of
the lantern.
A " single " lantern has but one iUuminant
and optical system ; a " biimial " has two,
one above the other ; and a " triunial " (now
but rarely used) has three. When oil is the
iUuminant it is necessary to have the systems
(actually separate lanterns) side by side. Biunial
and triunial lanterns were much used in earlier
days for the production of the then popular
dissolving views {which see).
The screen may be a white sheet, or a plastered
wall painted " flat " or " dead " white. Col-
lapsible frames for sheet screens af e commercial
articles. When the lantern is behind the
screen and the audience in front, the screen
should be wetted to make it more translucent,
and the slides should be inserted into the carrier
with the fronts facing the screen. Ordinarily,
when both lantern and audience are in front of
the screen, the slides are inserted with their
fronts facing the operator, who stands to one
side of and slightly to the back of the lantern
stage. Always, the slides are inserted upside
down, but unless they have been carefully
" spotted " beforehand {see " Lantern Slides,
Masking, Binding, and Spotting "), some of them
are sure to be shown upside down on the screen.
The lantemist should accept unspotted slides
only at the lecturer's risk.
In connection with the calculation of the
size of the disc on the screen, of the distance of
the lantern from screen, or of the focal length
of the lens to be employed, it should be said
that the use of a set of interchangeable objec-
tives renders the lantemist largely superior
to the difficulties frequently caused by par-
ticularly small or large haUs, and by the in-
convenient placing of pillars, lights, etc., in the
building.
The size of the disc of light projected by a
lantern upon a screen depends upon the focal
length of the lens and the distance between
lantern and screen. Assuming the diameter of
the slide to be 3 in., the size of the disc under
certain conditions is found by multiplying 3 by
the distance (in feet) between lantern and screen
and dividing by the focal length of the lens in
inches. Thus, at a distance of 40 ft., a 7-in. lens
gives a picture more than 17 ft. in diameter, as
^ ^J^° = 17}. To determine the focal length
of lens necessary under certain conditions, mul-
tiply 3 by the distance and divide by the
diameter of the desired disc. Thus, at a distance
of 24 ft., and to produce an 8-ft. disc, a lens
of 9-in. focal length would be necessary, as
- — 5—2- = 9. To determine the distance at
o
which a given lens will produce a given disc,
multiply the focal length by the diameter of
the disc and divide by 3. Thus, a 9-in. lens
would produce a lo-ft. disc at a distance of 30 ft.,
as — = 30. A simple calculation on the
lines of the above saves the lantemist the trouble
of trying different lenses or of shifting his
apparatus.
The " opaque " lantern — that is, a lantern for
projecting images of opaque objects — ^is described
under the heading " Aphengescope."
OPTICAL LANTERN ILLUMINANTS
Given in the order of their efficiency, optica
lantern illuminants include the oil-lamp, incan
descent gas, acetylene, limelight, and the arc
lamp. Metallic filament electric incandescent
lamps are also used occasionally, but these share
with the oil-lamp and incandescent mantle the
disadvantage of the light being emitted by
relatively large surface instead of coming from
a point, or, at most, a spot. The oil-lamp »■
becoming more and more a thing of the past.
It has two, three or four wicks, and much of the
light emitted by it is wasted ; in addition, if
not kept scrupulously clean it is smelly, many
patterns are liable to smoke, and the heights of
wick and chimney are matters for careful
adjustment. The incandescent gas mantle is
much more cleanly in use, but the illumination
is not much increased, and the mantle, after
one use, is very fragile. Acetylene {which see)
gves a much more intense light than either oil
cr incandescent gas, but it needs a generator,
to the employment of which many people have
objections, but which, if of reliable make and
properly used, is a perfectly safe device ; the
use of compressed (actually dissolved) acetylene,
obtainable in cylinders, opens up possibilities
where the light itself is preferred, but the
generator objected to. Limelight {which see)
was, until quite recent years, the most popular
and the most generally convenient iUuminant,
but in aU places where electric current is available
it must now give place to the arc lamp {which
see). Lantern arc lamps are generally of the
hand-feed type, it being necessary to adjust the
distance apart of the two carbons as they bum
away, as otherwise the unequal consumption
would cause the arc to shift its focus and the iUu-
mination of the image to suffer. For low powers,
the Nemst electric lamp has proved useful.
OPTICAL SENSITISERS
Dyes which have the property of modifying
colour sensitiveness. Treatment of a sensitive
photographic film with certain dyes in solution
has the efiect of increasing its sensitiveness
Optics
384
Ortol
to difEerent regions o£ the spectrum; thus
eosine or erythrosine will make an " ordinary "
plate sensitive to yellow, as in the original
isochromatic plate of Tailfer and Clayton, while
cyanine increases the sensitiveness to red.
The dyes may be added to the emulsion before
coating the plate, or a. finished plate may be
bathed in the solution. The latter procedure
is generally adopted in the case of panchromatic
plates. {See also " Colour Sensitising," " Iso-
chromatic Plates," etc.)
OPTICS (See
headings.)
' Lens " and various other
ORANGE BICHROMATE
A synonym for potassium bichromate.
ORANGE LIGHT
Orange light for dark-room illumination was
in general use before the introduction of dry
plates, for which, however, it was found not
to be sufficiently safe, and ruby light was
substituted. Orange or yellow light (light
filtered through orange- or canary-coloured
fabric or glass) may safely be used for most of
the m.odem bromide papers and lantern plates
and also for very slow plates. {See also " Canary
and Orange Medium.")
ORDOVERAX
A proprietary name for a process of repro-
ducing line drawings ; the process is allied to
ink printing {which see). A dean, flat zinc plate
is coated with a colloid of special composition ;
an exposed but undeveloped blue-print (made
from the drawing) is then laid downwards on
the plate for a moment and removed. The
parts that were in contact with the unexposed
lines of the blue-print wiU now take ink from
a roller, while the groimd repels the ink. The
plate is inked, and paper, cloth, etc., is pressed
into contact to produce an excellent repro-
duction of the original drawing.
ORGANIC COLOURS
A term applied generally to aniline colours
to difierentiate them from colours obtained
from inorganic or metallic sources.
ORGANIFIER
A preservative applied to the sensitive sur-
face. The word is used more frequently than
preservative. The organifiers or preservatives
recommended in the early days of the collodion
process (about 1864) were solutions or infusions
of tannin, gum, tea, cofiee, beer, tobacco, and
albumen, and also sherry wine. (See also " Cer-
amic Process.")
OROHELIOGRAPH (Pr., Orohiliographe ;
Ger., Oroheliograph)
A panoramic camera designed by Noe for
taking photographs of the whole visible horizon.
The lens points upward to the sky, the plate
being beneath it in a horizontal position. Above
the lens is adjusted a convex paraboloid mirror
that is, a mirror of circular cross-section and
parabolic vertical section. This mirror reflects
a view of aU surrounding objects downward to the
lens, which forms a circular image on the plate.
The arrangement much resembles that adopted
in some forms of periscopes for submarines.
Such views, though distorted, are useful for
checking surveying and photogrammetric obser-
vations.
ORTHOBORIC ACID (See " Boric Acid.")
ORTHOCHROM T (Pr. and Ger., Orthochrom T)
Synonym, ^-toluchinaldin-j>-toluchinolinethyl-
cyauine-bromide. Soluble m water and alcohol.
One of the isocyanine dyes introduced by the
Hoechst Dye Works as a sensitiser. It is most
satisfactory, giving with reasonable exposures
a closed band from the blue to the D lines ;
that is, it sensitises for blue-green, green and
yellow, with a much less marked drop in the
blue-green than erythrosine, but with practically
no red sensitiveness. The best results are
obtained by bathing the plates in —
Orthochrom T solu-
tion (i : 1,000) . 192 mins. 20 ccs
BistiUed water to . 20 oz. 1,000 „
for three to four minutes, and then rinsing and
drying. These operations must be conducted in
the dark or in a very faint red light. By replacing
one-third of the above quantity of water with
alcohol, clean-working and quicker-drying plates
which do not require rinsing are obtained.
ORTHOCHROMATIC {See "Isochromatic")
ORTHOCHROMATISM
The quality possessed by plates that are
sensitive to parts of the spectrum besides the
violet and blue. Practically synonymous with
isochromatism, and fully treated under the
headings " Colour Sensitising," " Isochromatic
Plates," etc.
ORTHODIHYDROXYBENZENE
A synonym for pyrocatechin.
ORTHOGRAPH AND ORTHOGRAPHIC
LENSES
Names given at one time to lenses of the
rapid rectilinear (doublet) type. {See "Lens.")
ORTHOHYDROXYBENZOIC ACID
A synonym for salicylic acid.
ORTHOMETHYLAMIDOPHENOL
One of the constituents of ortol.
ORTHOSCOPIC LENS
A rapid rectilinear doublet lens. {See " Lens.")
ORTHOSTIGMAT LENS
A series of cemented anastigmats introduced
by Steinheil, of Munich, and manufactured in
England by Beck. They were made with
initial intensities of //6-3 and //6-8, and were
convertible, the single lens having an aperture
of //i2-5 ; in addition there was a rapid wide-
angle lens (nearly 110°) with an intensity of
//"•3.
ORTOL (Pr. and Ger., Ortol)
Hauff's developer, containing orthomethylami-
dophenol, CjH^ OH NHCH,, and hydroquinone
GROUP OF INSECTS' EGGS
By J. I. PiGG, F.R.M.S., F.R.P.S.
PHOTOMICROGRAPHY
14
Ortol
38s
Oxalic Acid
introduced from Germany in 1897; in charac-
ter, intermediate between metol and pyro-soda.
It is a yellowish-white crystalline powder, very
soluble in water, with whidi it forms a colourless
solution which gives a blackish image. It will
not work alone ; combined with sodium sulphite
it works very slowly, some hours being required
to produce an image ; but in conjunction with
sodium or potassium carbonate it forms a steady
working developer, with a factor of 10. It is
suitable for all dry plates, lantern plates, and
bromide and gaslight papers. When properly
used, it does not stain the negative, but when
ammonia or acetone is used, or sulphite is
added to the ortol solution, a reddish stain
sometimes appears. The use of metabisulphite
and of a carbonate, however, tends to prevent
staining, but should it appear it may often be
removed with methylated spirit.
Ortol may be used in a one- or, preferably,
two-solution form : —
One-solution
Ortol . . .80 grs. 9 g.
Potass, metabisulphite 20 „ 2-25 ,,
Sodium sulphite . 2 oz. no „
Potassium carbonate . 640 grs. 73 ,,
Potassium bromide . 4 „ .5 „
Water . . .20 oz. 1,000 ccs.
This is best made up as required, the ortol and
metabisulphite being dissolved in one half of
the water, the remainder of the chemicals in
the other half, and the two solutions mixed
together.
Two-solution
A. Ortol . . 140 grs. 16 g.
Potassium meta-
bisulphite . 70 ,, 8 ,,
Cold water . 20 oz. 1,000 ccs.
B. Sodium carbonate 2^oz. 138 g.
Sodium sulphite . 2^ „ 138 „
Water . . 20 „ 1,000 ccs.
B. Potass, carbonate
I oz.
55 g-
Sodium sulphite .
2* „
138 „
Water
20 „
1,000 ccs.
Use equal parts of A and B.
If a restrainer is needed, add a few drops of
a 10 per cent, solution of potassium bromide, or
embody the bromide in the developer when
making it by adding to either of the B solutions
from 8 to 16 grs. per 20 oz. (i to 2 g. per 1,000 ccs.).
A weak solution of " hypo " has been recom-
mended as a restrainer, but it needs to be used
with great caution. A 10 per cent, solution
of a caustic alkali may be used as an accelerator
in cases of under-exposure. By increasing the
proportion of A, harder negatives will be pro-
duced ; and the converse also holds good. A
lower temperature than 66° P. (19° C.) will
retard development, and during very cold
weather the potassium bromide may with
advantage be omitted. The high lights of the
image appear normally in from 20 to 30 seconds,
and then the half-tones and shadows, the
density being added at the same time ; develop-
ment is usually complete in from four to five
minutes.
26
OUNCE
In apothecaries' weight (by which formula
are made up), 480 grains, or one-twelfth of a
pound ; 3i-ioi5 grammes. In avoirdupois weight
(by which chemicals are bought and sold),
437i grains or one-sixteenth of a pound ;
28-4 grammes. In fluid measure, 480 minims, or
one-twelfth of a pound ; 28-4 cubic centimetres.
{See also " Weights and Measures.")
OVALBUMEN
A synonym for egg albumen.
OVALS, MARKING AND CUTTING
The so-called oval seen in. photographic cut-
out mounts is strictly an ellipse, an oval being
really egg-shaped. The easiest way of marking
an ^pse is by means of two pins and a piece
of string, as shown in the illustration. The pins,
c and D, are stuck tightly in the cardboard to
be marked, and a pencil, E, is placed in the
Marking an Oval
loop and moved round, keeping the string taut.
This is done first on one side and then on the
other, thus tracing an ellipse. If an endless piece
of string is used, ttie elUpse can be drawn without
withdrawing the pencil from the loop. The
length (major axis) of the eUipse is always equal
to that of the greatest stretch of the string, while
the width (minor axis) depends on the distance
apart of the pins and may be regulated by a few
trials. It is preferable to mark the ellipse on a
sheet of thin metal, using this as a template
and keeping it for future use. For cutting the
moimt a mount-cutter's knife is employed, but
a keen penknife may be used.
A machine has been constructed for the use
of process workers for cutting and marking
ovals. Any dimension may be obtained by
shifting the bed out of the centre, and also by
shifting the tool along the bar. The former
movement registers the difference between the
major and minor axes of any determined oval,
whilst the latter movement sets the tool to the
major axis.
OVEN, DRYING (See "Drying Box or
Cupboard.")
OXALATE DEVELOPER
Better known as the ferrous oxalate developer
{which see).
OXALIC ACID (Pr., Acide oxalique ; Ger.,
Oxalsaure)
C2H2O4 2HjO. Occurs in colourless and
odourless prisms with strong acid and bitter
taste. Solubility, 12 per cent, in cold and
100 per cent, in hot water ; insoluble in alcohol.
Ox-gall
386
Ozobrome, Oil
It is used in the sensitising of platinotype paper,
and as a preservative for the pyro developer,
from 2 to 3 per cent, being used. It is very
poisonous, the antidotes being chalk or magnesia
mixed with milk or wafer.
OX-GALL
The purified and evaporated gall of the ox ;
used when tinting prints with water colours
in order to overcome the greasy or repellent
surface of the print. The gall is purchased
either in a solid form, or as an evil-smelling
' sticky mass. A small quantity of it is dissolved
in warm water, and when cold brushed over
the print and dried. It was used largely in the
days of albumen prints, for which it is parti-
cularly suitable.
In process work, ox-gall is used for preparing
the surface of glossy prints for taking the
retouching colours, or for admixture with the
colours. It is also sometimes used in blocking-
out negatives for preventing the colour from
running. It is used in collotype work for
preparing the plate.
OXYCALCIUM LIGHT
An early name for the limelight.
OXYCHLORIDE OR OXYHALOID
THEORY
The theory that the latent image consists of
the oxychloride, oxybromide, or oxyiodide of
silver. The objection to this theory is men-
tioned in the article under the heading " Latent
Image."
OXYETHER LIGHT
A system of limelight in which oxygen,
saturated with ether, is burnt in a jet to provide
the heat for raising the lime to incandescence.
OXYGEN GAS FOR LIMELIGHT {See
" Compressed Gas " and " Limelight.")
OXYHYDROGEN LIGHT (See " Limelight.")
OXYMAGNESIUM LIGHT
A system resembling limelight, but employing
magnesium instead of lime. (See also " Magne-
sium Beads.")
OXYMEL (Fr. and Ger., Oxymel)
A mixture of honey and dilute acetic acid,
used in the old collodion dry-plate days as a
preservative.
OXYPHENYLGLYCINE
A synonym for glycine.
OYSTER SHELL MARKINGS
A defect met with in the wet-plate process,
and caused by unequal drying.
OZOBROME
A method of producing carbon pictures from
bromide prints, patented by Thomas Manly,
in 1905. Its advantage is that it makes the
-worker independent of daylight. Bromide
enlargements can be made for producing carbon
pictures, thus saving the trouble and expense
of making enlarged negatives. Whether the
carbon image is produced upon the bromide
print or whether the pigment image is trans-
ferred to another support, the resulting picture
is correct with regard to right and left. An
ozobrome pigment plaster (paper coated with
pigmented gelatine) is soaked in a bath of
diluted ozobrome pigmenting solution, trans-
ferred to an acid bath for a few seconds, squeegeed
to a wet bromide print and left for about twenty
minutes for the insolubiUsing action to take
place. The method of workmg is as follows :
Place the bromide print in a dish of water,
immerse the pigment plaster in the diluted
ozobrome pigmenting solution until soft and
limp (about one or two minutes), and then with-
draw the plaster and immerse it for ten to
fifteen seconds in a bath of —
Chrome alum (pure) .
Bisulphate of potass.
(cryst.)
Citric acid
Water .
36 grs.
5 „
5 oz.
i6-s g.
5-5 „
2-3 „
1,000 ccs.
An immersion of, say, 20 seconds will produce
a soft, delicate picture from a strong bromide
print, and an immersion of, say, 7 to 10 seconds
will give a strong, deeply-coloured picture from
a weak and grey bromide print. For a good,
well gradated bromide print, an' immersion of
from 12 to 15 seconds would be sufficient. After
removal from the acid bath, the soaked pigment
plaster is brought into contact with the bromide
print lying in the dish of water. The two
papers (clinging together) are quickly with-
drawn, squeegeed together, and allowed to
remain in contact for 15 to 20 seconds. One
of two methods may then be selected to produce
pigmented pictures. In the non-transfer
method, the bromide print itself forms the
support of the gelatine image. The adhering
papers are plunged into water at about 160° F.
(41° C), the plaster backing is removed, and the
development carried out as in the ordinary
carbon process. In the transfer process the
plaster and bromidt j)rint are separated in cold
water, the pigment plaster carrying an impres-
sion of the image. The plaster is squeegeed to
a soaked piece of transfer paper and left for
ID to 15 minutes, when the development is
carried out in hot water in the usual way. The
second method is preferable to the first one, as
it j^elds a pure carbon picture with a choice
of paper support, and leaves the bromide print,
after redevelopment, available for further
transfers.
OZOBROME, OIL
Oil ozobrome is a modification of bromoil.
A bromide print is treated in such a manner
that the altered image will retain greasy ink
while the unchanged portions will repel it. A
bromide print is bleached in the following
bath :—
Ozobrome pigmenting
solution . . . 1 oz
Chrome alum acid bath 5 „
Sodium chloride (salt) J ,,
Water . . . 4 „
The bleached print is rinsed for a few seconds
and transferred to a fixing bath of " hypo "
30 CCS
150 „
17 g.
120 CCS.
Ozotype
387
Ozotype Process, Gum
3 oz., and water 20 oz., where it should remain
for five to six minutes. After washing for five
minutes, the print may be inked up, but it is
better to allow it to dry and then resoak for
five to ten minutes in water at 65° to 70° F.
(about 18 to 21° C).
Oil Transfer Process. — In this process the
resulting image will be reversed in regard to
right and Irft ; therefore, in enlarging, the
negative should be reversed in the lantern.
A sheet of ozobrome transfer paper is immersed
in the bleaching bath specified above, whilst
the bromide print is soaking in water. The
transfer paper, saturated with the bleaching
solution, is placed face upwards on a sheet of
glass, and the wet bromide print carefully laid
down upon it and squeegeed into contact. The
bleaching takes from 10 to 45 minutes to com-
plete, the progress of the action being easily
observable by holding the adhering papers in
front of a strong light. When bleached, the
papers are separated and washed for about
ten minutes untU all yellow coloration has dis-
appeared. The transfer paper, carrying a copy
■of the image, should be hung up to dry and the
bromide print redeveloped. When dry the
impressed transfer paper is soaked for 20 to
30 seconds in cold water, and after removing
the superfluous water it is ready to ink up.
The bromide print is available for further
transfers.
OZONE BLEACH
A synomym for " Labarraque's solution " and
"eau de Javelle."
OZOTYPE
A pigmented gelatine process, patented by
Thomas Manly in 1899, differing from the usual
carbon method. Sized paper is coated with a
solution containing a bichromate and a man-
ganous salt. This preparation is sensitive to
light, and under a negative produces a positive
image in manganese chromate. A pigment
plaster (paper coated with pigmented gelatine)
is soaked in an acidulated solution of a reducing
agent, such as hydroquinone or ferrous sulphate,
and applied to the washed image. The action of
the acid produces chromic add which is imme-
diately reduced by the hydroquinone or ferrous
sulphate, with the result that the gelatine is
taimed. In practice, the ozotype process is
-carried out by coating well-sized drawing paper
with the ozotype sensitising solution, thoroughly
drying, and printing under a negative in day-
light. The image is of a Ught brown colour and
distinctly visible. When all details appear the
image is carefully washed for a limited time,
as it is slightly soluble. A piece of pigment
plaster is then soaked for 30 to 60 seconds
in the following bath : —
Glacial acetic acid
Hydroquinone
Copper sulphate
Water .
50 nuns. 4 CCS.
12 grs. I g.
12 ,. I ..
25 oz. 1,000 CCS.
As soon as the pigment plaster is quite Ump
the chromium print is expeditiously brought
into contact with it in the bath, and both papers,
clinging together, are withdrawn and squeegeed
genSy together. The adhering papers are left
for 30 to 60 minutes for the action to take place,
when they will be ready for development, which
is carried out by separating the papers in water
at about 110° F. (about 43° C), and dissolving
away all soluble gelatine. The advantages are
(i) a visible image; (2) no reversal of the
image ; (3) almost unlimited control with the
brush.
OZOTYPE PROCESS, GUM
The application of the ozotype principle to
the production of images in pigmented gum
was easily foreseen after the introduction of
gelatine ozotype. The paper is prepared and
the image obtained as in ordinary ozotype, but
a rather stronger printing is required. A pig-
mented gum mixture is made up as follows : —
Water .
Gum Jirabic
Powdered colour
2 parts
I part
q.s.
Also make up the following acid reducing
bath:—
Sulphuric acid
Copper sulphate
Hydroquinone
Water .
i dim. 10 CCS.
180 grs. 72 g.
60 „ 24 ,,
6 oz. 1,000 CCS.
The gum and pigment are worked and ground
togetier with a palette knife on a sheet of
glass, and about the same quantity of the
acid reducing solution added. The mixture is
pounded in a glass mortar, evenly spread over
the image with a flat hog-hair brush, and
finished off by means qf a badger-hair softener.
The coated paper is then allowed to dry slowly
in a cupboard, in which a wet cloth is hanging
with the object of keeping the atmosphere
moist. When dry, the image is developed in
cold or tepid water. The advantages of the
process are: (i) A visible image; (2) the
tanning action proceeds from the image upwards
through the film of gum, resulting in the pre-
servation of all detail ; (3) the operation can
be carried out in full daylight.
PACKHAM'S CATECHU STAINING {See
"Catechu Toning.")
PACKING NEGATIVES FOR POST
The following is considered one of the safest
ways of packing negatives to be sent by post.
Put the bottom one film up and on it a sheet
of clean white paper, then the next negative
film side downwards, then another sheet of
paper, and so on, all the negatives, except the
bottom one, being film side down. Wrap the
whole tightly in brown paper, and force into a
plate box in such a. way that the negatives
cannot rub together. Tie tightly and wrap
the box in a strip of corrugated paper, cut
to the length of the box, and then in another
strip cut to its width. In this way the corru-
gated folds are at right angles, and prevent
twisting and breakage. Finally, wrap in brown
paper and tie firmly. It is advisable to use
a tie-on label.
PACKING PLATES
The question of packing — or, rather, re-packing
— plates after exposure is of importance to the
tourist. He shotdd remember not to throw away
the outer wrapper and the inner packings, as
these will come in useful. The best way to
remove the outer wrapper from a box is to cut
across the centre all round with knife or pocket
scissors, so that each half may then be slid off,
as shown. When required, the two halves may
Plate Box Cut Open
be replaced and bound together with strips of
gummed paper, thus making it practically
impossible to open the box accidentally. Ex-
posed plates should be placed film to film, and the
pairs — usually six — -wrapped in a solid block in
brown or other opaque paper and pressed into
the original box, using paper pads at the ends
and sides of the box to prevent the plates
rubbing together and shaking about loose in
the box ; the lid is then replaced, then the outer
wrapper, and the whole tied with string or
bound with gummed paper. It is a common
practice to put pieces of paper between the
film sides of the plates, but newspaper or other
printed matter must not be used, because the
printer's ink has an action upon the sensitive
film and becomes transferred to the picture,
invariably showing badly when the plate is
developed. If the printer's ink is seen upon the
plates before development, it may sometimes
be removed — in the dark-room, of course — ^by
rubbing with benzene upon cotton-wool. Even
when white paper is used between the plates
there is a risk of fogged patches appearing, and
cigarette papers have been known to fog plates
very badly. It has been suggested that white
paper possesses luminiferous or phosphorescent
properties — extremely faint, of course, but suf-
ficient, over a period of several weeks, to cause
fogging. In spite of this, however, white paper
is commonly employed.
Other errors in packing are due to ignorance
of the fact that pressure will exert an influence
upon the sensitive emulsion. An envelope con-
taining an exposed plate is often written upon,
and if the writing is done upon the side rest-
ing upon the film a reproduction will more
often than not be found upon the negative.
Should it be necessary to mark exposed dry
plates, the writing should be done in very small
characters on one of the extreme corners of the
film side.
PAINTINGS, PHOTOGRAPHING
The general principles to be observed in photo-
graphing paintings are given under the heading
" Copying," but the arrangement for holding the
original and the camera so that the picture and
the sensitive plate are parallel cannot often be
employed. Carefully ruled penal lines on the
focusing screen, forming perfectly true rectangles,
will assist in avoiding inaccuracy. Glass should
always be removed from glazed paintings, if
possible, it being so difficult to kill reflections
entirely. When the glass may not be removed,
a black screen should be hung immediately
behind the camera, and the last-mentioned
should be covered with a black cloth ; or the
screen should be hung close in front of the
camera, with a small aperture through which
the lens may project. Folds or undulations in
the surfaces of screen and cloth shoidd be
avoided, so that the picture reflects only a
uniformly dark mass. A lens of long focal
length is preferable, it being then easier to avoid
the sheen on an oil painting interfering with the
rendering. In the case of water-colour draw-
ings, the chief consideration is that the lens
should cover the plate with crisp definition, and
the proportion of focus to plate is immaterial.
After the image has been focused, the lens
and focusing screen should be removed and the
picture examined through the lens opening from
the back of the camera. In the case of an oil
painting without glass this examination deter-
mines whether sheen on the surface is visible ;
in the case of a picture under glass, it shows
whether reflections are destroying the image.
Sheen or reflections at the top of a picture can
frequently be avoided by raising the camera ;
those at either side can be obviated at times by
means of a screen.
388
Palladiotype
389
Panchromatic Plates
Isochromatic plates should be used for this
■work, together with a yellow screen or light
filter. A green screen is an advantage with
some subjects. (See also " Monochrome, Ren-
dering Colours in.") The screen should be used
behind the lens when possible, and the final
focusing should be done with the screen in
position.
The exposure must be gauged by the aid
of a meter held with its back iiat against the
picture. For an oil painting in good, bright con-
dition, using a plate of the speed of 200 H. and
D., and a lens aperature of //16, the exposure'
should be half the time necessary for matching
the meter tint in the case of a Wjmne meter,
or one-fourth the meter tint in the case of a
Watkins meter. For an old or very dark pic-
ture, from twice to three times this exposure
wiU be necessary. For a water-colour drawing
the exposures will be shorter. For a very dark
or sohdly painted picture the exposure will be
about one-third the meter tint of a Wjmne meter,
and one-sixth that of a Watkins, using the same
plate and lens aperture as given above. For a
light and delicate sketchy drawing these expo-
sures may be reduced to one-eighth of the Wynne
meter tint, and one-sixteenth of the Watkins.
All the above exposures are those necessary
without a colour screen or light filter ; and they
must be multiplied by the number of times extra
exposure that the screen necessitates. They are
all given for copying the same size as the original,
the lens aperture being that marked //16 on
the diaphragm scale, and not calculated from
the extra extension. Proportionate exposures
for other scales will be found under the heading
" Copying."
PALLADIOTYPE (Fr., Palladiotype; Ger.,
Palladiotypie)
A printing process resembling platinotype, but
employing palladium instead of platinum ;
originated by Alleyne Reynolds.
PALLADIOUS CHLORIDE (Fr., Chlorure de
palladium ; Ger., Palladiumchlorid)
Synonyms, palladium chloride, dichloride of
palladium. PdClj? Molecular weight, 177-5.
A dark brown mass or powder, very delique-
scent, obtained by the action of aqua regia
on palladium. Occasionally used for toning
prints.
PALLADIOUS POTASSIUM CHLORIDE
(Fr., Chlorure de palladium et de potasse ;
Ger., Kaliumpalladiumchlorid)
Synonyms, chloropalladinite of potash, palla-
dium and potassium chloride. PdClj 2KCI.
Molecular weight, 326'5. SolubUities, soluble iu
water, slightly soluble in alcohol. Prismatic
crystals obtained by adding potassium chloride
to a hot solution of palladious chloride. They
are dichroic — that is, they appear red or green
as seen across or along the axis. Occasionally
used for toning prints.
PALLADIUM (Fr. and Ger., Palladium)
Pd. Atomic weight, io6'5. A silvery white,
hard, but ductile metal, obtained from its ores.
Used to prepare the chlorides which enter into
a few toning formulae.
PALLADIUM TONING (Fr., Virage d palla-
dium : Ger., Schonen mit Palladium)
Palladium toning is expensive and has no
advantages over gold and platinum toning. It
gives tones of various shades of brown. The
print is reduced slightly, and loses a little colour
in the fixing bath ; allowances must there-
fore be made. For ordinary P.O.P. the bath
is : —
Palladious chloride
. 2 grs.
•45 g-
Sodium chloride
• 20 „
4-5 „
Citric acid
• 20 „
4-5 „
Water
. 10 oz.
1,000 ccs.
I gr. -22 g.
60 grs. 13-5 „
10 oz. 1,000 ccs.
The sodium chloride (salt) may be omitted
from the bath if desired, in which case the prints
should be washed in a weak solution of salt
in water before toning. The salt ensures the
conversion of any free silver remaining in the
paper, although it retards the toning action, and
sometimes is apt to stop it entirely. It is also
advisable to put the prints after toning in a bath
of \ oz. of common soda in 20 oz. of water in
order to neutralise the acid and prevent sulphur
toning, afterwards fixing and washing in the
usual way.
A toning bath for plain salted paper, giving
tones similar to those of platinum, is : —
Palladious chloride
Sodium sulphite
Water
Use as above.
For chocolate-brown tones on glossy papers
Mercer advises : —
Palladious chloride . i-6 grs. -36 g.
Ammonium molybdate 16 „ 3-6 „
Citric acid . . 16 „ 3-6 „
Water . . .10 oz. 1,000 ccs.
For matt papers, substitute common salt for the
molybdate. The fixing bath must be dis-
tinctly alkaline.
PANAPLANATIC
A term applied to a lens exceptionally free
from spherical aberration. A microscope con-
denser by Swift is sold under this designation.
PANCHROMATIC LENS
A lens corrected for the secondary as well as
the primary spectrum, and therefore suitable
for use in three-colour work. (See also " Apo-
chromatic")
PANCHROMATIC PLATES
Plates made sensitive to the entire spectrum,
and used either for isochromatic photography
with a suitable screen where a full colour render-
ing is required, or for colour photography by
the three-colour process. They can be made by
bathing slow ordmary plates with certain aniline
dyes, particularly some of the isocyanine deriva-
tives. Either of the two following baths is
suitable for panchromatising : —
A. I : 1000 alcohoUc
solution of pina-
chrome . . 8 mins. 2 ccs.
Ammonia (-880) . 4 „ i „
Distilled water . 400 „ 100 „
Panel
390
Pantoscope
B. I : 1000 alc»hoUc
solution of homo-
col (Bayer)
Ammoma ('880) .
Distilled water
12 mins.
8 „
480 „
3 CCS.
2 „
120 „
Instructions for bathing will be found under
the heading " Isochromatic Plates." Particular
care must be exercised as to cleanliness, pure air
for drying, and rapidity of drying in the case of
red-sensitive plates, as they are liable to fog on
the least provocation. A truly panchromatic
plate should be evenly sensitive to the whole
visible spectrum, but with practically all plates
there are " gaps " in the sensitiveness — that is,
comparatively less sensitiveness towards certain
regions, particularly the bluish-green — due to
minima of absorption in the dyes used. Both
pinachrome and homocol plates exhibit two
minima in their spectrum sensitiveness, which
can be filled up to some extent by the use of
supplementary dyes.
Colour filters for either three-colour work or
isochromatic photography m.ust possess minima
in their absorption spectra to compensate for any
minima in the spectrum sensitiveness of the plates
to which they are adapted.
Development should always be carried out
with a cool solution, and in darkness or in a
green " safe " light.
In process work, panchromatic dry plates are
largely used for the three-colour process, the
exposures being made directly through the
colour filter and the half-tone ruled screen.
PANEL
A commercial size of photographic mount
which accommodates whole-plate prints trimmed
to panel shape, and measuring about 8 in. by
4 in. Therefore, ordinarily, a panel mount may
measure about 9 in. by 5 in., but it may be much
larger, according to the margin allowed ; 1 3 in.
by 7|- in. is a common size. " Large Panel "
mounts measure about 17 in. by loj in. ; " Grand
Panel," 23 in. by I3j- in. ; and " Paris Panel,"
10 in. by 7J in. There are also " midget panels,"
the term panel being somewhat loosely apphed
to any mount which is of panel shape.
PANEL LENS
A lens adapted for the production of panel-
sized portraits. Any good portrait lens or
anastigmat of about 20 in. focal length answers
well for a 12-in. by lo-in. plate, if it covers it.
PANIKONOGRAPHY
Gillot's process of zinc etching. (See " GiUot-
age.")
PANNOTYPY, OR PANNOTYPIE
A process of transferring a collodion negative
film to a dark oilcloth, so that a positive effect
is obtained.
PANORAM CAMERA {T?i.,ChambrePanoram;
Get., Panoram Kamera)
A camera invented by Colonel Stewart, R.E.,
by means of which a complete circle, or several
circles in succession, could be photographed on
a band of film. It rotated in one direction on
its optical axis, while the film revolved in an
opposite direction, the two movements being
so synchronised that a stationary image was
obtained.
Also the name given to a daylight-loading
Kodak hand camera, with which long, narrow,
panoramic pictures are obtainable. The lens
swings roimd on its nodal point during the
exposure, so that the image remains motionless
and the celluloid film is bent to a curve.
PANORAMIC CAMERA (Pr., Chambre
panoramique ; Ger., Panorama-kamera)
Cameras for obtaining panoramic views were
made at quite an early date, perhaps the first
being that constructed by Marten, of Paris, in
1845, for use with curved daguerreotype plates.
Other important panoramic cameras are treated
under separate headings. {See " Cydograph,"
" CyUndrograph," " Oroheliograph," " Panoram
Camera," " Pantascopic Camera," etc.)
PANORAMIC VIEWS (Pr., Vues panoram-
iques ; Ger., Rundgemdlde)
Panoramic views are best obtained with a
camera intended for that class of work, or with
a very wide-angle lens, such as the pantoscope.
They may also be made by revolving a stand
camera on its tripod, and taking a series of
photographs, each one continuing the subject at
the point where the previous picture left off.
Prints from the resulting negatives are trimmed
carefully so as to join satisfactorily, and are then
mounted to form a continuous picture. Pano-
ramic views have been obtained by taking a
series of negatives from slightly separated stand-
points, keeping the camera in line, and joining
the prints as before. This, however, is much
more difficiHt than the previous method and only
of limited utility.
PANTASCOPIC CAMERA (Pr., Chambre pan-
tascopigue ; Ger., Pantaskopische-hamera)
A panoramic camera, invented in 1862, by
J. R. Johnson, arranged to rotate on a circular
base by means of clockwork, and which photo-
graphed the entire horizon on a flat plate.
PANTOGRAPH
Besides the well-known drawing instrument
for proportionally enlarging a photograph or
sketch, the term designates an apparatus used
by lithographers for enlarging or reducing
transfers. A rubber sheet is stretched on a
metal frame with mechanical arrangements for
stretching the rubber from all four sides, either
equally or unsymmetricaUy. Thus, after a
print is transferred to the rubber it can be
stretched to enlarge it or unstretched to reduce
it, after which the altered image can be trans-
ferred to a stone or plate for printing from.
Pantograph machines are also used by engravers
for enlarging or reducing designs or lettering,
and for copying reUef objects (such as medals)
on to a flat surface. These machines are on the
principle of the drawing instrument, but are
much more elaborately constructed.
PANTOSCOPE (Fr., Pantoscope; Ger., Panto-
skop)
A lens first made about 1865 by Emil Busch.
of Rathenow, and still esteemed for its special
purpose. It consists of two symmetrical achro-
Paper
391
Paper Negatives
matic combinations of deep curves, works at//22,
and gives the very wide angle of from lOo" to
1 10°. It is extremely useful for work in confined
situations, architectural subjects, panoramic
views, etc.
The name pantoscope was also given to a
viewing apparatus for photographs, much re-
sembling the alethoscope, lantemoscope, and
neomonoscope.
PAPER (Fr. and Ger., Papier)
The raw material of paper is linen, cotton-wool,
hemp, flax, esparto grass and wood pulp ; but
for photographic purposes the absence of the last
two substances is essential, save in such processes
as carbon, where the paper only forms a tem-
porary support for the tissue. The raw material
is mechanically torn up, bleached, and then
mixed into a piilp with water and the pulp spread
on fine-meshed wire, so that the water can drain
off and the paper pulp or felt be dried. All
paper, except blotting and filter paper, is sized
to prevent the xmdue absorption of water, and
very frequently, in addition, filling is used to
render the paper more opaque and give it a
greater glaze, but at the same time lessening
somewhat its strength. The filling may be either
silicates, such as kaolin, the carbonate? of lime,
barium, zinc or lead, or sulphates, such as those
of calcium and barium.
Paper contains as a rule about 5 to 10 per cent,
of water, and is always more or less hygroscopic,
and according to the sizing so it will absorb a
greater or less amount of water. Photographic
papers are almost always sized in the stuff or
mass, but in some cases, especially with the so-
called drawing or water-colour papers, the sizing
is so poor that it is necessary to remove it by
treatment with acid and subsequent washing,
and then to re-size with a colloid-like gelatine,
agar-agar, etc., in order to keep the photographic
image on the surface.
Paper for photographic work must be free
from wood pulp, which rapidly yellows on expo-
sure to light, and spoils the emulsion coating or
decomposes the free silver salts of printing-out
papers. Equally important is the absence of
metallic particles — ^iron, brass, copper, etc. —
which might be introduced from the paper-mak-
ing machine ; such particles cause black spots in
the case of papers containing free silver nitrate,
and generally white insensitive spots in the case
of development, though often in the latter case
the little white spot will be seen to have a
minute black centre, when examined micro-
scopically. The quaUty of the water used in pre-
paring the paper pulp is also of great importance,
as this may introduce foreign matter which acts
prejudicially on emulsions. Naturally, too, the
absence of " antichlor " is all-important, as in
every case this spoils the sensitive film and
usually results in spots.
Many photographic papers are primarily coated
with an emulsion of barium sulphate (see " Baryta
Paper "), which prevents the sensitive film from
penetrating the paper, and gives the prints a
special surface. The preparation of this coating
is as important as that of the paper, and it may
also be the cause of peculiar markings and spots,
but even this will not allow of a poor quality
raw stock being used. One important point in
connection with baryta paper is the homogeneity
of the coating, for if the coating is not absolutely
even in thickness or hardness, the sensitising
material, especially in the case of printing-out
papers, will penetrate more or less deeply into
the same, and the results are that the prints
show a peculiar and characteristic defect known
as measles or mealiness.
Jn process work, the expansion and contraction
of paper is of serious importance. For instance,
in photo-Uthography by paper transfers it
affects the scale in such work as map reproduc-
tion, and makes the joining up of sections diffi-
cult. To overcome this it is usual to allow a
definite amount for expansion whilst the paper
is damped for transferring, the sheet being
measured between two points by means of a
trammel rule provided with needle-points. The
paper is further damped if it does not reach the
required measurement. In colour work the
risk which paper undergoes often affects the
registering of the colour, and has to be allowed
for. As the expansion is greatest in the direction
of the web, and is fairly uniform, it is a good
plan to mark this direction and use it always
the same way, when several pieces have to join
or to register.
(For the preparation of the various kinds of
papers, see under separate headings. The coating
of paper is described under its own heading.)
PAPER NEGATIVES
Fox Talbot, in his calotype process, worked
extensively between 1841 and 1856, made his
negatives from paper coated with a sensitive
silver salt, but this system became almost obso-
lete when Archer introduced his collodion process
on glass. About 1885, however, paper as a
medium for negatives again came to the front
owing to the increasing popularity of bromide
paper, which originally was intended solely for
printing by devdopment. In 1884 a specially
rapid bromide paper was introduced for negative
work, and the Eastman Company and other firms
followed with improvements. At the present
time celluloid films, roll or flat, have almost
superseded paper as a support for the emulsion,
but there are still a few photographers who use
bromide paper for negative making. Compared
with glass, paper is hghter, halation is impossible,
it is not brittle, it can easily be stored, it is cheap,
and it can be easily cut ; but it is not transparent,
and, consequently, the time taken in printing is
rather long ; the grain may be troublesome, and
print at the same time as the image, although,
if the printing is done on a matt or rough paper,
it will be considerably minimised, and possibly
caused wholly to disappear. Paper cannot be
obtained with so high a rapidity as the fastest
plates, and there is a slight difficulty in keeping
it flat in the dark-sUde and in developing and
fixing it.
Generally, bromide paper can be used in
exactly the same way as a dry plate, the thinnest,
with a semi-matt surface, being the most suitable.
Up to half-plate it may be kept flat in the dark-
sUde without difficulty, but beyond that size
some little care is necessary, while it will be
advisable to place a sheet of glass or cardboard
at the back of the paper, and it may be necessary
to coat the extreme edge of the glass or card
Paper, Varieties of
392
Para-amido-phenol
backing (or the division plate, if a backing is not
used) with a mixture of gelatine and glycerine
or similar adhesive. The exposure with aJi
average paper is about three times as long as
with an average dry plate ; but it depends on
the circumstances. Under-exposure must be
particularly guarded against. The developers
advocated by the paper-makers should be used,
and not those specially for plate work ; those
most suitable are the clean-working developers,
such as metol, hydroquinone, amidol, rodinal,
etc. Pyro is unsuitable, as it tends to give the
shadow (white paper) parts a yellowish tinge,
thus prolonging the period of printing. When
developing, remember to judge the density by
looking through the paper and not upon it. The
developed negative is fixed in an acid fixing bath
in order to avoid stains, and make the negative
as clear as possible. The paper negative is
washed, dried, reduced, intensified, toned, etc.,
in the usual way. Printing is facilitated by
waxing the paper to render it more translucent,
but most makes of thin smooth bromide paper
do not need this treatment.
Four methods are here given for increasing
the translucency of paper negatives : —
(i) Rub on warm vaseline with a clean rag to
the back of the negative, and apply a warm
flat-iron, interposing a sheet of blotting-paper.
Should any vaseline get on the film side, remove
with benzine. (2) Use white wax and a warm
iron as above. Any superfluous wax may be
partly removed with turpentine. (3) Apply, as
above, a mixture of alcohol 4 oz., and castor oil
I oz. Ironing is not necessary in this or in the
next method. (4) Apply, as above, a mixture
of turpentine 5 oz., and Canada balsam i oz.
PAPER. VARIETIES OF {See under separ-
ate headings.)
PAPIER JOSEPH (Ger., Seidenpapier)
A term of French origin and designating a
fine tissue paper of a silky character, similar to
the best Japanese tissue paper. Used for polish-
ing glass.
PAPIER MACHE (Ger., PapiermacM)
A term of French origin, and designating a
material manufactured from paper pulp mixed
with size and other substances, and then forced
into a mould previously oiled. After drying,
the articles are soaked with linseed oil and
dried at a high temperature. Largely used for
making dishes, trays, and studio accessories.
PAPIER MIn£:RAL (See "Mineral Paper.")
PAPIER SEPIA (See " Sepia Paper.")
PAPIER v6g6TAL (Ger., Papier zum Durch-
zeichnen)
Tracing paper. A term of French origin, and
designating a very transparent tracing transfer
paper used in lithography.
PAPIER VELOURS
A pigmented paper used in the Aitigue process
{which see), and introduced in 1892 by V. Artigue,
of Bordeaux. The pigment appears to be held to
its paper support by means of gum, gelatine, etc.
PAPYROGRAPHY, OR PAPYROTYPE (Fr.
and Ger., Papyrographie)
The name given to various methods of trans-
ferring impressions on paper, secured by photo-
graphic means from line negatives, to stone for
photo-lithography. According to Sir W. Abney,
any stout paper may be coated with a thin layer
of gelatine and hardened in a chrome alum bath.
It is then coated with : —
Potassium bichromate . i oz. 44 g.
Nelson's flake gelatine . ij „ 66 ,,
"Water . . . 25 ,, 1,000 ccs.
When dry, the paper is exposed under a line
negative, and drawn through (not soaked in)
cold water, being then squeegeed down on a zinc
plate. The surplus water is blotted off and the
paper inked over with lithographic chalk ink
mixed with one-fourth its bulk of palm oil, this
being applied with a gelatine roller. The ink
takes on the lines which have become insoluble
by exposure to light, but is repelled by the moist
ground. The inked print is suspended to dry
and is exposed to light, in order that the bichro-
mate, which has not been completely washed out
of the film, may exert a hardening effect. The
print is then transferred to stone by the usual
lithographic methods. There have been many
variations of this process.
PAPYROTINT (Pr. and Ger., Papyrotint)
A process of photo-lithography invented by
Husband, in which paper or tinfoil coated with
bichromated gelatine and other ingredients is
used to obtain a print by exposure to light under
a half-tone or line negative. The print is then
placed in water for a few minutes, blotted off,
and rolled in with a soft lithographic ink, which
takes on the lines or image only. Having been
dried the print may be transferred to stone or
metal for lithographic printing. The method is
a modification of the papyrotype process.
PAPYROXYLINE (Fr., Papyroxyline ,■ Ger.,
Papyroxylin)
Pyroxyline prepared from paper, usually pure
tissue or filter papers, instead of from cotton-
wool. It was first introduced by Pelouze in
1838, and used by Crookes, Lyte, Elliott, Sutton,
and I/iesegang. It presents no particular advan-
tage over pyroxyline prepared from cotton-wool,
and has faUen into disuse.
PARA-AMIDO-PHENOL
Para-amidophenol, para-amido phenol, and
paramidophenol are other forms of this term.
In the form of a preparation by Lumi^re, this
developer is also known as " Paranol." It is a
white crystalline compound, really para-amido-
phenol hydrochlorate (C,H,OHNHj), which is
widely used for making up highly concentrated
developers in liquid form ; for example, rodinal.
Amidol resembles, but is not identical with, para-
amido-phenol. A concentrated one-solution de-
veloper like rodinal may be made as follows : —
Potass, metabisulphite . 3 oz. 33 oz.
Para-amido-phenol . i „ no „
Distilled water (hot) . 10 „ 1,000 ccs.
Dissolve in the above order and add slowly a very
strong solution of caustic soda or potash until
Para-amido-phenol Citrate
393
Parallax Stereogram
the precipitate first formed is dissolved. For
use, dilute with. lo to 30 parts of water, an
average strength being 24 drops to each ounce
of water (i in 20).
Developers may also be made up in an ordinary
one- or two-solution form as follows : —
One-solution
Sodium sulphite . 2 oz. 220 g.
Sodium carbonate . i ,, no ,,
Para-amido-phenol . 55 grs. 12 „
"Water . . .10 oz. 1,000 ccs.
The above is ready for use.
Two-solution
A, Para-amido-phenol . 100 grs. 23 g.
Potass, metabisnlphite 50 „ 11-5 „
Distilled water . . 10 oz. 1,000 ccs.
B. Sodium sulphite . 300 grs. 69 g.
.Potass, carbonate . 300 ,, 69 „
Water . . . 10 oz. 1,000 ccs.
For use, mix i part of A with 2 parts of B.
Para-amido-phenol developers are suitable for all
makes of papers and they do not stain. Solutions
keep good for a long time even in uncorked
bottles.
PARA-AMIDO-PHENOL CITRATE
A developer advocated by Dr. Liesegang, who
foxmd that citric acid is an excellent solvent for
para-amido-phenol, 97 parts (by weight) of which
are soluble in 200 parts of a 50 per cent, solu-
tion of citric add in water. The para-amido-
phenol should be added gradually at a tempera-
ture of from 65° to 68° (18° to 20° C). The
citrate of para-amido-phenol so formed is
employed as a developer in the following pro-
portions : —
Para-amido-phenol citrate sol. . i part
Sod. sidphite sol. (concentrated) 5 parts
Sodium carbonate . . • 5 »
Caustic potash (10% sol.) . 2 „
Water .... So „
This is ready for use, and may be employed
repeatedly. It gives blue-black images with
normal exposure, and is said to be suitable for
all kinds of plates and papers.
PARABOLIC LENS
A lens whose curves are those of a parabola
and not spherical. It has not been found prac-
tical to manufacture photographic lenses of this
form with the necessary degree of accuracy,
although they have been employed in the illu-
minatiug systems of microscopes.
PARABOLIC REFLECTOR (Pr., Riflecteur
parabolique ; Ger., Pardbolischer Spiegel)
A mirror or reflector ground or bent to a para-
bolic curve, a parabola being the section of a cone
tut parallel to its slant side. If an iUuminant is
placed in the focus of such a mirror or reflector
the reflected rays are perfectly parallel, which is
only approximately the case with a spherical
mirror. Parabolic mirrors are used in photo-
micrography and for various purposes where
parallel rays are necessary, while white reflectors
of parabolic or paraboloid curve are employed
to secure even illumination of the negative in
enlarging by artificial light when a condenser is
not used.
Jn process work, parabolic reflectors are used
on arc lamps, but not so generally since the
" enclosed " type of arc lamp has come into use,
a semi-parabolic shade reflector being commonly
used instead.
PARABOLOID REFLECTOR (See "Parabolic
Reflector.")
PARAFFIN (Fr., Parafjine ; Ger., Paraffin)
A solid crystalline mass, transludd, odourless
and tasteless, obtained by dry distillation from
wood or bituminous minerals, such as petrolema.
It is insoluble in water, 3 per cent, soluble in
boiling alcohol, soluble in ether and oils, benj,ole
and chloroform. It is used for making paper
translucid and waterproofing wooden dishes.
PARAFORMALDEHYDE
(COHj),. A white crystalline substance,
known also as metaformaldehyde and trioxy-
methylene. Slightly soluble in water, alcohol or
ether, soluble in an aqueous solution of sodium
sulphite. Advocated in 1903 by Lumi^re and
Seyewetz as an addition to developers. Fornio-
sulphite contains paraformaldehyde.
PARAHYDROXYGLYCINE
A synonym for glycine.
PARALLAX STEREOGRAM
An invention of P. E. Ives, of America. The
parallax stereogram photograph consists of a
single transparent image divided into lines (100
to 150 to the inch), alternate lines forming one
of a stereoscopic pair of images, and the inter-
mediate lines forming the other image, so that
it has the appearance of a pair of stereoscopic
images mechanically superposed. In order that
each eye may see only the lines belonging to
its respective view-point, the transparency is
covered by a line -screen, with a definite separa-
tion from the surface of the photograph such
that lines of the photograph covered by screen-
lines to one eye are seen by parallax of vision by
the other eye. The combiuation of the photo-
graph and line-screen in suitable adjustment
constitutes the parallax stereogram, whieh, when
viewed from a suitable distance, directly in front,
shows the object in stereoscopic relief. The
method of production is by means of a camera
having at the front a single plano-convex lens
about 3 in. in diameter, behind which are two
—^rs^v\f~\
_7WWW\ I
A. Camera for Producing Parallax Stereograms
small openings about 2| in. apart in a horizontal
plane (see A) ; thus an image is formed from two
view-points, corresponding to the separation of
the eyes. The image thus formed may be a
perfectly sharp single image of objects at some
Parallax Stereogram
394
Parts," Formulae in
one distance from the camera, in which case
objects at every other camera distance will form
two images laterally displaced and superposed,
exactly as in two ordinary stereoscopic images
mechanically superposed. It is then only neces-
B. Inverted Prisms in Front of Lens Apertures
sary to cover the plate with an opaque line-
screen suitably adjusted with reference to the
spacing of the lines, separation of view-points, and
camera extension, in order that the light coming
from the two camera apertures may form sepa-
rate images in juxtaposed lines. A transparency
from the negative thus obtained is covered by
a line-screen with adjustment like that in the
camera, and viewed from a point corresponding
to the position of the lens apertures, in order to
produce the effect of an ordinary double stereo-
gram in the stereoscope. If, however, these
conditions are strictly adhered to, the result will
be pseudoscopic instead of stereoscopic, just as
in ordinary stereoscopic photography the results
are pseudoscopic unless the photographic prints
are cut apart and transposed before mounting
them for inspection in the stereoscope. The
stereoscopic efiect is obtained by shifting the
cover-screen laterally the width of one screen-
line, but with the result that the perspective is
distorted when a moderately large angle view
is embraced. In order that the path of the rays
to or from every point of the stereogram may
be absolutely identical in photographing and in
viewing, the image formed through each aperture
in the camera should be laterally inverted, so
that the two pencils of light belonging to near
objects bisect before reaching the screen, and
pencils from far objects after passing through it.
This may be effected by placing laterally inverted
prisms in front of the lens apertures, as shown
at, B in which w represents the path of rays
coming from an object more distant from the
lens on one side than the screen and sensitive
plate on the other. With this arrangement, the
objects will be laterally reversed, unless photo-
graphed from an intervening mirror, but in other
respects the results are much better than without
the inverting prisms. The use of the inverting
C. Using Two
Separate Lenses
D. Using Two
Pinholes
prisms also permits of the large lens being dis-
pensed with. The fact that the prisms may be
disposed so as to direct the two pencils of rays
towards the axis of the camera in the same
manner as the prismatic edges of a single lens,
permits of the use of two separate lenses C,
or even of pinhole apertures without lenses D,
and this method of controlling the parallax
independently of the focal length of the lenses
possesses certain practical advantages. Objects
can be photographed so as to appear to be at
the plane of the photograph, or within or beyond
it, at will. When the arrangement shown at C
is employed, it is advantageous to have pairs of
lenses of various foci, in order to keep to one
camera extension, and owing to the small size
of the apertures, simple lenses may be used.
The most perfect screen for this work is a
100 line to the inch uncovered Levy single-
line screen with " hard filling," and opaque Imes
twice as broad as the clear spaces. A card-
mat separator is used, and the sensitive plate
pressed flat by a thick plate-glass at the back
in the dark-slide. The requisite thickness of the
card separator depends upon the camera exten-
sion, which can be readily calculated. The cover
screens for the parallax stereograms are made by
contact printing on transparency plates from a
negative made by contact printing from the
original Levy screen, and intensified by mercury
and ammonia. The lines should be quite opaque,
and the spaces perfectly clear, and, while good
enough for this purpose, such screens are not
good enough for use in making the negatives.
Owing to the fact that neither the transparencies
nor the cover-screens are ordinarily flat, it is
necessary, in mounting them together, to use a
third glass, convex side (preferably ground)
against the back of the transparency.
PARA - METHYL - AMIDO - PHENOL-SUL-
PHATE
A synonym for metol.
PARAMIDOPHENOL
phenol.")
(See
' Para-amido-
PARAMOL (See "Edinol.")
PARANOL (See " Para-amido-phenol.")
PARAPHENYLENE-DIAMINE
C,H4(NHij)2. One of the hydroquinone series
of developers.
PARCHMENT (Fr., Parchemin; Ger., Perga-
ment)
Paper which has been superficially treated with
sulphuric acid, and thus converted into so-called
parchment, has been occasionally used for print-
ing, but has not come into general use.
Parchment is used by process workers for
covering the tympans of typographic proof
presses. It is also used instead of glass, for the
autocopyist collotype process.
PAROLOGRAPH
An instrument used for obtaining photographic
records of the voice.
"PARTS," FORMUL/E IN
The system of stating formulae in " parts " has
some advantages. A " part " may mean any-
thing : a drop to a gallon in liquids, or a grain
to a ton in solids ; and as long as one keeps to-
the same unit and multiplies tins by the number
'Parts," Formulae in
395
Passe-partout
in tie formula it is impossible to go wrong. The
following table will be found useful, as it will
save some calculations when quantities are ex-
pressed in " parts " :
British
Parts
I
2
3
4
5
10
20
50
6o
lOO
250
500
1,000
2,500
5,000
Solids
Grains
I
2
3
4
5
10
I scr.
I dr.
* i'oz.
r „
2i „
54 ..
Hi
10,000 I lb. 6J oz. 49
50
2 scr.
32 grs.
62 „
16 „
94 .,
79
Liquids
Minims
2
3
4
5
10
20
50
I dr.
5 oz
10 ,,
20 „
„ 4omjns
i oz. 10 „
» 20 „
40
40
20
40
idr
3 „
6 „
Metric
Solids (g.>
or Liquids
(ccs.)
I
2
3
4
5
10
20
50
60
100
250
500
1,000
2,500
5.000
10,000
* Avoirdupois oz. of 437-5 grs.
This table may be used to some extent for roughly
converting amounts in one system to the other.
Say, for example, it is reqtiired to convert the
following or any similar " part " developing
formula into one for a solution containing 10 oz.
of water : —
Kachin .
16 parts
Sodium stdphite
24 „
Sodium carbonate .
50 „
Water .
. 1,000 „
The water is to equal 10 o«., then i part is equal
to 4-8 mins., or 4-5 grs. (precisely, 4-37), for i oz.
is equal to 480 mins. or 437'5 grs. :
Kachin .
Sodium sulphite
Sodium carbonate
Water .
.(16 X4i) = 72 grs.
.(24X4i) =108 „
.(50 X4i) =225 „
= 10 oz.
It is near enough in photographic formulae to
take a "part" as meaning i gramme or i cubic
centimetre. Thus, the formula above given will
work out as follows : —
British
approx.)
Metric
Parts
Calculated
from
British
[approx.)
Calculated
direct
from
formula
Kachin . 16
Sodium
sulphite . 24
Sodium
carbonate 50
Water . 1,000
72 grs.
108 „
225 „
10 oz.
i6-5 g.
25 ,.
50-5 „
1,000 ccs.
16 g.
24 »
50 „
1,000 ccs.
Of course, there is a percentage of error, but
this is of small importance in the generality
of photographic solutions.
PASSE-PARTOUT
This is a cheap and very effective method of
preparing prints for the wall, and is a good sub-
stitute for the more orthodox method of framing.
The chief drawback is that the absence of the
support given by a stout wooden frame results
in fragility ; so that while passe-partouts are
quite satisfactory for home use, they run serious
risks if sent to exhibitions. Briefly, the method
consists in binding together by the edges a sheet
of glass, a mounted print, and a backboard, and
providing a means for hanging up. The actual
work is carried out with many variations, but
the outline of one course of procedure will be
sufficient to indicate the general lines to be
followed.
The mount of the print should be sufficiently
stout to ensure its lying flat, as with a thin paper
mount it is difficult to secure such close pressure
against the glass as to prevent buckling. A sheet
of glass the size of the finished picture is cut,
taking care that the edges are as clean-cut as
possible, and the shape truly rectangular. This
glass is used as a template for trimming the print
and for marking out a rectangle on a piece of
very stout strawboard. If this latter is of the
right kind and thickness it will have less " give ''
in it than a similar piece of wood. It is extremely
hard to cut with a knife, and those who have a
fine-cut saw, or even a fret-saw, available will
find it an advantage. Glass, mount, and back-
board should now be of the same size, with the
edges flush and even all round.
Before binding up, the backboard is fitted
with a hanging arrangement. Tapes are some-
times glued on for this purpose, but a better
method is to use paper fasteners and curtain
rings. The former should be of large size, say
about I J in. or i J in. long ; the latter are hollow
brass rings about f in. in diameter. The back-
board is pierced with two holes, a ring is slipped
between the forks of the fastener and drawn
tight up to the head, and the fastener is then
pushed through the hole, opened out, and ham-
mered down flat. If the rings are so held as to
occupy the best position for taking the pull of
the cord, it wiU be found that the flattened paper
fasteners incline towards each other, and are not
parallel to the sides of the backboard. They will
resist a pull very much greater than will be put
upon them by the weight of the finished picture.
Excellent binding for the edges can be bought
in rolls, and of different colours. Grey, black,
and brown are the most useful. The strips are
of tough " pebbled " paper, already gummed
with a strong adhesive. The glass having been
thoroughly deaned the three component parts
are put evenly together, and laid, glass side up,
so that one side projects very slightly over the
edge of a table. A piece of edging the length of
this side is cut from the roll, drawn under a
straight-edge or through the fingers to remove
the ciurl,, and the gummed side moistened with a
brush, bemg carefi3 not to take off the adhesive.
With a little practice this strip can be laid evenly
along the edge of the glass, using the thumbs at
each end to adjust it, and keeping about one-
third of the width on the glass. The strip is
then thoroughly rubbed down into close contact
with a duster. The whole thing is now turned
carefully over, and the free edge of the strip
Paste
396
Patents
drawn tigntly ovet and rubbed down on to the
backboard. The opposite edge is done in the
same way, and then the other two edges, allow-
ing time between each for the last strip of edging
to set. Some prefer to mitre the corners of the
strips, but if one is placed over another the
difference cannot be detected at a little distance.
Should alternations of wet and dry weather
subsequently cause the edging to leave the glass
in places it can be re-damped and rubbed down
again. In extreme cases it is a simple matter
to renew the binding altogether.
PASTE {See "Encaustic Paste" and "Moun-
tants.")
PASTELS
Prints, upon paper or opal, coloured with
crayons ; the pastel proper, however, has no
photographic basis. Pastel colours are opaque,
and the print selected for colouring should be
light and of a cold tone. Details are hatched or
stippled with the point of the crayon, but broad
tints are rubbed in with the finger or stump.
Such pictures when coloured are liable to injury
because of the colours being in a kind of powder
on the surface. If not mounted up at once in a
frame and behind glass the work should be
sprayed with a weak solution of rice water, or
with the following : — A. Mastic, 24 grs. ; amyl
acetate, 3 oz. B. Celluloid (old photographic
films washed free from emulsion), 7 grs. ; amyl
acetate, 3 oz. Dissolve, and when, after some
hours, both solutions are clear, mix together and
keep in a tightly corked bottle. Another method
is to strain over the crayon work a piece of thin
nainsook, and then rapidly and lightly to brush
over a weak solution of isinglass.
PATENTS
The governments of the civilised countries
grant inventors the sole right to their inventions
for a term of years, in consideration of a fuU
disclosure of the invention, the payment of
certain fees, and conformity to certain regula-
tions. Application for a British patent may
be made in two ways, (i) By lodging what is
known as a provisional specification, to be
followed within six months by a complete
specification. (2) By lodging a complete speci-
fication in the first instance. In most cases it
is best to adopt the first course, as the period
ensuing between a provisional and complete
application affords the inventor an opportvmity
of developing his ideas and ascertaining by
practical tests the best ways and means of
carrying his invention into effect. The pro-
visional specification, however, must clearly
foreshadow the object of the invention and
indicate to some considerable extent the methods
to be adopted in carrying the invention to a
practical issue ; hence, as the provisional forms
the basis for the complete patent, it should be
prepared with the utmost care, especially as
nothing which has not been intimated in the
provisional may be included in the complete
specification. If the inventor discovers im-
provements after filing his provisional, he can-
not include them in his complete specification, but
he may (in virtue of the Patent Act of 1907)
apply for a patent of addition, in respect of any
modifications or improvements upon the in-
vention as originally patented, and no renewal
fees beyond those in respect of the original
patent will be involved. OflScial patent forms
are supplied free of charge. For a provisional
application, one copy of Patent Form No. i
and two copies of Patent Form No. 2 are required.
Before it is lodged at the Patent Office, No. i
will require the Government stamp (cost ^i) to
be impressed thereon. No stamp is required on
the two copies of Form No. 2 ; and No. i may
be obtained already stamped before filling in the
form, if desired.
The provisional specification is commenced
on Form No. i, and continued on wide-ruled
foolscap paper, leaving a margin of i in. on
the left - hand side. It may be delivered by
hand or sent by post, on receipt of which it will
be officially dated and numbered.
A provisional specification is not published,
but remains secret during the period of pro-
visional protection, and until the acceptance
of the complete specification. As soon as a
provisional appUcation has been filed the
inventor may safely show his invention to any
interested party, but he should be quite certain
that he has properly described his invention
and satisfactorily covered his idea. Provisional
protection lasts for six months, or seven months
by payment of a fine, and at any time before
the expiry of the period of provisional protec-
tion the inventor must file his complete speci-
fication, otherwise the application is considered
to be abandoned.
Complete specifications, with their all-im-
portant claims, should not be filed without
expert assistance. It is a good plan for the
inventor himself to make a preliminary search
for novelty, before involving himself in the
necessary expenses of completing the patent
through a qualified agent. The Patent Office
in Chancery Ivane, London, offers every facility
to visitors to make their own searches, but it
is a long task to anyone unacquainted with the
system, and in any case involves time and
patience. For this reason the services of
special search agents are useful. Persons who
cannot go to the Patent Office in person, and
yet have time at their disposal for the search,
may obtain copies of all specifications filed, in
either the original or an abridged form. For
example, suppose an inventor of some photo-
graphic appliance wishes to ascertain how
much novelty exists in his invention ; he may
purchase ten volumes at is. each, post free, in
which he will find tabulated and conveniently
indexed all patents in photography from the
year 1617 almost to date. The abridgments re-
lating to photography come under Class No. 98.
From the index he may find all inventions which
have any serious bearing on his particular
apparatus. After selecting any which may be
thought to encroach upon his ideas, he may
further obtain the full specifications for 8d. each.
Having satisfied himself with respect to these
he may bring his search up to date by engaging
an agent, to furnish information of any other
specifications a view of which can only be got
by visiting the Patent Office itself. Such a
procedure often saves an inventor the expense
of lodging a complete specification and then
Paul's Animatograph
397
Pellet Process
in the end discovering that he has been com-
pletely anticipated. The Comptroller of Patents
causes a search to be made through British
specifications for fifty years back from the date
of every application for a. patent. Only com-
plete specifications, either after provisional, or
complete in the first instance, are subject to
the search, and the Comptroller has the power
to insist on the amendment of the specification
or on the insertion of a reference to existing
patents, and so to place it in interference there-
with. A preliminary and independent search
by the inventor before filing a complete specifi-
cation often reveals prior applications with
which he may be able to avoid clashing by means
of judicious wording in his complete specification,
thus obviating the addition of troublesome
references to prior patents — references which
are likely to discount the value of his patent.
A sealed Royal Letters Patent alone enables
an inventor to obtain absolute protection for
fourteen years, and allows of legal action being
taken against infringers, annual renewal fees
being payable from the end of the fourth year.
The complete specification must be begun
upon Patent Form No. 3 (stamp, £3), and con-
tinued on foolscap paper. An unstamped dupli-
cate copy is also required. The specification
shoidd contain a fuU and detailed description
of the invention, of such a nature that the in-
vention could be carried into practical effect
by a competent workman. Drawings are also
required where a mere description would fail
to make everything absolutely clear. Instruc-
tions to applicants for patents (supplied free)
give clear directions not only for drawings but
also for the mode of applications, provisional and
complete. The complete specification, together
with its claims, is a most important document.
The drafting of claims is a task that should be
done by a fully qualified and registered patent
agent, because when a specification comes to
be construed in a court of law, the wording
of the claims is subjected to a searching scrutiny,
and if there is any flaw the patentee will generally
fail to support his monopoly. Further than this,
the claims should always be drafted in the first
instance as wide as is reasonably possible,
because there will then be an opportunity of
reconsidering them in the light of the fuller
knowledge of prior patents disclosed by the
Patent Office search.
The total amoimt of Government stamp
duty for a British patent is £1 on provisional
application, £3 on completing same ; or £4 on
complete application in the first instance. A
further fee of £1 is payable in order to obtain
the issue of a patent on an accepted applica-
tion. Before the end of the fourth year, dating
from the first application, £s becomes due in
respect of the fifth year ; before the end of the
fifth year £6 in respect to the sixth year, and
so on, increasing £1 each year during the
period (fourteen years) the patent may be kept
in force. The period is extended only in very
special circumstances.
PAUL'S ANIMATOGRAPH
One of the earliest commercial kinematograph
machines, patented by R. W. Paul, and at first
called the " Theatrograph."
PAYNETYPE
A photo-mechanical process invented by
Arthur Payne. Zinc plates are coated with a
gelatino-bromide emulsion and exposed direct
in the camera. In order to obtain the necessary
reversal of the negative image the plate is coated,
before the application of the emulsion, with a
resinous varnish. After exposure and develop-
ment with an alkaline developer, the image is
treated with a 5 per cent, solution of potassiimi
bichromate, which hardens the image so that it
can be developed with hot water, like a carbon
print. Thus the soluble gelatine forming the
half-tone dots or lines of the negative image is
washed away, leaving the varnish ground clear
in those parts. The plate is then dried and
immersed in methylated spirit, which dissolves
the varnish in the places uncovered by the gela-
tine, the zinc thus being left bare. A coating of
ink is next applied and attaches itself to the
bare zinc, whilst it can be developed away in
the parts which are still covered with varnish
and gelatine. The plate is then ready for the
etching process.
PEARL-ASH
Impure potassium carbonate.
PELLETONES
An early name for chemicals sold in a com-
pressed form. Pyrogallic acid was the first to
be sold in this way. The term has also been
applied, but very rarely, to the results of the
Pellet iron-printing process.
PELLET PROCESS
An iron (blue-print) process — the true cyano-
type, which gives blue Unes on a white ground
when a copy is made from a line tracing. It is
a " positive from positive " process, and unsuit-
able for use with ordinary negatives because
negative prints wotdd then be obtained. The
process is also known by various other names,
such as " Cyanofer," " Positive Ferrotype " and
" Cyanographic," and is largely used for the
reproduction of technical drawings. Pellet's own
formula has always been kept a trade secret,
but Dr. Iviesegang gives the following, which
answers quite well : —
Common salt . .144 grs. 33 g.
Tartaric acid. . . 156 ,, 36 „
Ferric chloride . . 384 ,, 88 „
Gum arable . . .2-5 oz. 275 „
Water . . . . 10 „ 1,000 ccs.
Dissolve the gum in one half of the water, the
other ingredients in the remaining hah ; mix,
apply to paper in the manner described under
the heading " Blue-print Process," and dry
quickly. An exposure, under the tracing, of
one or two minutes is sufficient in bright sun-
light. The print is developed by floating it face
downwards on a saturated solution of potassium
ferricyanide (none must reach the back of the
print) ; then wash for a minute or two in water
and immerse for about ten minutes in a clearing
solution of water 100 oz., hydrochloric acid 8 oz.,
sulphuric acid 3 oz., finally thoroughly washing
and drying.
A modem formula, due to PizzigheUi, is given
on the next page
Pellicle Processes
398 Periscope, or Periscopic Lens
A. Pure gum arable . 264 grs. 60-5 g.
Water . . . 3 oz. 300 ccs.
B. Ferric ammonio-
citrate . . 220 grs. 50 g.
Water . . . i oz. 100 ccs.
C. Ferric chloride
(crystals) . . 220 grs. 50 g.
Water . . . i oz. 100 ccs.
The gum solution does not keep well, but the
others do, if stored in the dark. For sensitising
paper take of —
Solution A (gum) . 2 J oz. 250 ccs.
B (citrate) . i „ 100 „
,, C (chloride) . 5 dims. i „
Add E to the gum, shake well, add C, and shake
again. If mixed in any other way the gum may
coagulate. The paper is coated and dried like
blue-print paper and exposed under a tracing.
Exposure is very brief (a minute to a minute and
a half in strong sunlight), the image showing
faintly. The print is developed in a solution
of I oz. of potassium ferrocyanide (yellow
prussiate of potash) in 10 oz. of water. The
lines should develop to a brilliant blue, without
any blueness in the ground, which would indicate
under-exposure ; broken and feeble lines are
due to over-exposure. The print is washed
for a few seconds in order to remove most of
the developer, and then fixed in an acid bath,
sometimes called a bleaching bath, made by
mixing J oz. of strong sulphuric or 2 oz. of hydro-
chloric acid with 20 oz. of water. The prints,
face upwards, remain in this bath for fi.ve or six
minutes, and are then thoroughly washed. A
light blue deposit is often seen upon the white
parts of the paper, but this washes off, or it
may be removed with a very soft brush or cotton-
wool. Any blue stains (or, in fact, the whole
of the image) may be removed with a solution
of about 70 grs. of potassium oxalate in i
oz. of water (4 g. in 250 ccs.), washing weU
afterwards. (For selection of suitable papers,
method of sensitising, etc., see " Blue-print
Process.")
PELLICLE PROCESSES
Early dry-plate processes in which the pre-
pared emulsion was supplied for the purpose of
melting up and coating plates at home. Ken-
nett patented a pellicle (a compound consisting
of gelatine, silver nitrate, bromide, etc.) in
November, 1873.
PENCIL, BROMIDE
A specially prepared pencil for spotting and
working-up bromide prints, for particulars of
which see " Bromide Pencils."
PENCIL. RETOUCHING (See "Retouching.")
PENTANE (Fr. and Ger., Pentane)
Synonym, amyl hydride. CjH,j. Molecular
weight, 72. A colourless, mobile liquid, obtained
from coal tar or petroleum. Boiling point,
98° to 100° P. (36-6° to 377° C). Its vapour is
extremely inflammable. It is used in the pen-
tane lamp.
PENTANE LAMP
A special form of lamp adopted by the Board
of Trade as a standard light. Ordinary coal gas
is passed over the surface of pentane, of which it
absorbs some, and thence to an Argaud burner.
If precautions are taken as to the pressure and
height of flame, it gives a very constant light
source, which, however, is open to the objection
that its spectrum is very poor in violet and
ultra-violet, and therefore not comparable to
daylight for photographic purposes. It is fre-
quently known as the Dib^-Harcourt pentane
lamp, and may be obtained of either ten or
one candle-power. It is used as a primary light
standard for photo-chemical work.
PENTATHIONIC ACID (Pr., Acide penta-
thionique ; Ger., Peniathionsdure)
H2S5O,. Molecular weight, 258. One of the
higher sulphur acids, of very little practical
interest. Lumi^e and Seyewetz suggested the
use of lead pentathionate dissolved in " hypo "
as a toning agent instead of gold; but it has
found no practical use, as the final image
consists of lead, silver, and sulphur, and is
somewhat liable to change.
PEPPERTYPE
A process of making ceramic enamels.
"PER CENT" SOLUTIONS (See "Solu-
tions, Making up.")
PERCHROMIC ACID
A term sometimes used as a synonym for
chromic acid (chromic anhydride), though the
formula for perchromic acid is written CrjO, HjO
and that of chromic acid is CrO,.
PERIOD
A term proposed by SchefEer to denote the
size of the units of screens and screen-plates. The
period for lines equal in width to the interspaces
is twice their separating distance. Thus, in the
diagram, which represents a black-and-white
screen of equal spacing, the period is shown at
i
Diagram of Black-and-white Screen
of Equal Spacing
the top by P ; the elements of the screen are
indicated at S. Any screen of which the period
is TT^ of the distance from the eye can be
resolved into separate lines. From this it is
obvious that, assuming 8 in. or 20 cm. as the
distance of normal vision, the screen period will
be tJ,- in. or J mm. Therefore the separate
unite of the screen will be invisible if they are not
larger than ^ in. or fj mm.
PERISCOPE, OR PERISCOPIC LENS
Usually an uncorrected rectilinear lens. The
earliest model was made by Steinheil, in 1865,
and consisted of two very thin meniscus lenses
mounted closely together. It embraced a very
wide angle (nearly 100°), and had an initial
intensity of //40. The modem periscopes are
Permanency
399
Perspective
usually more rapid in action, say ff^ to //ii,
but their visual and chemical foci do not coincide.
PERMANENCY
The stability of a photographic image is deter-
mined primarily by the process by which it was
produced, but it is limited by the durability of
the medium on which the image is supported.
If the image will endure without serious loss of
quaUty as long as the medium will last, it may
be regarded as permanent. In some cases the
image is almost indestructible, and therefore has
much greater durability than its support. Deteri-
oration is far more frequently the result of defec-
tive or careless working than an inherent weak-
ness of the process. Gelatine, thoroughly hard-
ened, is an enduring substance. Paper of good
quality and purity will last for hundreds of years
without other change than a mellowing of its
colour. In silver processes, imperfect fixing is
a frequent cause of fading in negatives and
prints, even the washing being of secondary im-
portance. A properly fixed and washed nega-
tive should be permanent, especially if varnished
to protect it from the atmosphere. Properly
made carbon and platinotype prints are quite
permanent ; imperfect adhesion of the carbon
tissue to its final support, or incomplete removal
of the iron salts from platinotype, win cause rapid
deterioration, although metallic platinum is
absolutely permanent. A sulphide-toned bro-
mide print should be as enduring as any photo-
graphic print, silver sulphide being a most stable
substance. An ordinary bromide print should
be as enduring as a negative, but all prints on
gelatine papers shotdd have the gelatine coating
hardened ; in its soft condition it will absorb
moisture from the air, and this is prejudicial
to its stability. Silver prints on the various
printing-out papers are generally considered to be
far from permanent ; but the trouble is invari-
ably due to imperfect work, and is not inherent
in the process. Silver prints have been kept
for nearly twenty years without showing any
change beyond the mellowing of the paper.
PERMANENT SUPPORT
The paper used for the second transfer in the
double-transfer method of the carbon process.
PERMANGANATE INTENSIFIER
A process of intensification by means of potas-
sium permanganate, described by T. Thome
Baker before the Royal Photographic Society
in 1905. In the result, the contrasts are slightly
reduced. The negative is washed and placed in
the bath given below for between one and three
minutes, during which time the image is trans-
formed into a reddish-pink, ajid apparently loses
very much in density : —
Potass, permanganate. 96 grs. 22 g.
Hydrochloric acid (con-
centrated) . . 50 mins. 10 CCS.
Water . . .10 oz. 1,000 „
It is rinsed in water and developed, preferably
by hydroquinone with caustic soda. The red
plate, when immersed in the developer, quickly
becomes brown, and finally black, the whites
again becoming perfectly clear. Finally, the
negative is washed.
PERMANGANATE REDUCER (S««" Reduc-
ing Negatives by Chemical Means.")
PERSAL
An etching mordant for copper, based o^
ferric perchloride, and obtainable in either solid
or liquid form.
PERSISTENCE OF VISION
The impression made by light upon the
retina of ih& eye does not instantly disappear
when the light is removed, but remains for an
appreciable length of time which largely depends,
upon the length of the period during which the
eye has been exposed to the light and also
upon the intensity and colour of the light. A
sentence, which is probably the first written,
having reference to persistence of vision, is con-
tained in the fourth book of " De Rerum Natura,"
by Lucretius, written about 65 B.C. He there
says : " This [perception of movement] is to be
explained in the following way : that when the
first image passes ofi, and a second is afterwards
produced in another position, the former then
seems to have changed its gesture. This we
must conceive to be done by a very rapid
process," etc. There are many simple and
familiar illustrations of the phenomenon of per-
sistence of vision. Thus, a flash of lightning
appears much longer than it really is, and a
burning stick whirled rapidly round appears to
be a circle of fire. If the seven prismatic colours
be properly arranged in their due proportions
in a circle, and this turned rapidly on a central
axis, a white surface is the result. This law of
the persistence of vision constitutes the funda-
mental basis upon which the kinematograph
exhibition rests, and the motion picture is the
finest demonstration of the facts it is possible
to conceive, though not, perhaps, so self-evident
as it becomes in the simpler appliances, such as
the so-called " Wheel of Life," or the phena-
kistoscope.
PERSPECTIVE (Fr., Perspective; Ger., Pers-'
pektive)
Assuming that lenses are free from distortion,
that they are opposite the centre of the plate,
and that the plate is vertical, all lenses will give
the same drawing or perspective from the same
standpoint. If the focal lengths vary, more or
less of the subject will be included, but such
objects as are rendered by all will be identical
in perspective.
A good deal of misapprehension has arisen
from the fact that, more often than not, lenses
include far more than can be seen clearly by the
eye from the same standpoint. If a lens of very
short focus is used on a large plate, the resulting
picture is sometimes said to have incorrect per-
spective. It is only incorrect in the sense that
the eye, placed in the same position as the lens,
is not adapted for seeing the same amount of the
subject. If the eye could include as much as
the lens, it would see precisely what the lens
renders. As, however, photographs are made
to be looked at, it is desirable to avoid this
" unnatural " perspective. This can be done
by using lenses of such focal length that the
pictures they draw approximate to those seen
by the eye. When a lens has included so much
Perspective, Aerial
400
Phenakistoscope
that the efEect to the eye appears strained and
unnatural, the exaggeration may be removed
by trimming away more or less of the outer
parts. Another cause of abnormal drawing is
the taking of what was originally a. subject at
one side of a picture and presenting it apart, as
though the lens had originally been directed
straight at it.
The point of view has a great deal to do with
the perspective or " drawing " of an object. In
every case the perspective will be accurate for
that particular viewpoint, but the resulting
arrangement will not necessarily be pleasing
simply because it is correct. So that, inasmuch
as the photographer does not have to concern
himself at all with the correctness of the " draw-
ing," he must direct his efforts to the consider-
ation of such a point of view, and the use of
such a lens, that the result shall appear natural
and pleasing to the eye.
The unnatural appearance of a wide-angle
picture is accentuated if the whole of the sub-
ject is enlarged. This is because a large print is
generally viewed at a greater distance than a
small one, whereas the shorter the focal length
of the lens employed the closer to the print
should the eye be placed for the perspective to
appear natural. The unnatural appearance is
also emphasised when some of the objects in-
cluded were comparatively close to the lens.
For example, an upright picture on a near wall
may apparently be elongated into a horizontal
one, and only assumes its natural proportions
if it can be viewed at a distance something Uke
that of the focal length of the lens used. {See
also " Perspective, False.")
PERSPECTIVE, AERIAL {See " Aerial Per-
spective.")
PERSPECTIVE, FALSE
That the photographic lens cannot render a
scene in false perspective has been stated under
the heading " Perspective," but it is there pointed
out that photographic images are not always
pleasing to the eye. The terms " false per-
spective " and " distortion " are often applied
to views which show "violent" or "sudden"
perspective, due to the use of a wide-angle lens.
Perhaps the nearest approach to false per-
spective which can be obtained in photography
is by the use of the swing back, which is often
brought into operation in order to secure depth
of definition when using a comparatively large
aperture. An example of this may be found in
an ordinary street view, in which one side of
the road is much nearer to the camera than the
other, and consequently is out of focus when the
centre is sharp. To remedy this, one side of
the swing back is pulled out, thus bringing
the near portion into focus, but of course oa a
larger scale than it would have been if the plate
had been kept at right angles to the axis of
the lens. Something similar occurs when the
vertical swing is used to obtain covering power in
portraiture, general sharpness being obtained
by tilting the back to bring the hands and knees
into focus at the cost of truthfulness.
PETROLEUM SPIRIT
A synonjrm for benzine.
PETZVAL, J.
A Vieimese mathematician who, in 1841,
devised the first " rapid " portrait lens. It was
of short focal length, worked at what was then
a large aperture, and was manufactured by
F. Voigtlander, of Vienna. It consists of a front
combination formed by a biconvex lens of crown
glass cemented to a plano-concave lens of flint
glass. The back combination is composed of
two separated lenses, a concavo-convex of flint
glass and a biconvex of crown glass. (For
illustration, see " Lens.") It enabled exposures
to be reduced to one-tenth that previously
necessary. In 1858, Petzval worked out the
" orthoscopic " lens for landscape work, but this
lens was little superior to the single landscape
lens, although the subject of great claims. {See
also " Lens.")
PHANEROGENE
A developer introduced in 1894 by Reverdin
and De la Harpe, and having a character resem-
bling that of amidol ; now of but small import-
ance.
PHANTASMOGRAPH (Fr., Phantasmo-
graphe : Ger., Phantasmograph)
An early apparatus used for printing lantern
slides, consisting of a long box or tube having
a hinged door at one end to admit light, the
negative, with the lantern plate in contact, being
placed at the opposite end. Apparently, the
object was to exclude all possible extraneous
light.
PHANTOM DEVELOPMENT
A fanciful term applied to a method of develop-
ment with a solution strong in the developing
agent but weak in alkali, so that a faint image
is first obtained, and then continuing with a
solution strong in reducer, alkali, and restrainer.
PHENAKISTOSCOPE
Synonym, stroboscope. An instrument in-
vented simultaneously, by. Plateau, of Ghent, and
Stampfer, of Vienna, in the year 1832. It has
been made in various forms, an example of
which is illustrated. Two discs are mounted
on a common spindle ; they rotate in the same
Phenakistoscope
direction and at an equal speed. One disc is
perforated with slots, through which an observer
may view a series of pictures depicted on the
inner surface of the companion disc. The
series of pictures consists of successive phases of
By p. R. Salmon, F.R.P.S.
INFLUENCE OF THE LENS ON PERSPECTIVE
The upper view, taken with a narrow-angle lens, conveys but little idea of distance
between the footbridge and the farm. In the lower view, however, taken with
a wide-angle lens and from a much nearer standpoint, the distance appears to be
greater. The bridge is of approximately the same scale in both views.
13
Phenic Acid, Phenol, etc.
401 Phosphate Plates and Papers
any object in motion ; as for example, a girl
skipping. The number of phases corresponds
to tiie number of slots in the viewing disc.
On making the discs rotate rapidly, the observer
gains a momentary view of each picture in the
series as each slot arrives opposite its respective
image. In virtue of the law of persistence of
vision, therefore, a blending of all the pictures
in the series takes place on the retina of the
eye, giving the impression of a single figure
invested with life or motion. In a modified
form of the instrument, the disc bearing the
pictures, as shown in the figure, is dispensed with,
by depicting the pictures on one side of the
slotted disc and viewing them through the slots
by reflection in a mirror ; this, indeed, was the
earliest form of the apparatus. "Phenakisto-
scope is the name given to the instrument by
Plateau, while Stampfer calls it by the name of
stroboscope. As an early instance of confusion
of terms it may be mentioned that Snell, writing
in 1835, calls the stroboscope by the name of
" Phantascope " or " Kaleidorama." Miiller, in
1846, applied this instrument for the demonstra-
tion of wave-motion, and Poppe, Savart, and
others employed it for the synthesis of other
natural motions. The first attempts at projecting
animated effects upon the lantern screen were
foimded on the type of machine here illustrated,
the disc bearing the series of pictures being on
transparent material, and light thrown first
through it, then through slots, scad finally on to
the screen by means of an objective. This was
done by Uchatius between 185 1 and 1853, but
Plateau himself had practically attacked the
same problem in 1849 in a modification of his
anorthoscope, in which apparatus he produced
four non-distorted images from a distorted
original by the introduction of compensating
lenses. Plateau placed sixteen images in pro-
gressive series roimd the margin of a glass disc,
and in front of this, in a reversed direction,
revolved, at a four times greater speed, an
opaque disc with four slots. The front of the
apparatus could be observed by many people at
once, and to prevent confusion the parts of the
disc showing the non-erect images were screened
off. It will be seen that as a slot passed the
aperture in the screen one image would be
viewed and the light then cut off while the
transparent disc turned one-sixteenth of its
diameter and the opaque one one - quarter.
The next image would then be revealed, by itg
coincidence with the slot, in the same position as
that in which the previous image was observed.
(See also "Zoetrope.")
PHENIC ACID, PHENOL, PHENYLIC
ALCOHOL, AND PHENYL BY-
DRATE
Synonyms for carbolic acid.
FHENYLAMINE
A synonym for aniline.
PHLOXINE
A variety of cosine.
PHOSPHATE PLATES AND PAPERS
Plates or papers coated with an, emulsion in
which silver phosphate is practically the light-
sensitive salt The light-sensitiveness of this
26
substance was discovered by Stromeyer about
1830, but Fyfe, about nine years later, was the
first to use it for printing out, and he salted
his paper with sodium phosphate, sensitised on
silver nitrate and again floated on sodium
phosphate. He also used an ammoniacal solu-
tion of silver phosphate, and recommended
merely washing with water or ammonia for
fixing.
Many years later, Lyte used this salt for
albumenised paper and employed nitric acid for
fixing; later (published, 1856) he used a mix-
ture of sodium phosphate and tartrate, Rochelle
salts in sugar of m^ and gelatine, and stated
that there was no precipitate formed, thus
antedating the later use by Meyer of silver
phosphate dissolved in an organic acid. It was
also tried by Himt and Hardwich. Meyer
{Brit. Journ. Phot., 1899 and 1900) precipitated
his phosphate and dissolved it by the addition
of an organic acid, such as citric, tartaric, acetic,
etc., and used it with and without a vehicle on
paper. Silver phosphate alone or with excess
of silver nitrate, however, gives an exceedingly
long range of gradation, so that unless extremely
vigorous negatives are used the prints are very
fiat, wanting in intensity, and without any
whites. Valenta, in 1900, took up the study of
the subject, and suggested a collodion emulsion
by ad(£ng silver nitrate to phosphoric acid
collodion, but this also possessed the same fault,
though to a less degree. Further experiments
were made to increase the intensity and reduce
the gradation by mixing it with varying propor-
tions of collodio-chloride' emulsion, or by the
addition of uranyl and cupric chlorides ; and
finally, in 1905, he gave a satisfactory working
formula, which can not only be printed out, but
also physically developed : —
Raw collodion (3-3 J %) 20 oz. 1,500 ccs.
Phosphoric acid (20%) 128 mins. 20 „
Mix, and add —
Citric acid
Alcohol .
. 384 grs.
, 640 mins.
60 g.
100 ccs.
Then add —
Silver nitrate
(powdered) . 384-512 grs. 60-80 g.
Liquor ammoniae (-880) q.s. q.s.
Enough ammonia should be used to form a
perfectly clear solution, and then —
Absolute alcohol . 3i oz. 250 ccs.
added, the mixture being added in small quan-
tities at a time to the acid collodion, shaking
all the time. Then add —
Ether ..-34 °^-
Glycerine alcohol ( I : i) 128 mins.
This may be coated in the usual way on matt
or glossy baryta paper. It may be fully printed
out or only until Oie outlines of the image are
just seen, and should then be developed with
the following: —
Metol
Glacial acetic acid
Distilled water .
For use, 40 drops of this should be diluted with
250 ccs.
20 „
155 grs.
10 oz.
35-5 g-
i,ono ccs.
10 „
1,000 „
Phosphates
402
Photo Salts
3i oz. or 100 CCS. of water. The colour of the
prints thus obtained varies from sepia to brown-
ish black or purple.
Recently, several makers have placed phos-
phate papers on the market which may be
treated as outlined above.
PHOSPHATES (Pr., Phosphates: Ger., Phos-
phats)
Salts prepared by the combination of a metal
with phosphoric acid. There are generally three
forms: the mono- or acid phosphate, such as
sodium orthophosphate, NaHjPO, HjO ; the
di-orthophosphate, Na^HPOj laHjO ; and the
tri-orthophosphate, NajPOi 12H2O ; these are
obviously formed by the replacement of one,
two, or three hydrogen atoms respectively of
orthophosphoric acid H3PO4.
PHOSPHORESCENCE
The researches of T. A. Vaughton and others
seem to have demonstrated that the sensitive
silver salts, such as the bromide, iodide and
chloride, if precipitated and kept in the dark,
have the property, under certain conditions, of
emitting light in degrees proportionate to their
sensitiveness. In a red light, an unexposed
bromide plate is placed in an ordinary p3TO-soda
developing solution for ten minutes, removed
and washed. Next, in total darkness, plunge it
suddenly into a dish containing a saturated
solution of aluminium sulphate, and the plate
and the solution will immediately become
phosphorescent, the light dying away in the
course of a minute or two. On pouring the
solution into a. bottle, the whole body of the
liquid becomes luminous and remains so for
several minutes, the light being increased by
shaking. K half the plate is exposed to the
action of white light for a second before treating
with the pyro-soda solution, that half remains
dark and emits no Ught when the plate is put
into the aluminium sulphate. If the plate is
given a short exposure in the camera, and
developed and put into the aluminium sul-
phate solution, the image will appear dark on a
phosphorescent background. Precipitated silver
bromide (which has been kept a few days in
a corked test-tube in the dark), contained in
a porcelain dish and exposed to a bright-red
light while adding the pyro-soda solution,
appears black, but on pouring oflf the solution the
precipitate gradually assumes a bright green
appearance under the red Ught, while in white
light it appears dark grey or black.
As the result of a series of supplementary
experiments, H. Edwards has stated that not
only the plate itself, but also the used developer,
will give phosphorescence with aliuu solution.
Quinine sulphate or hydrochloride is not luminous
when the used developer is added, but becomes so
if a few drops of sulphuric acid are subsequently
introduced. The experiment may be still more
easily made by mixing potassium bromide and
silver nitrate solutions in dim gaslight, decanting,
and shaking up the resulting silver bromide with
pjrro-soda. A red liquid results which gives a
luminous effect when poured into alum solution
or dilute stilphuiic add.
Dr. J. Precht explains the phenomenon of
phosphorescence as follows: (i) The alkaline
pyiogallic acid solution liberates oxygen on the
addition of acids, by which the sodium sulphite
is oxidised to sulphate, this oxidation being
accompanied by phosphorescence. (2) The acid
pyro solution suddenly takes up oxygen on the
addition of sodiiun sulphite and soda, and also
this oxidation is accompanied by phosphores-
cence. Thus easily reducible substances pro-
duce phosphorescence with an alkaline pyro solu-
tion.
Potassium permanganate, for instance, is
phosphorescent when a mixture of pyrogallic
acid and soda is added to it. It is assumed that
an intermediary product is formed of alkaline
pyro solution and oxygen, which gives off again
the oxygen only on the addition of acid, and that
the then liberated oxygen gives rise to phos-
phorescence by combining itself with the sulphite
to form sulphate. Phosphorescence is liable to
fog gelatine plates should these retain traces of
the pyro developer, and therefore, in practice,
such plates should not pass from the pyro
developer into a solution of alum or of citric
acid, or, indeed, to any other solution, before the
last traces of the developer have been removed
from it by careful washing. Exceedingly small
quantities of pyro, less than -005 per cent.,
are sufficient in some cases to cause a bright
phosphorescence of the film.
PHOSPHORESCENT PHOTOGRAPHS {See
" Luminous Photographs.")
PHOSPHORIC ACID (Fr., Acide phosphorique;
Ger., Phosphorsdure)
Synonym, orthophosphoric acid. HgPO,.
Molecular weight, 98, Solubilities, miscible in all
proportions with water and alcohol. Obtained
from phosphorus by oxidation. It occurs in a
crystalline state, and is then nothing else but
phosphoric acid; but usually the so-called
syrupy " acid is met with, and this contains
8; per cent, of phosphoric acid, and has the
speafic gravity of i -725. Another acid, of specific
gravity 1-347, contains 50 per cent.; and the
dilute, of specific gravity i-o$y, contains 10 per
cent. A 20 per cent, solution, having a specific
gravity of i-i2, is the one usually employed for
acidulating the platiniun toning baths.
In process work, phosphoric add is used in
photo-zincography as an addition to the gum
and nutgalls solution used for damping the plate
before rolling-up with ink, its object being to
preserve the deanliness of the white parts of the
plate. Also it is used in preparing aluminium
for lithographic printing.
PHOTO SALTS
A name given first by Carey Lea to the coloured
reduction product formed by the action of light
on silver chloride, and later applied generally to
the coloured salts obtained chemically by Lea,
who considered the coloured reduction product
to be a. chemical combination of silver chloride
AgCl and silver sub chloride AgjD. Hodgkin-
son, on the other hand, ascribed to it the formula
AgaCljAgjO, as he considered that the ever-
present aqueous vapour or water played an
iaiportant part in its formation. According to
the latest theories, this product is a solid solution
of AgjCl in AgCl. Lea prepared the dark-
Photo-algraphy
403
Photo-corrector
coloured products by the action of an alkaline
hypochlorite or ferric chloride on finely divided
metallic silver, by partial decomposition of
silver oxide by heat and treatment with hydro-
chloric acid, by reducing silver chloride dissolved
in ammonia by ferrous sulphate, or by the action
of cuprous chloride on silver nitrate, etc. The
colour of these photochlorides varied from purple
to golden or rose red, and they were then capable
of assuming the colours of the spectrum or any
coloured objects to which they were exposed.
These salts are of great interest, as no doubt
they play an important part in the formation
of the colours in the Seebeck or Poitevin pro-
cesses of heliochromy on paper. Photo-bromide
and photo-iodide have also been prepared, but
they are not so colour-sensitive as the photo-
chloride.
PHOTO-ALGRAPHY
The application of photo-mechanical repro-
duction processes to aluminium lithographic
printing.
PHOTO-AQUARELL
Photogravure printing in colours by inking
the plate locally with tampons, masks being
used to indicate the portion to be inked.
The term has also been applied to a litho-
graphic process of printing in colours from three
etched stones.
Also a process of making coloured photographs
on Whatman paper.
PHOTO-AQUATINT
A modification of the photogravure process,
•worked out by Thos. Huson, R.I., and fully
described in his book entitled " Photo Aquatint."
The principal difference between this process
and ordinary photogravure is that, instead of
using different densities of etching solution,
practically only one strength is used, and the
negative, transparency, and carbon resist have
accordingly to be adapted to the process.
PHOTO-AUTOCOPYIST {See "Autocopyist.")
PHOTO-AUTOGRAPHY
A process of printing from lithographic stones
on etched plates in colour, the image being applied
by photo-mechanical means.
PHOTO-BIOSCOPE
An instrument constructed on the lines of the
thaumatrope, and invented by Chevalier Bonelli,
of Milan, in 1867. By its means both stereo-
scopic and kinematographic effects could be pro-
duced.
PHOTO-CERAMICS (See " Ceramic Process.")
PHOTO-CHROMATIC
One of the terms applied to the process of
photography in natural colours.
PHOTO-CHROMATIC PRINTING
A process for printing photographically upon
textile fabrics, the invention of R. Smith, of
Blackford. The fabric is treated with a sensitive
solution, and is wound off a roller, passing under
a glass plate on which the design has been drawn ;
the material is thus exposed one section at a
time, then passing through guiding rollers to a
fixing trough, finaily being washed. According
to the fixing solution used, various colours are
obtained. To produce a design pale blue on a
white ground, or white on a blue ground, solu-
tions of the citrate or tartrate of iron with potas-
sium ferrocyanide are used. Brown or buff
tints are obtained with a solution of potassium
bichromate. The fabric is afterwards plunged
in a dilute solution of sulphuric acid.
PHOTOCHROME PROCESS
A method of lithographic colour printing
worked out and operated by the firm of Orell
Pussli, Zurich. It is believed to be a process
of printing a bitumen film on stone imder a
continuous tone negative, and treating in such
a way that a reticulated grain image is formed.
PHOTOCHROMOSCOPE
A name by which the kromskop was at one
time known.
PHOTOCHRONOGRAPHY
Chrono-photography, which is described under
its own heading.
PHOTO-COLLOGRAPH
A term applied to any kind of collotype
print, especially to prints made by Albert's
photo-lithographic process.
PHOTO-COLLOGRAPHIC PROCESS
A sjoionym for collotype, but it has been more
particularly used by the inventor of the Sinop
photo-collographic process.
PHOTO-COLLOTYPE
A synonym for collotype or photo-coUography .
PHOTO-CORRECTOR
An arrangement for preventing distortion in
portraits, invented by H. Van der Weyde in
1892. It consists in the employment of an
additional lens immediately in front of the
plate, as shown in the diagram. The dotted
Two Forms of Photo-corrector
lines indicate light rays proceeding from the
lens and falling upon the plate. I^ocal reduction
of size is produced by placing a plano-convex
lens close to the plate and covering the part to
be reduced. Used as at A, a halo would appear
on the plate round the lens, and to overcome
the difficulty the lens is embedded in a sheet
of glass (see B) as large as, or larger than, the
plate. By using lenses of different shapes and
sizes — plano-concave and plano-convex — it is
possible to produce a variety of effects. The
accessory has not come into general use.
Photo-crayon
404
Photoglyphic Engraving
PHOTO-CRAYON
A style of portrait at one time poptilar ; origin-
ated by Sarony, of Scarborough, in 1870. A
transparency was made upon glass, finished in
the usual way, and backed up with white paper
on which crayon colours had been placed, the
effect being that of a coloured photograph.
PHOTO -DYEING (Sea " Phototincture.")
PHOTO-ELECTRICITY (Pr., Photo-ilectriciU ;
Ger., Photo-elektriziMt)
Electrical phenomena excited by the action of
light. The converse — optical phenomena set up
by electrical action — are classified as belonging
to electro-optics. Modem research leads to the
conclusion that light and electricity are identical,
a fact first asserted in 1864 by Clerk-Maxwell,
according to whom light waves are due to
magnetic and electric strains in the ether that
pervades space. Maxwell prophesied that, imder
suitable conditions, magnetic waves could be
propagated through space with the same speed
as those of light. This was experimentally veri-
fied by Heinrich Rudolph Hertz, in 1888, who
proved the existence of electrical waves, of
similar velocity to those of light, and, although
invisible, capable likewise of reflection, refrac-
tion, diffraction and polarisation. These waves
were turned to practical account in G. Marconi's
system of wireless telegraphy (1895). In the
same year Konrad Wilhelm ROntgen showed
that invisible electric rays of another kind — the
X-rays — were able to penetrate opaque sub-
stances, forming an image or shadow on a
photographic plate. A familiar instance of an
electrical effect influenced by light is afforded
by the behaviour of selenium, the resistance of
which to the passage of an electric current is
greatly reduced when light impinges on it — a
fact utiUsed for the telegraphic transmission of
photographs.
PHOTO - ELECTROGRAPH (Fr., Photo-ilec-
trographe ; Get., Photoelektrograph)
An apparatus used by meteorologists to
obtain a photographic record of variations in
the electrical condition of the atmosphere, as
indicated by the movements of a sensitive gold-
leaf electroscope.
PHOTO-ELECTROTYPE (See " Electro-
phototypy" and " Electro typing.")
PHOTO - ENGRAVING, AND PHOTO -
ETCHING
Synonymous terms applied generally to line
and half-tone etching ; fully discussed under
many separate headings.
PHOTO-FILIGRANE (See " Filigrane.")
PHOTO-GALVANOGRAPHY (See "Gal-
vanography, Photographic")
PHOTOGASTROSCOPE (Pr., Photogastro-
scope: Ger., Photogastroskop)
An instrument employed in surgery for
photographing the interior of the stomach, by
means of a tube introduced down the throat
and having a small electric lamp at one end
to furnish the necessary illumination. Mirrors
are utilised to transmit the image to the camera,
an air supply tube inflates the stomach, and the
lamp is kept cool by a water-circulating device.
PHOTOGENE
The name given by Gaudin in i86i to a sensi-
tive preparation made by him for coating upon
glass or paper. " The name," he stated in
La LumUre (April 15, 1861), "can be applied
to any sensitive compound containing iodide
of silver with excess of free nitrate of silver."
He prepared photogene by dissolving silver
nitrate in hot alcohol with a little water, adding
it to collodion, and finally adding a few drops
of iodised collodion. It was not satisfactory.
The word was also used by J. Moule to describe
a pyrotechnic compound for burning in his lamp
(patented February 8, 1857) for the purpose of
teking photographs at night. The powder was
composed of pure and well dried potassium
nitrate 1 5 parts, flowers of sulphur 5 parts, pow-
dered antimony sulphuret i part, and powdered
red orplment 2 parts. After well mixing, the
powder was passed through a fine sieve.
PHOTOGENIC DRAWING, OR PHOTO-
GENY
The name given by Fox Talbot in 1835 t° ^^
results of his early experiments, which consisted
in coating paper or white leather with a silver
nitrate solution and obtaining thereon, by the
action of light, images of leaves, etc. Talbot
communicated his experiments and showed ex-
amples of his photogenic drawings to the Royal
Soaety, on January 31, 1839, six months prior
to the pubUcation of Daguerre's process. The
following description of the process of producing
photogenic paper is adapted from his own words.
Paper of a good, firm quaUty and smooth sur-
face is dipped into a weak solution of common
salt and water (25 grs. to the ounce) and wiped
dry, by which means the salt is uniformly dis-
tributed. A solution of silver nitrate is spread
on one surface only, and dried before a fire. This
paper, if properly made, is suitable for all photo-
genic purposes. A sheet thus prepared is washed
with a saturated solution of salt and then dried.
It will be formd, especially if the paper is kept
for some weeks before the trial is made, that its
sensibility is greatly diminished, and in some
cases is quite extinct. But if it is again washed
liberally with the solution of silver, it becomes
again sensitive to light, and even more so than
it was at first. In this way, by alternately
washing the paper with salt and silver and drying,
Talbot succeeded in increasing its sensibility to
a degree that is requisite for receiving the images
of the camera obscura. The prints were fixed
in a strong solution of common salt, or in a solu-
tion of potassium bromide or iodide. Later
improvements resulted in the introduction of
the calotype process (which see).
PHOTOGLYPHIC ENGRAVING, OR
PHOTOGLYPHY
A process of photogravure invented by Pox
Talbot, but now entirely superseded by the
Talbot-Klic process. The metal plate was coated
with gelatine, sensitised with potassium bichrom-
ate, and exposed to light under a negative. It
Photoglyptie
405
Photo-lithographic Paper
was then dusted with finely powdered copal
resin and warmed until this melted. When cold,
the plate was treated with a suitable etching
flviid, which soaked through those portions of
the film unacted upon or only partially acted
upon by light, attacking the plate underneath
in proportion to the varying thickness and hard-
ness of the gelatine.
PHOTOGLYPTIE
The French name given to the Woodburytype
process.
PHOTOGRAM
By some people considered the correct name
for a photographic picture of any kind. They
contend that graph " is a termination in-
dicating the active verb, whereas " gram "
indicates the noun. For example, " telegraph,"
to write at a distance ; " telegram," the writing
made at a distance. Several attempts have been
made to oust the older term, but with small
success.
PHOTOGRAMMETRY (Fr., PhotogrammStrie,
MMrophotographie : Ger., Photogrammetrie,
Messbildverfahrung)
The science of measuring and surveying by
the aid of photography. The camera is exten-
sively used in the preparation of maps and for
other topographical purposes. With a high-
class lens free from distortion, a rigid camera
and stand, and a fixed vertical position of the
plate with regard to the lens, the size and arrange-
ment of objects in the negative will bear a con-
stant ratio to those of the original subject.
If two or more photographs are taken, for in-
stance, of any prominent building or natural
feature from different standpoints, noticing
carefully the part of the compass to which the
camera is directed in each case, it is possible
by means of the various points appearing in
the resulting negatives or prints, and by a
series of triangulations, to draw an accurate
dimensioned plan. The camera for photo-
grammetric purposes is generally provided with
levelling screws and a graduated drctdar scale
at the base, while four fixed points are arranged
at the back to register on each plate exposed the
position of the horizontal line and of the lens
axis. It is usual, also, for a magnetic compass
and a theodolite to be attached to the camera.
The subject is too large to treat otherwise than
briefly, but a few of the simpler formulae used in
photogrammetry may be quoted. It is assumed
that tiie lens is at its principal focal distance
from the plate and that the camera back is
strictly vertical. Let O «= height of object, I =
height of image in negative or print, F = focal
length of lens, and D = distance of object from
lens, measiiTed from nodal point. Then, to find
height of object, O = ^=- The width may be
found in the same way, provided the plane of
the object is known to be parallel to the focusing
screen. If the size of the object is known the
OF
distance may be calculated, D = —r^-
The distance and size of an inaccessible
object may be found by taking two photographs
at a measured distance apart, but each in Une
with the object — i.e. the latter should be central
in both negatives. The distance apart may be
measured either from the nodal point -of the
lens, or more conveniently from the focusing
screen. Let S = the distance between the
two standpoints, and Ij, Ij = the heights of
the two images in the photographs, then O ■»
S X Ii X Ij. i.., TN OP OF.
Fx(i:-ij' ^""'^ ^ = IT' °"^ 17
PHOTOGRANULOTYPE
An American process of graining an ordinary
photographic negative by the application of the
air brush, so that a granular negative image was
obtained for printing on stone or metal.
PHOTOGRAPHY
The art of obtaining images by the chemical
agency of light upoii sensitive surfaces. The
word itself cannot be traced farther back in
English Uterature than the title of a paper read
before the Royal Society by Sir John Herschel
on March 14, 1839. Derived from (^wTflj,
genitive of <paos or ^«s, "light," and ypi<t>a,
" I draw." Hermann Schnauss, however, states
that Nicfephore Niepce was the first who used
the word photography, who indeed created it.
On May 9, 18 16, Niepce wrote to his brother
Gaude that it is not necessary that there
should be bright sunshine when photographing
objects out of doors.
PHOTOGRAVURE (Ger. aniTt., Heliogravure)
The process of photogravure as now generally
understood and practised is that known as the
Talbot-Khc process. Talbot's original method
{see " Photoglyphic Engraving ") with modifica-
tions is still worked in France. The following
is an outline of the photogravure process : — A
well-cleaned and polished copper plate is put
into a dusting box, in which it receives a deposit
of a fine dust of asphaltum or resin, which is next
fixed by heating. A piece of carbon tissue is
printed under a transparency and transferred to
the grained copper plate on which the image is
devdoped, and, when dry, etched with ferric
perchloride in successive baths of varying degrees
of strength (from 43° down to about 33° Beaum6).
The weaker solutions penetrate the gelatine the
most easily. After clearing off the resist the
plate is seen to be etched in different depths in
proportion to the tones of the picture, the
shadows being deepest and consequently holding
most ink. The plate is inked and printed from
in the usual copper-plate maimer.
PHOTO-HELIOGRAPH
A combination of telescope and camera used
in solar photography. The exposure is made by
the passage of a narrow slit.
PHOTOHYALOGRAPHY AND PHOTO-
HYALOTYPY
Processes based on the transfer of the collo-
type image, described by G. Scamoni, of St.
Petersburg. (See also " Hyalography.")
PHOTO - LITHOGRAPHIC TRANSFER
PAPER
Paper coated with hardened gelatine for sensi-
tising with potassium bichromate in order that
Photo-lithography
406
Photomicrography
it may be printed vinder a negative to form a
transfer. Ready-made photo-lithographic papers
of excellent quality are obtainable, those of Jaff^,
Albert, and Husnik beir.g among the best known,
and it does not pay the worker to prepare his
own paper. The double transfer paper used in
carbon printing answers well for transfers.
PHOTO-LITHOGRAPHY
Under this term is included a large number
of processes which may be classified into two
leading divisions — ^namely, transfer processes
and direct processes, both of which may be sub-
divided into line and half-tone.
The transfer processes are all based on the
principle that light acting on a bichromatised
colloid, such as gelatine, will render the lines
or other elements of the image capable of attract-
ing greasy ink, whilst the other parts will repel it.
The simplest method is to coat a good tough
paper, such as bankpost, with gelatine, and after
drying immerse it in a bath of potassium bichrom-
ate (usually about 5 per cent, strength). "When
dry, this sensitised paper is exposed under a line
negative for a sufficient time. The paper is then
thinly coated with transfer ink applied with a
roller. On immersion in water, and by gentle
rubbing with a tuft of cotton-wool, the surplus
ink comes off, leaving the image in lines of ink.
The print is dried, and is then ready for trans-
ferring to stone or metal. Por half-tone work
the paper may be exposed under a negative
made through a ruled screen, or the half-tone
may be formed by means of a reticulated graiu,
as in the papyrotint process.
In the direct process the stone or metal
(usually zinc) is prepared with a sensitised coat-
ing of bichromatised glue, gelatine, or jilbumen,
or with bitumen, exposed under either a line or
half-tone negative, inked over if a bichromatised
film, and developed with water ; if a bitumen
film it need not be inked, and it is developed
with turpentine. The bitumen attracts the
greasy ink so that the image can be rolled up
for printing. To obtain grained half-tone
images, various ingredients are added to the
colloid coating, as in the papyrotint or Pretsch
processes ; or, in the case of bitumen, the image
may be made to reticulate by dissolving the
bitumen in a mixture of ether and alcohol.
In several processes of photo-lithography the
image is prepared on a glass or metal plate similar
to collotype, and transfers are pulled therefrom
for re-transfer to stone or metal.
PHOTO-LITHOPHANE
The production of photographic transparencies
from semi-transparent material (porcelain), the
lights and shades of which depend on the greater
or lesser thickness of the material employed. The
photographic part in this process consists in the
production of a swelled chrome-gelatine relief
from a photographic negative, and a plaster-of-
paris cast from it. The rest is done by the porce-
lain worker.
PHOTO-MECHANICAL PROCESSES (Pr.,
Procidis photomScaniques ; Ger., Pfioto-
mechanische Verfahrungen)
A term, applied to all processes in which the
action of light upon chemical substances is the
means of preparing printing surfaces, from which
many impressions can be made without any
further assistance from light action. Generally,
the photographic image is made capable of giving
impressions in greasy inks by typographic or
lithographic methods, but the term also includes
Woodburytype, although the printing in this
case is not done with greasy inks. Particulars
of photo-mechanical processes wiU be found
under the headings of " Collotype,'' " Photo-
lithography," " Photogravure," " Half - tone
Process," etc.
PHOTO-METALLOGRAPHY
A term applied to processes of printing from
photo-mechanical images on zinc or aluminium
by the lithographic method.
PHOTOMETER (Fr., PhotomHre ; Ger., Photo-
meter)
An instrument for comparing the intensity of
two light sources. (See " Sensi tome try.")
PHOTOMETRY {See " Sensitometry.")
PHOTO-MEZZOTINT
A name given to the gum-bichromate process
of Maskell and Demachy.
PHOTO-MEZZOTYPE
A fancy name for one of the early half-tone
processes.
PHOTOMICROGRAPHY
The photography of minute objects by the aid
of the microscope. The essential apparatus in-
cludes microscope and stand, lenses and camera,
and it may be said that many kinds of hand
cameras can be utilised. A stage or base-
board is necessary to receive the microscope and
camera (with lens removed), which are placed in
position on the stage as shown at A. A small
platform is fixed on the stage to bring the lens
Arrangement for Photomicrography
flange of the camera, a, to the level of the micro-
scope tube when the latter is brought over to a
horizontal position. If a fairly long camera
extension is used, the fine adjustment of the
microscope will be out of reach of the hand ;
consequently a connecting-rod will be necessary
for focusing purposes. A brass rod, B, fitted with
a grooved whed at one end and a milled head
disc at the other may be fixed on the camera
stage ; the grooved wheel, F, is placed immediately
Photomicrography
407
Photomicrography
beneath tlie fine adjustment of the microscope
and the milled head disc, h, below the focusing
screen of the camera. A band or small strap G is
placed over the groove of the fine adjustment
of the microscope, and passed round the groove
in the connecting-rod wheel. The image can
then be focused by turning the milled head below
the focusing screen. If toe camera has a short
bellows extension, no connecting-rod will be
necessary, as the fine adjustment can be reached
by the hand while the operator examines the
image on the focusing screen. When transparent
objects are photographed the light is placed
behind the camera stage in a direct line with the
objective and focusing screen. For low power
work, an oil lamp, E, is a convenient illuminant.
With high powers, the Nemst, incandescent gas,
or acetylene lamp is preferable. As the mirror
is not used, some kind of condenser is necessary
to focus the light on the object. If no sub-stage
condenser, d, is available, a bull's-eye condenser
will answer the purpose.
For experimental purposes some well-mounted
object with which the operator is perfectly
familiar should be selected. Failing this, the wing
of a house fly can be mounted (dry), and being
very transparent, with opaque lines, is easily
focused. An objective of low power should be
used. The object is placed on the stage and
focused ; the eyepiece and draw-tube are
removed, and the microscope brought over to a
horizontal position. The inside of tiie tube must
be lined with black paper, or the light reflected
from the microscope tube will be found to give
a flare spot on the plate. The microscope is now
placed in position on the baseboard with the
body-tube, B, projecting into the lens flange of the
camera, the camera lens of course being removed.
The photograph can be taken with the eyepiece
in the microscope, but the consequent loss of
light is considerable, and the difficulty of focusing
proportionately increased. The lamp is placed
in position behind the microscope, and the light
is focused by the condenser on to the object.
When the focusing screen is examined no
image of the object may be visible. The coarse
adjustment is turned slowly to bring the objective
nearer the object, and, when the image appears,
sharp focus is obtained by means of the fine
adjustment. If the lamp and condenser are
properly arranged, the image will appear brightly
and evenly lighted. If there is any unevenness
of Ulumination, the position of lamp and con-
denser must be readjusted.
When the operations of arranging the illumina-
tion and focusing are completed, a dry plate is
inserted in the dark-slide and a trial exposure
made. No definite rules can be given for calcu-
lating exposure, but the following data of a
trial exposure wiU assist the beginner in form-
ing an estimate : —
Object photographed, head of gnat larva, clear
specimen, mounted in Canada balsam ; oil-lamp,
|-in. wick ; objective, § in. ; bull's-eye condenser,
I j^ in. diameter ; distance of object from focus-
ing screen, 26 in. ; distance of flame from object
7 in. ; rapid plate ; exposure, 10 seconds.
For photomicrography with high powers, a
sub-stage condenser, a more powerful light, and
for critical work a projection eyepiece are neces-
sary. Coloxxr filters, C, are often of great assistance
in photomicrography, especially when, as some-
times happens, the visual and actinic foci of the
objective do not coincide. In the older types of
objectives this fault was not uncommon. A
yellow screen will overcome this difficulty, but
except orthochromatic plates are used, the
exposure is unduly prolonged. Objects which
have been stained with a blue or violet dye
should always be photographed with a yellow
screen. When opaque objects are to be photo-
graphed, unless the objective is furnished with
a Lieberkiihn, the light must be placed at the
side of the object, upon which it is focused
by means of a bull's-eye condenser. A strong
light is necessary, and unless a Nemst or incan-
descent gas lamp is available magnesium wire
should be used.
A Lieberkiihn is a parabolic mirror, named
after the inventor, for illuminating opaque ob-
jects. It is fitted on to the objective, which
projects through the centre of the mirror.
The approximate comparative actinic values
of the various illuminants are as follow : — Oil
lamp, j-in. wick, i ; incandescent gas (new
mantle), 15; Nemst, 20; acetylene, 30; arc
lamp, 5 amps., 1,000 ; magnesium ribbon, 1,500.
The oil lamp is somewhat feeble, and its yellow
colour is a serious drawback. Incandescent gas
is convenient, but in critical work some difficulty
is caused by the pattern of the mantle. Acety-
lene gas gives perhaps the best all-round light,
but the trouble of manufacturing the gas before
beginning work militates against its popularity.
The arc lamp is excellent ; smaU arc lamps for
use with an ordinary 16 c.-p. plug and switch
are now available. The Nemst lamp, with its
small bright flame, gives an excellent light, but
the filaments are fragile and are liable to give a
troublesome image. The metallic filament
electric lamp gives a fairly actinic light, but the
long zigzag filament is a serious objection to its
use. The use of groimd glass or tissue paper to
obviate the formation of a pattern is not satis-
factory, as direct rays from a small illimiinating
area are essential.
Transparent objects or sections are photo-
graphed by transmitted light ; opaque objects
by refiected light. In the former case the
source of Ught is placed in a direct line with the
objective and object, and the hght, brought to
a focus by some form of condenser, passes
through the object into the lens. In the photo-
micrography of opaque objects the light is con-
centrated by means of mirrors or condensers
upon the object, and is reflected by the object
into the lens. Opaque objects require a much
more powerfrd illiuninant than transparent ones,
and tiie difficulty of obtaining sufficient light
renders the work extremely difficult. A method
of illuminating opaque objects which is especially
useful for high powers is by means of a cover-
glass fixed diagonally inside the tube of the
microscope. The light reaches the cover-glass
through an aperture in the side of the body tube,
and is deflected, from the surface of the glass,
through the objective to the object, which
reflects it through the microscope to the
camera. Thus tiie light has to pass twice
through the objective, in this way producing
much scattered light, which mars the brilliancy
of the image. J. I. P.
Photophane
408
Photostone
PHOTOPHANE (Pr. and Ger., Photophane)
A fancy name given to the collotype process
as worked by a London firm.
PHOTOPLASTIC
An electrotype obtained from a chromated
gelatine photo-relief. (See " Galvanography,
Photographic")
PHOTOPOLYGRAPHY
A process resembling pinatype, but much
older, having been described in 1897. A glazed
paper is coated with gelatine, sensitised in a
bidiromate bath, dried, printed imder a negative,
and washed. The outstanding relief is stained
with methyl violet, and the dyed image trans-
ferred by pressing into contact with ordinary
paper.
PHOTOTOPOGRAVURE
The reproduction of maps by photographic
means.
PHOTORADIERUNG
A German name for a process of coating a
negative with a yellow varnish and scratching,
with an artist's etching needle, through the film
in lines which interpret the tones of the photo-
graph. The numerous processes of this kind put
forward may be classified under the term of
" factitious negatives."
PHOTO-RELIEF ENGRAVING
A term given to processes in which, by photo-
graphy and subsequent manipulation, a printing
surface is obtained in which the parts receiving
ink stand up in relief like type characters. Thus
line and half-tone etched blocks may be said to
be photo-relief engravings, but the term is pro-
perly applied to processes of making a hardened
gelatine relief which may be printed from as in
the Pretsch process, Dallas process, Husnik's
Leimtype, and the swelled-gelatine process. The
Woodburytype process is often termed a photo-
relief one, although here the image itself is in
relief, the printing block being an intaglio one.
The aerograph process may be correctly de-
scribed as photo-relief engraving.
PHOTO-ROTOSCOPE
An instrument on the old peep-show principle,
for enabling a number of persons simultaneously
to view animated photographs in daylight.
Also the name of a particular make of kine-
matograph machine invented by W. C. Hughes.
PHOTO-SCULPTURE
A term which had its origin in 1863, when the
sculptor Willdme, of Paris, patented his process
and set up a studio for the work. He photo-
graphed his models with a number of cameras
placed at the sides and top of a kind of building
having a cupola ; and he afterwards utilised the
photographs in constructing the model, employ-
ing pantographs in order to facilitate his work.
Poetschke, in 1891, improved the process, and
Selke, a year later, substituted for the ordinary
photographic apparatus the kinematograph, and
projected on to the sitter a shadow which
advanced progressively in the direction of the
kinematographic camera. In this manner, ac-
cording to Carlo Baese, the apparatus registered
a considerable number of silhouettes correspond-
ing to the number of parallel planes in the model.
Each of these negatives, about 500 in all, had to
be enlarged separately upon bromide paper, and
each was then pasted upon card and cut out
with scissors. When these silhouettes had been
cut into sections, they were stuck one over the
other, and so built up, it is said, to form the
portrait, but exactly how it was done has not
yet been made clear. The use of bichromated
gelatine (discovered in 185 1) is more satisfactory.
(See "Relief, Photographs in.")
Por artificial reliefs — tiiat is, prints that appear
to be in relief — see "Plastic Photographs." Carlo
Baese, who has paid particular attention to the
production of portraits in the form of medallions,
works on the lines described imder the first
named heading, and secures better modelled
effects than are possible ia. the ordinary way,
by the use of an optical lantern and mirrors, by
which he projects and reflects light upon certain
parts of tiie face which it is desired to show in
high relief. His process was described before
the Royal Photographic Society, on October 1 1 ,
1910, and by its means wonderful results are
obtainable.
The term " photo-sculpture " is also applied
to a kind of trick photography. A sketch of a
bust without the head is made, natural size, on
a sheet of cardboard, which is then cut out or,
preferably, a papier mSch6 arrangement may
be purchased ready for use, and placed on a
pedestal of a convenient height, the sitter being
posed behind it in such a way that the Uving
head " sits " realistically. A photograph is next
taken. Parts of the image that are not required
may be scraped from the dry negative, or a
print is made, blocked out with black or red
water-colour paiat, and copied in the camera.
Another method is to cover the parts (arms, etc.)
of the figure not required with a black cloth.
The background should be quite black, and it
may be necessary to powder the hair, eyebrows,
etc., to give them, in the photograph, the appear-
ance of stone.
PHOTO-SENSITIVE
A term applied to a substance that is sensitive
to Ught.
PHOTO-SPECTROSCOPY (See "Spectro-
photography.")
PHOTO-STEREOTYPE
A stereotype made from a plaster cast taken
from a gelatine relief. (See " Swelled Gelatine
Process" and "Wash-out Gelatine Process.")
The term has also been applied in America
to a block made by reproducing a drawing
obtained from a photograph by the bleaching-out
process.
PHOTOSTONE
A photo-chromo-lithographic process worked
by an English company some years ago. It ia
understood that transfers were pulled from a
collotype plate and put down on as many zinc
or aluminium plates as colours were required.
These plates were worked on by artists to stop
out or remove all but the parts required to print
Photo-surveying
409
Photo-telegraphy
the particulai colour for which the plate was
to be worked.
PHOTO-SURVEYING (See " Photogram-
metry.")
PHOTOTEGIE
A process introduced by CoustS, in 1904, for
making transparencies, and reversed or duplicate
negatives. The negative should be exposed as
usual and developed with any developer except
pyro till the deepest shadows are seen on the
back of the film ; it is next well washed, and the
following operations may then be conducted in
daylight. Make up a solution of —
Hydrochloric acid
Barium peroxide
Water
I OZ. 100 CCS.
250 grs. 57 g.
10 OZ. 1,000 CCS.
This should be mixed in a glass bottle, stand-
ing in cold water to keep it cool ; add the acid
to the water, and then the barium in small
quantities at a time, with constant stirring or
shaking. The developed negative (not fixed)
should be immersed in this solution, which should
be kept rocked. The film begins to dissolve
gradually, and as soon as this has well begun
the barium solution is poured back into the
bottle and the negative placed in water. The
gelatine and reduced (developed) silver slowly
dissolve away, and should any of it stick it can
easily be rubbed off with a pad of cotton-wool,
or the finger tip, or the barium solution may
be again poured on. The result is an image
consisting of various thicknesses of gelatine and
unreduced (undeveloped) silver salt. The last
named can be dissolved out in an ordinary fixing
bath, and after well washing, the film should be
stained in a solution of dye. Or, if desired, the
unreduced silver may be left in the film and
redeveloped with any ordinary developer. For
making duplicate negatives, it is first necessary
to make a positive by contact and treat this in
the manner described above, so as to reverse it
— that is, turn the positive into a negative. The
dyed gelatine relief serves as a negative or a
positive as the case may be, the dense parts
being dyed deeper than the clear parts where
the gelatine is thin.
PHOTO-TELEGRAPHY
The transmission of a photographic image
from one place to another by means of telegraphy.
The idea of telegraphing pictures dates back to
i860, and even earlier, but it is only during the
last few years that any successful results have
been obtained commerdaUy.
There are two systems which have been used
extensively by newspapers : one is the invention
of Prof. Kom, who was the first to produce a
really practical system ; the other is the inven-
tion of T. Thome Baker.
Professor Korn's Systems. — (I ) By means of the
original selenium process, the photograph to be
telegraphed is printed as a transparency on
celluloid, and this film is attached to a glass
cylinder, c in diagram A. Light from a Nemst
lamp N is made to pass, by tibie lens I,, through
the cylinder where the beam comes to a focus ;
what light passes through the cylinder reaches
a prism f, and is reflected on to a selenium cell
S S. As the cylinder is rotated spirally (by mean*
of a motor) difierent consecutive portions of the
image intercept the light beams, and hence the
intensity of the illumination falling on the cell
SS varies. The cell has the peculiar property
of varying in its electrical resistance, according
A. Transmitting Apparatus of Horn's Early
Photo-telegraphy System
to the strength of light falling upon it ; hence
the current from an electric battery, E, which
passes through the cell into the telephone lines
connecting the sending apparatus with the
receiver, also changes, and at the receiving
apparatus, B, one gets an electric current varying
in intensity each instant, according to the density
of the photograph, as the image is traversed by
the beam of light. The current received is passed
through an exceedingly fine silver wire w sus-
pended between the poles of a powerful electro-
magnet M ; to this wire is attached a small
shutter, which cuts off a beam of light passing
from a lamp N through lens i, and a hole in the
magnet poles. When a current passes through
the wire w it is magnetically displaced, and light
consequently passes through the magnet and
arrives at a lens T, which concentrates it upon a
sensitive film attached to a drum t> ; this drum
rotates in a light-tight box synchronously with
the transmitting cylinder, c in diagram A. The
wire, w w, is displaced to a distance depend-
ing on the current, which itself is regulated by
the density of the photograph at each instant.
Hence, the light acting on the sensitive film
varies always according to the density of the
picture being transmitted. On developing the
lelffihom Line ■*-
B. Receiving Apparatus of Korn's Early
Photo-telegraphy System
film, a replica of the original photograph is
obtained. There are, of course, various fiectrical
complications in the process, but these need not
be dealt with here.
(3) Prof. Korn's more recent apparatus is his
telautograph, by means of which half-tone
Photo-telegraphy
410
Photo-xylography
photographs prepared with a single-line screen
can be telegraphed. The photograph is printed
in fish-glue on a thin copper sheet, developed,
and attached to the metal drum, d, in diagram C.
A metal stylus s traces a spiral path over the
photograph, and as it travels over each glue line
TeJephone Line
C. Kom's Telautograph
the flow of current from a battery, E, through the
cylinder and stylus is interrupted. The same
form of receiving apparatus is used, but a great
many improvements have been made in the
galvanometer used, with the result that a picture
7 in. by s in. can be telegraphed in a few minutes,
with as many as 1 50 lines to the inch.
T. Thorne Baker's System.— The telectrograph
has been largely used commercially between
Manchester, I^ondon and Paris. Its great advan-
tage over other systems is that it does away with
the reception on a photographic film. The whole
operation, therefore, is conducted in full light,
and the image can be watched during its entire
reception. A portable transmitter was designed
in 1910 by the inventor, and this was used between
Brighton and London in that year. The system
is shown diagrammatically at D. a and B are the
metal cylinders of the transmitter and receiver.
A is provided with a steel stylus S, and B with a
platinum stylus T. A halt-tone single-line photo-
graph printed on lead foil and pressed perfectly
smooth is attached to A, and a piece of chemically
prepared paper is wrapped roimd B. The
battery E supplies the electric current. When-
ever the steel stylus is in contact with the metal
of the picture, that is, when it is not travelling
over a glue line, current flows through the wires
to the receiver, and a black dot appears under the
stylus T. The original picture is thus reproduced,
dot for dot, at the receiving machine, and a
picture 8 in. by 5 in. can be transmitted in from
ten to fourteen minutes. The system is explained
here in its simplest form ; in practice, the receiv-
ing apparatus is complicated, owing to the fact
that the electric currents, in passing through long-
distance wires, become lengthened in period and
D. T. Thome Baker's Telectrograph
changed in intensity, with the efiect of distorting
and blurring the received photograph. The
various difficulties have been overcome by means
of the line balancer invented by T. Thome Baker,
to which the success of a system based on many
earlier attempts has been due.
PHOTOTINCTURE
Villain's process, invented in 1891, for the
production of photographs on fabrics and paper
by means of dyes. The fabric is sensitised by
a few seconds' immersion in a solution of —
Ammon. bichromate
Ammon. vanadate
Water
S oz. sso g.
240 grs. 55 „
10 oz. 1,000 CCS.
The material is dried in the dark at a temper-
ature not exceeding 75° P. (24° C), for at 85°P.
(29° C.) the transforming action begins and shows
itself by veiling the whites. The dried material
is exposed to daylight under a negative, the time
being found by experiment, the image being
visible, and washed to eliminate the chromium
salt not acted upon by light, leaving the fabric
mordanted where exposure has fixed upon it the
chromium and vanadium oxides. Next the
fabric is boiled in a dye bath, preferably of
alizarine or purpurine, this being gradually
heated to boiling point, at which it is maintained
for fifteen minutes. "The fabric is then washed
and, if the whites are not pure, passed through a
warm bath of soap and sodium carbonate, or a
cold bath of chloride of lime to which has been
added a few drops of hydrochloric acid, it being
necessary before drying to drive out every trace
of the acid by the use of a bath slightly alkaline.
The fabric is finally washed and dried. The
dyes fix them.selves only on the parts where the
mordant is fixed ; and the parts where the light
has not acted (high lights) will give the whites,
unless the materials were impure or a mistake
has been made. The colouring products used
by Villain were the artificial alizarine sold under
the name of alizarine for violet, alizarine for
red ; alizarine blue S ; alizarine black S ; gallo-
flavine ; purpurine ; anthracene brown (antho-
gallol) ; alizarine orange ; aUzarine yellow A ;
alizarine chestnut ; alizarine green S ; alizarine
blue indigo S, and galleine.
PHOTOTINT
A name given both to a collotype and a half-
tone block process. Cocking's process of photo-
tint consisted in printing from two negatives,
one being an ordinary photographic negative
and the other prepared by hand. Striking effects
of light and shade were thus produced.
PHOTOTYPE
A name formerly given to a secret process
of carbon printing invented by Joubert ; has
since been applied to collotype, and also to half-
tone blocks.
PHOTO-TYPOGRAPHY
A general term applied in photography to a
large number of processes in which relief printing
surfaces for letterpress printing are produced by
the aid of the chemical action of light.
PHOTO-VERROTYPE
A modification of the collotype process,
worked about the year 1870.
PHOTO-XYLOGRAPHY
Processes of photographing on boxwood blocks
as a guide for the engraver instead of draw-
ing the image. The blocks may be prepared
Photo-zincography
4"
Pigmenting
mth albumen and sensitised on a silver nitrate
bath ; or a silver emulsion may be spread on the
block ; or a carbon tissue may be developed
upon it ; or a film, developed on a glass plate,
may be transferred to it ; or a greasy ink
transfer may be applied.
PHOTO-ZINCOGRAPHY
A process worked out by Col. Sir Henry James
at the Ordnance Survey OfSce in Southampton,
and at first simply a method of preparing a
photo-lithographic transfer and applying it to a
zinc plate, afterwards printed from. Direct prints
from negatives are now made on the zinc plates,
and the Vandyke process is largely employed
for map and plan work. In this process the
original drawing is printed through, instead of
using a glass negative.
PHOTO-ZINCO PROCESS
I<ine etching on zinc was originally called by
this name, but the term is not now often used.
PHOTO-ZINCOTYPY
Ordinary line etching on zinc.
PHYSICAL DEVELOPMENT
The formation of the image by chemical
deposition on the film of the plate, instead of
by a chemical decomposition of the haloid
salts in the film, as is generally the case. For
example, in the wet coUodion process the silver
image is not formed from the bromides or iodides
in the film, but by reduction of the silver nitrate
sensitising solution on the surface by the ferrous
sulphate developer, the latent image forming in
some way a nucleus for this deposition, although
not itself reduced. Another instance is afforded
by the possibility of developing a gelatino-
bromide plate after it has been fixed, by
means of an alkaline developer containing
silver nitrate {See also " Fixing Before De-
velopment.")
PHYSIOTYPE
Nature printing from leaves, flowers, etc.
PICRIC ACID {See " Tri-nitro-phenol.")
PICTORIAL COMPOSITION {See "Com-
position, Pictorial.")
PIGMENT PLASTER
A paper coated with a mixture of soft gelatine
and pigment. It resembles insensitive carbon
tissue, and is used in the ozobrome process.
PIGMENT PROCESSES
Various printing processes in which the image
is formed of a pigment primarily embodied in
a sensitive support — ^for example, carbon, ozo-
type, giun - bichromate, and similar processes.
A. L. Poitevin, in 1855, was the first to suggest
the use of a pigment with chromated gelatine
or its equivalent. J. Pouncy, of Dorchester,
followed in 1858 ; he used a vegetable carbon
with gum and potassium bichromate, and is
supposed to have been the first to produce
a really successful pigment (carbon) print.
Beauregard patented a method of obtaining
pigment prints in 1857. In the dusting-on
process, pigment is applied after exposure.
PIGMENTING
Under the headings " Oil-pigment Process "
and " Bromoil " have been indicated the means
by which a print is obtained in gelatine relief,
and in each case it remains to produce the
actual picture by the application of a pigment
or ink.
At least one brush of pole-cat hair, of fair size,
is necessary, and smaller brushes will be found
useful for local work. A small quantity of ink
(a piece the size of a pea will be ample for even
a 12 in. by 10 in. print) is taken and rubbed
down with the palette knife on a piece of clean
glass or opal until of such a consistency that it
can be spread on the glass in a thin film. If the
pigment is too hard it may be thinned down
with a softer ink, or with a trace of megilp
or Roberson's medium. A thick ink tends to
give hardness and brilliance, a thin ink softness.
Black and Venetian reds are useful pigments, as
by their use colours can be obtained ranging from
black, through warm black, sepias and browns,
up to red. The print is pigmented on a support
made as follows : The foundation is a sheet of
glass or zinc, or a pulp slab ; over this are placed
two or three smooth sheets of wet blotting-paper ;
and on top is stretched a piece of damp muslin.
The soaked print is placed on this, and the
moisture removed from the gelatine surface by
gently wiping with a mtoistened pad of soft Unen.
A brush is now dabbed once or twice on the
film of pigment, and then on a clean portion of
the glass. The object is to secure that each
hair-tip holds a minute trace of pigment. The
charged brush is then applied to the print with a
gentle dabbing motion, and if all is right the
image will gradually appear as the gelatine
accepts or rejects tiie pigment in accordance
with the light action that has taken place on the
bichromated gelatine. The print must be worked
upon patiently and systematically all over. It
is best after each re-charging of the brush to
work first on the stronger parts of the subject and
then pass to the more delicate parts (such as the
sky) when the pigment in the brush is diminished
Gentle brush action and a thin ink will cause the
print to accept colour more readily than a more
vigorous dabbing and thicker pigment. High
lights may be brightened by taking a clean
flat-cut brush and " bouncing " or " hopping "
it vertically on to the print. The more patiently
the ink is applied in small quantities by con-
tinued and gentle dabbing the finer will be the
deposit and the better the gradations of tone.
Variations in brush action, the use of pigment
of a different consistency, the ability to lighten
or strengthen parts locaUy, all provide means of
exercising control over the final result. But
the beginner would be well advised to direct
his efforts at first to obtaining "straight"
prints with a. fine deposit and a full scale of
gradations.
The finished print is hung up to dry. The ink
will set almost as soon as the paper is dry, but
the prints should be carefully handled until the
image is thoroughly hardened. The brushes
should be cleaned immediately after use. This is
easily done by rubbing their surface on a piece of
flufSess material moistened with petrol. The
blotting-paper should also be dried after use or
it will develop mould.
Pigmoil
412
Pinhole Photography
PIGMOIL
A somewhat mharmonious term invented to in-
dicate the oil-pigment process (which see).
PINACHROME {See " Isocyanines.")
PINACHROMY (Fr. and Ger., Pinachromie)
Koenig's three-colour printing process intro-
duced in 1904 by the Hoechst Dye Works,
founded upon the light-sensitiveness of the leuco
bases of aniline dyes. These are colourless bodies
formed by the reduction of dyes especially of the
triphenyl-methane series, and differing from
them by the addition of two hydrogen atoms ;
they oxidise, or in other words form dyes, much
more quickly in light than in the dark. Ostwald
Gros was the first to discover the light-sensitive-
ness of these bodies, and that they became
strongly coloured, more especially by those rays
which were complementary to the colour of the
dyes from which the leuco bases were formed.
The leuco bases were dissolved in collodion to
which was added nitro-glycerine, nitro-mannite,
or some other nitrogenous body, and then printed
under the constituent negatives one after the
other, a different leuco base being coated between
each printing. The process is theoretically inter-
esting but practically valueless, as the colours
formed were not stable to light, and the stock
leuco base solutions extremely fugitive.
PINACYANOL
A dye of the isocyanine group, used for
colour-sensitising plates. It gives sensitiveness
up to the extreme visible red.
PINAKOL (See " Amido-acetic Acid.")
PINATYPE (See "Three-colour Photography.")
PINAVERDOL (See " Isocyanines.")
PINHOLE PHOTOGRAPHY
Photography by means of a pinhole camera,
that is, a camera in which (see A) instead of a
lens there is a small hole made by a needle in a
metal plate, card, etc. If a pinhole is pierced
through one side of a light-tight box, the light
rays proceeding from any object (say a candle
flame) placed in front of the hole will form an
image of the object on the opposite wall of the box
inside ; the size of the image depends upon its
nearness to the camera, and its distinctness or
definition depends upon the size of the hole.
Photographs obtained through a pinhole possess
a pleasing softness of outline, distortion is absent,
and any angle may be included upon the plate,
a wide angle by having the hole near the plate
(see A) and a narrow angle by having the hole
farther from it (see B). On the other hand, the
definition is not critically sharp, and the necessary
exposure is so long that it is impofsible to photo-
graph moving objects. Within certain limits a
pinhole has no plane of focus, as proved by the
fact that results practically as good as one another
can be obtained by having the sensitive plate
at different distances from the hole.
Any camera may be used for outdoor pinhole
photography, as may also any light-tight box,
but the former has the advantage that the dis-
tance between pinhole and plate is easily altered,
remembering that, while this is not necessary for
focusing, the shorter this distance the greater the
angle of view, and consequently the more of the
subject included upon the plate. For indoor
work, failing a regular camera, any light-tight
box C may be used, the plate being supported
by means of a printing frame or drawing pins.
The pinhole must be circular, with perfectly
A B
Wide-angle and Narrow-angle Pinhole Cameras
clean edges without the slightest burr ; at its
edges the thickness of the material must be less
than the diameter of the hole. The presence
of a burr on the edge would give precisely the
same effect as photographing through a tube,
namely, to limit the angle included. A pinhole
of T^ in. diameter bears the same relation to
metal ^ in. thick that a i-in. lens bears to a
tube 4 in. long. The reflections from the interior
of the hole in a comparatively thick plate of
metal would also interfere wiOi the brightness
and definition of the image. TinfoU is the
material often used, but it is very fragile when
mounted up in place of the lens. Many prefer
to use thin brass, in which a boss (see D) has
been made by means of a steel punch. The
boss is rubbed or filed down and the pinhole
made through the thinnest part (see B). The
" pin "-hole is best made with a needle, which
should be inserted gradually and alternately
from both sides of the hole so as to obviate
biirr. Any other way of making the hole may
be adopted as long as the result is a. circular
hole with dean edges.
The effect of the distance between plate and
hole has been referred to. The diameter of hole
should vary with the distance, and the rule
proposed by Sir W. Abney is very useful in this
connection. To find the diameter of the hole,
divide the square root of the distance by 120.
To find the distance, multiply the diameter of
the hole by 120 and square the result. Thus,
assuming the distance to be 25 in., the square root
C. Improvised
Pinhole Camera
Production of Pin-
hole in Metal Plate
is 5, and this divided by 120 equals ^ in.,
which is the diameter of the required hole. In
the case of a hole jV in. in diameter, the dis-
tance will be 9 in., since ^ x 120 « 3, and
32 (3 X 3) r= 9. But extreme latitude is possible
because of the great depth of focus.
Pinhole Photography
413
Pitch, Mineral
With regard to determining the diameter oi
the pinhola, it may be measured more con-
veniently if pierced with a needle of standard size
The following table is based on Abney's rule : —
Size
of
Pinhole
Distance
of Plate
from Hole
iJait'o 0/
Aperture to
Focal Length
or Distance
in.
in.
rJu
li
//1 50
5TJ
2
//1 80
A
2i
//1 80
tV
3
//210
i?,r
4
//240
5
//250
^r
7
//31S
^
9
//360
^
iif
//411
A
16
//480
^
23
flS7S
A
36
//720
The following tables of needles, their sizes
and diameters, are due to Messrs. Alfred
Watkins and E. J. Wall :—
HaK (S- Co.
' s Needles
ii:»V6)' &■ Co
.'s Needles
Number
Diameter
Number
Diameter
in.
in.
I
iV
2
TiV
2
^
3
^
3
A
4
^<y
4
A
6
A
5
^1-
7
h
6
A
9
A
7
tV
10
A
8
A
12
7V
9
A
16
ffV
10
3^
For most practical purposes pinholes of ^ in.,
■f^ in., and ^ks i^^- ^^ ^^ sufficient, and they
can be used at any distance from i|^ in. to 30 in.,
although theoretically the respective distances
are 5 in., 2^ in., and ij in. The largest hole
will be usefm for all out-door work, Hie medium
hole for architecture, both interior and exterior,
and the smallest for copying and short focus
work.
The pinhole having no definite plane of focus
it is obviously unnecessary to focus on a ground
glass, but the photographer will need to know
the amount of view included upon the plate.
The amount of hght coming through the pinhole
is generally so small that it will not be easy to
examine the image on the ground glass. By
far the most practical plan is to take a piece of
millboard just large enough to slide into the
grooves in which the dark-slide is usually
carried, and in the card to cut an aperture the
size and shape of the plate used. If a half -plate
is used in a half-plate camera there will be no
need for the card, but smaller plates than the
camera usually takes are often used for ex-
perimental pinhole work. Turn back the focus-
ing glass from the camera, slide in the card (if
necessary), direct the back of the camera
towards the view, and look through the pinhole
from the front. It is then possible to judge the
suitability of the pinhole, and, by racking in
or out, the amount of view included. Then
swing round the camera, insert the plate, and
make the exposure.
The usual method of exposing is to fit the
pinhole in a pill-box arrangement, using the lid
as the cap, or to fit a flap or revolving disc over
the pinhole. In the first of the tables the ratio
aperture ("stop value") is given for n certain
extension of the camera ; if any other extension
is used the ratio aperture must be found by
dividing the distance between pinhole and plate
by the diameter of the pinhole. The usual law
relating to exposure holds good, namely, that the
exposure varies as the square of the aperture
number ; thus, if a lens working at //8 requires
a quarter of a second, with f/600 the exposure
, , , i X 600^ i X 600 X 600 , ,
would be - — p = g-^j-g = (approx.)
1,400 sees. = (approx.) 24 minutes.
The calculation of tie exact exposure fortun-
ately does not matter so very much, as, owing to
the smaUness of the aperture, there is an immense
amount of latitude.
PINHOLE THEORY IN HALF-TONE
WORK
The formation of the half-tone dot on the
negative is explained in the pinhole theory,
it being assumed that each opening in the net-
work of the ruled screen acts as a pinhole.
PINHOLES IN NEGATIVES
Small transparent spots in the image and
gelatine on the negative generally caused by
dust. {See " Dust Spots.")
PINT
In British measure this is equal to 20 fluid
ounces (160 drams, or 9,600 minims), and the
eighth part of a gallon. In America the pint
is equal to 16 fluid ounces (128 drams, or 7,680
minims). One pint (British) equals 568 ccs.
and the American pint 454-5 ccs.
PIPETTE
A glass tube drawn to a point at one end;
used for measuring small quantities of liquids.
{See also "Dropping Tube.")
PITCHBLENDE
Synonym, uraninite. A native ore containing
uraiuum, helium, radium, and other rare ele-
ments. It is the main source of uranium
salts.
PITCH, BURGUNDY
A resinous pitch used in etching inks and
etching grounds. {See "Burgundy Pitch.")
PITCH. JEW'S
Bitumen of Judea or asphaltum {see the last
named).
PITCH. MINERAL
A synonym for asphaltum or bitumen.
Pits in Negatives
414
Plain (Salted) Paper Printing
PITS IN NEGATIVES
Holes in the gelatine film on negatives, fortun-
ately rare, but sometimes found after drying ;
they must not be confused with pinholes. They
vary in size from a pin's-head to a threepenny
piece, and usually appear at a time when the
air is laden with moisture and the negatives
take a long time to dry. They are said to be
due to the decomposition of the gelatine, and
the best preventive is to soak the negative
after washing in a 10 per cent, solution of
formaUne.
PIZZIGHELLI'S PROCESS
In this is used a print-out platinum paper
invented by Capt. PizzigheUi, of Vienna, in 1887.
The ejcposure may be judged as accurately as
with ordinary P.O. P., and development of the
paper is unnecessary. Any good plain paper
may be used, and the sensitiser may be as
follows : —
A. Potass, chloroplatinite 734 grs. 168 g.
Distilled water . 10 oz. 1,000 ccs.
B. Ammonium ferric
oxalate . . 3 J oz. 412 g.
Powdered gum arable 3I „ 412 „
Potass, oxalate (5% sol.) 7 „ 700 ccs.
Glycerine
100 mins. 21
Heat the potassium oxalate solution to about
115° F. (46° C), and dissolve in it the ferric salt
and glycerine; then add to the gum and stir
well.
C. Solution B • • 3i °^- 1,000 ccs.
Potass, chlorate (1 in 20
sol.) . . . 135 mins. 80 „
D. Potass, oxalate (5% sol.) 11 drms. 535 ccs.
Merc, chloride (5% sol.) 338 mins. 200 „
Gum arable (powdered) 370 grs. 242 g.
Glycerine . . 34 mins. 20 ccs.
C and D are sensitive to light and should be
kept in the dark. For black images, sensitise
the plain paper with the following : —
A solution (platinum) . 100 mins. 100 ccs.
B solution (iron and gum) 120 „ 120 „
C solution (gum and
chlorate) . . . 40 „ 40 „
For sepia prints use —
A solution .
C solution .
D solution .
Lay the paper on a sheet of glass, working in
a yellow light, and apply the sensitiser wiOi a
pad of cotton-wool. Dry quickly and preserve
in a calcium tube. Print under a negative in
daylight until the image is fully out, and then
<:lear by passing through dilute hydrochloric acid
< 1 in 80) ; finally wash for from flEteen to twenty
minutes in clear water.
The time of printing PizzigheUi paper may be
shortened if, after the deepest shadows have
appeared, the prints are developed in a cold
5 per cent, solution of potassium oxalate or
common washing soda. The following bath has
also been recommended in place of the hydro-
chloric acid bath: Copper sulphate, 154 grs.;
water, 34 ozs. The PizzigheUi process cannot be
•depended upon for regular tones.
100 mins. 100 ccs.
80 „ 80 „
80 „ 80 „
PizzigheUi also invented a paper of the
" PeUet " type. {See " PeUet Process.")
PLAIN (SALTED) PAPER PRINTING
This employs a paper sensitised by immersing
in a soluble diloride, and floated afterwards in
a bath of silver nitrate. The paper is either only
slightly sized or not sized at aU, with the result
that the original surface or texture of the paper
is retained, and the prints appear to be on plain
paper, hence the term. Such papers are prmted
out tmder a negative in daylight, and then toned
and fixed. Good writing paper serves well for
small prints and Whatman's or any other good
drawing paper for large ones. When sizing is
omitted some workers add just enough potassium
bichromate to the salting solution to colour it
faintly.
Arrowroot and gelatine sizes appear to be the
most popular. For the latter use —
Gelatine
Chrome alum
Ammonium chloride
Water
100 grs. 23 g.
4 „ I „
50 „ II-5 „
10 oz. 1,000 ccs.
The gelatine is soaked for thirty minutes in
8 oz. of the water (cold) and the chrome alum
dissolved in the remaining 2 oz. The gelatine is
next heated on a water bath, the ammonium
chloride stirred in, the whole strained through
fine muslin, the chrome alum solution poured
very gradually into it, and the whole stirred.
It is now ready for coating upon the paper, and
should be stood in hot water to keep it fluid.
The paper is pinned to a flat board or laid upon
glass and weighted at the corners. The salting
solution is sponged on as quickly and as evenly
as possible, being finally gone over with a
squeezed sponge tp remove superfluous solution.
Three minutes should be ample time in which
to salt a 2o-in. by i6-in. sheet ; and the quantity
of solution above given can be made to coat ten
such sheets. They should be kept flat for a few
minutes until the gelatine has penetrated, and
then hung up to dry in a warm place. The pre-
pared paper wiU keep good for several months.
When required, the paper is sensitised with
a silver nitrate solution : —
Silver nitrate
Citric acid
Distilled water
. 600 grs.
• 300 „
10 ozs.
138 g.
1,000 ccs.
Sensitising is done in a weak or yeUew Ught'
and the mixture is applied by floating, or pre-
ferably by brushing, and not by total immersion.
Any brush used must be in wood and not in
metal. Apply the sensitiser evenly and liberaUy,
and hang the coated paper in a warm dar^ place
for about ten minutes in order that it may
become surface dry, and then repeat the applica-
tion in order that there may be an excess of
silver nitrate, which is necessary for rich and
brilliant prints.
Printing can be done from almost any kind of
negative, thin or flat ones being the least suit-
able. The prints lose but little in toning and
fixing, therefore the printing need not be
carried very far beyond the result desired. When
taken from the printing frames, the prints should
be well washed, say, for fifteen minutes, to re-
move the acid and free silver salt, and are then
Plain (Salted) Paper Printing 4iS
Plano-concave Lens
ready for toning, for -whict any gold or platinum
bath may be used if weakened with water, the
following being spedally recommended : —
Sodium acetate . . 30 grs. 4 g.
Gold chloride . . i gr. -13 „
Water . . . . 16 oz. 1,000 ccs.
Mix about twelve hours before use. Toning
is very rapid, one minute's immersion giving, as
a rule, the best brown or sepia tones. Over-
toning is the commonest cause of failure, but as
prints always dry a colder tone than they appear
when wet, allowance should be made. The
toned prints should be placed in a solution of
■J oz. of common salt in 60 oz. of water, in order
to stop the toning action ; they are next washed
for a few minutes, fixed for ten minutes in a
" hypo " bath, and finally washed again.
Alternative Baths. — The following is a good
sensitiser : —
Silver nitrate
Water .
600 grs. 138 g.
10 oz. 1,000 ccs.
Add liquor ammoniae drop by drop, imtil the
precipitate first formed is dissolved.
The following sensitiser is suitable for papers
sized with arrowroot ; in the case of agar-agar
papers the citric acid should be increased to
100 grs. or 117 g. : —
Silver nitrate . .140 grs. 164 g.
Citric add . . • 55 „ 64 „
Distilled water . . 2 oz. 1,000 ccs.
Alternative toning baths are as follows : —
1. Potass, chloroplatinite 20 grs. 4-5 g.
Nitric add . .10 mins. 2 ccs.
Distilled water . 10 oz. 1,000 „
Tone and fix as usual.
2. Citric add . . 36 grs. 8 g.
Common salt . . 12 „ 2-7 „
Potass, chloroplatinite l gr. -23 „
Distilled water . 10 oz. 1,000 ccs.
Tone and fix as usual.
3. Borax ... 30 grs. 7 g.
Gold chloride . . f gr. -i „
Distilled water . 10 oz. 1,000 ccs.
Use as soon as mixed ; tone and fix as usual.
4. Sodium phosphate . 10 grs. 2 g.
Gold chloride . . i gr. "i ,,
Water . . . 10 oz. 1,000 ccs.
Use as No. 3, above.
The following is a plain paper which may be
called " self-toning," as excellent tones may be
obtained simply by fixing in a 2^ per cent, solu-
tion of "hypo" — say, 12 grs. to i oz. of water.
The paper (without water-marks) is given an
extra coating of size, made by rubbing up 90 grs.
of arrowroot with 5 oz. of cold water, adding
a solution of 20 grs. of glucose in 5 oz. of hot
water, and boiling in an enamelled saucepan for
two minutes. When cool, immerse the paper
tin thoroughly saturated, dry, and sensitise with
Nelson's gelatine .
Tartaric add.
Silver nitrate
Ferric ammonio-dtrate
Water . . .
60 grs. 14 g.
80 „ i8-s „
90 ,, 21 „
400 „ 920 „
10 oz. 1,000 ccs.
The solution, made as described earlier in this
artide, should be stored, if required, in a black
bottle. After proceedings are as already de-
scribed.
PLANAR LENS
A lens of symmetrical construction consisting
of two three-lens combinations, two glasses of
each being cemented and the third separated
by an air space {see illustration). The smaller
sizes are espedally useful for photomicrography.
/(
/
Planar Lens
;
while the larger ones are suitable for all dasses
of rapid work, portraiture, etc. There is an
apochromatic series suitable for three-colour
work. Planars are made by Zdss in a range of
focal lengths from f in. to i8|- in., while the
intensity varies from //3'6 to f/6-3.
PLANE TABLE (Pr., Planchette photograph-
ique ; Ger., Phoiographisch Messiisch)
A panoramic camera invented by Chevalier
and used in surveying by photography. A
vertical lens fitted with a reflecting prism or
mirror was made to revolve above a horizontal
plate, a complete circular picture of the sur-
rounding country being tims obtained. To
prevent overlapping, a revolving disc with a
narrow radial slit moved over the plate in
syndironism with the motion of the lens, its
centre being in line with the lens axis.
PLANES (Fr., Plans; Ger., Fldches)
The different positions or distances occupied
by the various parts of a subject. The nearer
planes contain the strongest light and shade
and the most pronounced detail ; as the planes
recede, the detail, light, and shade become less
apparent. The adequate rendering of the values
of the various planes produces good aerial per-
spective. Lighting and the state of the atmo-
sphere influence tie tone and quality of the
planes. Lack of difierentiation between one
plane and another gives an appearance of flat-
ness.
PLANISCOPE (Pr., Planiscope ; Ger., Planis-
kop)
A series of supplementary lenses intended to
be placed in front of an ordinary camera lens,
to shorten or increase the focal length. Pour
difierent kinds are obtainable, for wide-angle,
copying, portrait, or telephoto work respectively,
and each consists of a single achromatic lens
mounted in a metal rim provided with two
bow springs, by means of which the planiscope
may be fitted on the hood or body of the camera
lens.
PLANO-CONCAVE LENS (See "Concave
Lens.")
Plano-convex Lens
416
Plate Holder
PLANO-CONVEX LENS {See "Convex
Lens.")
PLANT LIFE, PHOTOGRAPHY OF
The life history of a plant from the first shoot
to the mature growth, the opening of a leaf-bud,
and the unfurling of the leaves, the expansion
of a blossom, and the various types of fruits are
examples of plant life that will yield interesting
photographs. A rigid stand camera provided with
a long extension of bellows is the most suitable
all-round instrument for the work, and quarter-
plate size will be found generally useful. The lens
should not be of less than S J in. focal length for a
quarter-plate, and a lens of 6^ in. or 7 in. focal
length would give more natural perspective. If
an anastigmatic lens working at f/$ or f/6 is
not too costly, it should be used, since its large
aperture is of great advantage when working
out of doors, though it must be remembered
that the larger the aperture, the less the so-called
depth of focus, and, therefore, the greater care
is necessary in focusing the object. A rapid
rectilinear lens will answer very well for indoor
work, and for the field in bright weather. The
most useful type of shutter is one that can be
fastened to the front of the camera, and is fitted
with removable lens panels, so that lenses of
different focal lengths can be quickly placed in
position. Orthochromatic plates should always
be used, and generally a yellow filter is desirable,
especially for flowers. If much flower work is
contemplated, obtain a set of three filters — a pale
yellow, a mediimi, and a heavy one, such as
Wratten's Ki, Kn, or Krn. A panchromatic
plate will generally be found to yield the best
results with flowers, but some skill and judgment
will be required in the selection of the filter to
be used.
The autochrome process of colour photography
lends itself particularly to photographing flowers,
and most beautiful results may be obtained,
showing every delicate shade of colour.
PLAQUE PHOTOGRAPHY
A method in which prints were given a concave
shape with the object of imitating the appear-
ance of a porcelain plaque. The print was pressed
whilst wet between rubber covered dies respec-
tively of convex and concave shape.
PLASTER CASTS FROM PHOTO RE-
LIEFS
Numerous processes have been based on the
principle of obtaining a relief in chromated
gelatine, and taking therefrom a plaster cast,
which might be used by itself as a plaque for
decorative purposes, or be the means for obtain-
ing a porcelain plaque, or for making an electro-
type or stereotype. {See " Galvanography,
Photographic," " Gelatine Reliefs," " Photo-
lithophane," " Photo-stereotype," etc.)
PLASTIC PHOTOGRAPHS
Photographs upon flat glass or paper and
giving the effect of bas-reliefs. A negative of the
subject is made in the usual way, then a trans-
parency (positive) by contact from the negative,
and when the positive is dry it is again placed
in contact with the negative (film to film). On
being held up to the light, one of the plates is
shifted very slightly to one side, so as to be a
trifle out of register, and the two are bound
together and then framed, printed from, or
copied in the camera. Profile portraits give
the best results. The effect is due to one side
of the image being represented as a white line
and the opposite side as a dark one, jKist as
a bas-relief would be if illuminated by a strong
side light.
PLATE
A term loosely applied, but generally under-
stood to mean a dry plate. When the plate has
been exposed, developed, etc., it is known as
a " negative," " positive," " transparency," etc.,
as the case may be.
In process work, the term " plate " is generally
applied to the surface to be printed from, and
also to the actual print from the plate, as illus-
tration plates in books, and plates for framing.
Plate-printing is distinguished from letterpress
or lithographic printing by its understood
reference to printing from intaglio, etched, or
engraved copper and steel plates.
PLATE ADAPTERS
The name given to various kinds of dark-
slides which render possible the daylight loading
and changing of plates, in light-tight envelopes
or in other ways. In addition, the term is
often applied to accessories which enable plates
to be used in cameras intended for films. {See
also " Plate Carrier.")
PLATE BACKINGS {See " Backings, Plate.")
PLATE CARRIER
Also known as an adapter. A light frame
of wood or metal fitting inside a dark-slide and
permitting the use of a smaller plate than that
Plate Carrier
for which the slide is made. The illustration
shows the usual form. Large slides are fre-
quently fitted with a nest of carriers.
PLATE CHANGING {See " Daylight Chang-
ing-")
PLATES, COATING {See "Coating" and
" Emulsion.")
PLATE HOLDER (Fr., Porte-plaque; Ger.,
Plattenhalter)
A clip of metal, celluloid, or other material,
used for hojding and lifting plates during
development, washing, etc., in order to avoid
touching them or immersing the fingers in the
Plate Lifter
417
Platinotype Process
solutions. A typical pattern is illustrated.
(See also " Pneumatic Holder.")
Plate Holder
This term is also often applied to the dark-
slide, plate-adapter, and, indeed, to anything
else that contains, holds, or supports plates.
PLATE LIFTER
A kind of lever of metal, ebonite or celluloid,
used for raising plates from the developing or
other solution, in order that they may be
Plate Lifter
examined or removed. Some developing dishes
have a lever attached at one side, as illustrated.
The device is made in many forms, and the
term is also often applied to the plate holder.
PLATE MARK
The indentation made in paper by the metal
plate when printing engravings, etc. Some
mounts for photographs have a similar impression
made upon them. Sometimes a print which has
been made from a masked negative so as to show
a wide margin of paper has an imitation plate
mark made around it by pressing into the paper
a sheet of card or nxetal slightly larger than the
print itself. In the case <rf a photograph such
a mark has no real meaning or justification.
PLATE SHEATH {See " Sheath.")
PLATE SPEEDS {See " Sensitometry.")
PLATE TESTING {See " Sensitometry.")
PLATE VICE
A screw vice or clamp used at one time to
hold the daguerreotype plate while buffing or
polishing, and still sometimes employed when
cleaning glass plates previous to coating with
collodion in the wet-plate process, and for other
purposes. It consists of a square wooden
frame with a sliding block adjusted by a screw,
usually of beechwood.
PLATE WHIRLER {See " Whirler.")
PLATES, VARIETIES OF {See separate head-
ings ; for example, " Albumen Process,"
" Collodion Process (Wet)," " Ferrotype
Process," " Isochromatic Plates," etc.
ST
PLATE-SUNK
A term used to describe a mount made with a
depression in imitation of the indentation in the
paper caused by the pressure of the metal plate
in printing etchings and engravings. {See " Plate
Mark.")
{See " Platinum Per-
PLATINIC CHLORIDE
chloride.")
PLATINO-BROMIDE
A grade of bromide paper with a matt surface
giving an effect intended to resemble platino-
type.
PLATINO-MATT
The term applied to the surface of some grades
of bromide and gaslight papers which are made
to give an effect in imitation of platinotype.
{See also " Platinum Paper, Substitutes for.")
PLATINOTYPE PROCESS
A printing process in which the image is
partially printed out and then developed to its
full strength, based on the light-sensitiveness of
iron salts and not directly upon that of a platinum
compound. The ferric salts are reduced by the
action of light to the ferrous state, in which con-
dition they partially reduce the platinum salt,
the conversion to metallic platinum being com-
pleted by the ferrous salt in the " developer."
The salt usually employed is ferric oxalate, the
light action upon which is shown in the following
equation : —
Fea(C204)3 + Light = 2FeCa04 + aCOa
Ferric Ferrous Carbonic
oxalate oxalate acid.
The action occurring during development may
be represented by the following equation, which
Berkeley (at one time manager of the Platino-
type Company) gave in 1882 : —
SPeCaOj + 3VtK,Cit =
Ferrous Potassium
oxalate chloroplatinite
2Fe,(Cj04), + Fe^a, + 6KC1 -|- 3Pt
Ferric Ferric Potassium Plati-
ozalate chloride chloride num
Hiibl pointed out (1883) that whilst the above
may be taken as the simplest form of equation
and practically correct, formic acid probably is
produced during exposure of the print to light,
and that this acid plays a part in the develop-
ment of the image, as follows : —
HjCOj + PtK,Cli =
Foimic Potassium
add chloioplatinite
CO 2 -t- 2Ha + 2KCI -t- Pt
Carbonic Hydro- Potass. Plati-
acid chloric acid cliloride num
Although the process is based on the sensitive-
ness of the iron salts and not on that of the
platinum compound, the latter certainly under-
goes some little change, and assists the decom-
position of the ferric salt, since a mixture of
the two is undoubtedly more sensitive than the
oxalate alone.
The first discovery of the action of light upon
a platinum salt is said to have been by Gehlen,
about 1804. But the first communication of
any importance was by Sir John Herschel before
Platinotype Process
418
Platinotype Process
the Oxford meeting of the British Association, in
1832. Robert Hunt, in 1844, also experimented.
The simple platinum process as it is now known
is due to W. Willis, who patented it on June 5,
1873 (No. 2011), and who, in 1 878, 1880, and 1887,
took out further patents for improvements.
Few photographers care to attempt to make
their own platinotype paper, as the materials
are expensive and extreme care and cleanliness
are necessary. However, all necessary instruc-
tions for doing so are here given. The late W. J.
Warren advocated the following sensitising
solution, which must not be acid : —
Potassium chloroplatinite
solution (i in 6) . 3 oz. 300 ccs.
Ferric oxalate solution
(as below) . . 2| „ 275 „
Water . . . i „ 50 „
The ferric oxalate solution consists of oxalic
acid I part, ferric oxalate 15 parts, water 60
parts.
A strong paper is sized with 1 5 grs. of arrow-
root, which is made into a cream with i oz. of
water and poured gently into 30 oz. of boiling
water, the whole being then boiled for eight
minutes. The paper is immersed in the size for
three minutes, dried, re-sized, dried again, laid
on a sheet of glass, and the sensitising solution
applied (in a yellow light) with a tuft of cotton-
wool, preferably wrapped with fine silk. The
paper is then iied at a temperature of 100° P.
(38° C), for which no variation is allowable, the
drying taking only from two to four minutes.
Beanland recommends an arrowroot sizing of
30 grs. in 4 oz. of water, prepared and used as
above, and the following sensitising formula,
which, by a little modification, may be used in
the preparation of " cold bath " papers for cold
tones and " hot bath " paper for sepia, tones : —
A. Potassium chloro-
platinite
Distilled water
B. Ferric oxalate
Oxalic acid .
Distilled water
60 grs. 15 g.
360 mins. 84 ccs.
84 grs. 21 g.
8 „ 2 „
720 mins. 168 ccs.
For cold bath paper mix A and B and add 60
mins. or 14 ccs. of water. For sepia paper mix
A and B and add 60 minims or 14 ccs. of a five
per cent, solution of mercuric chloride. The
addition of a few grains of potassium chlorate
(one grain to the ounce is advised by Warren)
will give increased contrasts to the print when
either of the above formulae is used. According
to Beanland, 140 to 170 mins. are sufficient to
coat a sheet of paper 26 in. by 20 in. The coat-
ing and drying are important as before.
The addition of a very small quantity of gold
chloride to the sensitising solution is said to be
■of great advantage, the following sensitising
mixture being recommended highly by some
American workers : —
Ferric oxalate
Chloroplatinite solution
(70 grs. per oz.)
Gold chloride solution
(5 grs. per oz.)
Potass, chlorate (satu-
rated solution)
90 grs.
90 g.
60 mins. 60 ccs.
Coat the sized paper with this and dry quickly.
For thin negatives the quantity of gold may be
slightly increased, but too much gold will spoil
the bath and precipitate the platinum. The
paper is developed on a cold solution of potassium
oxalate, but if a hot bath is preferred gold must
be omitted.
The following qualities of ready sensitised
papers are manufactured by the Platinotype
Company : —
For the cold hath process : AA, smooth,
medium thickness. KK, smooth thick paper,
fine surface, gives bright prints. CC, rough-
surfaced, thick and strong, suitable for large
work. TT, rough, thick, gives greater contrast
than CC. YY, very thick and smooth. ZZ, very
thick and slightly rough. For the hot bath process :
S, smooth, to give rich sepia colour. RS, rough-
surfaced for sepia, same substance as CC. The
qualities TT, YY, and ZZ can also be coated for
sepia. In addition there is a platinotype paper
having a hard and resisting surface with an
ivory-like sheen, of a brilliant black or sepia,
and of a warmer tone than that afforded by the
matt papers. These papers are supplied in air-
tight tins, each containing a piece of calcium
chloride to absorb any moisture. The paper
should be stored in the original tin with the
calcium, or transferred to a calcium tube. It
is a good plan to place a wide rubber band round
the joint between the lid and the tin box. The
paper needs careful handUng as the sensitive
surface when dry is liable to crack ; usually
the sensitive surface is easily distinguished by
its yellow colour, and is rolled outwards. Some
workers keep platinotype paper a long time
and in a damp condition in order to get certain
effects, but technically perfect prints can only
be obtained upon paper kept perfectly dry.
Should paper become damp it may be dried
in a warm oven or by keeping it in a calcium
tube.
Platinotype paper is printed in daylight under
a negative; the latter may with advantage be
warmed, and a piece of vulcanised rubber (also
warmed) placed between the paper and the back
of the frame. A clear and brilliant negative,
free from fog, gives the best results ; flat nega-
tives should be avoided.
The depth to which printing needs to be carried
can be ascertained only by experience. The
paper is more rapid than P.O. P., and prints in
approximately about one-third the time. When
the paper is sufficiently printed the image will
be very faint and of a pale orange or a delicate
purple colour on a yellow ground. Owing to
this faintness there is a tendency to over-print
and over-develop. The rule is to print until
all the details can be seen except those in the
highest lights, and this applies to both the
" cold bath " and " hot bath " papers. After
printing and before development the prints
should be kept bone dry, as otherwise they will
lack vigour, and the purity of the whites may be
impaired. The paper shoiJd never be roughly
torn, as there is a risk of the particles of platinum
falling on the paper and causing black spots
upon the print.
Cold Bath Process. — ^This gives black-and-
white prints. Development should be conducted
in a feeble white light or by gaslight, to avoid
Platinotype Process
419
Platinotype Process
any degradation of the whites. The paper
makers' special developer, or an ordinary
potassium oxalate developer, may be used. The
special salts supplied by the makers are known
as " D "' salts ; the contents of one tube (| lb.)
are dissolved in 48 oz. of water, which forms a
stock solution. One part of this is mixed with
I part of water, which then acts as a developer.
A popular developer is —
Potassium oxalate . 3 oz. 330 g.
Hot water . . 10 „ 1,000 ccs.
For use, mix i part with 2 parts of water.
The addition of i part of a saturated solution
of oxalic acid to 20 parts of mixed developer
tends to give warmer tones. Use the best
neutral potassiimi oxalate, because if alkaUne
the blacks will not be good. Another good
developer is —
Potassium oxalate . i oz. no g.
Potassium phosphate . i „ 28 „
Hot water . . 10 „ 1,000 ccs.
"When cold it is ready for use. Although the
process is known as the " cold bath," the
developer may be used warm if desired, and in
no case must the temperature be lower than
60° P. (IS'S" C). By raising the temperature
of the bath, even to 100° F. (about 38° C), under-
exposed prints may often be saved.
A. Developing Platinotype Print
The correct way to develop a platinotype
print is just to fill a flat dish with the developer,
and to take the dry print by the ends and hold
it face downwards near the surface of the solution
as at A ; then with one hand draw one end
along the surface of the bath {see the arrow),
bringing the opposite end on to the surface of
the solution gently and evenly so that no air
bells form between the two. After a few
seconds' treatment tium over the print in order
to see whether the solution is working properly.
A correctly exposed print may take half a minute
or more to develop. Although development
may be arrested before all the ferrous oxalate is
reduced by the potassium oxalate developer,
generally it is found that when development is
cut short the picture will not be entirely satis-
factory. A scum is apt to form on the surface
of the developer, and when this happens itshoidd
be skimmed ofE with a. stiff piece of paper ; if
allowed to remain it may cause marks upon the
print. The liquid should also be stirred or
rocked between each development in order to
break up any scum which may be left by a
previous print.
A fully developed platinum print must be
placed face downwards, and without washing,
into the following bath, which acts both as a
clearer and fixer : —
Hydrochloric acid (pure ,
sp. gr., i-i6) . . I oz. 16 ccs.
Water . . . 60 „ 1,000 „
Citric acid (i oz. per 20 oz. of water) may be
used instead. The print remains in a portion
of the acid solution for five minutes ; the dis-
coloured solution is then poured away and a
second portion used, following in the same way
with a third, so that the print is immersed in
three acid baths for five, ten, and fifteen minutes
respectively. The acid bath before use should be
perfectly dear, but the effect of introducing u
print is to turn it yellow, which fact affords a
method of testing whether the print is sufficiently
cleared or not. Until the print ceases to give a
tint to the acid bath it is safe to conclude that
it is not sufficiently cleared. So long as yellow-
ness can be seen, traces of iron (which it is the
function of the acid to remove) remain in the
paper, and the treatment must be continued.
The print is next washed in four or five changes
of water to clear away the acid, and the print
dried between dean white blotting-paper.
Common soda is sometimes added to the washing
water to neutralise the add, but with proper
washing it should be unnecessary.
Sepia Prints by Cold Development. — Baron Von
Hiibl gives the following particulars for pro-
ducing a spedal paper and for working it :
" Take 1 gr. of yellow oxide of mercury and
S grs. of dtric add, add 20 ccs. of water, and dis-
solve by heat. Filter the colourless fluid. This
is kept as a stock .solution for addition to the
sensitising bath. The paper should be prepared
with arrowroot and sensitised with 8 ccs. of
normal iron solution, 4 ccs. of platinum solution
(i in 6), I to 4 ccs. of citrate of mercury solution.
The addition of a little citrate or oxalate of
ammoniimi will keep the high lights pure, and
the gradation may be modified by adding sodium
chloroplatinite, or bichromate of potash. The
paper should be sensitised in the usual manner.
The developer should be strongly acididated
with oxalic acid, and the strength of the solution
of oxalate of potash may vary between 12^ to
25 per cent. The formula may be stated as
follows : Water, 1,000 ccs. ; neutral oxalate of
potash, 120 to 250 grs.; oxalic acid, 10 grs.
The development may take place in a dish
in the ordinary way, or a brush may be used.
The prints must, however, be at least five
minutes in contact with the developed to effect
complete reduction, otherwise they will lose con-
siderably in the fixing bath, which should be a
I per cent, solution of hydrochloric add. Leave
the prints for half an hour in the fixing bath, and
then wash thoroughly. The colour and grada-
tion of the image may be modified considerably
by the composition of the sensitising solution,
the developer, and the peculiarities of the paper
used." In Baron Von Hiibl's work, " Der Plat-
indruck," the normal iron solution is given as
composed of 20 per cent, of ferric oxalate, to
each 100 ccs. of which i to 2 grs. of crystallised
oxalic add are added.
The Hot Bath Process. — ^The paper used for
the hot bath process gives sepia prints. The
paper is sold, stored and printed in the same
Platinotype Process
420
Platinotype Process
•way as cold bath paper. The sepia paper is a
trifle more sensitive than the black paper, and
more easily affected by faint light. The Platin-
otype Company's " D " salts may be used for
developing, in which case the half-poimd is dis-
solved in 32 oz. of water. The stock solution of
potassium oxalate is the same as that first given,
but for use 10 parts are mixed with i part of a
saturated solution of oxalic acid ; this mixture
should be thrown away after use, as it soon loses
quality. The solution, in use, should be main-
tained at a temperature of from 160° P. to 170° P.
(71° C. to 77° C), although good results are
obtainable with a cooler bath ; the solution can
be heated in a porcelain dish, or, more safely, in
an enamelled iron vessel supported over a spirit
lamp or gas ring (B). A tinplate, asbestos sheet,
or sand bath should be interposed between the
fiame and a porcelain dish in order to prevent
cracking. The developing and clearing (fixing)
are precisely the same as for cold bath paper.
Owing to the temperature of the bath some
evaporation takes place and it becomes necessary
to add from time to time sufficient water or more
solution to bring the liquid up to practically its
B. Heated Developing Dish
original bulk. A cracked enamel dish must not
be used, as any exposed iron would cause the
prints to be discoloured ; the sepia developing
bath after use must be kept in the dark and not
used for cold bath (black) pictures. As the
sepia prints, unlike the black ones, may be
affected by light when in the acid bath, and in
the developer, they must be manipulated in a
very weak light. The black and sepia papers
should not be kept together in the same tin,
and neither should the two kinds of prints be
cleared and fixed together in the same bath, as
otherwise the purity of the blacks in the cold
bath paper will suffer.
Red Prints by Development. — The Photo Zeitung
published the following formulae : —
A. Oxalate potash
(neutral) . . i oz. 120 g.
Water . . 4 oz. 154 mins. 480 ccs.
B. Copper chloride . 32 grs. 8 g.
Water . . 2 oz. jj mins. 240 ccs.
C. Mercuric chloride . 120 grs. 30 g.
Water . . 2 oz. yy mins. 240 ccs.
D. Lead acetate . 8 grs. 2 g.
Water . . i oz. 38 mins. 120 ccs.
Take 12 parts of A and 4 parts of B, stir together,
and add 4 parts of C and i part of D ; heat
until the precipitate is dissolved, filter, and use
at a temperature of 185° P. (85° C). Fix in
dilute hydrochloric acid, follow by ■■\ weak bath
of ammonia, and finally wash in water.
Development with Glycerine. — The addition of
glycerine to a developer allows of considerable
control and of local development. The print is
laid flat and the shadow parts coated with
glycerine. Three vessels are filled as follows : —
No. I, with full strength developer ; No. 2, with
a developer weakened a little, together with an
equal quantity of glycerine ; and No. 3, with a
still weaker developer with glycerine. No. i is
painted over the portions which are likely to be
too light, and then the other parts are rapidly
brushed over with the weaker solutions, using
strong or weak developer afterwards to get the
desired effect. Care should be taken to blend the
parts together so as to prevent the occurrence
of sharp dividing lines. Where backgrounds
are very light it is possible to get effective
vignettes simply by not working upon the edges-
with the developer. Some American workers
have paid particular attention to this process,
particularly Messrs. Stieglitz and Keiley, wha
give the following as their method of working : —
Using the heavier grades of paper, printing should
be carried further than for ordinary development,
as far, in fact, as to record the half-tones in the
high lights. When printed, the print is laid upon
a sheet of glass, a little glycerine being smeared
on the glass to keep the print flat and from
slipping about. The face of the print is then
evenly coated with pure glycerine, and blotting-
paper is pressed down upon it ; the print is then
thinly recoated and developed by means of
brushes, two solutions being used, one (A) con-
sisting of equal parts of normal developer and
glycerine, and the other (B) pure developer.
A is just used on those parts which it is thought
desirable to bring up furst ; B is used where a
pronounced shade is required. When develop-
ment has been carried far enough, the print is
blotted at that place, which should be re-covered
with glycerine and not again touched. To
introduce warm tones and so produce a print
in two colours, three additional solutions are
required: — (i) A strong solution of mercuric
chloride ; (2) ordinary developer plus the mer-
cury solution, and (3) glycerine developer plus
the mercury solution. The print is treated at
one place with mercurised developer and at
another with ordinary developer. The mercury
tone is more transparent than the ordinary
black tone so that development may be carried
farther. The work must be carried out in a
subdued light, as otherwise the high lights wiU
be discoloured. When development is complete,
the prints should be cleared in the ordinary
hydrochloric acid bath and washed.
Intensifying and Reducing. — The following
method, invented by Hiibl in 1895, wiU give
vigour to an under-exposed and pale black
print. Make up : —
A. Sodium formate .
48 grs.
11 g-
Distilled water
I oz.
100 ccs.
B. Platinum per-
chloride
10 grs.
2"3 g-
Distilled water
I oz.
100 ccs,
Add about 15 drops of each to i pz. of water,
immerse the weak print therein, rock the dish
until the picture is dark enough, and then wash
and dry. Some processes of intensifying weak
platinum prints alter the tone. One worker
has advocated an acid mixture of gallic acid
and silver nitrate, another an acid hyfiroquinone
and silver intensifier, and another a. ferrous
oxalate developer to which a. few drops of a
Platinous Chloride
421
Platinum Paper Substitutes
chloroplatinite solution have been added. Some
of the toning processes (Dolland's, for example,
which see) intensify as well.
To reduce over-printed platinotype prints,
immerse them in a saturated solution of chloride
of lime, and when sufficiently reduced transfer
them to a 5 per cent, solution of sodium sulphite
to stop the action of the lime, then wash and
dry. This reducer causes the paper to deteriorate
and is recommended only in exteeme cases.
Toning. — There are many processes for toning
black platinotype prints to other colours.
Both the Packham and DoUand processes are
good (see under the headings " Catechu Toning "
and "Dolland's Process"), the former giving
brown tones and the latter rich black ones.
Uranium is widely used for brown, red, and blue
tones, but does not give very permanent results.
An excellent formula is that advocated by Hiibl :
A.
Uranium nitrate .
96 grs.
28 g.
Glacial acetic add
96 „
28 „
Water .
2 02.
250 ccs.
B.
Potass, ferricyanide
96 grs.
28 g.
Water .
2 oz.
250 ccs.
C.
Ammonium sulpho-
cyanide
I oz.
138 g-
Water .
2 ,.
250 ccs.
For brown and red tones, add 5 drops of each
to I oz. of water. Thoroughly clear and wash
the prints, place in the toner, and allow to
remain until they are of the colour desired;
they go from black to brown, and then to a
red. The process slightly intensifies the print,
the darkest portions gaining more in proportion
than the light ones. For blue tones the A bath
is not wanted, the following being used instead: —
D. Ammonia-iron-alum
Hydrochloric acid
Water .
96 grs. 28 g.
96 mins. 25 ccs.
2 oz. 250
Add 12 drops of D to 5 oz. of water, then add
successively 5 drops of B and 12 drops of C.
Immerse lie print therein and rock tiie bath
until of the desired tone. The dish must be
thoroughly cleaned before using for brown tones.
Stale Platinum Paper. — ^When stale paper
must be used, potassium bichromate may be
added to the oxalate developer, but a more
satisfactory salt is the neutral potassium chro-
mate, f gr. of which should be added to i oz.
of the ordinary developer diluted with one-third
water. Paper five years old has been known
to give good bright prints by this treatment.
J gr. per ounce has been known to give good
results on paper two years old.
PLATINOUS CHLORIDE (See "Platinum
Bichloride.")
PLATINOUS POTASSIUM CHLORIDE (See
" Potassiimi Chloroplatinite.")
PLATINUM (Pr., Platine : Ger., Platin)
Pt. Atomic weight, i93'4. A white heavy
metal found native in the state of impure ores.
It is very infusible and practically unaffected
by the atmosphere or most adds, but readily
soluble in aqua regia. When deposited in a
finely divided state it is an intense black and
forms the image in the platinotype process.
PLATINUM BICHLORIDE (Pr., BicMorure de
platine : Ger., Platindichlorid)
Synonyms, platinous chloride, platinum
dichloride, platinochloride. PtCl,. Molecular
weight, 264-4. Solubilities, insoluble in water,
soluble in hot hydrochloric acid. A greyish
green or brown powder obtained by reducing
platinum perchloride by heat or sulphurous
acid. It is not used in photography, but it is
used to prepare potassium chloroplatinite.
A solution of this salt in hydrochloric add
yields chloroplatinous acid HjPtCl, or PtClj
2HCI.
PLATINUM PAPER, SUBSTITUTES FOR
Many attempts have been made to produce
on bromide and other papers effects similar to
those given by platinotype. A number of the
platino-matt papers may be made to produce
platinum-Uke prints, but the two can always
be distinguished by applying a drop of a solution
of mercuric chloride as used for intensifying.
The solution bleaches the part of the bromide
print to which it is applied, but has no effect
upon a platinum print.
Spedal papers have been made for yielding
prints resembUng platinum, and of the home-made
kinds, that prepared according to the formula
worked out by Dr. Vollenbach, and published
in the Deutsche Photo. Zeitung, is considered one
of the best. It is said to yield rich deep platinum-
like blacks even from weak negatives. Paper
is immersed for three or four minutes in : —
Gelatine ... 22 grs. 5 g.
Citric add . . 13 „ ^3 „
Chrome alum (sol. i : 20) 220 mins. 50 ccs.
Aluminium chloride
(10% sol.) . . 44 „ 10 „
Distilled water . 10 oz. 1,000 „
After immersion hang up to dry. It is sensi-
tised (in yellow light) with : —
A. Gelatine . . 2-2 grs. \ g.
Salicylic add . -4 „ i-io „
Distilled water . 1 oz. 100 ccs.
B. Green ammonia
dtrate of iron . 38 grs. 20 g.
Distilled water . i oz. 100 ccs.
C. Silver nitrate . 55 grs. 12-5 g.
Distilled water . 1 oz. 100 ccs.
D. Uranium nitrate . 38 grs. 20 g.
Distilled water . i oz. 100 ccs.
By using more of C, softer prints are produced ;
more of B gives hard prints ; less of D gives
browner tones ; and more of D gives blue-black
tones. For greyish - black resembling platino-
type, use I part of A and B and 2 parts of
C and D. Mix in the order above given, or
else a predpitate is formed and a muddy solu-
tion results. Pour the solution on the paper,
pinned to a board, in a littie pool and then
distribute with a wad of cotton-wool ; finaHy
dry quickly but evenly. Expose the same as
with platinum paper until detail is faintly
visible, and develop with —
Ferrous sulphate
Acetic add
Distilled water .
188 grs. 43 g.
67 mins. 14 ccs.
10 oz. I,ODO „
When sufficientiy developed, place the print in a
Platinum Perchloride
422
Platinum Toning
I per cent, solution of nitric acid for three
minutes and then fix in —
Sodium hyposulphite 785 grs. 180 g.
Sodium sulphite (cryst.) no „ 25 „
Sulphuric acid . . 14 mins. 3 ccs.
Water ... 10 oz. i.ooo „
The prints are apt to reduce slightly in the
fixing bath.
PLATINUM PERCHLORIDE (Pr., Chlorure
de platine ; Ger., Platinchlorid)
Synonyms, platinic chloride, platinum tetra-
chloride, chloroplatinic acid, muriate of platina.
HsPtCl, 6H2O or PtCl,2Ha 6H2O. Mole-
cular weight, 516-4. Solubilities, i in i water,
soluble in alcohol and ether. A dark brown
mass or red crystals obtained by dissolving
platinum in aqua regia and evaporating. It is
chiefly used as the starting point for the manu-
facture of potassium chloroplatinite, but is also
occasionally used for toning.
PLATINUM TETRACHLORIDE {See "Plat-
inum Perchloride.")
PLATINUM TONING
The theory of platinum toning is the same
as that of gold toning, explained under that
heading, except, of course, that platinum is
substituted for gold. The earliest form of bath
consisted of i gr. of platinic chloride in 15 oz.
of water, and it was not until the introduction
of the platinotype printing process, when
potassium chloroplatinite was made available,
that platinum toning became almost if not quite
as popular as gold for silver prints, particularly
those upon matt papers. As with gold, almost
any tone may be obtained.
Print-out Silver Papers. — Two stock solutions
are necessary : —
A. Common salt
Alum .
Water .
i OZ.
55 g-
55 „
1,000 ccs.
This may be made up with hot water, and is
ready for use when cold.
B. Potassium chloro-
platinite . . 40 grs. 9 g.
Water . . 10 oz. 1,000 ccs.
The chloroplatinite is sold in sealed glass tubes
containing 15 grs. Soak off the label, place
the unbroken tube in the bottle or measure
with the water, and break the tube while in
the water. Each quarter ounce (120 drops) of
the solution will contain i gr. of the chloro-
platinite ; the mixture should be kept in the
dark. Tones may be varied from red-brown
to warm black by using a mixture of from 10
to 160 drops of B, I oz. of A, and 10 oz. of
water, this quantity being sufficient for ten
half -plate prints or their equivalent. The prints
dry of a darker tone than they appear when
wet ; and therefore toning should be stopped
just before the desired tone is reached, judging
the tone by looking through the prints. Toning
invariably continues in a slight degree during
the washing previous to fixing, unless a " stop
bath " be used, such a bath consisting of 100 grs.
of sodium carbonate crystals in 10 oz. of water.
After toning, prints are washed and fixed as
usual.
Alternative Baths for Silver Prints. — Some
alternative baths will now be given.
Cowan's Bath
Common salt . . 10 grs. 2-3 g.
Potass, chloroplatinite i „ -23 „
Chrome alum ( I % sol.) 10 oz. 1,000 ccs.
Phosphoric Bath
Potass, chloroplatinite 4 grs. 2 g.
Phosphoric acid (sp. gr.,
I-I20) ... I drm. 28 ccs.
Distilled water . 4I oz. 1,000 „
The phosphoric acid is the " acidum phosphor-
icum dilutum " of the British Pharmacopoeia.
Wash and fix as usual. (Many other acids can
be used in this way.) Prof. Namias states that
the phosphoric acid may be advantageously
replaced by oxalic acid.
Platinum may be used in the combined
toning and fixing form. A good formula is : —
Sodium hyposulphite i oz. 1 10 g.
Lead nitrate . . 60 grs. 14 ,,
Alum . . . 60 ,, 14 ,,
Sodium formate . 20 „ 4-6 ,,
Formic acid . . i drm. 6 ccs.
Platinum bichloride . 2 grs. -5 g.
Hot water . . 10 oz. 1,000 ccs.
Dissolve the lead and sodium formate in a smalt
quantity of the water, then the " hypo " and
the other ingredients (except platinum) in the
remainder. Mix together, allow to stand in an
uncorked bottle for 24 hours, and then add the
platinum bichloride. The prints (P.O.P.) should
be passed through a weak salt and water bath
before toning.
A formula for the " Haddon " platinum
toning bath is given in an article under that
name. For platinum and gold baths (combined)
see under " Gold and Platinum Bath."
Bromide Papers. — Most of the above baths
may be used for bromide papers, and the follow-
ing is recommended : —
Hydrochloric acid . 50 mins. i ccs.
Potass, chloroplatinite 5 grs. i g.
Distilled water . 10 oz. 1,000 ccs.
Toning for about twenty minutes should give
a good black image. Wash, fiix in " hypo,"
and wash again thoroughly.
C. W. Somerville's toner (1902) is as follows : —
Potass, chloroplatinite 20 grs. 4-6 g.
Merciuric chloride . 10 „ 2-3 „
Citric acid . . 90 ,, 200 ,,
Distilled water . 10 oz. 1,000 ccs.
I oz. of this will tone three or four half-plate
prints in about twenty minutes ; the print is
previously fixed and washed, and after toning,
again fixed and washed. H the sepia toned
print is immediately subjected to an ordinary-
developer as used for bromide paper, the black
colour will return with great intensification,
but washing will prevent this.
Lantern Slides. — Lantern slides of the gelatine
variety may be toned by any of the above pro-
cesses, but the most widely used bath is —
Platystigmat Lens
423
Pneumatic Release
Hydrochloric acid . i mia. "2 cc.
Platinum chloride . i gr. -2 g.
Water . . .10 oz. 1,000 ccs.
This tones rapidly, but reduces slightly.
PLATYSTIGMAT LENS
An anastigmatic lens introduced by Wray,
and consisting of two nearly symmetrical
cemented triple combinations. It has an
initial intensity of ///-J and an extreme angle
of 90°. The back lens may be used alone, and
nas a focal length about double that of the
complete combination.
PLAYERTYPE
A process for the direct copying of engravings,
invented by J. Hort Player in 1896. The
engraving (line drawing) to be copied is laid
face downwards upon a perfectly flat surface,
the sensitive (bromide) paper is laid film side
downwards upon it, and a sheet of glass placed
over all. A yellowish light is then held over
the glass, the exposure being made through the
glass and the sensitive paper. From three to
ten minutes may be necessary in yellow light
according to the sensitiveness of the paper ;
with white light the exposiire is much shorter.
The developer recommended for this work
which is screwed to the side of the camera with
its edge parallel to the back. The bottom of
the pendulum will then point to a notch on the
plate when the back is vertical. Pattern B has
a pivoted needle weighted at the lower end, and
attached to the side of the camera as before
described ; the point of the needle indicates on
a scale whether or not the back is upright.
PLUMBAGO
A synonym for blacklead.
PLUMBAGO PROCESS
The " dusting-on " process, with plumbago
(blacklead or graphite) used as the powder.
Employed in the ceramic process and for making
duplicate negatives. Wood engravers some-
times make use of it as a means of obtaining
prints on wood.
PNEUMATIC HOLDER (Pr., Ventouse pneu-
matique : Ger., Pneumatischer Platten-
halter)
A rubber bulb with a flat disc at one end, as
illustrated. It is used to hold plates by " suc-
tion " when coating with collo^on, varnishing,
etc. The bulb is pressed to expel the air and
the disc is held against the plate, to which, on
Hydroquinone .
Sodium sulphite
Sodium carbonate
Water
30 grs. 7 g.
120 „ 28 „
240 „ 56 „
10 oz. 1,000 CCS.
Development is continued jintil the image
appears to be buried. Having obtained a
negative in this way, prints may be obtained
from it by contact printing. The method
has the advantage of giving a direct copy (a
paper negative) of the same size as the original,
and, of course, without using a camera. The
clearer and more contrasty the original drawing
of engraving the better will be the copy on the
bromide paper, but should the latter be faulty,
it may be intensified, reduced or cleared. The
process was modified somewhat in 1900, when
a sheet of green glass was laid over the paper
and the exposure, of from five to ten minutes,
made through that.
PLUMB INDICATOR (Pr., Phmb photo-
graphique ; Ger., Photographische Blei-
wage)
An appliance fitted to stand cameras to enable
the back to be rendered truly vertical. The
Two Patterns of Plumb Indicator
pattern shown at A consists of a swinging
pendulum or pointer attached to a brass plate.
Pneumatic Holder
releasing the pressure on the bulb, it immediately
clings, enabling the latter to be lifted as if by a
handle and supported in any required position.
Those of red rubber are best. It is advisable
to immerse the holder in lukewarm water before
using, or the part of the plate directly over the
bulb may be chilled, and imeven coating result.
PNEUMATIC RELEASE (Pr., Poire pneu-
matique ; Ger., Pneumatische Birne)
A rubber ball with tube connection, by means
of which the camera shutter can be operated
without the necessity of touching it, or, if
needful, worked from a convenient distance by
having a sufficient length of tubing. Many
diaphragm shutters have a metal tube at one
side, in which a piston connected to the mechan-
ism slides up and down. The free end of the
rubber tubing is stretched over this metal tube,
when pressure on the ball at the other end
compresses the air, pushes up the piston, and
releases the shutter. RoUer-blind shutters
usually work on a difierent principle; these
have at the end of the tubing a small rubber
bulb, which is adjusted beneath the catch that
retains the wheel regulating the spring blind.
In this case pressure on the ball inflates the
bulb, which pushes up the catch and releases
the wheel. Studio pneumatic shutters mostly
have a tap next to the ball ; this, if turned after
pressing the latter, prevents the return of the
compressed air, so that the shutter remains open
Pocket Camera
424
Poisons, Sale of
for focusing, etc., until the tap is turned in the
contrary direction.
POCKET CAMERA (Pr., Chambre de poche :
Ger., Taschenkamera)
Very small hand cameras are now made,
some of them capable even of going in a waist-
coat pocket. When well-made and fitted with
a first-class lens they are apt to be expensive,
as the mechanism and adjustments call for
great neatness and accuracy. The shutters are
usually marvels of compactness and ingenious
design. With the short-focus lenses used, great
depth of definition is attainable, and the small
negatives wiU bear any reasonable degree of
enlargement. Such cameras call for considerate
handling. If one is constantly carried, it is
well to have a small leather bag to protect it
from dust and grit.
POISONS AND THEIR ANTIDOTES
The table given below is due to J. V. Elsden,
and is reprinted from the Brit. Journ. Phot.
Almanac. Br. R. J. Hillier, in commenting
upon Elsden's table, which he regards as reliable
and accurate, recommends that in all cases of
poisoning a doctor should first be sent for, and
in the meantime an antidote given, and vomiting
induced by tickling the throat or by drinking
strong mustard and water or lukewarm water.
Acids are antidotes for alkalis and vice versa,
but there is danger in giving strong acids and
alkalis as antidotes, and unprofessional treat-
ment should seldom go beyond some such
emetic as mustard and water. Except where
strong acids and alkalis have been taken,
25 grs. of zinc sulphate forms a good emetic.
If a highly irritant poison, such as a strong add
(not pyrogallic) or alkali, or potassium cyanide,
has been swallowed, the only hope of saving
life is the prompt application of the antidote.
POISONS. SALE OF
The following statement is due to B. J. Wall,
and is reprinted from the Photographic
Dealer. According to the Pharmacy Act,
1868, it is illegal for any person not being a
duly registered pharmaceutical chemist or
chemist and druggist, to sell certain chemicals
and substances, which are included in a schedule,
this being divided into two parts. In the first
part are included those substances which can
only be sold when the purchaser is known to
the seller, or is introduced by some person
known to the seller, who must enter the date of
sale, name and address of purchaser, name and
quantity of article, purpose for which it is re-
quired, which must be attested by the purchaser's
signature ; and the parcel or vessel must be
labelled with the name ot article, the word
" Poison," and the name and address of the
seller. For those articles included in Part 2
of the schedule only the three last requirements
have to be fulfilled. There are really very few
photographic chemicals included in the schedule,
and not any that are used in considerable
quantities. Corrosive sublimate, mercuric per-
diloride or mercuric chloride, is included in
THE CHIEF PHOTOGRAPHIC POISONS AND THEIR ANTIDOTES
Poisons
Remarks
Characteristic Symptoms
ocm t Oxalic Acid,
9^^ \ including
;>o; ( Potassium Oxalate
C Ammonia
Potash
Soda
'Mercuric Chloride
S g
8-£
Lead Acetate
Potassium Cyanide
Potassium Bichrom-
ate
^Silver Nitrate
Nitric Acid
HVDROCHLORIC AciD
Sulphuric Acid
Iodine
Ether
Pyrocallol
I dram is the smallest
fatal dose known.
Vapour of ammonia may
cause inflammation of
the lungs.
3 grains the smallest
known fatal dose.
The sub-acetate is still
more poisonous.
a. Taken intCTnally, 3 grs.
fatal.
b. Applied to wounds and
abrasures of the skin.
a. Taken internally.
6. Applied to slight abra-
sions of the skin.
2 drams have been
fatal. Inhalation of
the fumes has also
been fatal.
\ oimce has been fatal.
1 dram has been fatal.
Variable in its action ; 3
grains have been fatal.
Poisonous when inhaled.
2 grains sufficient to kill
a dog.
Hot burning sensation in throat
and stomach ; vomiting, cramps,
and numbness.
Swelling of tongue, mouth, and
fauces ; often followed by stric-
ture of the oesophagus.
Acrid, metallic taste, constriction
and burning in throat and
stomach, followed by nausea and
vomiting.
Constriction in the throat and at
pit of stomach ; crampy pains
and stiffness of abdomen ; blue
line round the gums.
Insensibility, slow gasping respi-
ration, dilated pupils, and spas-
modic closure of the jaws.
Smarting sensation.
Irritant pain in stomadi and
vomiting.
Produces troublesome sores and
ulcers.
Powerful irritant.
Corrosion of windpipe and violent
inflammation.
Acrid taste, tightness about the
throat, vomiting.
Effects similar to chloroform.
Resembles phosphorus poisoning.
Chalk, whiting, or magnesia sus-
pended in water. Plaster or
mortar can be used in emergency.
Vinegar and water.
White and yolk of raw eggs with
milk. In emergency, flour paste
or " hypo *' solution may be used.
Sulphates of soda or magnesia.
Emetic of sulphate of zinc.
No certain remedy ; cold affusion
over the bead and neck most effi-
cacious.
Sulphate of iron should be applied
immediately.
Emetics and magnesia, or chalk.
Common salt to be given immedi-
ately, followed by emetics.
Bicarbonate of soda, or carbonate
of magnesia or chalk, plaster of
the apartment beaten up in water.
Vomiting should be encouraged,
and gruel, arrowroot, and starch
given freely.
Cold affusion and artificial respira-
tion.
No certain remedy. Speedy emetic
desirable.
Acetic Acid, concentrated, has as powerful an effect as the mineral acids.
Poitevin, Alphonse Louis
425
Polyscope
Part I. " Cyanide of potassium and all metallic
cyanides and their preparations " is another
item in Part i. It is an open question whether
this term may not be strictly held to include
the ferri-, ferro-, and sulpho-cyanides ; as a
matter of fact, however, it is held that these
preparations are not to be classed as scheduled
poisons. Part 2 includes preparations of mer-
curic chloride ; therefore any intensifier contain-
ing this cannot be sold except by a registered
chemist. It qlso includes oxalic acid, which is
but rarely used, and mercuric iodide and sul-
phocyanide.
Under the Poisons and Pharmacy Bill, 1908,
Section 5 states, " It shall not be lawful to sell
any poison to which this section appUes by
retail, unless the box, bottle, vessel, wrapper
or cover in which the poison is contained is dis-
tinctly labelled with the name of the substance
and the word ' Poison,' and with the name and
address of the seller of the poison." The poisons
here enumerated are sulphuric, nitric, and
hydrochloric acids, and tiie soluble salts of
oxalic acid. Presumably this would include
even the dilute acids, although no differentia-
tion as to strength is made. " Soluble salts of
oxalic acid " naturally includes neutral potassium
oxalate, and the oxalates of ammonium, sodium,
and iron, also presumably potassium ferric
oxalate and all preparations in which these
may be contained. It will be seen that really
there are very few scheduled poisons used in
photography, but it must not be forgotten that
there are many chemicals which are poisonous
beyond these, and it would be as well to label
as " Poison " aU ferro-, ferri-, and sulpho-
cyanides, bichromates, pyro, and all prepara-
tions of copper, uranium and cerium. If this
is thought too drastic, then at least a warning
label should be devised, somewhat on the
following lines, " Care should be exercised in
the use and storing of this chemical, as when
taken internally it is poisonous." There is no
difficulty in a firm of dry plate makers, etc.,
selling a poison to a wholesale house so long
as it is marked " Ploison." The Act only applies
to sale to the public.
POITEVIN, ALPHONSE LOUIS
Bom at Conflans, Prance, 18 19; died at the
same place 1882. He was a chemist and engineer,
and took up the study of photography immedi-
ately after Daguerre's (fiscovery was made
known. He secured an award for a method
of photo-chemical engraving upon plates coated
with silver and gold. In 1855 he patented a
" heUo-plastic " process, by which films of
bichromated gelatine were exposed to light
under a negative and then soaked in water ;
parts of the picture were then in relief and a
mould was taken. In the same year he discovered
that bichromated gelatine which had been
exposed to light would allow greasy ink to
adhere to it, ^though it repelled water. Upon
these facts he in 1856 based a photo-lithographic
process, and he is looked upon as the practical
founder of the carbon process, photo-lithography
and collotype printing. In 1867 he was awarded
the greater part of a prize of 10,000 francs for
the discovery of permanent photographic print-
ing processes.
POLARISATION
The splitting up or division of a ray of light
into two distinct refracted parts.
POLARISCOPE (Pr., Polariscope ; Ger., Po!ar-
iskop)
When a ray of light falls on a crystal of Iceland
spar in a direction not parallel with the principal
axis, it is doubly refracted and split into two
parts. One part, known as the ordinary ray,
obeys the usual laws of refraction ; the other,
known as the extraordinary ray, behaves in
quite a different manner. For examining the
phenomena of polarised light a polariscope is
employed ; this usually consists of two Nicol
prisms mounted in separate tubes, the lower
Nicol Prism
one being known as the polariser and the upper
as the analyser. A Nicol prism is a rhomb of
Iceland spar cut along the long diagonal, as
shown at A, the two halves being then cemented
together with Canada balsam. The ordinary
ray has a higher refractive index than the
bisam and is accordingly got rid of by total
reflection, as at B, while the extraordinary ray
passes through without interruption. If the
analyser is rotated above the polariser the field
is gradually darkened, and when the two planes
are at right angles the light is extinguished.
The polariscope is frequently used with the
microscope. {See also " Nicol Prism.")
POLARISER
A Nicol prism mounted in a tube, as described
under the heading " Polariscope."
POLARISED LIGHT
Light rays that have been doubly refracted
or split up.
POLYCHROME. POLYCHROMATIC, AND
POLYCHROMOTYPE
Terms applied to photographs and photo-
graphic reproductions in several colours.
POLYPOSE PORTRAIT
A portrait in which the sitter appears in two
or more different positions. (See " Doubles " and
" Multiple Photography.")
POLYSCOPE (Pr., Polyscope ; Ger., Polyskop)
An apparatus patented by Robert H. Baskett.
A suitable box contains two surface-silvered
mirrors, with provision for adjusting these to
any angle, which must, however, be capable
of dividing into 360° without remainder. On
placing a suitable object, such as a piece of
lace, fiagree work, floral decoration, or, in fact,
almost anything of pleasing outlines, at the
end of the box, the pattern is repeated sym-
metrically as in the kaleidoscope. H the subject
Ponton, Mungo
426
Portrait Lenses
is then suitably lighted and a camera placed
■with its lens pointing into the box at the junction
of the mirrors the ornamental arrangement may
be photographed. Such patterns are of great
assistance in making commercial designs.
PONTON, MUNGO
Born at Balgreen, 1802 ; died at Clifton, 1880.
He was the first to observe the effects of the
sun's rays on potassium bichromate, and on
May 29, 1839, he communicated to the Society
of Arts for Scotland " a cheap and simple
method of preparing paper for photographic
drawing in which the use of any salt of silver is
dispensed with." His process was to spread a
solution of potassium bichromate upon paper
and expose it with a suitable object laid upon
it to the sun's rays ; the light acted upon and
hardened certain parts, while those which were
not acted upon could be dissolved away, leaving
the object white upon a yellowish brown ground.
He obtained copies of drawings and images of
dried flowers in this way, and fixed them
simply by washing in water. In 1849 he
published a method of registering the hourly
variations of the thermometer by means of
photography.
P.O.P.
Printing-out paper. Generally understood
to mean gelatino-chloride paper, used for all-
roimd work. The initials were first used by
the Ilford Company in 1891.
P.O.P. GASLIGHT PAPER
Ordinary P.O.P. can be made into gaslight
paper by a process of converting the soluble
silver salts into silver bromide, or into a mixture
of silver haloids with a predominance of bromide.
The P.O.P. should be immersed in the following
solution for five minutes in the dark-room or
in a very weak light and then washed and dried
in the dark : —
Potassium bromide
Potassium iodide
Copper sulphate
Water
36 grs. 3-3 g.
12 ,, i-i „
25 oz. 1,000 ccs.
A 5 per cent, solution of potassium bromide
may be used with some papers instead of the
above. After drying, the paper may be treated
as gaslight paper.
PORCELAIN CLAY (See "Kaolin.")
PORCELAIN DISHES {See "Baths.")
PORCELAIN, PHOTOGRAPHS ON
The usual method of producing photographs
upon porcelain is by the carbon transfer process.
They may also be produced by the photo-
ceramic and blue-print processes, etc., when the
porcelain can be coated and sensitised. Photo-
graphic opals are sometimes referred to as
porcelain plates. {See also " Photo - litho-
phane.")
PORCELAINOGRAPHY
A name given in the early 'fifties to the art
of printing photographs upon porcelain, opal,
and similar substances.
POROTYPE (Fr., Porotype ; Ger., Porotypie)
A Continental process of copying engravings,
depending on the fact that the ink lines are
practically impervious to a certain gas as com-
pared with the paper. A paper coated with a
chemical pigment that is bleached by the gas
is pressed into contact with the engraving, and
the back of the latter is subjected to the gaseous-
fumes, which are obstructed by the lines of the
picture ; these therefore remain pigmented in
the copy, while the unprotected ground is
bleached.
PORTA. GIAMBATTISTA DELLA
An eminent Italian naturalist; born 1543,
died 161 5. He is the reputed inventor of the
camera obscura (1569), but he more probably
only improved the instrument.
PORTRAIT LENSES
Almost any lens working at an aperture o£
//6 or larger is suitable for portraiture provided
that its focal length is not less than ij times
that of the longest side of the largest plate
which it will have to cover. The name is,
however, by common consent confined to the
Petzval form, known as the " ordinary " portrait
lens, and also to the Dallmeyer, or " patent,"
portrait lens. The principal features of this
type of lens are great rapidity, some lenses
having an intensity of //2, and extremely good
definition over a moderate angle. The field
of a portrait lens is usually curved, and this may
in some cases be regarded as an advantage,
inasmuch as it allows the knees and feet of a
sitting figure to be focused equally well with
the head without reduction of aperture. The
Dallmeyer type of portrait lens has a great
advantage over the original Petzval, as it allows
the focus to be softened and distributed over
several planes by turning the back cell, and thus
increasing the difference between the two glasses
which compose the back combination. Starting
with absolute sharpness, the definition may be
softened by degrees until fuzziness ensues by
simply rotating the back cell. The latest
model of this lens has the back cell fixed, and
the softness is obtained by rotating the entire
lens tube. The front combination of most
portrait lenses may be used alone, and if they
are to be employed for portraiture it is advisable
that they be left in their normal position — that
is to say, with the convex side to the sitter.
By so doing sharper definition over a. limited,
but sufficient, field is obtained, without serious
reduction of aperture. Should it be desired
to use the front lens for landscape work, it is
desirable that the flat side should be turned
to the view, and the diaphragm closed until
the desired sharpness is obtained. Portrait
lenses may be used for outdoor work, and
latterly have been in demand for reflex cameras.
Portrait lenses are liable to give " flare spot "
when used out of doors with small apertures,
but this tendency is minimised if the diaphragm
is placed in front of the lens instead of in Sie
ordinary position. In selecting a portrait lens
care should be taken not to choose one of too
short a focal length. If possible this should be
about twice that of the trimmed print, say
8 in. for cartes, iij in. for cabinets, and 20 ia.
Portraiture, Composite
427
Portraiture
to 24 in. for panels. Besides the recognised
portrait type, special portrait lenses are made
on the Cooke model, and these have the " diffu-
sion of focus " adjustment. Most enlarging
objectives are of the Petzval portrait lens con-
struction, and may be used in the camera with
good results. Magic-lantern lenses are also of
this type, but are usually corrected for the visual
rays only, and will not give a sharp image on
the photographic plate.
PORTRAITURE, COMPOSITE {See "Compo-
site, Analytical, or 'Average' Portraits.")
PORTRAITURE
In all portraiture, the question of appar-
atus is not nearly so important as those of
posing and lighting. The camera should pre-
ferably be of the stand variety, but hand cameras
are also capable of producing good work ; the
ordinary fixed-focus pattern without magnifiers
is not to be recommended for the work, as unless
a very small stop is used the image will not be
in focus, although such a camera answers for
full-length portraits if the subject is suflSdently
far enough away. I^enses that work at a fairly
large aperture are the best for indoor portraiture.
(See " Portrait Lenses.") The focal length of the
lens is a matter of importance ; the greater the
focal length the more truthful is the result, as
a rule ; if a lens embracing a very wide angle
is used, distortion is almost sure to occur, and
the size of the nose, ears, hands, or feet will
appear exaggerated. The question of iso-
chromatic versus ordinary plates for portrait
work need not be discussed here. Either may
be used; but an isochromatic plate will do
all an ordinary plate will do and a little more.
More truthful rendering of colour is obtained
by using a screen, but the exposure is thereby
prolonged. Many professionals use isochromatic
plates for certain subjects — such, for example,
as very freckled faces, yellowish hair, coloured
dresses, etc. A rapid plate is the most suitable
for indoor work where the exposure is to be
perhaps somewhat lengthy. Many of the plate
makers give in their instructions special
developers for portrait work, and photographers
cannot do better than use them. They are com-
pounded to give soft negatives, and are specially
suitable for Qie plates with which they are issued.
If no such special formula is given the usual
developer will generally serve, but if the results
are too hard the developer may be diluted with
water so as to secure a softer result. Adurol,
pyro-soda, and pyro-ammonia are very suitable.
When " single solution " developers, patent
concoctions or otherwise, are used, the safest
way of securing a soft result is to develop until
the image just appears, and then to transfer to
a dish of clear cold water in which the image
will go on developing slowly, giving it if required
a moment or so in the developer occasionally
and then transferring to the water. This
method of developing brings out detail and
gives softness in a remarkable manner. When
the negative has sufficient detail and density
it should be fixed in the usual manner.
Outdoor Portraiture. — This is one of the com-
monest forms of photography and one in which
failure frequently occurs. The old rule of
placing the sitter in the brightest light possible
does not in these days of rapid lenses and plates
give the best results as a rule. It is the too
strong light that spoils many attempts at outdoor
portraiture, and the more the light can be con-
A. Equal Lighting, causing Flatness
trolled, the better and more artistic are the
portraits likely to be. Outdoor portraits fre-
quently lack diaracter, are flat, and devoid of
any efiects of light and shade which characterise
professional studio work ; and yet by working
carefully one may easily obtain an effective
portrait of a sitter. With two sitters this is
more difficult, and it increases as the number
of sitters grows. The usual defect in the outdoor
portrait is flatness, caused by the light reaching
the sitter from both sides and the top alike, as
in A. Here it is supposed that the model is
placed against a wall, hedge or other foliage to
serve as a background, there being nothing on
either side of or above the sitter to stop the
immense flood of light, as represented by the
arrows A, B and C. What is wanted is a trifle
more light on one side of the face than the
other, in order to obtain " roundness." It is
sometimes difficult to get the required light and
shade in the open, but a big tree is a useful
accessory when utilised as shown at B. If the
sitter is placed by the side of the trunk it may
serve to cut off some of the side-light, while the
boughs above will cut off superfluous top light.
More portraits are perhaps taken in back yards
or gardens than in the field ; in such cases a
dark folding screen, or even an open umbrella,
<^o
B. Side Light cut oH by Tree
may be used with advantage to check the exces-
sive light, but more often the trouble is overcome
by arranging the positions of the camera and
sitter. C represents the plan of part of a garden
or back yard of the ordinary type. Against a
Portraiture
428
Portraiture
door is a favourite place to pose a model, say as at
B, and success will depend upon the lighting, type
of door or portico, etc. Doors may be made
to serve admirably if the portrait is professedly
an outdoor one and the figure three-quarter or
n
C. Portraiture at
Back of House
D. Portable
Studio
full length. It is, however, almost hopeless to
take a bust porteait with an artificial back-
ground placed as at B, because ordinarily there
would be an equal amount of light on each side
of the face. If a portrait head is to be taken
and the effect aimed at is an artistically Ughted
studio effect, it would be better to place the
sitter in the angle, as at A, and the camera parallel
to the waU as shown. By so doing, the wall
acts as a screen, and one side of the face is
slightly in shadow. By allowing the camera
to remain in the same positipn and placing the
sitter at c, the result would even be flatter than
at B, because the sitter is at a greater distance
from the wall. In cases where the precise
positions shown cannot be taken up, it is possible
to carry out the same principles of lighting in
other ways. The sitter could, for example, be
placed in the angle A, and the camera parallel
to the house at c, in which case the wall, possibly
with foUage, would serve as a background, and
the house itself as a screen for the light. There
are many other obvious ways of securing more
light on one side of the face than the other,
which system of Ughting will alone give the
necessary roundness and lifelike appearance
to portraits taken out of doors.
E. Frame for Portable Studio
Backgroujids are usually required for studies of
heads, particularly when taken out of doors,
as any bricks, foHage, etc., appearing behind the
head are apt to distract the attention. For full
and three-quarter figures, however, natural back-
grounds serve very well, but in no case should
they be so sharply focused as the subject.
Ugly and unpromising backgrounds may very
often be made to serve by placing the sitter
well in front, using a large stop in the lens,
F. Side Light causing Harsh Lighting
and focusing the eyes of the model and not the
background.
When much portrait work is to be done out
of doors, as in the case of pageants, bazaars,
fgtes, etc., it is advisable to make a kind of
portable studio, as shown at D and E, a
useful size for which is 8 ft. by 6 ft. Three
frames are made of 3-in. by i-in. wood, 8 ft.
high and 6 ft. broad ; one serves as the back
and the two others are hinged thereon to serve
as wings ; a fourth frame is made to fold over
the top, and is covered with white mushn, as
are also the two top halves of the wings. The
bottom halves are covered with dark material.
Blinds are fitted over the white muslin at the
side and top, in order that the amount of light
reaching the interior may be regulated. Hooks
or bolts keep the wings and top in position
during use. A plain cloth background is then
fitted to the back frame, or, if preferred, it may
be left open and when in use pushed back
against a suitable natural background.
A common defect in amateur portraits taken
out of doors is the dark appearance of the
sitters' faces, usually due to under-exposure,
or to the use of a too brilliant background.
When the sky is the background for a person's
head, the face invariably comes out very dark,
and halation often occurs. Models without
hats are usually represented as having darker
faces than those who wear large hats, because
the latter act more or less as backgrounds and
serve to isolate the face from the sky. An
open umbrella or sunshade may occasionally
be used to make the face appear clearer.
E F
G. Room used as Studio
Indoor Portraiture. — Home portraiture indoors
is a difficult branch of photography, because of
the limited amount of light admitted by an
ordinary window, and because what light there
is comes from one point, which, in the absence
Portraiture
429
Posing
of precautions, gives harsh black - and - white
efEects. A simple experiment, and one which
embodies all the principles of indoor lighting
for portraits, is the following : In a darkened
room place a lighted candle upon a table and
window is a large bay or French window, and
the glass goes almost to the ground level. All
sorts of lighting may be obtained in a home
studio such as Uiat described, as the sitter can
be placed at any spot between s and a with
^^
1
s^\
w
/ ^
4c
w W
w
/.
I J K L
Six Kinds of Lighting Available in Room-studio
beside it an orange or a ball, as shown at F.
The sphere is strongly lighted on one side only.
If a sheet of tissue paper or muslin is held at
A B, not only is the light softened on the candle
side of the sphere, but it is also diffused, so that
the shadow side does not appear so dark. If,
in addition, a sheet of white paper or cardboard
is held at c D the light will be reflected on to
the shadow side of the sphere, to the great
advantage of the lighting or modelling. This
illustrates both the principles and practice of
indoor portrait lighting, the window being
represented by the candle and the sitter by the
sphere. The only way of securing satisfactory
results is by diffusing the light and using a
reflector. G is a diagram of an ordinary room
having comers D, E, F, G. Should there be two
or more windows on opposite sides, all but one
of these should, in most cases, be blocked up,
as otherwise the cross-lifting will produce
unsatisfactory results. One window is really all
that is required, and it must be one into which
the sun does not directly shine. By placing
the camera at c against the blocked-out window
(the background at b) and the sitter at s, one
would, if neither reflector nor diffuser be used,
get a harsh result because all the light would
come from the window side. Therefore, tissue
paper is placed over the bottom half of the
window and the top half is left clear. The blind
can be worked over the top half so as to admit
or block out top Ught as desired. A reflector —
white paper, cardboard, or a sheet — should be
N. Controlling Lighting
with Two Curtains
O. Simple Arrange-
ment for Lighting
Heads
used at R, and the degree of reflection regulated
by its size and the angle at which it is placed.
Too much, however, must not be expected
from the home studio, and the beginner will do
well to attempt nothing but busts unless the
equally good results, and the position of the
camera can also be altered. Even the difficult
" Rembrandt " lighting can be secured by
placing the camera and sitter somewhere about
H and I respectively. Diagrams H to M (based
on illustrations appearing in the Photo Revue}
show six kinds of lighting obtainable in such
a room. The letters indicate the position of
window w, sitter s, camera c, background b,
and reflector R, and the arrow indicates the
direction in which the model is looking. The
lightings illustrated are : H, ordinary lighting
with one window ; I, normal lighting witti two
windows ; J, " Rembrandt " lighting ; K and
I/, profiles with different lightings ; M, " against
the light" effect.
In some cases a large and suitable window
may be available at the end of a corridor or in
a room which does not permit of the camera
being placed in the positions shown in the
diagrams. An American worker (W. C. Vivian),
who produces excellent work, has such a window
and he adapts it as shown in diagram N. He
uses two curtains, one, A, dark and opaque, to
pull up from the floor high enough to serve as a
background for the figure ; this will necessitate
the camera being pointed directly at the window
The top curtain, b, which is drawn down and into
the room to reflect the light from the window
on to the figure, should be drawn far enough
below the top of the dark curtain to prevent
direct rays of light from entering the lens. The
top of a white curtain rests on brackets which
project out from the wall several feet, with
notches to enable one to shift the curtain to or
from the window top, by which means there may
be obtained an over-head light or a more direct
light on the face, as may be required.
A very simple system of lighting heads is
shown at O. A window should be fitted with a
long white blind, which is pulled down (or out)
as far as possible, and suspended above a sitter
posed against the window. The top part
serves as a reflector for top light, while the
lower acts as a reflector for side light. The
light at the window is controlled by means of
tissue paper or muslin.
Hints on work in the studio are given under
the heading "Studio Portraiture."
POSING
In photography the posing of the figure has
to be cousi(£red from a different standpoint from
Posing Chairs and Head Rests 43°
Positives in Colours
■what would be suitable in painting, on account
of the exaggeration of perspective in short-focus
lenses. Care should be taken so to pose a figure
that the whole arrangement of figure and dress
is as much in the same plane as possible. With
sitting figures, the chair should be placed slightly
turned to one side, so that the legs and feet
•do not unduly extend into the foreground. The
arms and elbows should rarely be allowed to rest
on both arms of the chair, but ease of pose is
often obtained by resting on one arm — the one
farther from the camera ; in photographing
ladies, it is in most cases better to avoid the use
of chairs with arms, as a much more graceful
pose can be obtained by allowing the dress to
fall over the side of the chair. The standing
figure allows of much variety of pose, in which
the hands play a very important part, but great
care must be taken to see that they are so
arranged as not to appear awkward. If the
body is turned so as to present a side view to the
camera, one foot — preferably that farther from
the camera — should be advanced in front of the
other. Should one arm hang down at the side
towards the camera, it should be slightly bent.
The hand should be in such a position that the
breadth of the back of the hand does not show,
but turned so as to show its side and therefore
narrowest view ; the fingers should be arranged
so that the index finger forms a continuation of
the chief line.
When the profile is pretty, the head may
assume a looking-down position, but such poses
need careful arrangement, and there should be
an obvious reason for the position. In such a
position, and should a book be held, avoid any
parallel position of the two arms ; this is easily
done by holding a top corner of the book with
■one hand and with the other the diagonal corner.
Sunshades, fur boas, and ribbons, all provide
useful accessories for obtaining graceful poses by
giving opportunities for the arms to be raised in
many difierent positions, always remembering
to avoid straight lines and sharp angles which
a.ie particularly undesirable.
For head and shoulder pictures, the model
may sit on a chair having a small and somewhat
high seat. Allow the figure to lean slightly
forward away from the back of the chair, as this
avoids any appearance of rigidity. The head
turned in a slightly difierent position from the
direction of the body gives a suggestion of alert-
ness.
POSING CHAIRS AND HEAD RESTS
Various kinds of chairs are made for studio
use, with a head-rest attached, a revolving seat,
and sometimes a platform on castors so that the
sitter may be moved to where the best lighting
is obtainable without altering the pose. In these
days of rapid plates, however, with artificial
Uluminants to render the operator independent
of dull weather, such mechanical aids as the
head-rest are falling into disuse, the more so as
they tend to render the average sitter uncom-
fortable and constrained. The modem aim is
to make the studio as much like an ordinary room
as possible, and to avoid fussy preparations or
too deliberate posing. But with some sitters, or
where a perfect light is not obtainable, such
accessories are very necessary.
POSITIVE
The direct opposite to a negative ; a repro-
duction of the object with lights and shadows
as in nature. A photographic print is a positive,
but the term is rarely used except to describe
pictures upon glass — chiefly transparencies.
The word was first used by Sir John Herschel
in 1840.
POSITIVE ABERRATION
The most usual form of spherical aberration,
in which the marginal rays come to a focus nearer
the lens than do the central rays.
POSITIVE BATH (Pr., Bain positif ; Ger.,
Positivhad)
An indefinite and practically obsolete term
applied to the silver nitrate solution used for
sensitising collodion positives, to the sensitising
solution employed with albumenised and plain
salted papers, and also to the tanks or dishes
holding these.
POSITIVE FERROTYPE (See "Pellet
Process.")
POSITIVE FOCUS
The focal length, or the position of the sharpest
image of a distant object when projected by a
positive lens. Negative focus is the reverse of
this, a negative lens having a degree of concavity
sufficient to neutralise a positive lens of any
given focal length.
POSITIVE LENS
A lens capable of producing a convergent
beam of rays or of projecting a real image.
All photographic lenses, and telescopic and micro-
scopic objectives are positive lenses. Formerly
a positive lens was necessarily convex in its
external form, but recent improvements in glass
manufacture have rendered it possible for a
positive lens to be made with two blank surfaces,
or even to have a small amount of concavity.
POSITIVE PROCESSES
Processes that produce a positive result from
direct exposure, as distinguished from processes
that yield a negative. The term is correctly
applied to all methods of obtaining a positive
result, whether by optical means or printing
from the negative. The first photographic
process, the daguerreotype, was a positive
process, and for many years collodion positives
were very largely produced, but, strictly, the
latter are negatives, the images being formed
of a light coloured deposit, while the dark colour
of the enamel of the ferrotype or a piece of
dark velvet placed behind the glass forms the
shadows. A similar result can be obtained on
an ordinary dry plate by developing lightly,
bleaching Uie image in mercuric chloride after
fixing and washing, and, after again washing and
drying, backing it up with a piece of dark velvet.
The autochrome and other screen-plate processes
are positive after the reversal.
POSITIVES IN COLOURS
There have been many methods of obtaining
positives in colours. E. J. Wall, in American
Photography, has summarised them as (i) the
Positives, Direct
431
Positives, Direct
so-called diazotype processes (fully described
under the heading " Diazotype "), in which the
action of light on diazo compounds is utilised
by the formation of dyes from the compounds
thus formed or decomposed by light. (2) That
class in which a silver image is obtained in the
ordinary way, and then converted into a salt
which acts as a mordant for the dye. The
second class was first described by Georges
Richard in Comptes Rendus, 1896, and ten
years later Traube, of Munich, patented a pro-
cess, known as " diachrome," which is the
application of Richard's principle. Traube
converts a silver image into silver iodide by
immer.sion in —
Iodine
. 87 grs.
20 g.
Potassium iodide
• 218 „
50 „
Distilled water to
10 oz.
1,000 ccs.
and then after washing immerses the positive
in a solution of a basic dye which immediately
precipitates or forms a lake with the iodide and
gives a coloured image. Dissolve the iodide in
a fifth of the water, add the iodine, stir till
dissolved, and add the remainder of the water.
The silver iodide is of course opaque, but this
may be dissolved out by potassium cyanide or
a " hypo " bath containing tannin or tartar
•emetic, the action of these substances being to
prevent the washing out of the dye. After
fixation the positive is merely washed, and the
image consists of a perfectly transparent dye
and is of extraordinary brilliancy and trans-
parency in the shadows. Basic dy^s must be
used, as so far the only acid dyes which give satis-
factory results are those of the triphenylmethane
series to which the cosines belong. The following
dyes are therefore available : acridine orange,
chrysoidine, rhodamine 6 G, rhodamine B,
xylene red B, methyl and crystal violet, victoria
pure blue B, and all the other victoria blues,
methylene blues, methylene green, brilliant,
€merald, diamond, and victoria greens, and all
the eosine group of dyes which comprises eosine,
«rytlirosine, rose bengal, phloxine, uranine, etc.
Compound tints are best obtained by successive
baths of different dyes, as mixtures are apt to
stain unequally. Frequently, too, good effects
may be obtained by first staining up with a basic
dye and then applying an acid dye ; and if the
combinations are suitably chosen, very intense
colours may be obtained in this way, as the basic
acts as a mordant for the acid dye.
Traube's process has been modified by many
workers, Tauleigne and Namias being notable
among them.
POSITIVES, DIRECT
The simplest method of obtaining a direct
positive upon a dry plate is to expose (avoiding
over-exposure) and develop in the usual way,
but not fix. After washing, immerse in
Potassium
ganate
Sulphuric acid
Water
perman-
5 grs. 1 g.
10 mins. 2 CCS.
10 oz. 1,000 ,,
until the image disappears. Next soak in a
weak solution of oxalic acid (4 grs. per ounce,
or about i g. per 100 ccs.) until the brown stain
is cleared from the gelatine. The plate is then
well washed, exposed to actinic light, again
developed, fixed m " hypo," and washed. For
the re-development the following is excellent : —
Metol ... 50 grs. ii'S g.
Sodium sulphite . 100 „ 23 ,,
Caustic soda . 50 ,, ii'5 ,,
Water ... 10 oz. 1,000 ccs.
The permanganate reversing (or reducing)
bath may be replaced by a 5 per cent, solution
of ammonium persulphate with 5 per cent, of
alum, the weak oxalic bath being omitted.
Major-General Waterhouse recommends re-
ducing the exposure to one-thirtieth of the
normal, developing and fixing as usual, but
using the following developer : —
Lithium carbonate . 50 grs. 11 '5 g.
Sodium sulphite . 50 ,, ii-$ ,,
Eikonogen . . 50 „ ir; „
Thiocarbamide (saturated
solution) . . Pew drops
Water ... 10 oz. 1,000 ccs.
Another method suitable for very slow plates
is to expose, develop until the image is seen on
the glass side, wash, and immerse in —
Potassium bromide
Iodine
Water
500 grs. 115 g-
100 „ 23 „
10 oz. 1,000 ccs.
until the image is bleached. Then wash, develop
with any developer in strong daylight, wash and
fix.
Lantern Slides and Bromide Paper. — ^The
above methods may be used, but the late
Douglas Carnegie worked out what is considered
to be a more certain process. The lantern plate
or other slow plate should be backed ; it is ex-
posed (avoiding over-exposure), developed with
metol - hydroquinone, washed, and immersed
for about two minutes in the following re-
versing bath, which, in hot weather, needs to
be diluted : —
Potassium bichromate
Nitric acid (pure)
Water
75 grs. 17 g.
45 mins. 9 ccs.
10 oz. 1,000 „
After bleaching in this bath for a moment only,
replace in the developer, rock the dish for about
30 seconds, and then, while still in the developer,
expose to light, for say 20 or 30 seconds, at a
distance of i ft. from an ordinary No. 4 burner.
The second development must not be pushed
to the point of fogging the background. Fix in
an acid fixing bath. Bromide prints may be
obtained direct in the camera in the same way,
using " glossy " paper ; a weaker light (equal
to one candle) is placed 2| ft. distant from the
print lying in the dish, and allowed to act until
the edges of the paper protected by the rebate
begin to darken. The colour is not very pleasing
and should be modified by toning, sulphide
being preferable.
Balagny recommends developing a plate
with acid-amidol (see " Amidol, or Diamido-
phenol"), washing thoroughly, exposing for
30 to 45 seconds to diffused daylight, and then
immersing (in the dark-room) in —
Potass, bichromate
Nitric acid
Water
150 grs.
60 mins.
35 g.
13 ccs.
1,000 „
Postage Stamp Photographs 43^
Postcards
This converts the image into silver chromate,
which is dissolved out by a lo per cent, solution
of sodium sulphite plus 3 per cent, of acid
bisulphite. The plate is next well washed, when
nothing remains but the exposed silver haloids,
which are developed with acid amidol minus
the bromide.
POSTAGE STAMP PHOTOGRAPHS
For producing these professionally, a camera
containing a battery of small lenses may be used,
its interior being partitioned into as many
sections as there are lenses, thus securing a
number of images on one negative. The illus-
tration shows a camera for taking nine photo-
Postage Stamp Camera
graphs on a quarter-plate. The back of the
camera has brass plates A to take the dark-slide ;
the front is at b ; and an easel for supporting
the original photograph at c. The box is 6 in.
by 5 in., its depth depending on the focal length
9f the lenses used. For a one-third scale reduc-
tion, as in reducing a quarter-plate original to
one-ninth that size, the distance between lens
and plate will be the focal length of the lenses
plus one-third that focal length ; the result
multiplied by three gives the distance between
lens and copy. Thus, with a 3-in. focus lens.
3 + -=4m.,
while
the distance between lens and
plate ; while 4x3 = 12 in., the distance
between lens and copy. The divisions are
of blackened wood or cardboard partitions.
In the front, but not illustrated, are circular
openings to take the nine small lenses, and the
hinged shutter D is worked by the projecting
rod E. The box is attached to a baseboard P.
Pinholes could be used instead of lenses, but the
exposure would be greatly prolonged.
The camera can be adapted for direct por-
traiture by providing focusing adjustment, and
omitting the easel. Printing from a negative
produced in this camera can be done in an
ordinary printing frame, using a suitable mask
and a multiple border negative for producing
the stamp effect. The perforations are done by
a special machine, after the backs of the sheets
have been brushed over with dextrine and allowed
to dry.
In the absence of a special camera, a succession
of images can be printed on a single sheet of paper,
using a repeating printing frame, and the result
may, or may not, be copied in the camera to
produce a negative from which a large number
of images can quickly be printed.
POSTCARDS
The popularity of the postcard (invented in
1869 by Dr. E. Hermann, of Vienna) has increased
enormously since about 1 894, owing to the intro-
duction of picture postcards, the authorising of
private postcards, and the withdrawal of the
c c
A. Arrangement for Printing Postcards
regulation confining the written matter to one
side only. As to who first produced a picture
postcard there appears to be some difference
of opinion ; it is known that at the time of the
Franco-German war a French stationer published
such a card to commemorate the visit of a popular
regiment to his city.
Postcards ready sensitised are supplied by
the dealers, or any good cards may be sensitised
at home by the blue-print, kaUitype, silver or
other processes. Plain postcards are sometimes
not pure enough to produce the best effects,
and it is always better to purchase them ready
sensitised with bromide or print-out emulsion,
or to obtain the unsensitised cards from a manu-
facturer of sensitised postcards.
As negatives may be larger or smaller than
the average postcard (5|- in. x 3^ in.) care is
necessary in printing and masking. Many
special kinds of postcard printing frames are
obtainable, but an ordinary large printing frame
can be made to serve. Half-plate is a handy
size from which to print a postcard, as the image
can then extend right to the edges. Smaller
plates than postcard size need masking, which
may be done by using a half-plate frame and
placing in it a piece of plain glass and a piece
of white or light cardboard. In the cardboard
is cut an aperture large enough to take the plate.
Lantern binding strips are then placed over the
junction of the card and the negative (see A),
to hold it in position and to serve as a mask for
giving a straight edge to the picture. When
the correct position of the image on the postcard
has been found guide marks c are made on the
cardboard to enable cards to be placed in posi-
B. Using Corrugated Paper as a Rack
for Drying Postcards
tion quickly (see diagram A). Packets of post-
cards very often contain black paper masks
with openings of various shapes, and these are
extremely useful. For the addition of borders,
see " Border Printing " and " Borders, Fancy,"
H
Post-mortem Photography
433
Potassium Borotartrate
and for the addition of titles, see " Lettering
Negatives and Prints." Postcards are exposed,
developed, toned, etc., in the same way as other
prints, but there is sometimes difSculty in causing
them to dry flat. Collodion and most self-
toning cards may be dried under pressure
between blotting-paper, but gelatine-surfaced
cards would be spoilt by such treatment, al-
though the risk would be reduced by hardening
with formaline. One of the best ways of drying
gelatine cards is to bend them archways, picture
side outwards, and catch the ends in corrugated
paper as at B. Large producers sometimes
nail laths to a board and use the board in the
same way as the corrugated paper. The cards
generally flatten out naturally when released,
or may easily be made to do so, whereas if
allowed to dry naturally, they curl inwards and
often crack, especially in the case of collodion
cards, when any attempt is made to flatten them
after drying.
POST-MORTEM PHOTOGRAPHY
Downey's photograph of the body of King
Edward VII., the most widely published post-
mortem photograph known, indicates that the
best results are to be obtained by placing the
camera on a level with the head or only very
slightly above that level, and showing the face
in profile. There should be a dark backgroimd,
or, failing this, the light should enter the room
from behind the camera so as to illuminate the
profile, the background being then dark by
comparison. The full-face view is less pleasing
and more difficult to obtain in the absence of
special facilities, which, however, are common
on the Continent, where post-mortem photo-
graphy is widely practised ; but photographs
of bodies for identification purposes are nearly
always taken fuU-face, and usually in a coffin,
the latter enabling the body to occupy a more
suitable position for photographing. One of
the most serious difficulties in this work is
due to the loss of brilliancy in the eyes, which
has a. large part in determining the character-
istic expression of the individual. Bertillon (of
finger-print fame) has recommended the injection
of glycerine into the eyes, and the restoration
of file colour of the lips with carmine.
POTASH ALUM OR POTASSIUM ALU-
MINIUM SULPHATE (See "Alum.")
POTASSA SULPHURATA
An old name for potassium sulphide.
POTASSIUM AMMONIUM CHROMATE
(See " Ammonium and Potassium
Chromate.")
POTASSIUM BICARBONATE (Pr., Bicar-
bonate de potasse ; Ger., Saures Kohlen-
saures Kalium)
Synonym, acid potassitun carbonate. KHCO,.
This must not be confounded with potassium
carbonate. Molecular weight, loo. Solubihties,
I in 3 water, almost insoluble in alcohol. A fine
white dry powder obtained by treating a solution
of potassium carbonate with carbonic add. It
is rarely used in photography. It should not be
confused with the carbonate, KjCO.
28
POTASSIUM BICHROMATE (Pr., Bichromate
de potasse: Gei. , Kaliumbichromat, Saures
Rotes Ckromsaures Kalium)
Synonyms, potash or potassium dichromate ;
acid or red potassium chromate. KjCr^O,.
Molecular weight, 294. Solubilities, i in 10
water, insoluble in alcohol and ether. Large
orange-red translucent crystals obtained from
chrome iron ore. It is poisonous, the antidotes
being emetics and the use of the stomach pump,
soap, magnesia, or calcium saccharate. It is
readily absorbed by the skin, and gives rise
in some people to extremely painful indolent
ulcers all over the body, but particidarly on the
hands and arms. Citrine ointment is recom-
mended as the best remedy to apply to the sores,
but it is stated that a liberal washing of the
hands with salt or sodium bisulphite solution
will prevent any ill effects from its use. It is
employed in the carbon process and many
photo-mechanical processes, as when in contact
with organic matter, such as gelatine, fish-glue,
and other colloids, it is decomposed by light
and renders them insoluble. According to
Lumi^e and Seyewetz the action of light may
be represented by the following equation :
KjCr^O, = CrjO, + Kfi + 3O.
The potash immediately acts on excess of the
bichromate and forms potassium chromate,
which is much less sensitive.
In process work, potassium bichromate is used
for sensitising photo-lithographic paper, carbon
tissue, collotype plates, and the albumen coat-
ing for zinc. The ammonium salt has largely,
if not entirely, superseded it for the fish-glue
enamel coating. In some formidae a mixture
of the potassium and ammonium salts is used.
By the addition of liquor ammonise to bichro-
mate sensitising solutions, the double compound
of potassium ammonium bichromate is formed
and makes a more stable solution. In the
Paynetype process a 5 per cent, solution of
potassium bichromate is used as a hardening
bath. It is also used with sulphuric acid as a
glass-cleaning pickle.
POTASSIUM BISULPHITE (Pr., Bisulfite
de potasse ; Ger., Saures Schwefligsaures
Kalium)
Synonyms, acid potassium sulphite, potassium
hydrogen sulphite. KHSO,. Molecular weight,
120. Solubilities, soluble in water, insoluble
in alcohol. A white crystalline powder smelling
of sulphurous acid and obtained by passing
sulphurous acid gas into potassium carbonate
solution. Occasionally it is used as a pre-
servative,
POTASSIUM BITARTRATE
Synonjmis, cream of tartar, acid potassium
tartrate. (CHOH), COOH COOK. Molecular
weight, 198. It is but seldom used.
POTASSIUM BOROTARTRATE (Pr., Tar-
trate boro^otassique ; Ger., Kaliumboro-
tartrat)
Synonym, soluble cream of tartar. C8H2(OH)a
(COO)jBOK. Molecular weight, 214. Solubili-
ties, I in '75 water. A fine white powder, com-
posed of equal parts of potassium metaborate
Potassium Bromide
434
Potassium Dichromiate
and bitartrate. It has been recommended as a
restrainer in development, but is rarely used.
POTASSIUM BROMIDE (Pr., Bromure de
potasse ; Ger., Bromkalium)
Synonyms, bromide of potassium or potash.
KBr. Molecular weight, 119. Solubilities, i in
i'5 water, i in 750 alcohol. White cubical crys-
tals prepared by adding bromine to caustic
potash or decomposing ferrous iodide with potas-
sium carbonate. It is used as a restrainer in
development, and in gelatine emulsion making
to form silver bromide. When added to a deve-
loper it actually slows the plate — that is to say,
it prevents the developer from bringing out the
very faintest traces of light action, unless the
development is very prolonged.
In process work, potassium bromide is used
in making up the copper-bromide intensifying
solution for wet-plate negatives. This solution
is also sometimes used for bleaching out silver
prints which have been drawn upon with pen
and ink.
POTASSIUM CARBONATE (Pr., Carbonate
de potasse ; Ger., Pottasche, Kohlensaures
Kalium)
Synonyms, potash, pearlash, subcarbonate
of potash, salt of tartar, salt of wormwood.
KjCOj. Molecular weight, 138. Solubilities,
I in 9 water, insoluble in alcohol and ether. A
white graniilar hygroscopic powder, obtained
from wood ashes. It is used as the accelerator
in development.
POTASSIUM CHLORATE (Pr., Chlorate de
potasse ; Ger., Chlorsaures Kalium)
Synonym, chlorate of potash. KCIO3. Mole-
cular weight, 122-5. Solubilities, i in i6'7 water,
slightly soluble in dilute alcohol, insoluble in
absolute alcohol. Colourless tabular cystals,
obtained by passing chlorine gas into a mixture
of milk of lime and potassiiim carbonate or
chloride, or electrolyticaUy from potassium
chloride. It is used in the sensitiser for platino-
type paper to give brilliancy to the image, but
its chief use is in flashlight mixtures. For the
latter purpose the powdered salt should be ob-
tained, and great care must be taken in mixing,
which should be done with a feather on a sheet
of paper, as the chlorate is very liable to explode
with friction.
In process work, it is used with hydrochloric
acid to form an etching solution for copper and
steel, known as the Dutch mordant.
POTASSIUM CHLORIDE (Pr., Chlorure de
potasse ; Ger., Chlorkalium)
KCl. Molecular weight, 74-5. Solubilities,
I in 3 water, insoluble in alcohol. It occurs in
white cubical crystals, and is prepared by neu-
tralising hydrochloric acid witii potassium car-
bonate. It is occasionally used in emulsion
making.
POTASSIUM CHLOROPLATINITE (Pr.,
Chloroplatinite de potassium ; Ger., Pla-
tinchlorusk alium )
Synonyms, chloroplatinite or platinochloride
of potash. KjPtClj. Molecular weight, 41 3-4.
Solubilities, i in 6 water, insoluble in alcohol.
It is in the form of ruby-red deliquescent crystals
obtained by reducing platinum perchloride with
sulphurous acid gas or cuprous chloride and
adding potassium chloride. It is used chiefly in
the platinotype process and also for toning silver
prints.
POTASSIUM CHROMA TE (Pr., Chromate de
potasse ; Ger., Chromsaures Kalium)
Synonyms, neutral or yellow chromate of
potash. KaCrOj. Molecular weight, 194. Solu-
bilities, I in 2 water, insoluble in alcohol. It
takes the form of lemon-yellow rhombic crystals,
and is obtained from chrome iron ore. It is
occasionally used as a light filter for sensito-
metric or ttiree-colour work. The acid chromate
is potassium bichromate.
In process work, the chromate has been sug-
gested as a sensitiser in place of bichromates,
but it has not come into favour.
POTASSIUM CITRATE (Pr., Citrate de
potasse; Ger., Citronensaures Kalium)
Synonym, tribasic citrate of potash.
KaCeHjO, HjO. Molecular weight, 342. Solu-
bilities, I in 0'6 water, slightly soluble in alcohol.
It is an extremely deliquescent granular powder,
prepared by neutralising citric acid with potas-
sium carbonate. It is used as a restrainer in
alkaline development, and also in the copper
toning bath. In consequence of its deliquescent
nature it is as well to prepare this salt in solu-
tion. To make 480 grains or 480 g., dissolve
295 grs. or g. of citric acid in 2 oz. or 960 ccs.
of hot water, and add gradually with constant
stirring 290 grs. or g. of potassium carbonate,
or enough to make the solution neutral to litmus
paper aEter heating. Pilter the solution and
make the total bulk up to 4 oz. or i ,920 ccs., which
will give a 25 per cent, solution. The stronger
the solution the longer it wiU keep ; when dilute,
it is extremely liable to grow myeHum fungus,
which may be prevented by the addition of a
little salicyUc add.
POTASSIUM CYANIDE (Pr., Cyanure de
potassium ; Ger., Cyankalium)
Synonyms, cyanide of potash, cyanide. KCN.
Molecular weight, 65. Solubilities, i in 2 water,
decomposed by heat, slightly soluble in alcohol.
It is very poisonous, the antidotes being chlorine
water, cobalt nitrate, 10 grains of iron sulphate
with I dram of tincture of iron in i oz. of water,
emetics, and ammonia. It shovdd be noted that
the gas given off by it is very poisonous also.
Occurs in white amorphous deliquescent lumps,
and is prepared by fusing potassium f errocyanide
with potassium carbonate in an iron crucible.
It is used as a fixing agent in collodion pro-
cesses, also in Monckhoven's intensifier, and
occasionally as a clearing agent for bromide
prints.
In process work, it is almost exclusively used
for fixing wet collodion negatives, and for the
" cutting " or reducing solution. Potassium
cyanide is also largely used in electro-deposition,
especially in plating with brass and copper, and
for cleaning the work before depositing on it.
POTASSIUM DICHROMATE (See
slum Bichromate.")
Potas-
Potassium Ferric Oxalate
435
Potassium Nitrite
POTASSIUM FERRIC OXALATE (Pr., Oxa-
late potassico-ferrique ; Ger., Kalium-
ferri-oxalat)
Pe(Cj04)3K;33HjO. Molecular weight, 491.
Solubilities, i in 16 water, insoluble in alcohol.
It is in the form of bright green crystals,
and is prepared by acidulating potassium
ferrous oxalate and exposing to light. A con-
venient solution can be made by adding ferric
chloride to potassium oxalate ; thus to make
480 grs. or g., dissolve 690 grs. or g. of neutral
potassium oxalate in 5 oz. or 2,000 ccs. of
distilled water and add 322 grs. or g. of lump
ferric chloride dissolved in a little water, and
make the total bulk measure 10 oz. or 4,800 ccs.
This will be a 10 per cent, solution. It is used in
some iron printing processes, but chiefly in
Belitski's reducer.
POTASSIUM FERRICYANIDE (Pr., Cyano-
ferride de potassium ; Ger., Ferrid-cyan-
kalium)
Synonyms, ferricyanide of potash, red prus-
siate of potash. KjPelCN),. Molecular weight,
329. Solubilities, i in 2-5 water, insoluble in
alcohol. It takes the form of deep red rhombic
crystals, prepared by passing chlorine gas through
a solution of potassium ferricyanide. Very
frequently the crystals become covered with a
yellow powder, which should be rinsed off before
use. It is employed in several iron printing pro-
cesses, but mainly as a reducer for negatives
and to bleach bromide prints before sulphiding.
In process work, it is largely used in making up
the lead nitrate intensifier, and in conjunction
with " hypo " as a reducer for dry-plate negatives.
POTASSIUM FERROCYANIDE (Pr., Cyano-
ferrure de potassium ; Ger., Ferrocyan-
kalium)
Synonyms, ferrocyanide of potash, yellow
prussiate of potash. K4pe(CN), 3H2O. Mole-
cular weight, 422. Solubilities, i in 4 water,
insoluble in alcohol. It consists of large yeUow
pyramidal crystals which are obtained by fusing
potassium carbonate with horn clippings, wool or
hair, and stirring with an iron rod. It is used
as a developer in some iron printing processes,
and has been suggested as an addition to pyro
and hydroquinone developers on the ground that
it prevents fog and gives greater density, but it
is rarely used for this purpose.
POTASSIUM FERROUS OXALATE (Pr.,
Oxalate de fer et potasse ; Ger., Kalium-
ferro-oxalat).
Pe(C204)jjKaH20. Molecular weight, 328.
Solubilities, insoluble in water and alcohol,
soluble in solutions of an alkaline oxalate or
citrate. It is a sandy-yellow powder, obtained
by adding potassium oxalate to excess of fer-
rous sulphate. Although it forms the actual
developing agent in iron development, it is
rarely used in the dry state, it being more con-
venient to make it as described under the head-
ing " Perrons Oxalate."
POTASSIUM FLUORIDE (Pr., Fluorure de
potassium ; Ger., Fluorkalium)
KP 2HaO. Molecular weight, 94. Soluble in
water. It is a white granular powder, prepared
by saturating hydrofluoric acid with potassium
carbonate. It is used for stripping films from
glass negatives ; the negative to be stripped
should be immersed in a 2 per cent, solution for
5 minutes and then immersed in a 2 per cent,
solution of sulphuric acid, when the film readily
lifts. It is more convenient than hydrofluoric
acid, as it keeps better and is less liable to attack
the mucous membranes, lungs, or skin.
POTASSIUM HYDRATE (Pr., Potasse caus-
tique ; Ger., Aetzkali)
Synonyms, caustic potash, potassium hy-
droxide. KHO. Molecular weight, 56. Solu-
bilities, I in -4 water, slightly soluble in ether,
I in 2 alcohol. It is poisonous, the antidotes
being vinegar, lemon juice, oil, and milk ; it
shoiJd not be handled, as it is an extremely
powerful escharotic and bums the skin. It is
in the form of white sticks, which are obtained
by decomposing potassium carbonate with milk
of lime. It is extremely deliquescent, and readily
attacks both corks and glass stoppers, so that
these should be well paraffined or vaselined.
It is chiefly used in alkaline developers.
In process work, the crude caustic potash
(American black ash) is largely used for clean-
ing old negative glass, for cleaning the resist and
it^ off zinc and copper plates after etching, and
for cleaning work previous to electro-deposition.
POTASSIUM HYDROGEN SULPHITE (See
" Potassium Bisulphite.")
POTASSIUM IODIDE (Pr., lodure de potas-
sium ; Ger., lodkali)
Synonym, iodide of potash, KI. Molecular
weight, 166. Solubilities, i in 0-75 water, i in
18 alcohol, -8 per cent, in collodion. It is in
the form of white cubical crystals, which are
obtained by adding iodine to caustic potash solu-
tion. It is used in emulsion making and for pre-
paring the mercuric iodide intensifier.
POTASSIUM METABISULPHITE (Pr., MHa-
bisulfite de potassium ; Ger., Kalium-
metabisulfit)
Synonym, metabisulphite of potash. KjSaOj.
Molecular weight, 222. Solubilities, i in 3 water,
insoluble in alcohol. It takes the form of clear
transparent crystals smelling of sulphurous acid
gas, and is obtained by passing sulphurous acid gas
through potassium carbonate solution and adding
absolute alcohol. It is used as a preservative in
developers and for acidulating the "hypo " bath.
POTASSIUM NITRATE (Pr., Azoiate de
potasse : Ger., Salpetersaures Kali)
Synonyms, nitrate of potash, nitre, saltpetre.
KNOj. Molecular weight, 10 1. Solubilities, i
in 3'8 water, very slightly soluble in alcohol. It
occurs native and is also obtained by decompos-
ing lime clays with urine. It is usually met with
in a fine white powder or prismatic needles, and
is used in the manufacture of pyroxylin and in
fiash powders.
POTASSIUM NITRITE (Pr., Azotate de potas-
sium : Ger., Kalinitrit)
KNO2. Molecular weight, 85. Solubilities,
I in I water, insoluble in alcohol. It occurs in
Potassium Oxalate
436
Potsissium Sulphocyanide
white deliquescent sticks. It is occasionally-
used for making actiuometer paper. It must
not be confounded with potassium nitrate.
POTASSIUM OXALATE (Fr., Oxalate neutre
de potasse ; Ger., Neutrales Oxalsaures
Kali, Kaliumoxalat)
Synonym, neutral oxalate of potash,
KjCjOiH^O. Molecular weight, 184. Solubili-
ties, I in 3 water, insoluble in alcohol and ether.
It occurs in white crystals, and is obtained by
saturating oxalic acid or acid oxalate of potash
with potassium carbonate. It is used in the
ferrous oxalate developer and for develop-
ing platinotypes, and must be either acid or
neutral.
POTASSIUM PERCARBONATE (Pr., Per-
carbonate de potasse ; Ger., Kaliumper-
carhonat)
KjCjOjHjO. Molecular weight, 216. Solu-
bilities, I in 15 water. It is a white crystalline
powder obtained by electrolysis of potassium
carbonate. It is used as a " hypo " eliminator,
and is sold under fancy trade names.
POTASSIUM PERCHLORATE (Fr., Perchlo-
rure de potassium ; Ger., Ueberchlor-
saures Kali)
KCIO4. Molecular weight, 138-5. Solubili-
ties, I in 65 water, insoluble in alcohol. It is
in the form of colourless rhombic crystals or
powder. It is used in flashlight mixtures, and
the same precautions should be taken in mixing
this as with potassium chlorate.
POTASSIUM PERMANGANATE (Fr., Per-
manganate de potasse ; Ger., Ueberman-
gansaures Kali)
Synonym, permanganate of potash. KMnOj.
Molecular weight, 158. Solubilities, i in 16
water, decomposed by alcohol. It occurs in
violet-black needle-like crystals with green
metallic lustre, obtained by fusing manganese
peroxide with potassium hydrate or nitrate. It
is used to reduce negatives, and when acidulated
with sulphuric acid tends to reduce the high
lights more than the shadows. In a neutral solu-
tion it practically acts as an intensifier, as a
manganese salt is precipitated on the silver
image which gives it a more nonactinic colour.
It is also used as a test for " hypo," as a " hypo "
eliminator, and to produce reversal of the image
in the Lumi^re autochrome process.
In process work, a few drops of a 10 per cent,
solution of potassium permanganate added to
the wet collodion silver bath, when it is sus-
pected of being charged with organic matter,
neutralises the bath and combines with the
foreign matter, precipitating it as a black
powder. The bath should be stirred whilst the
solution is being added, and when it assumes
a pale violet colour it should be exposed to sun-
light. As soon as the bath is clear, it should be
filtered and re-addiEed.
POTASSIUM PERSULPHATE (Fr., Persul-
phate de potasse ; Ger., Ueberschwefel-
saures Kali)
Synonyms, persulphate of potash, anthion.
KjSjOg. Molecular weight, 270. Solubilities,
1 in 50 water, insoluble in alcohol. It is in the
form of white crystals obtained by electrolysis
of potassium sulphate. When dissolved in
water it readily parts with its oxygen, and is
used to eliminate the last traces of " hypo."
POTASSIUM PHOSPHATE (Fr., Phosphat de
potasse : Ger., Phosphorsaures Kali)
Synonym, monopotassic orthophosphate.
KjHPOj. Molecular weight, 174. Solubilities,
soluble in water, insoluble in alcohol. It con-
sists of colourless crystals, and is used as an
addition to the developer for platinotype paper.
POTASSIUM PLATINOUS CHLORIDE OR
POTASSIUM PLATINO-CHLORIDE
(See " Potassium Chloroplatinite." )
POTASSIUM SILICATE (Fr., Silicate de
potasse : Ger., Kaliwasserglas, Kiesel-
saures Kali)
Synonyms, soluble glass, potash water glass.
Solubilities, i in 3 water, decomposed by alcohol.
It takes the form of vitreous masses with green-
ish tinge, and is obtained by fusing fine sand and
potassium carbonate. It is usually met with in
the form of a sjrrupy yellowish liquid. It is
occasionally used as a substratum for dry plates
and for collotype plates.
POTASSIUM AND SODIUM TARTRATE
(Pr., Sel de Seignette ; Ger., Seignettesalz,
Rochellesalz, Weinsaures Kalinatron)
Synonyms, Rochelle or Seignette salts.
KNaCjH^Oe 4H2O. Molecular weight, 282.
SolubiUties, i in 1-4 water, almost insoluble in
alcohol. It is in the form of colourless trans-
parent crystals or white powder, and is obtained
by boiling together cream of tartar and sodium
carbonate. Chiefly it is used in printing-out
emulsions, to form silver tartrate.
POTASSIUM SUBCARBONATE (See
" Potassium Carbonate.")
POTASSIUM SULPHIDE (Pr., Foie de soufre ;
Ger., Schwefelkalium, Schwfelleber)
Synonyms, Uver of sulphur, sulphurated
potash, potassium trisulphide. KjSj. Molecular
weight, 174. It consists of amorphous masses
with the colour of Uver, and is obtained by fusing
together sulphur and potassium carbonate. It
is very deliquescent, and absorbs carbonic acid
from the air and gives off sulphuretted hydro-
gen. It is used to precipitate silver sulphide
from spent " hypo " baths. Its old name was
potassa sulphurata.
POTASSIUM SULPHOCYANIDE (Pr., Sulfo-
cyanure de potassium ; Ger., Rhodan-
halium, Schwefelcyankalium)
Synonyms, potassium thiocyanate, sulpho-
cyanate, or rhodanide. KCNS. Molecular weight,
97. Solubilities, i in -46 water, soluble in
alcohol. It is in the form of transparent de-
liquescent crystals, and is obtained by fusing
together sulphur, potassium carbonate, and
ferrocyanide. It is chiefly used in the sulpho-
cyanide toning bath. It is also a solvent of
gelatine, and has been therefore suggested for
developiug over-exposed carbon prints.
Pounce
43;
Press Photography
POUNCE
A name for pulverised saudarach.
POUNCY'S PROCESSES
Pouncy, of Dorchester, was the first to work
in England the carbon process in the form it
was invented by Poitevin, the French pioneer
in photo-mechanical work. Pouncy invented
several processes of photo-lithography. In 1863
he patented a carbon tissue for photo-litho-
graphic transfers. The tissue was made by
coating tracing-paper with a mixture of print-
ing ink, asphaltum, benzole, and fatty matter,
with or without potassium bichromate. The
paper is exposed to light with the plain side next
to the negative, developed in turpentine, dried,
and transferred to a damp, cold stone.
POUND
In apothecaries' weight, by which formulae
are made up, a pound is 5,760 grs. or 12 oz., and
is the equivalent of 373-276 g. (say 373^ g.).
In avoirdupois weight, by which chemicals are
sold, it is 7,000 grs. or 16 oz., and is the equiva-
lent of 4S3'S9 g. Approximately, 1 kg. = 2-2 lb.
avoir. In fluid measure, it is 5,760 mins. or
1-2 oz., and is the equivalent of 340-8 ccs.
POWDER (OR DRY) DEVELOPERS
Powders which need only to be dissolved in
water to form workable developers. Almost
any developer may be made up in this way, the
quantities suf&cient for 10 oz. of water being
mixed together and divided into 10 parts, each
of which, when required, is dissolved in i oz. of
water. The powder must be kept as airtight
as possible, and should always be packed in
waterproof paper and also in tinfoil. The in-
gredients shomd be very fine, quite dry and
well mixed, and thoroughly dissolved before
they are applied to the plates or papers. In
many formulae, of course, it will be necessary
to have two packets of powder, one containing
the developer proper and the other the alkali,
and it is ad-yisable to use distinctive papers—
" Seidlitz powder " style. Anhydrous chemi-
cals should be used when possible.
A two-powder metol-hydroquinone developer
is given below as a sample formula : —
A. Metol
. 240 grs.
Sog.
Hydroquinone .
• 480 „
100 „
Boric acid.
• 120 „
25,,
B. Sodium sulphite
. 480 grs.
100 g.
Borax
• 120 „
25 ,.
Sugar of milk .
• 120 ,,
25.,
Make up A into lo-gr., and B into 20-gr. papers,
and, for use, dissolve one of each in i oz. of
water.
POWDER PROCESS
This is better known as the dusting-on pro-
cess (which see).
The following, however, was introduced as a
powder process, and is based on the reduction
of the persalts of iron into proto-salts by the
action of light. It was invented in 1858 by H.
Gamier and A. Salmon, of Paris, in competi-
tion for the award offered by the Due de Luynes
for the purpose of sol-ving the problem of pro-
ducing absolutely permanent photographs. Well-
sized paper is coated with a strong solution of
ferric ammonio-dtrate in water ; ha-vdng been
dried in the dark, it is exposed under a positive
tran.sparency to daylight until the image is
faintly visible. The paper is pinned to a flat
board, and, by diffused daylight, very dry and
fine lampblack or other pigment is brushed over
the paper with a pad of cotton-wool or a camel-
hair brush. By breathing upon the paper the
parts not acted upon by Ught become somewhat
sticky and retain the black pigment ; thus,
details of the image appear and in time the pic-
ture is complete. The print is fixed by immers-
ing in water, which washes out the sensitive iron
salts. The print is then dried and varnished.
In process work, there are several methods
of powdering to form add resists. For instance,
the so-called " dry enamel " method is a powder
process, development being performed by dust-
ing a hygroscopic film of gum and bichromate so
that the parts which have not been acted upon
by light absorb the powder. These parts are
readily deared away after the plate has been
burnt in. There is also the dragon's-blood
powdering process, which is very largely used
for zinc etching. The Austrian process of zinc
etching depends on a method of building up
the image with asphaltum powder.
PRAXINOSCOPE
An appliance resembling the phenakistoscope
and zoetrope, the motion pictures being seen in
mirrors.
PRECIPITATION
The separation of any solid from a solution.
It may be diemical, as in the case of the sub-
sidence of barium sulphate from a mixture of
sodium sulphate and barium chloride ; or it
may be due to the lowering of temperature, as
when a saturated solution of any salt at a
given temperature becomes colder and unable
to hold so much in solution.
PRESERVATIVES
Substances which preserve or keep unaltered
the original character of any substance. In the
early days of collodion dry plates a great num-
ber of preservatives (some of which are named
under the heading "Coffee Process ") were used,
which kept the sensitive film moist and acted as
halogen absorbers during exposure. In the pre-
sent day of alkaline developers, such chemicals
as sodium sulphite, potassium metabisulphite,
nitric add, etc., are used to preserve the actual
developing agent from oxidation. In sensitised
papers containing free silver nitrate, citric or
other organic add is used for the same purpose.
PRESS PHOTOGRAPHY
Photography with the object of obtaining illus-
trations for use in newspapers, magazines, books,
etc. All important papers that make a spedal-
ity of printing photographs of current events
have a permanent staff of photographers, are in
touch with agencies which also have a similar
staff, and have representatives here, there, and
everywhere ; they keep a keen look-out for sub-
jects of interest, and make arrangements for
recording everything that can be known before-
hand. "Thus almost the only chance for the
Pressure Frame
438
Print Indicator
outsider is to be fortunate enough to secure a
subject that could not be got by the usual press
photographers. Even then he must make haste
to turn his advantage to account. It is often
advisable to send the undeveloped plate or film
with all expedition to the paper likely to use the
subject ; and, failing that, the negative must
be developed, and clean bright prints made at
once and dispatched. There are several means
of expediting the production of a finished print
from a negative, and these must be taken advan-
tage of. Any necessary description or explana-
tion must also be supplied. Then there is the
class of work adapted for use in weekly papers
and magazines. This sometimes allows of a little
more time for preparation and dispatch ; but,
as before, dean bright prints are essential. Next
comes the work that can be used at leisure by
various magazines. This often takes the form
of a set of prints, probably accompanied by an
article which they illustrate. They vary in cha-
racter according to the publication for which
they are intended. They may illustrate tours,
travel in out-of-the-way places, various forms
of sport and pastime, persons and places of
interest, architecture, curiosities, and so forth.
Ivastly, there is a limited opening for work of a
purely pictorial character, and in this class alone
is it sometimes possible to employ processes
that permit of some control and modification to
secure the effect desired.
Although books are frequently illustrated
wholly or in part from photographs, it is
obvious that such work is already arranged
for and does not allow opportunity for casual
contributions.
The photographer who aims at supplying
prints to the press must possess a keen eye, an
alert intelligence for likely subjects and tiieir
adaptability for use, and must be a good tech-
nical photographer. He must be familiar with
the exact class of work likely to be acceptable
to any given publication ; he must know the
addresses of (iie papers, and the times when
matter must be to hand to admit of publication.
He should also know the prices to be expected for
various kinds of contributions.
The press photographer's outfit depends en-
tirely on the class of work he intends to under-
take ; and aU necessary information is given
under separate headings. Cameras of the reflex
pattern or with direct-vision finders are the
favourites for the usual run of newspaper work.
The points to be borne in mind in choosing the
lens are definition, covering power, and ability
to work at large apertures to allow of short
exposures. Quarter-plate, 5 in. by 4 in., and
half-plate are useful sizes, as enlargement is
an easy matter ; in urgent work, enlargement
should be left to the process-block maker.
PRESSURE FRAME
A name by which the printing frame is often
known, inasmuch as the back portion is so
arranged that it presses the sensitive surface into
contact with the negative. Por paper prints
springs are generally employed to give the pres-
sure ; but for printing on glass, metal, etc., in
process work, screws, wedges, or levers are
employed, and in some cases J>neumatic or
atmospheric pressure.
PRETSCH, PAUL
Bom in Vienna, 1808 ; died, 1873. One of
the pioneers of photo-engraving, and an experi-
enced printer. In 1842 he joined the Imperial
State Printing Office in Vienna imder the direc-
tion of Herr Auer, whom he assisted in working
out the process of Nature printing. In 1850
he was sent to Paris and London, and in 185 1
to London in charge of the Austrian printing
exhibits at the Great Exhibition. In 1852,
after his return home, he began working out his
idea of obtaining galvanoplastic reliefs by the
swelling of insolated chromated gelatine films.
In 1854, having perfected his discovery so far
as to be convinced of its success in a wider field,
he gave up his appointment in Vienna and went
to London, where he took out an English patent
for his process and started to work it in 1855.
Many of his plates are exceedingly good, but he
found it difficult to make the business pay, and
after a serious illness he returned to Vienna in
1863. He was re-engaged at the Imperial State
Printing Office, but his health had broken down,
and he made no further progress in perfecting
his methods. His processes, though no longer
worked, laid the foundation of modem photo-
engraving. He invented numerous processes ;
for the one chiefly associated with his name
see "Galvanography, Photographic."
PRIMULINE PROCESS {See " Diazotype.")
PRIMULINE YELLOW (Pr., PrimuUne ; Ger.,
Primulin)
Synonyms, camotine, polychromine, thio-
chromogen, aureoline, sulphine. Soluble in
water. It is an aniline dye, bright yellow in
colour, consisting of a complex mixture of thio-
toluidine sulphonates. It is used in the Diazo-
type process.
PRINCIPAL AXIS (See "Optical Axis.")
PRINT
An image produced by the action of light on
a. sensitive surface in contact with a negative or
positive transparency. It is usually restricted
to an impression on sensitised paper, prints
upon glass being known as positives or trans-
parencies.
In process work, the term " print " denotes
the image on the metal plate in line and half
tone etrhiug.
PRINT INDICATOR (Pr., Enregistreur ; Ger.,
Indikator)
A device for attachment to the printing
frame to register how many prints have been
Print Indicator
made from a given negative. The form illus-
trated consists of a small metal numbered dial
Print Meeisurer
439
Printing by Artificial Light
witi a movable hand that catches in slots at
each number. Every time a print is removed
from the frame the hand is moved one figure
forward by the printer, until it is seen that the
number of prints it is desired to make have
been secured. Other tjrpes of print indicators
are obtainable.
PRINT MEASURER (Pr., Mesureur des
ipreuves ; Ger., Positivermesser)
An apparatus for measuring the light reflected
from difierent portions of photographic prints.
In that designed by Chapman Jones two mirrors,
one on each side of an incandescent gas burner,
give two beams of light, which enter a velvet-
lined box by separate openings, illuminating
the print to be tested and a white comparison
patdi placed beside it. A shadow rod is em-
ployed, as in Rumford's photometer, to ensure
each patch receiving light only from its own
beam. One mirror moves along a graduated
scale while the other is fixed. The light on the
white patch is reduced by drawing back the
movable mirror until the two patches are of
equal brightness, when the distance read ofE on
the scale enables an accurate comparison to be
made.
PRINT METER {See " Actinometer.")
PRINT TRIMMER (Ft., Coupe-ipreuves ;
Ger., Beschneideapparat)
A small machine of the guillotine type, used
for trimming prints. The ordinary pattern,
shown at A, consists of a baseboard to one side of
A. Print Trimmer with Movable Blade
B. Print Trimmer with Movable Platform
which is pivoted a steel cutting blade having a
handle. At a right angle to the blade a gradu-
ated rule is fixed to the baseboard. The print
is laid on the baseboard and each side is then
trimmed in turn by pressing down the blade,
using the rule as a guide to the size. Another
type of trimmer, B, has a fixed blade and a mov-
able platform or desk. The print is laid on the
latter, placing its edge under a steel bar tmtil the
part to be cut ofi projects, and is cut by press-
ing down the platform, which, on removing the
pressure, springs back ready for the next cut
to be made.
The term " print trimmer " is also frequently
applied to any kind of knife or wheel-cutter
for trimming prints.
PRINT WASHER {See "Washers.")
PRINTER'S INK, PHOTOGRAPHS IN
Apart from the large number of processes
by which photographs are reproduced photo-
mechanically, there are many on the lines of the
following, difiering perhaps in matters of detail,
but based on the use of a gelatine film, sup-
ported by paper or other substance, sensitised
with potassium bichromate, printed upon under
a negative, washed, and dried. The film is
next soaked until the surface repels greasy litho-
graphic ink, applied with a roUer, except those
parts initially affected by the light through the
negative.
PRINTING
The exposing of a sensitive surface in contact
with a negative or positive transparency to the
action of light. The negative and sensitised
paper are h3d in contact in a printing frame,
winch is described in a later article, where will
be found any necessary instructions for the
extremely simple task of taking a print.
In process work, " printing " is the process
of exposing the sensitised plate, paper, or tissue
under a negative or positive. The taking of a
print on paper from the plate after inkmg-up
is termed " proofing " or " proving."
PRINTING BOX
Whilst in ordinary printing it is desirable to
avoid parallel rays of light, a diffused light being
much preferable, in process work it is sometimes
necessary to exclude all except the parallel rays
and to cause these to fall at right angles to the
negative. This is especially the case in gelatine
relief processes, and the method adopted is
to place the printing frame at the bottom of a
tube or box of from i ft. to z ft. in length and
blackened inside. The box is then tflted to
the best angle for receiving the incident light,
usually from the sky. J. Wheeler, the inventor
of the Metzograph screen, devised such a box
for use in connection with his screen. In this
box is placed a continuous-tone negative with
its glass side in contact with the Metzograph
screen, and its firm side in contact with a sen-
sitised zinc or copper plate. A grained image
is thus obtained, much the same as would result
from printing from a grained negative. Carriers
are placed at intervals in the box and at the
mouth to mask the light to suit the size of the
negative. Wheeler has also suggested the use
of this box and screen for silver printing, claim-
ing that it dispenses with retouching of portrait
negatives and gives a better modulation of the
image.
The use of a printing box in printing from a
cracked negative is illustrated under the head-
ing " Cracked Negatives."
PRINTING BY ARTIFICIAL LIGHT
Printing by the ordinary forms of domestic
artificial light can be conveniently carried out
Printing by Daylight
440
Printing Frames
only in two processes, bromide and gaslight.
The former is sufficiently rapid to give a fully
exposed print from a good negative of medium
density in twenty to thirty seconds at a distance
of three feet from a 16 candle-power light. The
latter is much slower, and the same negative
would probably require an exposure of one minute
at 6 inches from the same Ught ; but this slow-
ness carries with it the advantage of permitting
the development, etc., to be performed in very
weak white light. When shielding or controlling
is necessary, certain differences in working have
to be adopted when printing by artificial Ught,
as explained under the heading, " Control in
Printing."
Daylight printing processes can be success-
fully worked by electric arc light.
PRINTING BY DAYLIGHT
The silver printing-out, platinotype, and
carbon process and their many sub-divisions are
dayUght methods ; their sensitiveness is too
slight for artificial Ught to produce any useful
impression. The electric arc light may be used
for any of these processes. Daylight printing
should not be carried out in direct sunshine,
because any slight scratch, bubble, or mark on
the glass side of the negative would cast a defi-
nite shadow during printing and show a white
line or mark in the finished resiilt. Printing in
the sun is quite impracticable for negatives that
have been covered with matt-varnish or tracing
paper on the glass side, or that require to be
shielded or masked during printing. These
methods would always cause deficnite and harsh
lines. A bright diffused light is best for all
ordinary printing, the frame lying quite flat,
exposed to the sky, when shielding or masking
is necessary. It is frequently stated that sun-
shine will assist in securing soft prints from harsh
negatives, and a very feeble light enable more
brilliant results to be obtained from weak nega-
tives. Careful experiments have, however, failed
to confirm this, the best results being invariably
those taken in a very bright diffused light.
PRINTING, COMBINATION {See "Combina-
tion Printing.")
PRINTING FRAMES (Pr., Chassis positif,
Chassis de tirage, Chassis presse ; Ger.,
Kopierrahmen)
Appliances for keeping the negative and sen-
sitised paper in dose contact during exposure
to hght in printing. The ordinary pattern. A,
is made of teak or other hard wood, and the
divided hinged back, the inner side of which is
usually covered with cloth or felt, is fastened
by means of two metal springs that engage in
bent wire staples. To examine the progress of
printing, one spring is unfastened and half the
back is raised, keeping a firm pressure mean-
while on the remaining half with the fingers of
the other hand in order that the print may not
be shifted. Many workers prefer to have the
back unequally divided, so that the greater por-
tion of the print may be examined at once. Vari-
ous frames are now made with a non-sUp back,
one of the best being that shown at B, in which
projecting metal pegs extend from the hinges
and fit in metal grooves at the sides of the frame,
%
effectually preventing slipping. In another pat-
tern the back is hinged directly to the frame.
C shows a heavier type of frame, suitable for
large sizes, and holding a sheet of plate-glass.
A. Ordinary Pattern of Printing Frame
so that a negative of any size can be used ; this
has two hinged pressure-bars with springs on
their lower side, the bars being fastened down
by brass strips which fold over their ends.
For copying plans, etc., large frames are
used, with the back divided into several sec-
tions, each with its own pressiure-bar, as at D.
A great variety of frames are specially designed
B. Printing Frame with Non-slip Back
for combination, multiple, and border printing,
as well as for postcard, lantern sUde, and stereo-
scopic work.
In process work, considerable inventiveness
has been displayed in the design of printing
frames. For paper prints, spring pressure is
relied upon ; but for printing on metal plates,
etc., screw and wedge pressure is resorted to.
C. Heavier Type of Printing Frame
The oldest form of frame for printing on plates
has a number of wooden screws inserted in several
heavy bars across the back (see E). The screws
are now generally iron, threaded into iron bushes
Printing Frames
441
Prismatic Spectrunr
let into the wooden crossbars {see P). A fur-
ther improvement is to make the crossbars of
iron and connect them together into a frame or
" spider," with crab-like castings attached to
D. Printing Frame for Copying Plans, etc.
the back for taking the thrust of the screws, the
number of which has been reduced to two and
even to one. The frames are usually made of
wood, strengthened by iron clamps to take the
strain of the crossbars, or heavy steel screw
bolts are passed through from back to front.
The front is of plate-glass of from J in. to i|^ in.
thick, while the back is usually of wood heavily
clamped, although in America iron backs have
been used with the multi-screw frames. For
collotype, a wedge pressure is generally preferred,
the frame having no back and the wedges press-
ing directly on the thick glass printing-plate.
Frames operating by leverage have come into
general use in America ; in a popular pattern
the bars are pressed down on to heavy pads of
rubber by means of a quick-acting cam lever.
Vacuum frames are found effective for blue
printing, photo-litho transfers, and for printing
direct on thin zinc for photo-lithography.
These frames consist essentially of a wooden
frame in which is moimted a glass plate to form
the front. The negative and sensitive surface
are laid upon this and backed by a sheet of india-
rubber, which is pressed down by another frame
around the margin. The air is then exhausted
from between the front glass and rubber sheet
by means of a vacuum pump, the pressure of
the atmosphere on the rubber sheet then pro-
ducing contact. For thick zinc and copper
plates, a pneumatic cushion covering the back
of the frame, and held down by a heavy back
E and F. Process Printing Frames
board and crossbars is found more effective ;
after the frame has been shut down the cushion
is more fully inflated by means of a pump. A
hydraulic pressure frame has also been employed.
PRINTING-IN {See " Backgrounds, Printing-
in " ; " Clouds, Printing-in " ; and " Com-
bination Printing.")
PRINTING-OUT
Any method of printing in which a visible
image of full depth is obtained by exposure to
light. The best-known print-out process is that
employing gelatino-chloride silver paper, better
known as " P.O.P." (printing-out paper).
PRINTS STICKING TO NEGATIVES
If negatives or gelatine silver papers are put
to print in a damp condition, or if moisture, as
from rain, gets in between the negative and
print, they will become stuck together. They
should not be forcibly pulled apart, but at once
plunged into a " hypo " fixing bath and allowed
to soak, after which the print (quite mined) may
be pulled away from the negative, which, if the
work has been done carefully, ought to be quite
unharmed.
In process work, sticking is prevented some-
times by rubbing the negative over with paraflan,
or with a trace of vaseline.
PRISM, REVERSING (Pr., Prisme de ren-
versement ; Ger., Umkehr Prisma)
The prism used by process workers and others
for reversing images laterally is a block of
optical glass free from striae and cut in triangular
form {see A), so that two of its faces form a right
Reversing Prism
angle to one another, and its hypotenuse is at
an angle of 45°. The angles must be correct
and the surfaces groimd and polished with as
much care as those of a lens. The hypotenuse
is silvered, and the prism is mounted in a metal
box {see B) provided with a screwed ring for
attaching it to the lens. Usually it is fitted on the
front, but some workers prefer it behind the lens.
The prism reverses the image laterally, so that it
appears the right way on the negative ; thus the
metal plate printed from the negative has an
inverted image which in the final print again
comes right. If a prism were not used, any
lettering in the final result would read the wrong
way round, just as printed matter appears in a
mirror. Prisms are preferable to mirrors {see
" Mirror, Reversing "), as they remain perma-
nently in good condition, whilst mirrors soon
become tarnished and require repolishing or
resilvering. A slight disadvantage of the prism
is that it increases the exposure, but with the
powerful electric arc illumination used by pro-
cess workers this is not noticed.
PRISMATIC SPECTRUM (S«« "Spectrum.")
Process Block
442 Proportional Scales and Rules
PROCESS BLOCK
A typographic printing block produced by
photo-mechanical processes, as distinguished
from a block produced by wood engraving.
PROCESS PLATES
Dry plates prepared specially for photo-
mechanical work. They are slower than plates
used in general photography, the emulsion
being compounded with the object of giving a
hard black-and-white image. Two kinds of
plates are issued by some makers — " process "
for Une reproduction, and " half-tone " for
making half-tone negatives • in a typical case
the speed of the " process " plates is 16 Wat-
kins, 7/28 Wynne, or 25 H. and D., and that of
" half-tone " plates 30 Watkins, //39 Wynne,
or 47 H. and D.
PROCESS WORK
A general term embracing all kinds of photo-
mechanical reproduction processes.
PROFESSIONAL
Anyone who gets his living by the practice
of photography ; not necessarily anyone who
accepts remuneration for photographic work, as
explained under the heading " Amateur Photo-
grapher."
PROGRESS MEDAL (See "Royal Photo-
graphic Society.")
PROJECTION
The art or act of projecting or throwing an
image by means of an optical system. Examples
are the projection of a transparency for viewing
purposes by means of an optical lantern or kine-
matograph (see under both of these headings) ;
the projection by an enlarging apparatus of a
negative upon a sensitive surface (see " Enlarg-
ing ") ; the projection of an image by the lens
of a camera upon the dry plate ; and other
methods described imder various headings.
PROJECTION, STEREOSCOPIC (See " Ste-
reoscopic Projection.")
PROMENADE
A commercial size of photographic mount,
usually SJ- in. by 4 in., but subject to variation.
A " promenade midget " generally measures
about 3^ in. by i| in.
PROOF SPIRIT
A term which took its origin from an old test
for the strength of alcohol, in which a heap of
gunpowder was wetted with the spirit and then
a light applied. If the gunpowder did not
fire, the spirit was " under proof," or " U.P." ;
if it just fired it was " proof " ; and if it imme-
diately fired it was " over proof," or " O.P."
At the present time proof spirit should contain
49 per cent, of pure alcohol at 62° P. (nearly
17° C.) (See also " Alcohol.")
PROPORTIONAL SCALES AND RULES
Various forms of proportional scales or rules
have been suggested for the use of photographers
and process workers, principally with the object
of calculating exposures and the proportions of
reductions and enlargements. J. A. C. Bran-
fiU's proportional rule. A, has three members,
A, B, and c, which form a triangle graduated on
three sides. When c is slid along a, any triangle
formed wiU be similar to the original one, and
all its sides will be proportional. This enables a
fourth proportional to three known quantities
to be found. Thus, if it is required to find
^T X 6 by the rule, place c to 14 on a, set b
to 6 on c, slide c to s on A, when b will be
found to cut c at the dimension required. A
shows the positions of the members for this
calculation.
Another form of proportional rule, but with
a definite purpose, is the scalometer of W.
Laurence Emmett, for determining which
originals are in the same scale of proportion, so
that they may be photographed together on the
same plate. This instrument is illustrated in
the article under the heading " Focusing," and
is used as there described. By its means the
operator groups up on his copyboard all originals
which bear the same proportional number. By
B. Emmett's
Sizeometer
A. BranfUl's Pro-
portional Rule
a slight variation of the method enlargements
may be similarly dealt with. By means of a
printed scale sent out with the instrument, it
is possible to mark ofi the base of camera and
copying stand with numbers corresponding to
those on the-instrimient, so that the camera can
be instantly set to the proportion number
marked on the original, no focusing being then
required. A rule and system having the same
object was designed and introduced in America
by A. Pruwirth, who also applies scales to the
base of the camera. Geo. H. Benedict, of
Chicago, has a system worked with a chart of
curves. All these methods have the same
object, that of setting the camera to the pro-
portion of the original without the necessity of
focusing.
Various rules and scales have been devised
for determining the second dimension of a
reduction or enlargement, one dimension being
given. The sizeometer, B, is a good example of
a rule for this purpose. The slotted rule is laid
on the diagonal of the photograph, and the
right angle rule is then brought down to the
dimension of one side of the picture. The
second dimension is then read off on the other
limb. Carl Norman's proportional rule consists
of a strip of stretched elastic bearing a numbered
scale, the elastic being mounted between two
Prussian Blue
443
Pyraxe
clamps, so tnat one of them can be made to
slide along and thus alter the length of the elastic
ribbon, the scale on it altering proportionally.
Thus, the elastic is stretched until a number
on it corresponds to the required dimension of
the original. Then -without altering the elastic
the other dimension of the original is measured,
and the result is the second dimension.
A further series of proportional scales are those
used for measuring the surface area of blocks.
Branfill's chart (it consists of a series of curved
lines) is a good example. The block to be
measured is placed up to the top and left-hand
border line, and the required dimension read
off on the curved line adjoining the lower right-
hand comer of the block. Geo. H. Benedict, of
Chicago, is the author of a similar chart. Another
form of chart for the same purpose is ruled off
into J-in. squares, and the figures denoting the
square measurement are placed progressively
in these squares.
PRUSSIAN BLUE (Pr., Bleu de Prusse ; Ger.,
Berliner Blau, Preussischer Blau)
Synonyms, ferric ferrocyanide, Paris blue,
mineral blue, Berlin blue. Pe4Fe3(C8N5),.
Molecular weight, 860. Insoluble in water and
alcohol. A dark blue powder obtained by
precipitation of ferric salts with potassium
ferrocyanide. It forms the blue image in the
cyanotype and other iron printing processes.
PSYCHIC PHOTOGRAPHY
Known also as " spirit photography." Many
persons have claimed to be able to photograph
psychic and astral forms ; hence the name.
Psychic photographs are divided into many
classes, including (i) Portraits of psychic entities
not seen by normal vision. (2) Pictures of
objects not seen or thought of by the medium,
photographer or sitter, such as flowers, lights
and emblems. (3) Pictures having a flat effect
and the appearance of having been copied from
others. (4) Pictures of materialised forms visible
to normal sight. (5) Pictures of the " wraiths "
or " doubles " of persons still in the flesh.
(6) Portraits on plates which developers have
failed to bring into view, but which, it is said,
can be seen on the prints by certain persons;
and (7) Portraits that cannot be classed as
photographs because no camera is used. The
art originated in America in the year 1861, when
W. H. Mumler, of Boston, opened a studio
specially for the work. The first psychic photo-
graphs to be taken in England, it is believed,
were those produced by Mr. and Mrs. Guppy, in
March, 1872.
Psychic photographs are often called ghost
photographs, but the latter term is more often
used to describe " faked " or " trick " pictures,
which may be produced in many ways, the easiest
being to dress up a person in ghostly attire,
pose the " ghost," give a very brief and incom-
plete exposure, cap the lens, and allow the
"ghost" to move out of the scene, and then
complete the exposure. When the plate is
developed a faint image of the ghostly figure is
seen, and objects appear through the figure,
more or less according to the relations of the
exposures.
Another method to adopt is to draw a ghost.
or to paste a drawing of a ghost, upon a piece
of dead-black card, and to copy this in the
camera. The undeveloped plate is then used
to take a photograph in the usual way and
developed, when the two images will appear
together. Much depends on the relations of
the two exposures, as experiment will easily
show.
PSYCHOGRAPHY
The photographing of images retained in the
retina of the human eye. Many experiments
have been made — notably those by W. Ingles
Rogers, in 1896 — in this particular direction.
The method, in brief, is to gaze steadily at some
bright object — say, a shilling — in a good light,
and then to enter the dark-room and gaze for
about three-quarters of an hour on an unexposed
dry plate, whereon, it is claimed, a faint image
of the shilling will appear on development.
Whatever may be thought of the method, it is
quite a simple matter for any photographer to
put it to the test.
PUDDY'S REDUCER
An ammonium persulphate reducer for which
the formula is given under the heading " Am-
moniimi Persulphate."
PULL
A proof of a block or of type matter obtained
in a hand press in which the platen is lowered
to obtain an impression upon the paper by
pulling a lever.
PULP SLABS
Thin slabs of polished vulcanite or enamelled
composition, to which wet P.O.P. prints are
squeegeed in order to obtain a glazed surface.
Glossy celluloid sheets are also used. {See
"Glossy Surfaces on Prints.")
PUMICE POWDER (See " Abrading Powder.")
PUSH PINS
Glass-headed pins used for fixing bromide
paper to the easel in enlarging, pinning up
prints and films to dry, etc.
PYRAXE
Pyrogallic acid in a. compact and crystallised
form, which occupies about one-fifteenth the
space of ordinary sublimed pyrogallic acid. It
is used with potash or soda exactly Uke ordinary
pyro, and any pyro developer can be made up
with it by using the same weight of pyraxe as
pyro.
The two forms of developer, however,
specially recommended are :—
Pyraxe-soda
A. Pyraxe .
Sodium sulphite
Sulphuric acid
Or Citric acid
Water to .
B. Sodium carbonate
Water to
70 grs. 16 g.
2 oz. 220 „
6 mins. 1-25 ccs.
13 grs.
10 oz.
I oz.
10 „
3 g-
1,000 CCS.
no g.
1,000 CCS.
For use take i part A, 1 part B, and i part
water.
Pyro, etc.
444
Pyro for Bromide Paper
Pyraxe-potash
A. Pyiaxe. . . i oz. no g.
Sodium sulphite . 2J „ 275 „
Citric acid . . 7 grs. i-6 „
Water to . . 10 oz. ?,ooo ccs.
B. Sodium sulphite . ij- oz. 138 g.
Potassium carbonate 4J „ 495 ,,
Hot water to . 10 „ i,ooo ccs.
This is highly concentrated, 14 drops each of
A and B being sufBcient for i oz. of water.
Potassium, bromide is used for over-exposure, and
more water is added for tinder-exposure.
Use an acid fixing bath after development
with pyraxe.
PYRO, PYROGALLIC ACID, PYRO-
GALLOL, OR TRIHYDROXYBEN-
ZENE (Fr., Acide pyrogallique ; Ger.,
Pyrogallol, Pyrogallussdure)
C.HjIOH),. Molecular weight, 126. It occurs
in fine white feathery crystals produced by sub-
limation, and in heavy prismatic crystals of a
more compact form {see " Pjrraxe "). It is sold
generally in blue bottles containing i oz. It is
easily soluble in water, alcohol, and ether. It
is not actually an acid, being neutral to litmus.
It was introduced as a developer by F. Scott
Archer, in 1851, at which time it was very
expensive, the price, six years later, being one
shilling a dram. For many years it was the
principal developer used in the earlier processes,
and later for dry plates. In its earlier days it
was generally used with ammonia, which was
gradually superseded by sodium carbonate, and
to only a slight extent by potassium carbonate.
As it readily oxidises when exposed to the air,
the action being still more rapid in solution,
it is necessary to use a preservative, which is
generally potassium metabisulphite or sodium
sulphite ; in the latter case the solution should
be acidified with citric, sulphuric or sulphurous
acid. The most convenient way of keeping pyro
is in a 10 per cent, solution, an average formula
for which is : —
Pyro . . I oz. no g.
Potass, metabisulphite 36 grs. 8 ,,
Water . . . 10 oz. 1,000 ccs.
The pyro is added last. Every 10 drops will
contain approximately i gr. of pyro. Should
other preservatives be preferred the following
formula may be used : —
Pyro . . . I oz. no g.
Sodium sulphite . 4 „ 440 „
Citric acid . . 30 grs. 7 „
Water (warm) to . 10 oz. 1,000 ccs.
The citric acid may be replaced by 10 mins. of
sulphuric acid or 60 mins. of sulphurous acid.
Dissolve the sodium sulphite in about 7 oz. of
water, add the acid, then the pyro, and finally
the remainder of the water. This will also con-
tain about I grain of pyro per 10 drops, so that
any formula containing pyro can be nrade up
from it. Pyro combines with ammonia, soda,
potash, metol, acetone, etc. It may stain
negatives, hands and linen badly. Pyro-
developed negatives have a more or less strongly
pronounced yellow or greenish-yellow stain, and
therefore print more slowly and give greater
contrast than clean negatives in which the image
consists of plain developed silver, although the
density may appear the same.
PYRO FOR BROMIDE PAPER
Pyro when properly used gives exquisite
brown tones on bromide papers, the pyro-acetone
formxila being perhaps the best : —
A. Pyro . . . 220 grs. 50 g.
Sodium sulphite . 1,320 „ 300 „
Sulphuric acid . 30 mins. 6-25 ccs.
Water to . .10 oz. 1,000 ,,
B. Acetone . . -J oz. 55 g.
Water to . .10 „ 1,000 ccs.
Use equal parts of A and B. The tone can be
altered by varying the quantity of acetone.
The following formula also gives good colours,
but the mixed developer should be used for one
print only. Solutions A and B, mixed in equal
parts, may be used for lantern slides. Pour
solutions are required, from which two work-
ing solutions are made up, one for the actual
development and one for clearing : —
A. Pyro . . .55 grs.
Potassium meta-
bisulphite . . 40 „
Sodium sulphite . i oz.
Water to . .10 „
B. Sodium carbonate. 640 grs.
Water . . .10 oz.
13 g-
9 .,
no „
1,000 ccs.
146 g.
1,000 ccs.
A developer ready for use consists of equal
parts of A and B.
C. Potassium perman-
ganate . . 240 grs. 55 g.
Water . . .10 oz. 1,000 ccs.
D. Common salt . i oz. no g.
Water . . . 10 „ 1,000 ccs.
Sulphuric acid . 4 dims. 50 „
The clearing solution is made by adding J oz.
of D and 15 mins. of C to 10 oz. of -water. The
developer (A and B) is poured over the bromide
paper, which, when fuUy developed, is rinsed in
water and then flooded for not longer than
30 seconds with the clearing solution. It is
next washed for about a minute and fixed in an
acid fixing bath, preferably potassium meta-
bisulphite and " hypo."
Dr. Just's pjTTO developer is as follows : —
A. Pyro . . .20 grs. 4-5 g.
Glacial acetic acid 18 mins. 4 ccs.
Potassium meta-
bisulphite . 9 grs. 2 g.
Sodium sulphite .150 ,, 34 „
Water . . .10 oz. 1,000 ccs.
B. Potass, carbonate . 85 grs. 20 g.
Water - . .10 oz. x,ooo ccs.
Use equal parts of each. The developer is almost
colourless at first, but rapidly turns brown. For
many papers the addition of 6 drops of a i in 50
solution of potassium bromide to each 4 oz. of
mixed developer is necessary. After develop-
ment the print should be rinsed in a clearing
bath of very weak acetic acid in order to re-
move stains, and is then washed and fixed in
an add bath. The addition of a few grains of
hydroquinone to the pyro solution has been
advocated.
Pjrro Stains on Negatives
445
Pyro-Ammonia
PVRO STAINS ON NEGATIVES
These are of a yellow colour, and are caused
by exposure of the film when wet with the
developer to the air, or by using insufficient
sodium sulphite in the developer. It is not all
workers who object to them. To obviate them,
use a lo per cent, solution of sodium sulphite or
a 2|- per cent, solution of potassium meta-
bisulphite instead of plain water for diluting the
stock developer. If a stained negative has not
been dried, the use of a 2 per cent, solution of
caustic soda wiU remove some of the stain. If
it has been dried, it is rather more difficult;
but the following will be of help : —
Thiocarbamide . . 30 grs.
Citric acid . . 60 „
Chrome alum . ■ 30 „
Water to . . . 6 oz.
Soaking in the following (introduced by B. J.
Bdwards, in 1883), clears the stain to some
extent : —
7 g-
14 „
7 „
600 CCS.
Alum
i oz.
55 g-
Citric acid
■ i „
55 „
Ferric sulphate.
■ li „
165 „
"Water to .
• 10 „
I,CXX3 CCS
Berkeley's solution will act if the stains are
not of long standing : —
Alum . . . I oz. no g.
Sulphuric acid . . 2 drms. 25 ccs.
Water . . .10 oz. 1,000 „
Wash thoroughly after any of the above baths.
Namias recommends dissolving 48 grs. of
ammonium persulphate in 5 oz. of water, and,
in order to destroy the reducing action, adding
a few drops of liquor ammoniae. The stained
negative is immersed in this, rocked until the
stain disappears, and then well washed.
Chapman Jones, in 1890, stated that aU clear-
ing solutions hitherto proposed were founded
upon wrong principles, as alum (first used for
the purpose by Sir W.J. Newton in 1 8 5 5 ) actually
retards the washing away of stains, inasmuch as
it hardens the film ; further, acids, although they
lighten the colour of the stains, render them
insoluble. He considers a weak solution of
caustic soda to be the best clearing solution, as
the staining matter is kept in a soluble condition,
so that it may reaUy be washed away, and it is
also kept in its original highly coloured form, so
that its removal can be noticed.
PYRO-ACETONE
A one-solution pyro- acetone developer is given
under the heading " Acetone." The following
is a two-solution form : —
Pyro
. 180 grs.
41 g.
Sodium sulphite
4 oz.
440 „
Water .
10 „
1,000 ccs
Solution A .
5 oz.
500 ccs.
Water .
15 ,.
i>5oo „
Acetone
2 „
200 „
B is the developing solution proper, and it
must be neutral or faintly alkaline, certainly
not acid ; if, on testing, there is any acidity,
add sodium carbonate.
Metol combines well with pyro and acetone
as follows : —
. 60 grs.
■ 80 „
14 g.
18 „
• 7 „
• 360 „
1-6 „
84.,
. 10 oz.
I, coo ccs
. 240 grs.
55 g-
10 oz.
1,000 ccs
A. Pyro .
Metol .
Citric acid .
Sodium sulphite
Water, hot .
B. Acetone
Water .
Add I dram of each to. i oz. of water when
required for use.
PYRO-AMMONIA
The use of pyro with ammonia as a developer
dates from 1862, and it had its origin in America,
where ammonia was first used for fuming dry
plates before the application of an acid solution
of pyro. Major RusseU, the author of the tannin
process, was the first (in 1863) to publish full
working particulars. The composition of an
average developer, ready for use, is much as
follows : —
Pyro . . .15 grs. 3-5 g.
Ammonium bromide 14 „ 3-25 „
I/iquorammonise(-88o) 30 mins. 6 ccs.
Water . . .10 oz. 1,000 „
The following are two-solution developers : —
A. Nitric acid . . 2 mins. -4 cc.
Water . . . 10 oz. 1,000 ccs.
Then add pyro . 20 grs. 4-5 g.
B. Liq.ammom8e(-88o) 120 grs. 28 g.
Potassium bromide 30 „ 7 ,,
Water . . .10 oz. 1,000 ccs.
Use equal parts of each.
A developer which nearly corresponds to 10
per cent, solutions is the following, given by
Sir William Abney : —
A
Pyro .
50 grs.
n-S g-
Sodium sulphite .
150 „
34-5 ,.
Citric acid .
10 ,,
2-3 „
Water .
I oz.
100 ccs.
B
Potass, bromide .
50 grs.
"•5 g-
Water .
I oz.
100 ccs.
C.
Liq. ammonise ( -880)
2 drms.
25 ccs
Water .
2j oz.
225 ,,
Take of A 20 mins., B 30 mins., C 60 mins.,
and water 2 oz. ; i oz. of the mixed developer
contains approximately i gr. of pyro, if grs.
of potassium bromide, and 3J mins. of am-
monia.
Pyro-ammonia is largely used for developing
lantern slides because of the excellent brown
tones which it yields. The J . A. Hodges formula
is excellent : —
A. Pyro . . . I oz. no g.
Sodium sulphite . 4 ,, 440 ,,
Citric acid . . 2 drms. 25 ccs.
Water . . .10 oz. 1,000 „
B. I,iq.ammoniae(-88o) i oz. 100 ccs.
Water . . • 10 „ 1,000 „
C. Ammonium bromide i oz. no g.
Water . . . 10 ,, 1,000 ccs.
D. Ammon. carbonate i oz. no g.
Water . . . 10 „ 1,000 ccs.
This will give brown tones on a plate made for
black tones if the exposure is prolonged. A
mixture of 30 mins. each of A and B and 60
mins. each of C and D should give a rich brown.
Pyrocatechin
446
Pyro-soda
inclining to purple. Increasing D and decreasing
B gives warmer and more reddish tones.
It should be noted that, while in some formulae
an alkaline bromide is recommended, it is rarely-
necessary for modern dry plates.
J. B. B. Wellington's two-solution formula
gives rich sepia tones : —
A. Pyro . . .240 grs. 55 g.
Sodium sulphite . 2 oz. 220 ,,
Water to . .10 „ 1,000 ccs.
B. Am. carbonate . 480 grs. no g.
Potassium hydrate 360 „ 82 „
Am. bromide . 240 ,, 55 „
Water to . .10 oz. 1,000 ccs.
Take i dram of each, and add water to make i oz.
PYROCATECHIN (Pr., Pyrocatechine : Ger.,
Brenzcatechin)
Ortho-dihydroxybenzene ; known also as oxy-
phenic acid and catechol. C8Hi(0H)j. Solu-
bility, I in i"25 of cold water. It was sug-
gested as a developer in 1880, and came into
use in 1899. It occurs in prismatic colourless
crystals. It does not stain or fog ; it turns
brown in solution and on exposure to air, but
its developing powers are not impaired. It can
be used with the carbonates or caustic alkalis,
either in one or two solutions, and is not influ-
enced by temperature. The following is a
simple one-solution formula for negatives : —
Pyrocatechin . . 50 grs. 11 '5 g.
Sodium sulphite . 120 „ 2y$ ,,
Sodium carbonate . 240 ,, 55 „
Water to . . .10 oz. 1,000 ccs.
This is ready for use.
It may be made up in a highly concentrated
form, as follows : —
Sodium sulphite . i oz. no g.
Caustic soda . . 67 grs. 15 „
Hot water . . 3 oz. 300 ccs.
Dissolve, and add — ■
Pyrocatechin . . 96 grs. 22 g.
Water . . . i oz. 100 ccs.
For use, dilute i part with 15 parts of water.
A two-solution formula is : —
A. Pyrocatechin . 50 grs. 11-5 g.
Sodium sulphite . i oz. no „
Water to . .10 „ 1,000 ccs.
B. Potassium carbon-
ate or sodiurai
carbonate . 288 grs. 66 g.
Distilled water to 10 oz. 1,000 ccs.
For use, mix together equal parts.
Sodium tribasic phosphate is recommended by
Messrs. Lumidre as an accelerator: —
A. Pyrocatechin . 96 grs. 22 g.
Sodium sulphite . i oz. no „
Water . . . 10 ,, 1,000 ccs.
B. Tri-sodium phos-
phate . . 60 grs. 14 g.
Water . . .10 oz. 1,000 ccs.
Add I part each of A and B to i part of water.
For bromide paper the following one-solution
formula is recommended : —
Sodium sulphite
Sodium carbonate
Pyrocatechin
Water
This is ready for use.
60 grs. 14 g.
120 „ 28 „
20 ,, 4-6 „
10 oz. 1,000 ccs..
PYROLIGNEOUS ACID
Crude acetic acid.
PYRO-METOL (See "Developers, Mixed or
Combined.")
PYRO-POTASH
Dr. Eder and others have recommended the
use of the alkali potash to take the place of
ammonia or soda in the developer. Several
advantages have been claimed for it — namely,
the stable nature of the alkali and its freedom
from fog or stain, but its drawbacks are slow
working and possibiUty of frilling. The average
of the many formulae advocated is : —
Pyro
30 grs.
7 g-
Potassium carbonate .
120 „
28 „
Water
10 oz.
1,000 ccs.
Bromide is added as required.
Eder's formula is in a two-solution form, and
is much as follows : —
A. Pyro . . . 436 grs. 100 g.
Sodium sulphite 1,090 ,, 250 „
Sulphuric acid . 10 mins. 2 ccs.
Water . . .10 oz. 1,000 ,,
B. Potass, carbonate 2,000 grs. 460 ccs.
Sodium sulphite . 550 ,, 126 „
Water . . .10 oz. 1,000 ccs.
For use, add 135 drops of each to 10 oz. of
water. There are many other formulae.
PYRO-SODA
A developer that is popular on accoimt of
soda having many advantages over ammonia,
which in 1862 was introduced as an accelerator
for pyro. Washing soda is largely used in place
of crystallised sodium carbonate, but the latter
should always be used when sodium carbonate
is mentioned. This developer gives off nO'
fumes as ammonia does, and may therefore be
used with greater comfort ; it rarely produces
chemical fog, and negatives properly developed
are of a good printing colour.
The average of twelve of the best-known
formulae is : —
Pyro
Sodium sulphite
Sodiimi carbonate
Water to .
30 grs. 9 g.
240 „ 55 .,
240 „ 55 .,
10 oz. 1,000 ccs.
Some workers prefer to make up the developer
except the pyro, and add the latter just before
use. Lange's (which see) is typical.
The Hurter and Driffield standard pyro-soda.
developer for plate-speed testing is : —
Pyro ....
8 parts.
Sodirun carbonate (crys.) .
40 „
Sodium sulphite
40 „
Water to .
1,000 „
This should be used at a temperature of 65° P.
(18° C).
Pjrrolechnic Lights
PYROTECHNIC LIGHTS (Pr., LumUres pyro-
techniques ; Ger., Pyrotechnisches Licht)
Chemical mixtures giving a brilliant light on
ignition, at one time used for photography at
night and in dark interiors, but now completely-
superseded by magnesium and the various forms
of electric light. Typical formula were: (A)
Potassium nitrate 28 parts, sulphur 7 parts,
arsenic trisulphide (orpiment) 2 parts. This gives
ofi poisonous fumes, and if burnt in a room
provision must be made for carrying these ofi
by a chimney. (B) Potassium nitrate 7 parts,
sulphur 2 parts, black antimony sulphide i part,
red lead i part. All the ingredients must be
dry, and the potassium nitrate not too finely
powdered. In this case also the fumes require
to be led away.
PYROXYLINE (Pr., Pyroxylin: G&t., PyroxHn)
Synonyms, nitrocellulose, collodion cotton,
soluble gun-cotton, collodion wool. Solubilities,
insoluble in water and in alcohol, soluble in equal
447 Quick Prints from Negatives
parts of alcohol and ether, and in amyl acetate,
acetone, and glacial acetic acid. It is a white
flossy substance, resembling cotton, but harsher
to the touch and much more friable. It is pre-
pared by the action of nitric acid (or of potassium
nitrate) in the presence of sulphuric acid on
cotton-wool. The actual chemical formula for
this substance is a disputed point, but nearly all
photographic pyrojcyline consists chiefly of cellu-
lose-tetranitrate with a small quantity of tri-
nitrate ; the formula for the former would be
Ci2Hi„Oj(N03)i, and for the latter CijH„0;.
(NO,),. In the collodion days, it was of para-
mount importance, but has now — except in
process work — ^become of secondary interest,
and is used for prepared collodion, for nega-
tive and positive work, and for enamelling
prints.
In process work, from i to 4 per cent, is used
in collodion, but 2 per cent, is general. Celloidin
is replacing it more and more on account of
its greater uniformity.
Q
QUADRICOLOUR
A trade name adopted by an American firm
for the four-colour process, the fourth printing
being a black, which is printed last. The build-
ing up of a four-colour print is exemplified in a
plate accompanjdng this work.
QUARTER-PLATE
A commercial photographic size, ^i in. by
3J in., one quarter of a whole plate.
QUARTZ (Pr., Quartz; Ger., Quarz, Bergkrystall)
Synonym, rock crystal. Native anhydrous
sUicates of potash and soda, used for the con-
struction of lenses, prisms, etc., for the examin-
ation of the ultra-violet rays.
QUICK PRINTS FROM WET NEGATIVES
The work of taking a print from a wet nega-
tive. A sheet of bromide or gaslight paper is
soaked in water until quite limp, and the
negative placed in the water with it. The
two are then brought into contact, film to
film, while under water and of course in the
dark-room. The negative and paper are re-
moved from the water, the glass side wiped
dry, exposure made to the light, and the
print developed and fixed in the usual way. A
printing frame is not necessary, but if the light
used for exposing is very strong it is advisable
to shield the back of the paper with a piece of
cardboard. The paper should be taken from the
wet negative very carefully, and preferably under
water. Another plan is to immerse the rinsed
negative for five minutes in a 10 per cent, solu-
tion of formaline, then in hot water for about two
minutes ; it should take about five minutes to dry.
The arrangement for enlarging or reducing
direct from the wet negative, shown in the
diagram, may be much simplified if set sizes
are always used. In one end of an oblong box
is cut an aperture to take the wet negative, or
it may be dropped into grooves as shown. At
the opposite end is a hinged door, to which the
paper is pinned. A slidmg partition holds the
lens. The wet negative is placed in position,
ground glass substituted for the hinged door.
^^^^^^^
u^
Ml' J
iff
W
1
Arrangement for Enlarging or Reducing
from Wet Negative
and the image focused by moving the partition
holding the lens. The box is then taken into
the dark-room, where a piece of bromide paper
is pinned to the door, which is then closed and
the box taken into daylight for the purpose of
making the exposure. The size of the box will
depend upon the focus of lens used, size of
negative, and degree of enlargement or reduction.
The advantages of such an arrangement are
that the negatives do not need lengthy washing
before the print can be made, and that the
picture may be reproduced of any size upon the
paper. A fixed-focus enlarger for wet nega-
tives is on the lines of the apparatus shown at
A in the article " Enlarging by Daylight."
Quick Stuff
44S Quinone Sodium-sulphonate
QUICK STUFF
A term applied, in the early days, to acceler-
ators, which hastened development.
QUILLAIA (Fr., Scarce de quillay ; Ger.,
Quillajarinde)
Synonyms, quillaja, soap, Panama, China or
Murillo bark. The dried bark of Quillaia
saponana deprived of its peridermis. It is met
with in large flat pieces about \ in. thick, brown-
ish white outside, and smooth, shiny white
inside. The powder causes violent sneezing.
A semi-alcohoUc tincture is sometimes used as
an addition to paper emulsions, or the active
principle saponine is used in the same way, its
purpose being to give smooth, even coating. It
has also been used as a vehicle for the pigments
for colouring prints.
QUININE SULPHATE (Pr., Sulfate dequinine;
Ger., Schwefelsaures Chinin)
(CaoHjjNjOjjjHaSO, /HjO. Solubilities, in-
soluble in water, soluble in dilute acids. It is in
the form of white, lustrous, fragile, needle-like
crystals, obtained from cinchona bark. It is oc-
casionally used when dissolved in dilute sulphuric
acid as a screen to cut out the ultra-violet.
In process work, when reproducing drawings
in which Chinese white has been largely used,
it has been found advantageous to employ a
liquid filter consisting of a i per cent, solution
of quinine sulphate dissolved by the aid of a
few drops of sulphuric or nitric acid.
QUINOL
A synonym for hydroquinone.
QUINOLINE AND QUINOLINE BLUE
Synonyms for cyanine.
QUINOLINE RED (See " Chiuoline Red.")
QUINOMET (Pr., MStoquinone ; Ger., Meto-
ckinon)
Synonym, metoquinone. C,H4(OH)2 + CjHj
(OHXNHCHa)^. SolubiUty, i in 100 of water.
A developing compound composed, it is said,
of metol and hydroquinone, and introduced by
Messrs. I<umi^re and Seyewetz, of Paris, in 1903.
It can be used with or without an alkali. The
following is suitable for time exposures : —
Quinomet. . . 24 grs. 5-5 g.
Sodium sulphite (anhy-
drous) . . ,144 „ 33 „
Water . . . 10 oz. 1,000 ccs.
This is ready for use. Por " instantaneous "
exposures, 300 mins. of acetone should be added,
or 100 grs. of sodium tribasic phosphate, or
SO grs. of caustic lithia. The quinomet must be
dissolved in the water first.
QUINONE (Pr., Quinone ; Ger., Chinon)
Synonym, benzoquinone. CjHjOa. Molecular
weight, 108. It is in the form of golden-yellow
prisms obtained by oxidising aniUne witii sul-
phuric acid and potassium bichromate. Solu-
bilities, slightly soluble in water, soluble in
alcohol and ether and alkaline solutions. It
hardens gelatine, but stains it deep brown.
When dissolved as in the following formula,
Quinone .
Sulphuric acid
Water to .
24 grs. S-S g-
96 mins. 20 CCS.
10 oz. 1,000 »
it acts as a reducer, and, like ammonium per-
sulphate, acts on the high lights more than the
shadows. With potassium bromide, thus —
Quinone . . .24 grs. 5-5 g.
Potassium bromide .120 „ 28 ,,
Distilled water to . 10 oz. 1,000 ccs.
it converts a silver image into a reddish brown
compound, probably silver oxybromide Ag^Bt^O,
which can be treated with ammonia to form a
dark brown image ; sodium or potassium car-
bonate also gives dark brown, and at the same
time intensifies ; " hypo " reduces the image
without changing the colour ; sodium sulphite
or bisulphite gives greenish brown ; and amidol
behaves in the same way.
QUINONE INTENSIFIER AND TONER
Introduced in 1910 by Messrs. Lumi^e and
Seyewetz. By adding to solutions of quinone
and its sulphonic derivative a sufB.cient quantity
of a bromide or a chloride, and immersing a
negative therein, the silver image attains a
certain degree of intensification, its colour
becoming gradually reddish brown in the case
of quinone, and yellowish brown when using
the sulphonic quinone. The following are the
original formulae : —
Quinone
Quinone . . .22 grs.
Potassium bromide .110 ,,
5 g-
25 ,,
Water . . . 10 oz.
1,000 ccs.
Quinone Sodium-sulphonate
Quinone sodium-sul-
phonate . . 45 grs. 10 g. ^
Potassium bromide .110 „ 25 ,,
Water . . .10 oz. 1,000 ccs.
The image thus obtained has slight general
opacity, which disappears on immersing the
plate after a brief rinse in a solution of liquor
ammonias i part and water 10 parts. The
quinone-sulphonate gives a more yellowish and
less intense action, and the first formula is pre-
ferable to the'second.
QUINONE REDUCER
Certain quinone bodies in acid solution have
been found by Messrs. Lumi^e and Seyewetz
to act as reducers, giving effects similar to those
of ammonium persulphate. A formula is given
under the heading " Quinone " ; another is : —
Sulphuric acid . . 90 mins. 17 ccs.
Benzo-quinone . . 22-5 grs. 5 g.
Water . . .10 oz. 1,000 ccs.
The action is arrested by rinsing in water and
then in a sodium sulphite solution (i oz. in
5 oz. of water), afterwards washing well.
QUINONE SODIUM-SULPHONATE (Pr.,
Quinone sulfonate de sodium ; Ger.,
Ckinonnatriumsulfonat)
Synonym, benzoquinone sodium sulphonate.
CeHiOjSOsNa. Molecular weight, 2n. Por its
use, see " Quinone Intensifier and Toner."
A HEAD BY J. I. PIGG, F.R.M.S., F.R.P.S.
RADIOGRAPHY, OR X-RAY PHOTOGRAPHY
16
R
RACK AND PINION (Pr., CrimailUre ; Ger.,
Zahnstange und Getriebe)
The mechanical device by which the distance
between lens and focusing screen is usually
regulated. It consists of a steel pinion A work-
ing on d brass rack B, the grooves in which
engage with the teeth or flutings on the pinion.
Generally, two racks are fitted underneath the
extension frame of the camera, one at each side.
Hack and Pinion
the pinion being let into the baseboard at a right
angle with the racks and worked by a milled-
head screw at the side of the camera. For
accurate focusing, it is important that the rack
and pinion should not be too coarse, and there
should be no looseness or shake. Modem
cameras have frequently a rack and pinion
adjustment to other parts besides the focusing
arrangement — for example, on the rising and
cross front movements. Rack and pinion
adjustments are also fitted to enlarging lan-
terns, etc.
RACKS. DRYING AND WASHING
"Drying Rack.")
{See
RADIOACTIVE SUBSTANCES
Substances from which minute particles are
continually being propelled at a high velocity.
These particles afiect the sensitive film of a dry
plate or the crystals of certain chemicals which
fluoresce when brought into close proximity to
the radioactivity ; this fluorescence is visible to
the eye in a darkened room.
The most important radioactive elements
are radium, uranium, actinium, polonium, and
thorium, and from these three kinds of radiations
are emitted, known as alpha, beta, and gamma
rays. The alpha rays are readily absorbed by
air or any soUd matter which may lie in their
path. The alpha particles are of comparatively
large size, comparable to that of an atom, and
carry charges of positive electricity. They are
slightly deflected by a magnetic field. The
beta rays are negatively charged, and are
strongly deflected by a magnetic field. The
partides are much smaller than those of the
alpha rays, and are known as electrons. The
beta rays are similar to the cathodal rays of an
X-ray tube. Gamma rays do not seem to be
deflected by a magnetic field, and have the
greatest penetrating powers of any of the rays ;
they are probably the product of the beta rays.
RADIOGRAPH
A photograph produced by the X-rays.
RADIOGRAPHY
graphy.")
{See " X - ray Photo-
RADIOTINT PROCESS {See " Dansac-Chas-
sagne Colour Process.")
RADIUM (Pr. and Ger., Radium)
Atomic weight, 226'5. Radium occurs in
pitchblende, an oxide of uranium, in association
with uranium, lead, barium, and other metals.
It is prepared from pitchblende, or from the
residues after uranium has been extracted there-
from. In the preparation of radium, a barium
chloride which is highly radioactive is extracted
from pitchblende ; from this barium chloride,
radium chloride is isolated by elaborate processes
of fractional crystallisation. One ton of pitch-
blende yields fifteen pounds of barium chloride,
from which only a few grains of radium chloride
can be separated.
RAPID DEVELOPERS
Metol, rodinal, and other developers of the
newer type (so-called) are often referred to as
rapid developers because they produce the
image far more quickly than some of the other
developers — pyro, for example. As explained,
however, under the heading of " Development,
Factorial," those images which appear very
quickly need developing for a considerable time
in order to secure proper density, so that, after
all, one normal developer is not so very much
more rapid than another. The following table
was compiled by Alfred Watkins after making
some comparative tests ; the final density or
printing power was about the same, but the
results at the various stages before the desired
density was arrived at were very difierent : —
s^§-S
■1^1
Developer
Time o
appearan
in secon
n<
Total time
minutes)
developm
Pyro
i6
7
ij
Metol
5
22
If
Ortol
15
8
2
Adurol
SO
S
4
Kachin
42
9
6}
Hydroquinone
62
5
.Si
Glycine
62
6i
7
Metol-hydroquinone
7
13
If
29
449
Rapid Emulsions
450
Rectigraph
Thus a mixture of metol-hydroquinone is under
normal circumstances the most rapid developer,
even though the image takes longer to appear
than with metol alone. Pyro-acetone (see
" Acetone ") without bromide makes a very
rapid developer, and gives good negatives of
excellent density in three or four minutes. This
at first sight appears longer than the time given
for pyro or metol-hydroquinone developers in
the Watkins table on p. 449, but Watkins used
test slips for judging density, and not actual
negatives ; therefore the times of development
given in the table are only comparative, and a
rough calculation shows that were pyro-acetone
included in the table it would be about i.
RAPID EMULSIONS {See "Emulsions for
Development.")
RAPID PLATES (Pr., Plaques ultrarapide ; Ger.,
Hochempfindliche Flatten)
Plates coated with a highly sensitive gelatino-
bromide emulsion. Of recent years, the advances
in emulsion making have given us plates of very
high speed and of general satisfactory freedom
from fog. At the present time there is a great
craze, particularly among amateurs, for very
rapid plates, but in many cases equally as good
— if not better — results can be obtained on slower
plates, which are usually less prone to chemical
fog and possess a much finer grain.
RAPID RECTILINEAR LENS
This, the most popular type of photographic
lens, was introduced almost simultaneously by
J. H. Dallmeyer and Steinheil in 1866, and held
the premier position for all classes of outdoor
work until the arrival of the anastigmat. Even
now, most moderate-priced cameras are fitted
with R.R. lenses, mostly of excellent quality.
The rectilinear lens is composed of two cemented
combinations, usually symmetrical, and has an
initial intensity of //8 (approximately). Either
of the combinations may be used singly, but
require stopping down to about f/22 (//i i of the
complete lens) to secure an absolutely sharp
image. The rectilinear is an excellent lens for
copying, architectural, and process work, while
the larger sizes are useful for portraiture. {See
also " RectiHnear.")
RAPID SYMMETRICAL LENS
A rapid rectilinear lens, having both com-
binations of similar construction and of equal
focal length.
RAPIDITY
A term applied to the working aperture of
lenses (Fr., Rapiditi, ClartS ; Ger., Lichtkraft), and
also the speed of plates (Pr., Sensibility ; Ger.,
Lichtempfindlichheit).
RAY
In optics, a ray of light may be assumed to
have the properties of a line in geometry — that
is to say, it has length without breadth or thick-
ness. A bundle of rays which converge to or
diverge from a given point is called a pencil of
rays.
RAY FILTER (See " Colour Screen or Filter.")
RAYOMETER (Pr., RayonmHre : Ger.,
X-Strahlen Messer)
An appliance used in testing the sensitiveness
of plates to X-rays. One form consists of a
quadrant of aluminium of graduated thickness,
the difierent thicknesses being in concentric
steps. The sensitiveness of the plate, as com-
pared with another, is indicated by the thick-
ness of aluminium through which the rays are
shown to have penetrated when the plate is
developed. The rayometer may also be used
to compare the power of difierent vacuum tubes,
by placing it between the excited tube and a
fluorescent screen, the thickness penetrated being
visible on the screen.
READE, JOSEPH BANCROFT
Bom at Leeds, 1801 ; died at Bishopsboume,
1870. Chemist, microscopist and photographic
experimentalist and discoverer. He was the first
to employ " hypo " as a fixing agent (1837), and
tannin as an accelerator ; he was also the fijrst to
produce a negative on paper by means of gallic
acid and silver nitrate (1837). He was the first
to take photomicrographs with the solar micro-
scope, and these he called " solar mezzotints."
RECORD PRINTS
Photography has unique advantages as a
means of producing graphic records of persons,
places, and things, for future reference. In spite
of the enthusiasm and industry of several
associations, the work of securing permanent
records is still far from being attacked with
systematic completeness, and it is highly desir-
able that some effective co-ordination of work
and control of the results should be instituted.
Meanwhile, it would be well if every possible
opportunity were seized of making photographic
records of any worthy subject, making careful
notes of necessary data for future reference.
The best view-points and lighting should be con-
sidered, and the resulting prints should be made
in some permanent process, such as platinum or
double-transfer carbon. The work can only be
done adequately when the record maker has a
knowledge of what is desirable for his attention,
and this knowledge is frequently most easily
acquired by local workers. Hence the need for
a widely distributed army of capable photo-
graphers with an interest in record work.
Attention should be devoted first of aU to old
buildings and their details when there is any
hkelihood of their near disappearance ; to objects
of antiquity or historical interest ; to natural
scenery about to vanish before the builder ; to-
interesting local customs and ceremonies ; ta
obsolete forms of dress and equipment ; in short,
to anything interesting that is not likely to be
seen by future generations and of which a
pictorial record will be of value. The results
should be entrusted only to the custody of those
who appreciate their value and will assure their
preservation.
RECTIFIED SPIRIT {See "Alcohol.")
RECTIGRAPH (Pr., Rectigraphe ; Ger., Rekti-
graph)
A name given to certain makes of doublet lenses.
The term is equivalent in meaning to rectilinear.
Rectilinear
451
Reducing Negatives
RECTILINEAR
Capable of reproducing straight lines correctly
and without distortion. The term can be cor-
rectly applied to any non-distorting lens, includ-
ing all the anastigmats, but it is usually asso-
ciated with the older types of doublets known as
rapid or wide-angle rectilinears.
RED CHROM ATE OF POTASH (See " Potas-
sium Bichromate.")
RED FOG {See " Fog, Colour, etc.")
RED LIGHT {See "Dark-room Illumination"
and "Safe Light")
RED PRINTS
These can be produced by several processes.
Carbon prints in red chalk or terra-cotta red
are the most perfect and the most satisfactory.
Bromide prints toned by the sulphide process
can also be made to yield a good red, similar to
red chalk. Silver prints, very lightly toned, will
be a good red brown, but aU rich colours in silver
printoig tend towards purple brown rather than
a pure red brown.
Red prints are often made by printing on
plain paper and simply fixing with a " hypo "
bath for the purpose of drawing upon in water-
proof ink for the bleaching-out process.
RED PRUSSIATE OF POTASH {See
" Potassium Ferricyanide." )
RED SILVER CHLORIDE {See " SUver
Chloride.")
REDCOL
A " cold " enamel process for zinc, introduced
by Penrose. The zinc is first coated with a red
varnish of a resinous nature forming an acid
resist ; this is covered with bichromated fish-
glue, dried, and exposed under a half-tone
negative. The unaltered fish-glue is washed
away in development, leaving the red varnish
exposed between the dots. The plate is immersed
in methylated spirit, which dissolves the red
varnish uncovered by the fish-glue image. Next,
the fish-glue covering is wiped away, and the
image remains in the acid-resisting varnish, and
can be forthwith etched, without the buming-
in necessary in the fish-glue enamel process.
RE-DEVELOPER
A second development of a plate, either with
a similar developer to that first appUed or with
a modified solution, is possible. Many years ago
B. J. Edwards introduced a special method of
re-developing over-exposed plates which was
very efEective.
His special developer should take the place of
the normal developer as soon as the over-exposed
image flashes up : —
A. Pyro . . .170 grs. 39 g.
Sodium metabisul-
phite . . 170 „ 39 „
Water to . . 10 oz. 1,000 ccs.
B. Sodium carbonate 3 oz. 100 grs. 353 g.
Potassium bromide 340 grs. 78 „
Water to , . 10 oz. 1,000 ccs.
Use equal parts of A and B. The solution is so
highly restrained that it wiU hardly develop
detail, but density goes on increasing.
Re-development forms an essential feature in
Wellington's silver intensification process, and
also in re-halogenisation. It is also used in some
forms of mercurial and chromium intensification.
REDUCERS
Solutions used for reducing the density of
negatives, etc. They include potassium ferri-
cyanide in a solution of " hypo " (this is the
"Howard Parmer reducer"); potassimn per-
manganate, acidified (this is " Namias's re-
ducer"); ammonium persulphate ; ammonium
persulphate in combination with sulphite,
acidified (this is " Bennett's reducer ") ; ferric
chloride ; cerium peroxide. Details of the
methods of working wiU be found under the
heading " Reducing Negatives by Chemical
Means," and at the references there given.
REDUCERS. COMBINED
Potassium ferricyanide and ammonium per-
sulphate reducers, having respectively different
actions upon the density of a plate, have been
combined by Coustet (1905). The ferricyanide
increases and the persulphate reduces contrast,
and the combined reducer is suggested for use
with flat and imiformly fogged negatives. For
over-exposed or over-developed negatives,
Coustet's formula is : —
Ammon. persulphate 200 grs. 46 g.
Potass, ferricyanide 25 „ 5-75 ,,
Soditmi hyposulphite 250 „ 57-5 „
Water to . . . 10 oz. 1,000 ccs.
The proportions of ferricyanide and persul-
phate may be varied. Throw away after use.
When the negative is of correct density, immerse
it in a 10 per cent, solution of sodium sulphite.
For the two-solution form use : —
A. Potass, ferricyanide 96 grs. 22 g.
Sodium sulphite . 2 oz. 220 „
Water . . . 10 „ 1,000 ccs.
B. Ammonium persul-
phate . .192 grs. 44 g.
Water . . .10 oz. 1,000 ccs.
The negative is placed in A until the brighten-
ing action is complete, and then in B imtil the
high lights are reduced, finally well washing.
REDUCIN
A developing substance of German origin,
introduced in 1893. It acts very much Uke
amidol. Vogel's formula is : —
Reducin . . .26 grs. 6 g.
Sodium sulphite . 218 ,, 50 „
Sulphuric acid . . 5 mins. i cc.
Water . . .10 oz. i,coo ccs.
REDUCING NEGATIVES BY CHEMICAL
MEANS
Most of the methods of reducing negatives
modify the gradation by acting to a greater
degree at one end of the scale than at the other.
The special character of each being known,
advantage may be taken of its properties to
improve or modify an unsatisfactory negative.
The following are the chief methods of reducing
negatives by chemical means : —
Reducing Negatives
452
Reducing Negatives
(i) Potassium Ferricyanide in a solution of
" hypo " (Howard Farmer's reducer). Prepare a
10 per cent, solution of potassium ferricyanide
(red prussiate of potash) ; this solution will keep
indefinitely. When required for use from 10 to
60 mins. of the solution are added to an acid
solution of 2 oz. or 2^ oz. of " hypo " in 20 oz.
of water. The " hypo " must not have been pre-
viously used for any purpose. A solution strong
in ferricyanide should be employed if consider-
able reduction is required ; for less reduction a
weak solution is more under control. The ferri-
cyanide should be added to the " hypo " at the
moment of commencing reduction, as the mixed
solution deteriorates rapidly. Soak the plate in
water for half an hour before treatment, and
rock the dish during reduction to ensure even
action. When desired, the negative is with-
drawn and well washed. The general quality
will be improved by immersing it, after a
slight rinsing from the reducing solution, for
n few minutes in an acid " hypo " bath of the
same strength as that used for mixing the
reducer.
This reducer acts more on the weak tones, or
shadow portions, of a negative than on the strong
tones, or high lights. A moderate reduction of
the high lights may be accompanied by com-
plete obliteration of the feeble details in the
shadows. It is a very valuable method for
dealing with over-exposed, foggy or veiled
negatives, since it increases contrasts as it
reduces density. The character of the result is
not afiected by the strength of the solution or
proportion of ferricyanide present. A weak
solution acting for a long time gives the same
result as a strong solution for a shorter time.
(2) Ammonium Persulphate. — H. W. Bennett's
method is to prepare a stock solution containing
ammonium persulphate, sodium sulphite, sul-
phuric acid (pure), and water; the exact pro-
portions will be found under the heading " Ben-
nett's Reducer." The working solution is a
mixture of i part of the stock solution and
4 to 8 parts of water.
The negative must be soaked in water for an
hour, immersed in the solution, and the dish
rocked until sufficient reduction has taken place.
The solution will become slightly opalescent or
milky in appearance, but this is an indication of
its working satisfactorily. When desired, the
plate is removed from the solution, rinsed rapidly,
and placed for not longer than six minutes in
an acid " hypo " bath of the strength already
stated, afterwards well washing. A shorter
immersion in the " hypo " solution would be
sufficient to check the progress of the reduction,
but by remaining for six minutes the plate is
left in such a condition that subsequent in-
tensification or any other treatment can be
successfully applied if desired. Without the
" hypo " bath after treatment is practically
possible.
The character of the result given by reducing
with ammonium persulphate varies according to
the degree of reduction. In the early stages the
dense parts of the plate only are attacked, and
they may be appreciably reduced without any
perceptible action on the weak shadow details.
With a moderate degree of reduction, the high
lights will decrease considerably in strength
with only a slight loss in the shadows. After
this, however, the action gains in force in the
shadows, and prolonged reduction results in a
loss of strength in the shadow details equal in
proportion to that of the strong tones. The
most useful character of ammonium persulphate
is that of correcting or harmonising harsh con-
trasts, which it accomplishes by reducing the
strong tones to a much greater degree than the
weak details. But in order that full advantage
may be derived from this quality, it is essential
that the action should not be prolonged. The
plate must be carefully watched, and withdrawn
from the solution as soon as any action can be
detected in the weaker parts.
(3) Potassium Permanganate. — The use of an
acidified solution of potassium permanganate
followed by a weak solution of oxalic acid for
reducing negatives is due to Prof. Namias. The
oxalic acid bath, however, is injurious to some
plates, particularly those composed of soft
gelatine. It softens the film and causes the
more transparent parts to become opalescent and
useless for printing. With some plates it works
satisfactorily. The following modified method
of working is quite satisfactory and free from
the objections that apply to oxalic acid. Two
stock solutions are necessary : —
A. Potassium perman-
ganate . 20 grs. 4-5 g.
Water . . .10 oz. 1,000 ccs.
B. Sulphuric acid
(pure) . . 100 mins. 21 ccs.
Water . . .10 oz. 1,000 „
Take i dram or 10 ccs. each of A and B, and
add sufficient water to make i oz. or 80 ccs. For
considerable reduction use a larger proportion
of A and B. The negative should be soaked
in water for an hour, placed in the solution, the
dish being rocked until the reduction is sufficient,
rinsed rapidly in two or three changes of water,
immersed in an acid fixing bath for a few minutes,
and then washed and dried. A solution of
potassium metabisulphite may be substituted
for the acid " hypo," but the latter is prefer-
able. The reduction efiected by acidified
potassium permanganate is almost uniform
throughout the scale, but there is slightly
greater reduction in the strong tones than in the
weak shadow details.
(4) Cerium Peroxide. — This is obtainable in the
form of a concentrated solution which keeps
moderately well. To i drm. of this solution
add sufficient water to make i oz. ; immerse
the negative in this until the desired reduction
has been attained; then wash and dry. It
acts in a greater degree on the shadow details
than on the stronger parts, but the difEerence is
not quite so great as in the case of the ferri-
cyanide reducer. The plate, after reduction, is
very clean and the image is of a good colour.
(5) Ferric Chloride. — This reducer is different
in character from the preceding ones. The
following stock solution may be prepared, but
it does not keep well for more than a few weeks :
Ferric perchloride
Citric acid
Water
60 grs. 14 g.
120 „ 28 „
10 oz. 1,000 ccs.
For use, add to J- oz. of this solution enough water
Reducing Negatives
453 Reduction and Enlargement
to make i oz. Allow the negative to remain in
the bath for about two minutes, rinse, transfer
to an acid " hypo " bath for a few minutes, and
wash and dry. Ivonger immersion in the reduc-
ing solution will produce no greater efEect, as the
reduction is a fixed quantity. The degree of
reduction is slight, the negative losing about
one-eighth of its density uniformly throughout
the scale. The operation may be repeated, one-
eighth of the strength being removed each time.
Reduction by re-halogenisation is treated in
the article on re-halogenisation.
REDUCING NEGATIVES BY MECHANl-
CAL MEANS
These methods are suitable only for local
work. One method is to rub down the part that
it is desired to reduce by means of a soft rag
moistened with methylated spirit. Two thick-
nesses of soft rag may be stretched over the
finger-tip, moistened with the spirit, and rubbed
on the plate with a firm pressure. For smaller
portions the rounded end of a pen-holder may
be substituted for the finger ; while for very
small details the rag may be held on a small,
pointed stick. The film will not be scratched
or torn it the rag is kept thoroughly wet with
the spirit. Use a new portion of the rag each
time fresh spirit is applied, as the used part
will probably be black from the deposit worked
off the negative. The work should be done on
a retouching desk, so that its progress can be
watched. As it is purely mechanical, the efiect
can be graded or varied as desired, and no line
of demarcation will show either at the beginning
or the end. Halation and similar defects can be
very successfully treated by this method.
Baskett's reducer {which see) can be substi-
tuted for methylated spirit, and used in the
same manner. Instead of the metal polish, fine
tripoli powder may be used if preferred.
Both of these methods of reducing by mechan-
ical means may be employed very effectively for
removing iridescence or surface staining from
negatives.
REDUCING PRINTS
Prints can seldom be reduced satisfactorily.
Silver prints on P.O.P. may be slightly reduced
by means of Parmer's reducer, but if consider-
able change is attempted the general quality of
the print suffers, and the colour is spoiled. It
is better to make a new print when possible.
Bromide prints may be reduced the same way, or
with ammonium persulphate, but it is not desir-
able to carry the action far or the print will be
ruined. For reducing prints, the solutions
should be used very much weaker than for nega-
tives, one-fourth of the strength being ample.
REDUCTION AND ENLARGEMENT,
CALCULATING DISTANCES IN
The rule for finding distances when reducing
is : Divide the longer base of the image to be
reduced by the longer base of copy desired,
which will give the number of times of reduction ;
to this add i and multiply by the focal length of
lens used. The result will be distance between
lens and object, and this distance divided by the
ratio of image to object will give distance between
lens and plate. As an example, assume that a
picture measuring S-J- in. by 6J^ in. is to be re-
duced to a base of 2| in., using a lens of 1 1 in.
focal length. Then 8|^ -=- 2^ = 3I, number of
times of reduction; (3f + 1) x 11 = 48§, dis-
tance from lens to picture; 48 -4- 3f = 14J,
distance from lens to plate. It will be seen from
this that the working distance of lens is increased '
from 1 1 in. to 14^- in., and therefore the working
aperture of the lens is reduced ; thus //i i becomes
//14J, and this factor has to be taken mto account
when estimating the exposure.
The accompanying table supplies the data for
reducing or enlarging a copy, when the focal
length of lens is Imown. The figures given are
for linear enlargement ; for example, 3 in. to
12 in. = an enlargement of four times, or, vice
versa, a reduction to one-fourth. It is important
to note that when reducing (copying, slide-
making, etc.) the greater of the two numbers
given in each square of the table is the distance
from the original to the lens, and the smaller
number is the distance between plate and lens.
When enlarging, the greater of the two numbers
is the distance from the lens to sensitive paper,
and the smaller number is the distance between
lens and negative.
The figures in each square in line with the
focal length of lens give the distances on each
TABLE FOR ENLARGING AND REDUCING
h
Times of Reduction and Enlargement
1
2
3
4
6
6
7
S
In.
2
In.
4
4
In.
6
3
In.
8
2«
In.
10
2i
In.
12
2%
In.
In.
16
2^
In.
18
2i
2i
5
5
?l
10
3i
I2i
3i
15
3
28
20
2?
22i
2H
3
6
6
?i
12
4
15
3i
18
3l
21
3i
3^
27
3l
3i
7
7
loi
5i
'li
'7i
4f
21
4i
4A
28
4
3Ii
314
4
8
8
12
6
16
5i
20
5
24
4i
23
4t
'%
36
4i
4J
9
9
%
18
6
22i
5i
27
51
'\\
%
4oi
5iV
5
10
10
%
20
6f
25
6i
'I
%
'%
45
5i
5i
II
II
l6i
8
22
7i
271
6i
33
6J
ig
%
49i
6A
6
12
12
18
9
24
8
%
%
42
7
%
54
6i
7
14
14
21
loi
28
9*
\
42
8|
49
8i
56
8
%
8
16
16
24
12
?o,
40
10
It
1*
%
72
9
9
18
18
27
I3i
36
12
45
\u
63
Id
?o,
81
loi
10
20
20
30
15
40
I3i
I2i
60
12
Hi
80
II?
90
Hi
II
22
22
33
l6i
JJ?
55
13J
66
I3i
77
12S
88
I2f
99
12}
12
24
24
36
18
t
60
15
Hi
84
14
9\
13^
108
I3i
Reduction and Enlargement 454
Reflectors for Portraiture
side of the lens for copying same size and for
enlarging up to eight times. Assume that a
whole-plate print is to be reduced to a quarter
of its size and that a lens of 5-J in. focal length
is to be used. Look for the 4 on the top line
(number of times) and for the 5J in the left-
hand column (focal length of lens) ; where the
two columns meet will be found the numbers
27f and 6J, indicating that the distance between
print and lens will be 27J in. and between lens
and plate 6|- in. If, however, a negative is
being enlarged four times, 27! in. will represent
the distance between sensitive paper and lens, and
6f- in. the distance between lens and negative.
REDUCTION AND ENLARGEMENT:
CALCULATING SIZES OF IMAGES
By means of the simple rule of proportion,
sizes of reduced or enlarged images can readily
be found. If a print 9 in. x 4i in. is to be
reduced to measure 2|- in. on its longer edge,
then the shorter edge will be as 9 to 2j so is
4i to X. Or, 9 : 4J. : : 2f : x. li-^-M =
17 " I 187 ,. , .
4 4 9 144
A booklet published by Penrose gives tables
arranged as here shown : —
4 X 3i X 3 X 2j
Reduces to
3i X 3l X 2f X 2i
3 X 2| X 2j X i|
2| X 2|- X l| X if
2I X 2 X l| X if
Assume that a print 4 in. x 3 in. is to be reduced.
Select a table in which the black figure in the
top left-hand comer corresponds to the largest
dimension of the original, in this case 4 in.
Assume that this has to be reduced to 2^ in.
Run down the column imder 4 until 2f is reached.
Also run along the top line to the right of 4
until the other dimension (3) of the original is
reached. Then at the intersection of tiie col-
umns will be found the desired dimension —
namely, i|-, so that the 4 in. x 3 in. print will
reduce to 2^ in. x if in., as can be proved by
the nUe of proportion previously given.
REDUCTION, MECHANICAL
This includes the method of slightly reducing
density by expansion of the film {see " Enlarging
by Stripping"), and also those methods de-
scribed under the heading " Reducing Negatives
by Mechanical Means."
REFLECTED LIGHT
I/ight which does not reach the object direct,
but which is reflected thereon. The table given
under the heading " Light, Absorption and
Reflection of," shows the amount of light
reflected from various substances as compared
with that which falls upon their surfaces.
REFLECTING SCREEN
A reflector, usually of white material, and
used in portraiture. {See also " Reflectors for
Portraiture.")
REFLECTION {See "Mirror Photography.")
REFLECTIONS IN CAMERA
Unless a circular plate is used, and the camera
is so designed that all rays from the lens reach
the plate without obstruction, a certain amount
of reflection will be caused by light striking the
bellows or the internal woodwork. The bellows
should be coated with a dead black to minimise
those reflections that are unavoidable, and it
should not be allowed to get shiny. Reflections
are almost certain to occur when using a lens
capable of covering a larger plate than the size
for which the camera is intended. The super-
fluous light all round the image falls upon the
surrounding bellows and woodwork, and is
reflected and re-reflected from one part to the
other — sometimes even to the lens and back
again. Much of the reflected light is absorbed
by the dead black or trapped by the folds of
the bellows, but what escapes tends to fog or
degrade the brilliancy of the negatives. Re-
flections may be caused also by brasswork, such
as portions of the lens tube or diaphragm, from
which the black has worn ofE. When such places
are noticed they should be re-blackened. Where
reflection is suspected, remove the focusing
screen and place the eyes at the back of the
camera, covering the latter and the head with
a cloth to exclude all light but that coming
through the lens. After a few seconds, to get
accustomed to the comparative gloom, a fairly
good idea may be obtained whether or not the
fault is present to any detrimental extent.
REFLECTOR CAMERA {See "Reflex
Camera.")
REFLECTORS FOR PORTRAITURE (Pr.,
^cran d' iclairage, Riflecteur ; Ger., Be-
leuchiungsschirm, Reflektorschirm)
White or light-coloured screens used to prevent
heavy shadows on the sitter's face at tiie side
Studio Reflector with Head Screen
farthest from the light. They usually consist
of canvas, calico, musUn, or other suitable fabric
stretched on a frame supported by feet or by a
stand, and having provision for adjustment at
any desired angle. A typical studio reflector
with a head screen above it is here illustrated.
A pure white reflector is seldom desirable, cream
Reflex Camera
455
Refraction
or very light grey being preferable. For some
special pxirposes, thougli very rarely, mirrors are
used. The principle involved in the employment
of reflectors is explained under the heading
" Portraiture."
REFLEX CAMERA (Pr., Chambre miroir :
Ger., Spiegel-reflex Kamera)
Synonym, reflector camera. A camera in
which the image is focused on a horizontal
ground glass screen by the aid of a surface-
silvered mirror inclined at an angle of 45°, the
latter being automatically swimg out of the
Typical Reflex Camera
way when exposing the plate. The reflector
principle was suggested very many years ago
(see " Camera " and " Camera Obscura "), but
it is only of recent years that the mechanical
perfection of the reflex hand camera has been
achieved. A and B show respectively the ex-
terior and interior of a typical reflex camera, the
lettering being the same in both ; M is the
hiuged mirror, i, the lens, s the horizontal focus-
ing screen, H the hood shielding the last-named
from extraneous light, P the focusing pinion,
R the release that operates both shutter and
mirror, and p the position of the plate. The
dotted lines show the manner in which the image
is reflected to the screen. The hood folds down
flat when not in use. In designing these cameras
great care has to be taken to secure identity of
focus on the screen and at the position of the
plate. The mirror is usually arranged to swing
upward by means of springs or levers directly the
shutter release is pressed, and to resume its former
position after the exposure. In the majority of
reflex cameras a focal-plane shutter is fitted. The
advantages of the reflector principle are that a
full-size image is seen, and may be accurately
followed or focused up to the very moment of
exposure, using if desired, and seeing the efiect
of, the rising or swing front, or any oSier adjust-
ment. Large aperture lenses and lenses of long
focus may also be used on near objects without
stopping-down, as may frequently be necessary
in press work, whereas with an ordinary hand
camera it would be next to impossible to
secure sharp focus by scale under such con-
ditions.
Another form of reflex camera, but with a
fixed mirror, is the twin-lens camera.
REFRACTION
When a ray of light falls upon any transparent
medium it may be reflected, or it may pass
through it, but in the latter case the waves of
light are retarded in their passage, exactly in the
same way as the wind is retarded in passing
through a dump of thick trees. Take first a
sheet of glass, shown in section by a, b, c, d in
diagram A, on which falls a beam of parallel
light, the successive positions of the wave front
being represented by the transverse curves. On
meeting the glass at right angles to the surface,
A B, there is a slight retardation, but as practic-
ally the whole of the wave front meets the glass
simultaneously the relative positions remain the
same and the direction of ttie ray is unaltered,
although there is retardation in the glass, as
shown by the curves being closer. If the beam
strikes the glass at an angle, it is obvious that
B A
D C
A B
Diagrams illustrating Cause of Refraction
part of the wave front strikes the glass before
the other ; thus, as in diagram B, the point e
will strike the glass before the point F ; as the
wave is retarded in the denser medium, E moves
to G, whilst F is moving to h ; therefore, the wave
swings round slightly, or, as it is termed, is
refracted. Again, after passing through the glass,
I will meet the rarer medium, air, before j, and
wUl, therefore, have moved to K before j has
reached i,, and once more the ray swings round.
Now, take only one surface of the glass, A B, as
in diagram C, a b, and let l, be the ray incident
at the point d, which is refracted to E ; then,
with D as centre, describe the circle. Draw the
normal c, d, f at right angles to the surface, a b,
and from tibe point where the circle cuts the
incident and rrfracted rays, I, and E, draw the
dotted lines I,, M and E, n. Now it is obvious that
the angle l, d, m is greater than E, d, n ; the sine
of the angle of incidence, l, d, c, or sine t
_ h2^^ and the sine of the angle of refraction
I., D
or sine r = ^^ and the index of refraction is
D, E
?J5i?-? ; but it has just been shown that
sinef
L, M , . E, N
sme I = - — and sme r = — — ■
i<, D D, E
L, M
. • . sine i _ L, n
sine r E, N
D, E
but I,, D and d, E are radii of the same circle,
and, therefore, are equal to one another
. • . L, M
h^ i^ which is the index of refrac-
E, N E, n'
D, E
tion ; this is generally measured for the d line
(mean \ 5,893), and is denoted by the symbol ^.
Refractive Indices
4S6
Relief, Photographs in
Suppose in diagram C I,, M is 2 in. and E, n
is i'25 in. ; then
iL^ = ^ = 1-6
E, N 1-25
which would be the index of refraction for this
particular glass. The index of refraction is
C.
Diagram Showing How Index of
Refraction is Found
practically the ratio of the velocity of light in
one medium to the velocity in another medium.
In general, this refers to the velocity in the
given medium and in air, though the absolute
index of refraction is obtained when the medium
is in a vacuum.
REFRACTIVE INDICES {See " Refraction.")
REFRANGIBILITY
The quality or property of being refracted.
(See "Refraction.")
REGISTER (Pr., Registre ; Ger., Register)
A term employed to denote complete agree-
ment between the position of the ground glass
focusing screen and that of the plate in the
dark-slide, without which the negatives wiU not
be in focus. Lack of register between the dark-
slides and focusing screen is seldom met with in
good modem apparatus. To test the register of
a suspected slide, focus sharply, then take a
piece of ground glass the size of the plate, place
it in the dark-slide ground side outward, and
insert, the slide in the camera with both shutters
drawn and the separator removed. The ground
glass should be pressed close to the front of the
slide with the fingers, when if the image is still
in sharp focus that side of the slide may be
assumed to be in register.
REGISTRATION OF PHOTOGRAPHS (See
" Copyright.")
RE-HALOGENISATION
A method of converting into a haloid salt the
silver which forms the image of a negative, and
then, by re-development, obtaining a negative
of, if required, reduced density compared with
the original. One of the most simple and satis-
factory formulae is :
Potassium ferricyanide 80 grs. 18 g.
Potassium bromide . 120 „ 27,,
Water . . . 10 oz. 1,000 ccs.
The negative is immersed in this solution until
the image is thoroughly bleached, as in mercurial
intensification, and then well washed for about
twenty minutes. It is now ready for re-develop-
ment Any developer may be used. The plate
must be exposed to light after bleaching ; but
exposure during the washing will be found suffi-
cient. If the negative is fully re-developed, the
re-halogenised plate will be practically unchanged
from its original character. But shorter develop-
ment wiU natirrally convert only a portion of
the haloid salt into metaUie silver, thereby pro-
ducing a negative possessing less density than
the original. It is somewhat difficult to judge the
degree of strength produced, although the de-
velopment is carried out in white light ; the
unchanged haloid adds so much to the apparent
strength in the early stages of development.
The time will assist in judging the proportion of
the silver salt developed into metaUic silver ; the
full time would be the same as that originally
occupied in development. After re-development,
fixing is necessary in the same manner as with an
ordinary negative.
The only change that can be effected by this
method of working is reduction of density, and
this takes place uniformly throughout the scale.
The re-halogenised plate may be afterwards
intensified or reduced by any other method.
REHNERT'S PAPER
Particulars of producing this sensitive paper
for enlargements were published, it is believed,
by Rehnert, in 1897. Rives paper is immersed
in a solution of magnesium iodide, 2 parts ;
magnesium chloride, i part ; alcohol, 100 parts ;
and when dry sensitised by floating until white
on a I in 12 solution of silver nitrate, strongly
acidulated with acetic acid. It should be ex-
posed while wet, developed in a i in 200 solution
of pyro, fixed in " hypo," and washed. If more
brilHant results are wanted, the paper should
first be sized with starch before sensitising.
REJLANDER, OSCAR G.
Bom in Sweden, 1803 ; died in London, 1875.
Began photography in 1853, and practised at
Wolverhampton for many years. He was the
first to use a number of negatives in the produc-
tion of one picture, and to photograph the nude.
His first combination picture (1855) was from
three negatives. In 1857 he sent "The Two
Ways of I/ife " to the Manchester Exhibition of
that year ; thirty negatives were employed in
printing it, each being laid in turn upon the
sensitive paper and exposed, while the rest of the
paper was covered with black velvet. He was
one of the first to use photography for the pur-
pose of book illustration, his illustrations to
Charles Darwin's book, " The Expression of the
Emotions," being, perhaps, the best known.
RELIEF, GELATINE (See " Gelatine Reliefs.")
RELIEF, PHOTOGRAPHS IN
In the many processes of making photographs
in relief, the wdl-known property of chromated
gelatine losing its water-absorptive power
after exposure to light is taken advantage of.
Negatives having over-strong contrasts give the
most satisfactory results ; in produong such a
negative, the background should be black and
the sitter's face and hair powdered, and lighted
in such a way that the head stands out in the
greatest possible contrast to the background.
Relievo
457
Repairing Apparatus
The negative is printed upon a plate prepared
as follows : Mix together 2 oz. of gelatine, i oz.
of gum arable, 10 oz. of water and 48 mins. of
glacial acetic acid, and melt by the application
of heat. Pour a quantity on a bevelled sheet of
glass to the thickness of two or three millimetres,
and let it set and dry in a horizontal position.
The plate is sensitised by immersing it for a few
minutes in a 3 per cent, solution of ammonium
bichromate, with an excess of ammonia, and
dried in the dark. The plate requires a longer
exposure than if bichromate alone is used, from
a quarter to half an hour being required in full
sunlight, the printing frame being so placed that
the sun's rays fall upon it as perpendicularly as
possible. After printing, in which a certain
amount of guesswork is necessary, the prepared
plate is taken from the frame and placed in a
2 per cent, solution of alum to which a 2 per
cent, solution of citric acid has been added.
After soaking for several hours considerable
relief is obtained, which is suitable for cast-
ing in plaster-of-paris, or, after dusting with
graphite, can be electrotyped. In the latter case,
varnish the edges of the reUef plate before or
after printing, so as to prevent the film from
stripping when it is in the acid sulphate of
copper bath. {See also " Aerograph," " Cameo,"
" Bas-reUefs," " Electro-phototypy," " Galvano-
graphy. Photographic," " Gelatine Reliefs,"
" Photo - lithophane," " Photopolygraphy,"
" Photo-sculpture," " Plaster Casts from Photo
ReUefs," " Woodburytype," etc.)
RELIEVO
A type of photograph invented in 1857 by
Thos. C. Lawrence, of Greenwich. The sitter, in
monochrome, or slightly tinted, stands out in a
kind of stereoscopic effect against a coloured
hand-painted background. A wet collodion
plate is made in the usual way, and when dry
the whole of the photographic background is
scraped away. A suitable landscape or other
background is then painted in by hand on white
card, which is botmd up not quite in contact
with the photograph proper and then suitably
framed.
REMBRANDT EFFECTS
So named after the painter Rembrandt, who
lighted his portraits in a characteristic manner.
Almost any shadow portrait is now said to be
in the Rembrandt style. The sitter is so
arranged that the chief light comes from behind,
rendering most of the picture in shadow, which,
however, must not be so intense as to lose all detail.
In ordinary rooms this lighting is fairly easy to
obtain by placing the sitter between the camera
and the window, but not in the same direct line ;
the window should be at the side and behind
the sitter, so that it is out of the field of view
of the lens. A reflector is often needed to show
up details in the shadows. By far the best
effects are obtainable in the studio, by screening
ofE all front light ; especially must care be taken
to shade the lens so that no direct light enters
it, as otherwise fogging of the picture will ensue.
This style of lighting is very favourable for photo-
graphs of ladies having an extra fullness of the
chin and neck, as owing to the face being mostly
in shadow sudi fullness is not so noticeable.
REMBRANDT PROCESS
An adaptation of the photogravure process to
rotary mechanical printing, invented by Karl
Klic, and worked in England since about 1895
by a Lancaster firm. The details of their method
have been kept secret, but it is assumed that a
print on carbon tissue is made under a trans-
parency in the usual way, except that, either
before or after the print of a picture is made,
the tissue is exposed imder a negative line
screen — that is, a screen with transparent lines,
instead of the network of black lines used in
the half-tone process. The printed tissue is
squeegeed on to a copper cylinder, and there
developed with hot water as in the carbon pro-
cess. After being dried, the image is etched
through by means of ferric perchloride, as in the
ordinary photogravure process, the cylinder being
rotated in the bath, and solutions of different
strengths being used. On the resist being cleaned
off, the copper cylinder is seen to have on it an
intaglio ettiing which varies in depth, being
deepest in the shadows. The image is cut up
by thin lines formed by the screen, and the
square spaces between the h'nes serve to hold
the ink better than would the grain of the
ordinary photogravure plate. The cylinder is
mounted in a machine similar to that used by
wall-paper or calico printers. Above the copper
printing cylinder is the impression cylinder,
covered with an endless blanket, and below the
printing cylinder is an inking roller running in a
trough of thin ink. A steel knife-edge presses
against the printing cylinder and wipes off the
ink from the surface, whilst leaving the ink in
the hollows of the engraving. Paper in a long
band is drawn from a reel through the machine,
passing between the printing and impression
cylinders, and thereby being printed. After
leaving tie machine, the paper is led off to a
drjdng-room, where it is suspended in festoons,
or it is rewound on another reel, or it may pass
straightway into a cutting machine.
Recently the process has been developed into
colour printing under the name of mezzochrome,
and some very fine results have been produced.
Whether the foregoing correctly describes the
Rembrandt process or not, it is known that
several other firms have imitated the results in
this way, notably Bruckmann in Munich, Lowy
in Vienna, and Saalburg in America. The pro-
cess is also known under the name of mezzotinto-
gravure, altogravuie, Similiheliogravure, and
Vandyck-gravure.
REPAIRING APPARATUS
Owing to a fall, or similar accident, cameras
and other apparatus sometimes call for repair.
If the damage is serious, it is best to send the
apparatus to the manufacturer, or to a photo-
graphic dealer who undertakes repairs ; but
there are many trifling injuries within the power
of the amateur worker to rectify. The most
useful tools are a sharp penknife, a fretsaw, and
a small, thin screwdriver, together with some
good quality glue. When portions of woodwork
come asunder a little thin hot glue is usually
all that is necessary, appUed very sparingly,
and left until thoroughly set. Lost screws, if
small, can generally be matched at any iron-
monger's, but milled-head screws and special
Repeating Back
458
Residues
trass fittings need to be ordered of a photo-
graphic dealer. Pieces of woodwork chipped ofi
can frequently be matched by cigar-box wood,
cut carefully to shape, glass-papered, and glued
on, treating the part, when the glue has set, with
a little water-colour paint to match the tone of
the camera, and then rubbing on a trace of
ordinary negative varnish with a rag, or a little
French polish if handy. Ground glass can be
purchased cut to size to replace a broken focusing
screen.
REPEATING BACK (Pr., Chariot muUipUca-
teur ; Ger., MulHpUkator)
An arrangement enabling two, or a larger
number, of photographs to be obtained on the
same plate. It is made in many different pat-
terns, some of them being extremely ingenious.
The illustration shows a simple type, for obtain-
ing two cartes-de-visite on a hali-plate. A is a
Repeating Back
panel attached to the back of the camera, having
an aperture the size of the required picture, and
furnished with grooved rails B and C for the
dark-slide or the focusing screen. At D is a
spring bolt, engaging in either of two slots in
the edge of the dark-slide, these being so placed
as to bring either half of the plate alternately
into position against the opening in the panel.
The photographs are, of course, taken separately.
REPTILES, PHOTOGRAPHY OF
The most useful camera for photographing
reptiles is a reflex, fitted with as silent a release
as possible, and a lens of fairly long focus. Snakes
and lizards, toads, frogs, and tortoises are all
more or less shy creatures, easily alarmed (the
first-named are easily angered), so that some
amount of caution and patience is necessary.
When startled, a. snake generally retreats, but
should it find escape difficult or impossible, it
may turn and strike at its pursuer ; and this is
more particularly the case with poisonous
snakes. Therefore a long focus lens which will
enable one to obtain a fair-sized image on the
photographic plate, without approaching too
dose, wUl be found an advantage in many ways.
The wall and sand lizards at their play, or
capturing the insects upon which they feed,
make most charming and interesting subjects
for photography, but on accoimt of their ex-
tremely rapid movements and shyness, present
many difficulties. Tortoises are particularly
exasperating models at times, either shutting
themselves up tightly in their shells or march-
ing ofi in such a hurry that it is impossible to
get a satisfactory pose. The best chances of
success are when the tortoise first awakens in the
morning, before the sun has had time to warm
him thoroughly ; when he is busy feeding ; or
in the afternoon when he is about to go to sleep.
Progs are best photographed in an aquarium
with rocks placed on the bottom so that they
can sit with their head and shoulders out of the
water — a very favourite position in their natural
state. In the spring of the year they may
often be photographed sitting on the banks of
shallow ponds and ditches. A few weeks later
in the season they will not be so easily found,
while masses of their spawn will be seen floating
in the shallow water. The life history of the
tadpole can be easily watched and photographed
by placing some of the spawn in an aquarium,
and keeping it in a cool place.
Toads are not nearly so difficidt to handle or
photograph as are the frogs. They are much
bolder, and soon become quite tame if regularly
suppUed with worms, caterpillars, or meal-
worms. The toad has very considerable char-
acter, and therefore always makes an interesting
model.
Orthochromatic plates should always be used
for photographing reptiles, and as fuU an expo-
sure as possible given, so that a negative with a
long sc^e of gradation may be obtained. It is
rarely necessary to use a compensating filter,
except in such cases as the chameleon, when the
gradual changes of colour and re-arrangement
of spots and bands of colour may be brought
into greater contrast by the use of a suitable
screen. P. M-D.
RESIDUES (Pr., Risidus : Ger., Riickstande)
The collection of residues, from the amateur's
point of view, is hardly worth the trouble unless
he uses a very large quantity of material, though
probably about 60 to 70 per cent, of the total
sensitive salts are not used in the formation of
the actual images. Residues may be divided
into four kinds : ( i ) emulsion residues, (2) fixing
bath residues, (3) gold residues, and (4) platinum
residues.
(i ) Emulsion residues. — ^The general method of
collecting spoilt emulsions, etc., is to mix them
with plenty of water acidulated with impure
nitric or hydrochloric acid, and boil till the set-
ting property of the gelatine is destroyed. The
sensitive salts settle to the bottom of the vessel
in time, allowing of the decanting or syphoning
off of the supernatant fluid ; then the silver salts
are collected and dried.
(2) Fixing bath residues. — ^The fixing baths
both from negative and positive work should
be saved and mixed together, and when a
sufficient quantity is obtained they may be mixed
with a saturated solution of hver of sulphur,
which precipitates the silver as sulphide. This
process should be done outdoors, as sulphuretted
hydrogen is evolved, which is not only evil-
smelling but is detrimental to any sensitive sur-
faces. A better method is to add zinc filings or
magnesium powder, which decompose the silver
hyposulphites with the precipitation of metallic
silver.
(3) Gold residues. — Spent toning and com-
bined toning and fixing baths should be acidu-
lated with hydrochloric acid, and then an acidu-
lated saturated solution of ferrous sulphate added
till a precipitate is no longer caused.
(4) Platinum residues. — ^The developer and
Resin Dry Process
459
Restrainer
•first washing water of platinotype should be col-
lected and preferably boiled down to a smaller
bulk, a saturated solution of ferrous oxalate
added, afterwards boiling.
The various precipitates may be collected and
all the silver ones mixed, but the gold and
platinum should be kept separate, and they can
then be sent to the refiners, who will allow the
market value of the metals less a small percentage
for smelting.
Paper clippings of all kinds should be burnt
and the ashes added to the general residues.
Silver is obtained from the residues by fusing
with borax, charcoal, etc.
RESIN DRY PROCESS (Fr., Procidi risine ;
Ger., Harz Prozess)
An early dry collodion process, due to the
Abb^ Pujo, in which resin was used as a pre-
servative. In each oimce of bromo-iodised
collodion half a grain of ordinary resin was
dissolved. The plate was then coated, sensi-
tised, and washed, being ready for use when dry.
RESINISED PAPER (Pr., Papier risini : Ger.,
Harzemulsionspapier)
The use of resin for photographic paper was
first suggested in 1863, and the method adopted
was to make an alcoholic solution of resins with
a chloride and brush this over the paper or
immerse the latter in the solution, dry, and
sensitise subsequently by floating on a solution
of silver nitrate. Three years later an aqueous
solution of shellac in borax or sodium phosphate
was used. Later stUl, Cooper suggested the emul-
sification of bleached shellac in gelatine. In 1 891 ,
Valenta suggested the following method of work-
ing, which gives excellent matt surface prints : —
Hard gelatine . -350 grs. 80 g.
Soak in water for half an hour and drain well.
Pale French resin
. 350 grs.
80 g.
I/iquor ammoniae
. q.s.
q.s.
Distilled water .
. 10 oz.
1,000 CCS.
Powder the resin, rub up with the ammonia and
a little water, add the rest of the water, boil,
and add ammonia from time to time till a dear
solution is obtained. Add the gelatine, stir till
dissolved, and add — ,
Ammonium chloride . 88 grs. 20 g.
and filter. Finally add enough saturated solu-
tion of citric add to give a strong add reaction.
The add predpitates the resin as an impalpable
powder, which is suspended in the gelatine.
The paper should be brushed over with the
solution and then floated on the surface for
three minutes and dried, and then sensitised in
the usual way by floating.
A variant was suggested by B. J. Wall,
and consisted in the use of an ammoniacal
alcoholic solution of resin, which was added to
an ordinary gelatino-chloride print-out emul-
sion. These papers are particularly suitable for
platinum toning, and give fine black tones.
RESINS (See "Gums and Resins.")
RESORCIN (Pr., Rlsorcine ; Ger., Resorcin)
Synonyms, resorcinol, metadihydroxybenzene.
C,H4(OH)2. Molecular weight, no. Solu-
bilities, 1 in '6 water, i in '5 alcohol, soluble
in ether. It is in the form of white prismatic
crystals obtained by the action of caustic soda
on sodium dibenzene sulphonate. It has the
same formula as hydroquinone, but the hydroxyl
groups (OH)j are attached at different points
to the benzene ring, and it has no developing
power. It has been used as an addition to
emulsions without excess of silver nitrate to
obtain vigour in printed-out images.
RESORCINPHTHALEIN
A synonym for fluorescein.
RESTORING NEGATIVES (See "Broken
Negatives," " Cracked Negatives,"
" (Sacks in Varnish," " Scratches on
Negatives," etc.)
RESTORING PHOTOGRAPHS (See " Faded
f>regatives and Prints, Restoring.")
RESTRAINER (Pr., Modirateur : Ger., Zariick
halter)
Any compound which will check the too ener-
getic action of a developer. The most popular
restrainer for alkaline developers is a soluble
bromide, which works well with the caustic
alkalis, and in some cases with the carbonates.
When the alkali is ammonia, ammonium bromide
may be used ; otherwise, potassium bromide
may be employed. Bromide has more effect in
restraining the least exposed portions of a nega-
tive— that is, the shadows — than on the better
lighted portions, and as a result it gives greater
contrast and brilliancy. In cases of over-
exposure, where normally a flat and lifeless
negative would be the result, this property of
bromide is turned to account, the addition of
a very few drops of a :o per cent, solution to
the developer often sufficing to save an imder-
exposed plate. The generally accepted theory
is that the bromide forms a double compound
with the silver salt in the film, and that this
double compound is less readily acted upon by
the developer. With stale plates, a restrainer
is absolutely necessary, as the silver salts in the
film seem to undergo a certain amount of decom-
position, and reduction (development) takes
place where the light has not acted. Bromide
is also necessary with bromide and gaslight
papers, as it serves to keep the white parts of
the print dear while the image is being devdoped
to its proper density.
Some authorities recommend the omission of
a restrainer from the developer entirely, while
others advise its use with extreme caution.
Watkins, for example, says that the use of a
restrainer, such as potassium bromide, is a legacy
left from the early days of pyro development,
that its use introduces complication and varia-
tion from the usual simple course of develop-
ment, without suffident compensation, and that
with a good modem dry plate and sodium car-
bonate as the alkali, the restrainer is best
omitted from the normal devdoper and used
only exceptionally to " hold back " the lowest
tones or fog. Watkins illustrates this " holding-
back " power with two diagrams, A and B, the
former representing four steps of gradation,
A, B, C, and D, produced by, say, five minutes'
Retardation
460
Retouching
development without bromide. B gives an idea
of the result of the same exposure if the same
developer, with a little bromide added, is used
for the same length of time. The steepness of
gradation (and therefore the contrast in the
print) is identical in the two cases ; but the
bromide has retarded all the tones and prevented
the lowest one, A, from appearing at all. It has,
in fact, at this stage reduced the speed of the
plate. If development with bromide were
continued, the tone A would develop out, and in
due time take exactly the same place as if no
bromide were used. To utilise the restraining
power of a bromide, therefore, development
must be terminated while the holding-back
power is still in force. Watkins also points out
that with high factor developers the lower tones
come out so early in development, they rush up,
so to speak, that the holding-back power of
bromide is exhausted before a useful degree of
contrast is attained, and bromide is of very little
A B C D
"Holding Back" Power of Resirainer
use with this dass. But if a low factor developer
is used, the tones naturally come out very late
in development, and the bromide decidedly alters
results. It is with a low factor developer and
plenty of bromide that gross over-exposure can
be made to give good negatives. But when once
the tones have appeared it is quite useless to
add a bromide with the idea of holding back
fog or the lower tones. With high factor num-
bers, bromide has practically little result, except
to make development slower.
The only restrainers that are of any service
when development has once started are the
citrates {which see) ; they stop the shadows and
allow the high lights to go on developing.
The usual dose of potassium bromide is 5
drops per ounce of mixed developer; and, of
course, the ammonium and sodium bromides
may be used in a like manner. Potassium bromide
is bulk for bulk the weakest restrainer ; ammo-
nium bromide the strongest ; and sodium
bromide the medium, the most suitable propor-
tions being potassium 120, sodium 103, and
ammonium 98.
RETARDATION
A restraining of development by the addition
of a restrainer.
RETARDER
A sjmonym for restrainer. The addition of
plain water and the chilling of the developer are
the simplest retarders.
RETICULATION
Peculiar wavy markings in relief which are
common to colloids ; they sometimes appear on
gelatine negatives. In some photo-mechanical
processes reticulation is purposely brought
about, but it often occurs when not wanted and
ruins the negative, there being no known cure
for it. It appears mostly during intensification
with mercury, and is thought to be due to the
use of a too strong mercury solution which tans
the film ; this, when placed in ammonia for black-
ening, breaks up into pinholes or forms ridges.
In process work, the reticulation of the gela-
tine film is the basis of several photo-mechanical
processes — namely, Poitevin's photo-lithographic
process, the Pretsch process, the collotype pro-
cess, Dallas process, papyrotint, and numerous
others. It is believed that the reticulation of
the film is due to unequal contraction, due to
the various parts being variably acted upon by
light according to the depth of the tones of the
picture. It has been noticed that on the collo-
type plate the grain or reticulation occurs just
at the last moment? of drying. Reticulation is
also promoted by the addition of chemical sub-
stances, usually of an astringent nature, to the
film, and in this case the reticulation is prob-
ably due to a tanning action influenced by the
action of light.
RETOUCHER. AUTOMATIC
A retouching pencil or holder in which the
lead is made to move rapidly up and down by
an electric current, so that a fine stipple is
obtained on portrait negatives in a shorter time
than if applied by hand alone. The guidance
of a skilled retoucher is, however, still necessary ;
the automatic pencil merely facilitates work —
it does not supply the place of artistic dis-
crimination.
RETOUCHING
The working up of negatives and prints by
hand. In this article only the retouching of
negatives will be considered. For prints, see
" Working-up Prints."
It is rarely desirable to retouch a landscape
negative, but portrait negatives are commonly
retouched by professional workers. The easiest
way of improving portrait negatives in a small
degree is to coat the glass side with matt varnish,
and then, when dry, work on it lightly with a
lead pencil or a stump and powdered blacklead.
The parts covered with lead pencil print lighter.
This work is, however, not true retouching, and
win serve only for remedying broad patcies in
the negative.
For retouching proper, a retouching desk,
pencils, and a bottle of medium will be required.
Retouching desks {see A) may be bought ready
made, or may easily be converted from an
ordinary box, as shown at B. A hole, p, is cut
with a rebate in the lid to hold the negative, and
the lid fixed at a convenient working angle by
means of narrow strips of wood, Q, at each side.
An extra piece of wood, R, is fixed to the top in
order to shield the light from the surface of the
negative. All the light must come through the
negative, and it is advisable to place white paper
in the bottom of the box.
The worker should experiment with three re-
touching pencils — ^hard, medium, and soft; and
they should have a point literally as sharp as a
needle, to obtain which very fine glass-paper or
emery cloth is used. Place a piece flat on a table,
take the pencil between the thumb and fingers,
and carefully roll the point round and round on
Retouching
461
Retouching, Chemical
the rough surface until the lead tapers to a fine
point. Retouching medium may be bought, or
it may be made according to one of the foUowing
formulae : No. i . — ^Turpentine, 2 oz. ; powdered
resin, 60 grs. No. 2. — Sandarach, 80 grs. ; alcohol,
A. Retouching Desk
of Modem Design
B. Home-made Re-
touching Desk
I oz. ; castor oil, i|- oz. ; Venice turpentine, 40
drops.
The majority of beginners have an erroneous
idea of retouching, hence their failures. The
secret is not to attempt too much at first, but
to be satisfied if even only one freckle or wrinkle
has been removed. Now the general idea is that
the whole of the negative — or, rather, the face —
is worked on by the retoucher with his pencil,
which is wrong. Only the blemishes require to
be worked on, so as to bring such clear spots up
to the density of the surrounding parts ; dia-
grams C and D explain this. C represents in a
highly magnified form a. spot or freckle on a
negative which is to be worked out, the blemish
appearing as a clear spot in an almost opaque
part of the negative. If the pencil is worked,
and the lead is put on in even quantities aU over
the face, the opaque surroundings would be even
more dense, and the spot would contain only as
much lead as the dense parts ; therefore the spot
would still show, say, as iu D. The correct thing
The Retoucher's Various Strokes and Touches
to do is to leave the surrounding parts alone for
the time being, and to work the pencil only on
the blemishes, putting suflSdent lead in them
to bring them up to ttie required density. The
result, 2 carefully and properly done, would then
be as shown at E, that is, a perfectly even surface.
It is advisable to take a rough print of the
negative to be retouched on glossy paper, which
will show up the defects and serve as a guide to
the work. Dust the negative, put a drop of
retouching medium on the film side, and then,
with the finger-tip, rub the drop of medium in
a circular motion over the whole of the face to
be retouched ; continue rubbing gently until the
surface feels " tacky," and put the negative on
one side to dry. Place the negative film side
upwards over the hole in the retouching desk, so
that a good light comes through it, and, having
sharpened the pencil, begin filling up the clear
holes, taking particular care that the lead does
not go on the outside of the hole, or the result
will be as at P. The particular " stroke " or
movement of the penal needs consideration.
The four most used strokes are shown, G to J ;
G is known as the scribbling touch, and is most
useful for softening up and bringing together
high lights and shadows, such as the lines under
the eyes and down the nose ; H is a " comma "
touch suitable for large freckles and blemishes ;
I is the " cross hatch " used for filling up com-
paratively large spaces ; and the " dot " J is
the most useful touch of all for filling up freckles.
Begin, then, by dotting the smaller freckles
and continually take rough prints to note the
progress of the work. Be particularly careful
not to do too much or to lay on the lead too
thickly, or the working will show. When the
freckles and other blemishes are dotted out,
smooth the rough skin, soften the wrinkles and
places where shadows meet the high lights with
the scnbbling touch G. This is all a beginner
should attempt for some time, and even this
requires considerable practice and care to do pro-
perly. Work done roughly and unsuitably can
easily be rubbed off with a clean rag wetted with
the retouching medium, and a fresh start made.
Negatives are also retouched with the knife.
{See "Knife, Retouching.")
RETOUCHING, CHEMICAL (Fr., Retouche
chimique ; Ger., Chemische Retouchier)
Modifying or removing portions of a photo-
graph, usually in the negative, by means of
chemical solutions applied with a brush. Thus
in developing, any details that come up too
rapidly may be kept back by draining the nega-
tive and painting the parts with a 5 per cent,
solution of potassium bromide, afterwards return-
ing the plate to the dish and completing the
development. To reduce harsh lights or dense
portions, or to introduce clouds or shadows in
a finished negative, a solution of ammonium
persulphate (10 to 20 grs. to i oz. of water) may
be employed, placing the negative after reduc-
tion in a 5 per cent, solution of sodium sulphite
for a few minutes before washing. An alterna-
tive is to use Parmer's fetricyanide and hypo
reducer [see "Reducing Negatives, etc."). To
obtain a local increase of density, to insert high
lights, to strengthen thin portions, etc., a solution
of mercuric chloride or other intensifier may be
used. The negative, after washing, is pressed
with blotting-paper to remove the excess of
moisture, and is supported on a retouching desk,
as nearly horizontal as possible ; the solutions,
which should not be too strong, are applied
qtiickly with a brush, and the negative washed
directly the desired result is obtained.
Reversal, or Solarisation
462
Negatives are also improved by the use of
dyes, etc. Stain matt varnish with aniline dye,
red, green, or yellow heing suitable. Plow the
varnish over the glass side of the negative. Place
the negative in a frame film (not varnish) side
outwards, and expose to strong sunlight for
some days or until the dye has partially faded,
when the negative will give brighter and better
prints. This is really a dye process of intensifica-
tion. The light going through the outward film
to the dye beneath naturally causes it to fade,
the amoimt of fading being governed by the
density of the image.
REVERSAL, OR SOLARISATION (Pr. and
Ger., Solarisation)
A phenomenon occurring as the result of
extreme over-exposure, a positive instead of a
negative image being produced on development.
Abney has stated that preliminary exposure to
diffused daylight, the use of a powerful developer,
and the treatment of the plate with a solution of
an oxidising agent before exposure, facihtate
reversal ; and, in his opinion, it can only be
produced when there is atmospheric oxidation.
The addition of thiocarbamide to a well-restrained
developer will produce reversal, especially if
hydroquinone or eikonogen is used.
REVERSED NEGATIVE {See "Negative,
Reversed.")
REVERSING BACK
An adjustment whereby the back of the camera
may be turned, in order to obtain either upright
or horizontal pictures. Before the introduction
of the reversing back the only way of doing this
was to turn the whole apparatus on its side. The
usual form of reversing back consists of a square
wooden frame rebated on the inner side to fit
closely in the camera, and having on the outer
side suitable grooves to take the focusing screen
or dark-slide. The comers of the frame are
slightly recessed, two of them fitting under brass
plates on the camera, while the other two are
secured by turn catches. To reverse the back,
the catches are unfastened, the frame lifted out,
turned half-way round and re-inserted, being
then re-fastened as before. An improved form,
the revolving back {which see), does not need to
be removed from the camera.
REVOLVER {See " Qxm and Revolver
Cameras.")
REVOLVING BACK (Pr., Cadre de verre dipoli
rotatif ; Ger., Rotations Visirscheibe)
An arrangement whereby the focusing screen
or dark-slide may be changed from a vertical to
a horizontal position, or vice versa, without re-
moval from the camera. The frame carrying the
rails or grooves to take the focusing screen or
slide is attached to a. circular turntable let into
the camera back, and having ball catches to
check it at the two positions. With such a
movement it is possible to change from one
position to another with scarcely a second's
delay, even with the plate inserted and the
shutter of the slide drawn. The one disadvantage
of the revolving back is that the camera needs
to be slightly larger.
Robinson, Henry Peach
RHODIUM TONING
A method of toning with salts of rhodium (a
rare metal resembling palladium and, in a less
degree, platinum), was advocated about 1890,
in America, but it did not come into general use.
A formula is : —
Rhodium and sodium
chloride . . .22 grs. 5 g.
Acetic acid . . 96 mins. 20 ccs
Water (distilled) . 10 oz. 1,000 „
The metallic silver of the prints slowly takes a
yellowish-red colour which deepens in the fixing
bath.
RIPENING
Photographic sensitive emulsions imdergo a
process known as ripening, as explained under
the heading " Emulsion."
The term is also sometimes applied to toning
baths ; an acetate and gold toning bath, for
example, is ripened by allowing it to stand for
twenty-four hoiurs or more before use, while the
alum-" hypo " toning bath for bromides is
ripened by adding a few pieces of torn waste
silver prints.
RISING FRONT (Pr., DScentrement vertical:
Ger., Verschiebbares Obfektivbrett)
An adjustment enabling the lens to be raised
or lowered with respect to the plate, in order
to include more of the subject at the top or
bottom of the pictiure. It usually consists of a
panel carrying IJie lens and moving freely between
two grooved upright posts. The sides of the
posts are generally slotted, so that miUed-head
screws inserted in the panel may move up or
down with it, and enable it to be damped at any
desired height. The rising front is, however,
made in various forms, some modem high-grade
cameras having even the luxury -of a rack and
pinion movement to the front. Frequently, the
lens panel is separate from the front, upon wliich
it slides in horizontal grooves, thus giving a
" cross " adjustment as well as a rise and fall.
The whole front is often made also to swing.
{See " Swing Pront.") A rising front is almost
indispensable for practical work, but in using
it care must be taken that the lens is not raised
too far, otherwise the upper portion of the
negative will be badly lit, or perhaps will show
blank comers.
RIVES AND SAXE PAPERS
Specially pure raw papers, free from imper-
fections such as metallic particles, used for coat-
ing with sensitive emulsions. Both of them are
Continental productions. Rives paper had its
origin at Rives, France, and is thin and tough.
Saxe paper had its origin at Saxe, Germany, and
is thicker and heavier ; sometimes it is referred,
to as " Steinbach " paper.
ROBINSON. HENRY PEACH
Bom at Ludlow, 1830 ; died at Tunbridge
WeUs, 1 90 1 . He exhibited at the Royal Academy
when twenty-one. He began business as a pro-
fessional photographer at Leamington, in 1857,
and later (1868) built a studio at Tunbridge
Wells, where he practised until his retirement
in 1888. He produced many " combination '*
Rochelle Salts
463
Roller Slide
pictures, of which "Fading Away" (1858) and
Dawn and Sunset" (1885) were among the
best known. The latter is reproduced as a plate
to this work, and was awarded a medal by the
(now) Royal Photographic Society. Three sepa-
rate negatives were used, and the original mea-
sures 30 X 21 in. His most ambitious effort was
"Bringing Home the May" (1863). He was
Vice-President of the Photographic Society of
Great Britain (now the Royal Photographic
Society) in 1887 ; President of the Photographic
Convention of the United Kingdom (Leeds Meet-
ing), 1896. He was a writer on the art and busi-
ness sides of photography, his best-known works
being " Pictorial ^ect in Photography " (1869),
"Picture Making by Photography" (1884),
"The Studio and What to Do in It," and
" Letters on Landscape Photography."
The developer sometimes referred to as the
Robinson pyro - ammonia developer is as
f oUows : —
A. PyrogaUic add . 1 oz. 144 g.
Citric acid . . 40 grs. 12 „
Water . . . 7J oz. 1,000 ccs.
B. Potassium bromide . 120 grs. 36 g.
Liquor ammoniae ("880) i oz. 143 ccs.
Water . . . 7 „ 1,000 „
Take 3 oz. of water and add i dram each of
A and B.
ROCHELLE SALTS (See " Potassium and
Sodium Tartrate.")
ROCK AMMONIA (See "Ammonium Car-
bonate.")
ROCK CRYSTAL
A synonym for quartz.
ROCK SALT
An impure variety of common salt, which,
chemically, is sodium chloride.
ROCKER
An appliance for automatically rocking the
developing dish, so that the operator may leave
the plate in it while attending to other matters.
A simple form consists of a pivoted platform
below which a weighted pendulum is attached.
If set swinging by an occasional touch, this
keeps in motion for some time. Many clockwork
rocking devices have been invented.
ROCKING DISHES
Dishes containing photographic solutions re-
quire occasional rocking, oQierwise the plate or
prints may not be properly covered and the
action of the solution is likely to be imeven,
while air-bubbles and sediment have also a
chance to settle in one place. But continual or
excessive rocking is not necessary, and tends to
cause frilling.
RODINAL
A one-solution developer consistmg of a con-
centrated solution of para-amido-phenol
(CjHiOHNHj), introduced by Andresen ; it
needs only the addition of water to make a
working solution. Formerly it was obtainable
in powder forin, under the name of " imal."
The following is one of the formulae given by the
Chemische Zeitung for making rodinal : —
Potass, metabisulphite or sodium
sulphite . . . .3 parts
Para-amido-phenol chlorohydrate i part
Sodium hydrate (sat. sol.) . q.s.
Hot distilled water . .10 parts
When the first two are dissolved in the water,
a saturated solution of sodium hydrate (caustic
soda) is added very gradually tmtil the precipi-
tate first formed is dissolved and the solution
quite clear. Pew photographers attempt to
make it, however, as the commercial article is
so cheap and good. It keeps well, darkening in
colour with age. When diluted with water,
however, it assumes a reddish tinge and gradu-
ally loses its developing powers, but if diluted
with a 5 to 10 per cent, solution of pure sodium
sulphite instead of water it will keep quite well.
For normal exposures, use rodinal i part and
water 20 parts. In cases of over-exposure, use
less water, and add a few drops of a 10 per cent,
solution of potassium bromide. In cases of
under-exposure use from 30 to 40 parts of water.
The more dilute the rodinal the softer wiU be
the negative, and vice versa. When the extent
of the exposure is not known, it is well to begin
development with a i in 30 solution, and then,
if necessary, to correct over-exposure by adding,
drop by drop, a solution composed of 3 parts
each of rodinal and water and i part of potas-
siiun bromide. The solution should be added
to the developer in a measuring glass, and not
direct into the developing dish. It is better,
in a case of known over-exposure, to add the
bromide to the developer before it is applied
to the plate.
Many fail to get density with rodinal simply
because they do not develop long enough. The
image appears very quicWy, and there is a
temptation to remove at once the negative from
the developer instead of giving time for density
to be attained. Negatives developed with
rodinal appear to lose much of their density
dtuing fixing.
For bromide and gaslight papers rodinal
should be used in the proportion of i part to
20 to 30 parts of water, adding 2 drops of a
10 per cent, solution of potassium bromide to
each ounce of developer. The tone or colour of
the print varies according to the exposure and
strength of the developer, strong solutions giving
blue-black and weak solutions grey ; with too
httle bromide the high hghts may not be clear,
while with too much bromide there will be
greenish blacks. These remarks apply also to
lantern plates. For stand development the
strength usually employed is i part of rodinal
to 100 to 200 parts of water. Rodinal may be
mixed with other developers, as explained under
the heading " Developers, Mixed or Combined."
ROLL FILMS (See "Cartridge Fihn " and
" Film Manipulation.")
ROLLER BURNISHER (See "Burnisher.")
ROLLER SLIDE (Fr., Chassis ct rouleaux ; Ger.,
Roll-cassette)
A dark-slide specially designed for use with
roll films. First suggested by Relaudin, in
Roller Squeegee
464
Rouill6-Ladevfeze Printing
1855, roller slides were constructed by Melhuish
in 1856, Burnett in 1857, Audineau in 1862, and
Wamerke in 1875. These were all for use with
negative paper. It was, however, the Eastman
Company in 1885 who rendered this form of
slide really popular by the introduction of their
roll-holder, which also was at first used with
paper films. It consists of a box made to slide
into the dark-slide grooves of the camera back,
and having a draw shutter in front. Two rollers
or spools are contained in the box, one holding
the unexposed film, and the other furnished
with an external winding key by means of which
the film is wound ofE as exposed. Suitable
means are adopted to keep the film taut and
to indicate how far it is to be woimd for each
exposure. The spools are interchangeable.
ROLLER SQUEEGEE {See "Squeegee.")
ROLL-HOLDER (See " RoUer Slide.")
ROLLING PRESS (Fr., Presse d satiner dfroid ;
Ger., Satinirmaschine)
A machine for flattening and giving a glossy
surface to mounted prints. It consists of a large
flat steel plate moving under a single polished
roller, or with the roUer moving over the plate.
The term is also applied to a machine having
two rollers, one of which is nickeUed.
ROLLING PRINTS
The passing of moimted prints through rollers,
or between a roller and a steel plate, for the
purpose of improving their appearance and mak-
ing them Ue flat. The process is often confused
with that of burnishing, but is much more simple.
ROLLING-UP
The passing of an ink-charged roller over a
lithographic stone for the purpose of strengthen-
ing tie image. (See also "Photo-lithography.")
RONTGEN RAYS (See "X-ray Photography.")
ROSE BENGAL
Formula, potassium tetra-iodo-chloro-fluor-
escin, one of the eosine group, and formerly used
considerably for sensitising gelatine dry plates
and collodion emulsion for yeUow and green. It
has been used alone, and also in combination
with eosine. Soluble in water and alcohol. Von
Hiibl gives the absorption of rose Bengal as
approximately 542 /* (middle) from 563 ju
(maximum). This writer recommends, for the
negative for the red print, adding to 100 ccs.
of collodion emulsion 2 ccs. of the following
dye mixture, and bathing the plate before
exposure in ^ per cent, silver nitrate solution : —
Eosine yellow (i : 150)
alcoholic sol. . 90 mins. 30 ccs.
Rose Bengal (i : 150)
alcoholic sol. .30 „ 10 „
A I in 500 solution of picric acid in water is
used as a filter in a tank J in. (5 mm.) thick, or
a gelatine plate coloured with naphthol yellow G.
ROTARY SCREEN
For the three-colour half-tone process the ruled
screen is preferably of circular form and mounted
in a rotating carrier, so that the ruling may be
turned to a suitable angle for each colour. If
the angles are not properly chosen the super-
imposing of the colours will cause a moir^
pattern on the resulting print. The Levy rotary
Rotary Screen Carrier
screen, here illustrated, provides means of alter-
ing the angle with precision.
ROTARY SHUTTER (Fr., OUurateur rotatif;
Ger., Dreh-verschluss)
A shutter in which a circular disc with an
aperture towards the side is caused to revolve
across the lens by a coiled spring or similar
means, the opening exposing the plate as it
passes.
ROTATING BACK (See " Revolving Back.")
ROTATING STOPS (See " Diaphragms.")
ROTUNDITY
A quality usually associated with the images
produced by lenses of large diameter and aper-
ture which are believed by many practical
portraitists to give an impression of plasticity
and reUef, almost approaching a stereoscopic
effect.
ROTTENSTONE
A Derbyshire mineral, reduced to a fine
powder and used for polishing metals. It was
used for polishing daguerreotype plates.
ROUGE (Pr., Rouge ; Ger., Rot)
Red oxide of iron, used for polishing metals and
glass, including lenses. Process workers use the
very finest jewellers' rouge for polishing the sur-
face-silvered optical plane mirrors. The rouge
should be thorougUy sifted, warmed, and
broken up before applying.
ROUGHENING PRINTS
The roughening of prints to give them a matt
surface is now rarely resorted to. The simplest
method is to rub the surfaces gently with an
abrading powder, such as finely powdered and
sifted pumice stone or cuttle-fish bone. Another
method is to squeeze the wet and glazed
print down upon very finely ground glass or
matt-surface celluloid, the surfaces of the medium
selected and the prints themselves being treated
in precisely the same way as for glazing. (See
" Glossy Surfaces on Prints.")
ROUILLI^-LADEVllZE PRINTING
A pigment process for the production of per-
manent photographs, invented by Rouill6-
Ladevfize, of Paris. Prepare two solutions :
(A) 200 grs. of pure gum arable in i oz. of water ;
(B) 30 grs. of ammonium bichromate in i oz.
Roundness
465
Rytol
of -water. Mix together, filter through flannel,
and add, say, 300 grs. of tube water-colour, the
actual quantity depending upon the strength
and quaUty of the colour. The paper is brushed
over with the mixture in a weak yellow light,
dried in the dark, printed under a negative
(average time, 30 minutes), and developed by
washing in water at about 80° F. (27° C), which
removes the gum not insolubUised by the action
of light. The print is fixed on a sheet of glass
by wooden dips, immersed in water, and moved to
and fro until lie image appears. Finally it is dried.
ROUNDNESS
That quality in a print, and strongly desirable
in portraiture, which suggests proper modelling
and relief. The chief means to this end are suit-
able Ughting and the use of a large aperture.
ROUTING
In process work, a routing machine (first intro-
duced by Royle) is used for the purpose of
removing from the blocks the large spaces which
are to print white. This can be done by etching,
but is more quickly and efB.ciently done by the
routing machine. There are two forms of these
machines : one in which the cutter is stationary
whUe the bed carrying the plate is moved, and
the other in which the plate is fixed to, the bed
of the machine, whilst tiie cutter is mounted on
an arm which can be moved radially with a kind
of pantograph motion over any part of the plate.
The cutters resemble fluted drills, and by moving
the arm a channel the width of the cutter is
made in any direction.
ROYAL PHOTOGRAPHIC SOCIETY
The premier photographic society, founded in
1853, under the title of "The Photographic
Society of London," which, in 1874, was (±anged
to " The Photographic Society of Great Britain,"
and in 1894 was further modified by Queen
Victoria's commands to " The Royal Photo-
graphic Society of Great Britain." The objects
for which the Society was established may be
summarised in the phrase " the advancement of
photography." Meetings for lectures, demonstra-
tions, etc., are held at regular and frequent
intervals, and the members have the use of a
studio, dark-rooms, Hbraty, etc. A monthly
Journal is published and exhibitions are held. Its
first President was Sir Charles Bastlake, P.R.A.
(1853 to 1855). The Society awards a " Pro-
gress" medal nearly every year in recognition of
any important invention, research, or pubUcation,
the first to receive it being Captain W. de W.
Abney (1878) for his scientific work in the
advance of photography. The Fellowship
(F.R.P.S.) is open only to those members who
are able to satisfy the Council that they have
ability in one or other of the many branches of
photography ; elections to the Pdlowship take
place twice a year. Photographic societies may,
by the payment of one guinea per year, become
affiliated with the Royal Photographic Society.
RUBBER SOLUTION (See " Indiarubber.")
RUBY GLASS
Glass " flashed " with ruby (red) colouring
matter ; that is, the colouring does not go right
SO
through the glass, but the surface is coated
with vitreous colouring matter. It is used as a
screen or filter to stop Qie passage of actinic rays.
The subject of " safe " light is gone into fully
under the headings " Safe Light," " Bichromate
Lamp," " Dark-room Illumination," etc.
RUBY LAMP (See " Dark-room Lamp.")
RUBY MEDIUM
A ruby or red fabric used in the place of ruby
glass in the production of a. " safe " light. Sun-
light has a bleaching action upon it and pinholes
are so easily caused that its use should be
restricted to artificial light.
RUBY VARNISH
A varnish for application to windows, incan-
descent electric bulbs, etc., for dark-room use ;
it is inferior to ruby glass. Mix equal parts of
ordinary white hard varnish and methylated
spirit, and to every pint add J oz. each of
dirysoidine and coralline rouge, two aniline dyes ;
shake well, allow to stand for a day or two, and
then, if all the dye is dissolved, add more. If
the dye does not completely dissolve, use the
clear solution.
RUSSIAN DEVELOPER
A developer of Russian origin, and introduced
about 1889. It is said to give with dry plates
negatives which cannot be distinguished from
those yielded by wet plates. The formula is :
A. Sodium sulphite
Pot. f errocyanide
Sodium carbonate
Distilled water
Pyro
Ammonium chloride .
Distilled water
Trimethylamine
Distilled water
B.
34 g-
80 „
80 „
375 CCS.
17 g-
17,,
150 CCS.
Ig-
22 „
150 grs.
350 „
35° „
31- oz.
75 grs.
75 „
lioz.
5 mins.
95 „
To prepare the working developer, take of A,
300 mins. ; B, 40 mins. ; and C, 15 mins. More
of C can be added if great density is desired.
RUSSIAN VIGNETTES (See "Black Vig-
nettes.")
RUST SPOTS
Small black metallic spots which usually ap-
pear on gelatino-chloride papers (P.O. P.), and
caused by particles of rust in the first washing
water, the rust coming from water pipes, tanks,
etc. They may be prevented by giving the prints
(before toning) a bath of salt, soda and water :
Common salt . . i oz. 1 10 g.
"Washing soda . ■ i „ 55 „
Water . . . • 10 „ 1,000 ccs.
Immerse the prints for five or ten minutes,
wash, tone, and fix. This bath is not suitable
when platiniam is employed for toning.
RYTOL
A " tabloid " developer, supplied with an accele-
rator, also in tabloid form. For dry plates and
bromide papers one of each of the tabloids —
Rytol and accelerator — is dissolved in 4 oz. of
water ; for gasUght papers and lantern sUde.<i
(black tones) the water is reduced to 2^ oz.
SAFE EDGE
The opaque edging on negatives necessary for
carbon printing.
SAFE LIGHT (Fr., Eclairage inactinique ; Ger.,
Sicheres Licht fiir Dunkelzimmerbeleucht-
ung)
A term applied to the light obtained with the
use of coloured filters placed in front of the
dark-room illuminant. The ordinary commercial
coloured glass is rarely of any practical use,
except for the manipulation of positive materials,
and even for these specially made safe Ughts
usually give greater safety combined with greater
brilliancy. It is as well to divide them into the
several classes — namely, for positive, ordinary,
isochromatic and panchromatic plate work.
For positive work, such as lantern slide and
bromide print making, the light may be of a
bright orange or green colour, as these materials
are not very sensitive.
Tartrazine or naphthol
yellow . . . 200 grs. 20 g.
Rose Bengal or eosine . 10 „ i „
Distilled water to . . 20 oz. i ,000 ccs.
Gelatine . . . 800 grs. 80 g.
Soak the gelatine in the water till soft, melt in
a water bath, add the dyes, and when thoroughly
dissolved, filter and coat, allowing 20 mins. per
sq. in., or 20 ccs. for 100 qcm. of surface.
For a green light, the eosine or rose Bengal in
the above formiUa may be replaced by the same
quantity of naphthol green. For isochromatic
plates, one sheet should be coated with :
Tartrazine . . . 200 grs. 20 g.
Rose Bengal, or fast red . 100 „ 10 „
Gelatine . . . 800 „ 80 „
DistiUed water to . . 20 oz. 1,000 ccs.
and another glass with :
Methyl violet . . 100 grs. 10 g.
Gelatine . . . 800 ,, 80 „
Distilled water to . .20 oz. 1,000 ccs
This red screen transmits from the red to \ 5,900
in the yellow and the violet absorbs from \ 6,500
to A. 5,000, so that only the extreme red from
\ 7,000 to K 6,500 passes.
For red-sensitive and most commercial pan-
chromatic plates use :
Naphthol green . . 115 grs. 12 g.
Filter blue (Hoechst i %
solution) . . . 460 mins. 48 ccs.
Gelatine (8 % solution) to 20 oz. 1,000 „
For pinacyanol and dicyanine bathed plates, the
quantity of dyes may be reduced by one-third
in the above formula. The same quantity of
dyed gelatine per area should be allowed as
stated above.
For liquid filters, that is for solutions of dyes
in i-in. thick cells, the following may be used :
Naphthol yellow S (Bayer) 9 grs. i gr.
Violet dahlia B O (Bad-
ische) . . . 175 „ -18 „
Glycerine or water to . 20 oz. 1,000 ccs.
This gives a deep red only beyond about a. 685
— X 690.
A good green liquid filter is :
Add green . . .12 grs. -25 g.
NaphSiol green . . 12 „ -25 „
Tartrazine . . . 144 „ 2-00 „
Glycerine or water to . 20 oz. 1,000 ccs.
In all cases, it is advisable to soften down the
direct light by a sheet of ground glass or tissue
paper. Although a Ught is called safe, it is so
only in a relative sense, and, therefore, care
should be taken to expose the plate to it as
Uttle as possible.
SAL-AMMONIAC (See "Ammonium Chloride.")
SAL-SODA (See "Sodium Carbonate.")
SALICYLIC ACID (Fr., Acide salicylique : Ger.,
Salicilsdure)
Synonym, ortho-oxybenzoic acid. C,H4(0H)
COOH. Molecular weight, 138. Solubilities, i
in 450 water, i in 2-4 alcohol, i in 2 ether. It is
a Ught, fine, white crystalline powder, either ob-
tained from oil of wintergreen or sweet birch, or
by the action of caustic soda and carbonic acid
on phenol. It is occasionally used as a preserva-
tive in emulsions and solutions.
SALMON AND GARNIER'S PROCESS
One of the early iron or powder printing pro-
cesses, introduced about 1857, based on the fact
that tie ferrous or iron salt resulting from ferric
citrate is more hygroscopic than citrate itself.
Paper was coated with ferric citrate, exposed
under a positive transparency, and covered with
plumbago or other impalpable powder. The sur-
face was breathed upon, the powder then adher-
ing to the parts acted upon by Ught, while the
surplus could be Ughtly brushed ofE. The unacted-
upon citrate was then washed out, the picture
in powder being left. A later improvement was
the mixing of loaf sugar or sugar of milk with
the citrate. The dichromates subsequently were
found to answer better tiian the ferric salts. (See
also " Dusting-on (Powder) Process.")
SALON, PHOTOGRAPHIC
Ring.")
(See "Linked
466
SALT (Fr., Sel ; Ger., Salz)
The common name for sodium chloride. There
is a slight difference between the pure chloride
and common salt, but the latter may be employed
Salted Paper
467
Schwellenwert
in most cases when sodium chloride is named.
A weak solution of salt is often used to remove
or decompose the last traces of silver salts before
the toning of prints, to prevent black metallic
spots appearing on the pictures and, sometimes,
blisters. It is perhaps the most widely used for
seU-toning papers, a preliminary bath of salt
influencing the resultant tone considerably.
Before the introduction of " hypo " a strong
solution of salt was used for fixing. Salt acts
more or less as a restrainer in a developer.
In process work, salt has its uses as described
under the heading of " Dry Enamel Process " ;
further, it is used as an etching mordant for
aluminium, and for making red prints for the
bleaching-out process.
SALTED PAPER (See " Plain (Salted) Paper
Printing.")
SALTING (See " Sizing and Salting.")
SALTPETRE (See "Potassium Nitrate.")
SALTS. HALOID (See " Haloid.")
SAND BATH
Actually a bed of sand supported in an iron
vessel upon which is placed a dish containing
the material that is to be heated, it being
frequently undesirable to expose the dish or its
contents to the direct heat of a flame. A sauce-
pan cr deep frying-pan almost filled with silver
sand and heated over a gas burner or open fire,
makes a good sand bath. A sand bath is recom-
mended as a support for evaporating basins
when boiling down the silver bath in the wet
collodion process. Its object is to prevent the
naked flame impinging on the basins and to
diffuse the heat more uniformly. A layer of sand
is also recommended at the bottom of collotype
ovens.
SANDARACH (See " Gums and Resins.")
SANDELL PLATES AND FILMS (See "Mul-
tiple-coated Plates" and "Cristoid Film.")
SANGER-SHEPHERD COLOUR PROCESS
A process of obtaining three-colour trans-
parencies by printing on to celluloid coated with
bichromated gelatine containing a little silver
bromide, developing, staining, and superimposing
the results, after removal of the silver salt by
" hypo." A method of obtaining colour prints
on paper has been introduced by the Sanger-
Shepherd firm, in which a hard gelatine relief
is stained up and the dye transferred to a soft,
moist gelatine film.
SATIN, PHOTOGRAPHS ON (See "Fabrics,
Printing on.")
SATURATED SOLUTION (Pr., Solution d
saturation ; Ger., Gesdttigte Losungen)
A solution of a salt in any vehicle of such a
strength that it will not hold any more of the
salt in solution. The great disadvantage of
saturated solutions is that their strength varies
with the temperature, most salts being more
soluble in hot than in cold liquids. Their use
should be avoided as far as possible, and all
solutions made up of a definite and standard
strength.
SATURATOR
An appliance for carburetting oxygen with
ether and so forming a combustible gas to be
burnt in a special form of limelight jet. It is a
dangerous and now almost obsolete appliance.
(See also " Limelight.")
SATZ LENSES
A synonym for casket lenses, applied by Zeiss
to the sets of single anastigmats which could be
used alone or to form combinations of various
focal lengths.
SAVING WASTES (See " Residues.")
SAXE PAPER (See " Rives and Saxe Papers.")
SAYCE, B. J.
Bom, 1837 ; died 1895. Secretary and, later.
President of the Liverpool Photographic Associa-
tion. With W. B. Bolton, of Liverpool, he dis-
covered the collodio-bromide of silver emulsion
process (published 1864).
SCALE, FOCUSING (See "Focusing Scale.")
SCALES AND WEIGHTS (See "Balances.")
SCALOL
A registered name for a preparation of methyl-
paramidophenol (metol), for use in combination
with hydroquinone.
SCALOMETER (See "Focusing.")
SCHIENDL'S INTENSIFIER
A mercuric chloride intensifier. The negative
is bleached in a i in 20 solution of the chloride,
washed, and blackened in a i in 100 solution of
" hypo," to which a few drops of a gold chloride
solution and of ammonia have been added. The
method is said not to block up deUcate detail in
the high lights.
SCHLIPPE'S INTENSIFIER
An intensifier introduced by Carey Lea for
wet-plate negatives, but now seldom used. An
iodine solution (water, 2 oz. ; potassium iodide,
3 grs. ; iodine, ij grs.) was first flowed over the
plate and then a solution of Schlippe's salt, a
scarlet deposit being produced.
SCHLIPPE'S SALT
A synonym for sodium sulphantimoniate.
SCHWELLENWERT (Ger.) .
A term used by Eder to designate that quan-
tity of light which is necessary to produce a dis-
tinctly noticeable photographic effect. This is
usually translated " threshold " in English, and
is practically confined to the smallest amount of
exposure necessary to give a visible image after
development. It was at first assumed that this
Schwellenwert was a physical constant below
which no action whatever occurred, but it is
quite easy to measure far below it by counting
the number of silver grains under a microscope
(Mees and Sheppaid).
Scolik's Intensifier
468
Screen-plate Photography
SCOLIK'S INTENSIFIER
A mercuric chloride intensifier. The washed
negative is immersed until whitened in a solution
of 48 grs. of mercuric chloride and 48 grs. of
potassium bromide in 5 oz. of water, blackened
in a sodium sulphite solution, and finally washed.
SCRAPING NEGATIVES (See "Knife, Re-
touching.")
SCRATCHES ON NEGATIVES
A scratched negative is repaired satisfactorily
only if the photographer is expert with the
pencil. If the scratch is clean and shows as a
black line only in the print, the negative should
be varnished, a little retouching medium applied,
and the scratch gradually worked out with a
finely-pointed hard pencil. Avoid working
beyond the scratch, or filling it up too solidly,
and it is better to stop while the scratch can
still be seen as a faint grey line, rather than to
obliterate it completely, when it may print as a
white line. Abraded edges to a scratch, which
print white at each side of the black line, should
be carefully scraped away with a sharp knife
before varnishing the plate.
SCREEN, COLOUR (See " Colour Screen or
PUter.")
SCREEN. FLUORESCENT (See "Fluores-
cent Screens.")
SCREEN, FOCUSING (See "Focusing Screen.")
SCREEN, GRADUATED
A screen or light filter of glass or celluloid,
graduated in density (colour) from the top to
the bottom, the top part being as a rule, of a
deep yellow colour, which gradually decreases
in density until at the bottom quite clear
glass is reached. Such screens are used for
placing in front of the lens when photographing
landscapes, the denser part being so adjusted in
the holder, which fits on the front of the lens,
as to cover the sky portion, in order to retard
the action of the blue rays upon the plate. The
use of such a screen makes it possible to get
foreground and skies, both correctly exposed,
on one plate ; without it, if the foreground were
properly exposed, the sky would probably be
over-exposed and any delicate clouds lost.
SCREEN HOLDER
Process workers use various forms of holders
for fixing the colour filters parallel to the lens.
A and B. Screen Holders
Some of these holders are arranged to work in
front, but behind the lens is the more common
and the better position. Circular colour filter
cells are attached to the front of the lens by
means of a holder which clamps together the
glass components of the cell. A is a wooden
holder, which is attached to the front of the
camera, the lens being mounted in front of the
box. B is a box to hold three filters in line, so
that they may be pushed successively past and
behind the lens. In addition to these, circular
fittings of metal are used.
SCREEN, ISOCHROMATIC (See " Isochro-
matic Screens.")
SCREEN - PLATE COLOUR PHOTO-
GRAPHY
The process of producing photographs in the
colours of Nature by means of a screen plate is
based on the three-colour process enunciated by
Clerk-Maxwell, but instead of using three sepa-
rate colour filters and three separate plates and
prints, the colour filters are distributed on one
surface in small areas, coated with a panchro-
matic emulsion, and the picture obtained on this
support either by chemical reversal of the
negative into a positive or by printing on to
another plate of similar character.
The first idea of such a plate was conceived by
Ducos du Hauron, in 1862, in a letter which,
however, was not published till 1897. Ip. his
French patent (No. 8,361, of Nov. 23, 1868)
du Hauron says : " There is another method by
means of which the triple operation can be done
on one surface. The separation of the three
elementary colours may be efiected, no longer by
three coloured glasses, but by means of one
translucid sheet covered mechanically by a grain
of the three colours." In a little work by him,
Les Couleurs en Photographie, Solution du Prdb-
Ume (1869), he also deals with this subject,
but a more elaborate description of this idea
is given by Alcide du Hauron in Triplice
Photographique des Couleurs, in which will be
foimd the germ of all screen-plate processes, and
any introduced of late years have been but
variations of du Hauron's ideas.
In dealing with this subject the writer cheer-
fully acknowledges that he is following to a
great extent and sometimes borrowing freely
from a valuable paper on " Some Experimental
Methods Employed in the Examination of
Screen Plates," by Dr. Kenneth Mees and J. H.
Pledge (Phot. Journal, May, 1910, p. 197). Screen-
plates may be classified under two headings :
regular and irregular, or line and mosaic ; and
can be further subdivided into the following
methods of manufacture : (i) ruled hnes, (2)
dusting-on methods, (3) bichromated coUoid
methods, (4) section cutting, (5) mechanical
printing or mechanical methods and dyeing,
(6) other processes.
The first line screen by a ruling method was
patented by Joly in 1895, patent No. 14,161, '95.
In 1896, J as. W. McDonough took out patent
No. 12,645, '96- The Joly screen was com-
posed of lines having a width of -^Tsisi. (■12 mm.),
and a separate viewing screen, with slightly dif-
ferent colours, was issued. The taking screen
was placed in contact with a panchromatic plate,
and from the line negative thus obtained a posi-
tive was made and bound up with a viewing
screen so adjusted that the lines of the latter
Screen-plate Photography
469
Screen-plate Photography
fell into contact -with the correct lines of silver
deposit on the positive. The McDonough lines
were si-^ in. (o-8 mm.) wide, and some even as
fi"!^ ^ T3TV in. were made. The dusting-on
method was first patented by McDonough
(No. S,S97, '92), and he claims the use of par-
ticles of glass, transparent pigments, gelatine,
resin, or shellac suitably stained and subsequently
coated with a panchromatic emulsion.
The autochrome plate, patented (22,988 and
25,718 of 1904, and 9,100 of 1906) by Messrs.
Lumi^e, is prepared by sifting suitably stained
starch grains over a tacky surface, rollmg them,
and then fiUing the interspaces with a black filling,
The average size of the starch grains is rAu in-
(•CIS mm.). The plate is issued coated with an
emulsion, and the image needs to be reversed after
exposure, so that the original plate serves as
the positive.
According to Mees and Pledge, Fawcett sug-
gested in the British Journal of Photography
(February 22, 1901) the use of a screen plate
with the emulsion coated thereon.
Palmer's patent (22,228, 1907) claims the use
of ceramic colours or fluxes dusted on a tacky
glass plate, and then fired in a t-iln ; also in
another plate he uses gum elemi. The Aurora
screen plate (introduced by the inventor, E.
Fenske, in February, 1909) uses a mixture of
three dyed materials dusted on a tacky plate,
and fills the interspaces with a black filling.
The fragments vary in size from -siir in. (-03
n""!-) to tJj in. (-IS mm.), the average being
about -jI^ in. (-07 mm.).
In Bamber's patent (3,252 of 1908) dyed gela-
tine is hardened with formaldehyde, dried, im-
mersed in water, heated to 212° F. (100° C),
ground to powder, and sifted into varying sizes
by elutriation with petroleum spirit ; then it is
dusted on tacky glass and expanded by absorp-
tion of moisture from the air, the interspaces
being then filled up with black filling. The
average size of the particles is about ^^ in.
(•01 mm.).
The use of bichromated colloids was outlined
by Du Hauron, and the first plate manufactured
on these lines was the Warner- Powrie or Florence
plate. The lines in this had a width of about
j-§3 in. (-04 mm.), and the green lines were
formed first, then the red, and the interspaces
were filled with blue. Another Wamer-Powrie
experimental screen plate had green lines with
red and blue rectangles in between, thus follow-
ing more closely stSl the Du Hauron method ;
the diameter of the green line was yj^ in. (-05
mm.), the narrow diameter of the red areas
being -j^ in. (-07 mm.) and that of the blue
rfi) in. (-05 mm.).
Dr. Smith, of Zurich, patented (6,881, 1906)
a screen plate with regular geometric pattern,
triangles, hexagons, or rhombi. The Thames
plate (Finlay's patent, 19,652 of 1906) consists
of a series of red and green circles of about ^^
in. (-ii mm.), with a blue filling. It is inter-
esting to note that in an American patent
(561,687 of 1896) McDonough claims the use of
" a negative or positive photographic plate
made with recurring patterns — as dots, lines,
or figures — and having a portion where there
is a fixed or invariable and distinctive charac-
teristic which is produced in the sensitive material
of the plate, and by which the plate may there-
after be registered or adjusted in position in
use."
The Wratten patent (28,406 of 1907) has one
distinctly novel feature in that the matrix,
whether a lineEir or dot pattern, has the figures
in black, semi-opaque, and clear, and therefore
one would have, in printing on a bichromated
dyed colloid, a quite insoluble, a half soluble,
and a completely soluble film. After exposure,
the insoluble gelatine would be stained deep
blue, the half soluble only half that depth, and
a clear line left ; by immersing such a plate in
a yellow dye the half soluble Ime would absorb
the yeUow and give gugen, and the clear line
could be subsequently coated with a red colloid
and rendered insoluble. Practically this did
not work out so well as it promised.
The Dufay dioptichrome plate (patents No.
11,698 of 1908 and 18,744 of 1908) is prepared
by exposing a bichromated colloid imder a Une
screen, dyeing, and inking up with a greasy ink
which does not adhere to the stained lines ; and
this plate is now pressed against a gelatine-coated
plate and the ink and dye are transferred. This
second plate is coated with a varnish which
does not adhere to the greasy ink, and then
treated with a solvent which dissolves the ink
and does not attack the coloured Une ; and the
plate then has one third of its surface red and
two-thirds plain. A second printing at right
angles to the first gives the second colour, and
then the unstained gelatine is dyed by pressure
against another plate stained with the third
colour. The green line has a diameter of fi-^ in.
(•06 mm.), the red rectangle -yfg in. x ^is in.
(•07 mm. X •! mm.) and the blue area 5^, in. x
jis in. (-065 mm. x -09 mm.).
The only plates prepared by the fourth method
so far have been experimental ones. Senor
Cajal, of Madrid, suggested the use of coloured
fibres embedded in celluloid rendered opaque
by metallic silver and cut across with a micro-
tome. In 1893, Dr. Otto N. Witt applied for a
German patent (W. 14,564, iv., 57A, Novem-
ber i) for preparing linear filters by the super-
position of sheets of dyed celluloid, cementing
them together and then rolling them out to thin
veneers. On April 6, 1899, R- B. Liesegang
applied for a siroilar patent, in which the block
of superposed sheets of celluloid was to be cut
across at right angles to the direction of the lines,
and mosaic filters could be produced by cement-
ing such veneers into a block and again cutting
across. R. Krayn took out two English patents
(1,938 of 1906 and 495 of 1907) for precisely the
same ideas, and experimental films of this char-
acter were issued.
The Ejrayn screen, which has been actually
issued, belongs, like the Omnicolore plate, to the
fifth method, in which mechanical printing is
employed. The method is practically as fol-
lows : a greasy ink or waterproof varnish is
ruled over two-thirds of the surface of a gelatine-
coated or celltiloid film (Krayn), and the exposed
gelatine is dyed and the water-repellent material
removed and again applied so as this time to
cover the dyed gelatine and half the unstained
gelatine. The exposed gelatine is dyed and
mordanted and then the remaining clear gela-
tine stained up. In the Omnicolore plate there
Screen-plate Photography
470
Screen-plate Photography
are continuous blue lines of 3^ in. (-05 mm.)
width with green and red rectangles in between
at right angles, the area of the former being
about ^{i in. x tJtt in. (-08 mm. x -06 mm.),
and that of the latter -jl^ in. x ^i-,, in. (-06 mm.
X -04 mm.). In the Krayn celluloid film the
lines are red and about -g-Jj- in. wide, and the
blue and green rectangles are not at right angles,
but about an angle of 135 with the horizontal
red line, and the space between the two red lines
is about -^ in. (-ii mm.). Lumi&e's patent
(20,111 of 1908) for a regular grain screen is
based on the use of a greasy ink, which is appUed
to two-thirds of the surface of a gelatine film,
the remaining third being dyed ; then the whole
plate is varnished and the greasy ink and the
overlying varnish dissolved. A second greasy
ink is now appUed in the form of lines at right
angles to the first set, so that half the surface is
covered, and the exposed gelatine is dyed in the
second colour, again varnished, and the greasy
ink removed ; and the plate, which now bears
two colours, is dyed up as regards its remaining
surface with the third colour.
With regard to screen plates made by other
processes, there are not at present any on the
market, though several patents have been taken
out, such as Joly's (19,388 of 1895) for dyed
threads laid on a transparent support, Beeton
and Gambs' patent (20,834 o^ 1906) for a woven
tissue, and Szczepanik's (17,065 of 1908) on
the same lines.
The Szczepanik-Hollbom screen plates are
based on the affinity of basic dyes for acid tissues
and acid dyes for basic tissues ; the former have
a decided preference for collodion and acid dyes
for gelatine. Three solutions of gelatine or
other colloid are dyed, dried, powdered, mixed
in proper proportions, and dusted on to a moist
collodion plate. The dyes pass from the colloid
into the collodion, and the former is washed off,
leaving a mosaic of coloured areas. In the
second form only two colours are appUed in this
way and the third applied by a dyeing bath.
There are certain factors in the manufacture
of screen plates which are extremely important
for the successful reproduction of colour, and
the first is that the screen itself should be free
from colour when examined by white light ; that
is, it should be of a neutral shade. This has been
defined by Mees as the " first black condition,"
and it must be attained by adjustment of the
areas of the colour units, and not by varying the
depth of staining which controls their absorp-
tions. The second point is that the photo-chem-
ical effect of the spectrum through the screen
elements and compensating filter must corre-
spond with the luminosity curve, though this
point may be of less importance, as the retina is
able to perceive small variations from the correct
curve. The third point is the total visual absorp-
tion, as this affects the duration of exposure, for,
naturally, the greater the absorption of Ught
the longer wiU be the exposure. The above-
mentioned authors state that in order to fulfil
the first black condition the green area must
transmit about two- thirds of the light transmitted
by the plate, and under the best conditions for
the other filters it may occupy half the area of
the plate, and therefore half the plate will only
transmit one-third of the incident green light
or two-ninths of the incident white light, so
that the whole plate will transmit only one-sixth
of the incident white light as a maximum.
The question of invisibUity of the filter ele-
ments depends upon what has been termed the
" period," which is twice the distance of separa-
tion for lines equal in width to the spaces ; and
this must be less than ygVi of the distance from
the eye ; and if this be taken as 20 cm. the
screen period will be 0-2 mm. ; therefore the
separate filter elements will be invisible if
they are not larger than ^5- in. (-066 mm.), or
approximately ^Jy in., this naturally applying
to results examined in the hand. When, however,
it comes to the projection of the pictures, one
has to take into con.sideration the magnifica-
tion, and assuming this to be 40 diameters or
a lo-ft. screen, and the nearest observer to be
12 J ft. away, the screen elements must not be
more than -^ in., which requires the actual
screen elements to be ^^ in. When dealing
with irregular grain screens in which the units
are distributed by a dusting-on method, then
there may be clumping of the grains ; as many
as twelve grains may be clumped together, and
therefore the unit may become mudi larger.
The resolving power — that is, the power of the
screen plate to resolve a coloured object into its
form and colour — may be divided into three
heads. First, the objects are resolved both in
form and colour, when the images of the objects
are as large as or larger than the screen period ;
secondly, the images may be of the same size
as the screen elements, then they will be resolved
as to form but indeterminate as to colour ;
thirdly, if the images are smaller than the screen
units, they may or may not be resolved, accord-
ing to the resolving power of the emulsion.
The spectral absorptions of the filter elements
can only be those which are generally recognised
in three-colour work — that is, having a shght
overlap in the yellow and blue, considering the
taking of negatives only ; but as, in the majority
of cases, the screen is i\lso used for viewing, the
spectral absorption should be as pure as pos-
sible, and should agree as nearly as possible with
the three fundamental colours— red, green, and
blue. A compromise has therefore to be made,
and probably the red should transmit from the
extreme red to \ 5,900, the green from \ 5,900
to A. 4,900, and the blue from A 5,000 to \ 4,000.
The limitation of the size of the filter element
is determined by the invisibility of the element,
which has been previously dealt with, and this
should be not larger than ^1-^ in., or in the case
of irregular grain screens about one-tenth of
that, because of the dmnping. One of the factors
governing the TniTiimnTn size of grain is the
thickness of unit necessary to give sufficient depth
of colour, which is determined as to its diameter
by parallax. If the thickness is equal to the
diameter, any ray passing through the screen
at a greater angle than 10° will not only
pass through the particular element which it
first struck, but also the next, as shown in the
following diagrams.
A shows a screen plate in which the thickness
of the filter elements R, G, B (red, green, and blue)
is equal to their diameter. The ray striking
the blue element b passes only through this ; but
as the emulsion is of slightly greater refractive
Screen-plate Photography
471
Self-developing Plates
index it encroaches slightly on the neighbouring
green element, and therefore in the final result
the blue would have a very slight green tinge. In
diagram B the thickness of the elements is
one and a half times their diameter, and the ray
here passes not only through the blue, but
A // Emulsion ' ^ B
Light Rays striMng Screen Plates
through nearly the whole of the green ; therefore
the final colour would be strong greenish blue.
This is an important point because when using a
bichromated coUoid, such as gelatine, it is difficult
to get sufficient depth of colour with less than
54-5 mins. of s per cent, gelatine solution to
every 10 sq. in. (= i cc. per 20 qcm.), which
gives a thickness of dry film of y^ in. The
second factor limiting the size of the elements
is the irradiation of Ught in the emulsion film
itself, by which the Ught may be scattered from
the silver halide particles, underlying the par-
ticular screen element, to those under the adja-
cent ones.
Finally, in order to obtain correct colour
rendering, assuming that the first black condi-
tion is fulfilled, it is essential that the action of
light should be to give equal deposit under all
three elements. Now, as it is not possible to
sensitise any emulsion for red and green, so as
to give equal sensitiveness to these regions as
to the original blue-violet sensitiveness of the
emulsion, therefore a compensating filter is
used to cut down the excess blue- violet sensitive-
ness, and at the same time even up the sensitive-
ness of the red and green. This is called the
" second black condition."
The final speed of a plate is determined by (a)
the speed of the emulsion, (6) the multiplying
factor of the screen, and (c) the multiplying
factor of the compensator. Mees and Pledge
give the following table of these factors : —
II
s
i
11
0 s
1
Emulsion speed (Wat-
kins)
Screen factor .
Compensator factor .
EfEective speed .
35
12
2
120
8
10
22
7
2i
13
5
2
They also give the following very valuable
summary of the essentials to be fulfilled in the
manufacture of a screen plate : (i) The size of
the units. — For regular screens these should not
be larger than -3^1^ in., nor smaller than ^Jo _in.
For irregular screens not larger than -^ in.,
nor smaller than jr^JSo-in. It is quite needless
to strive for exceedingly small units. (2) The
interstices. — If these exist at all, they must be
filled in ; white interstices are fatal, even it they
only occupy one- twentieth of the arc of the screen
plate. (3) The colours of the units. — ^These
must be primary red, green, and blue violet.
(4) The rdative area occupied by each colour. —
This must be adjusted to fulfil the first black
condition. (5) Emulsion. — ^This must be coated,
for which purpose insidating varnishes will have
to be selected, as they must not act upon it.
Turpentine and ether, especially the former, are
inadmissible as solvents ; resin varnishes are
suspect. (6) The sensitising. — This must be
performed so that the actions under the red and
green filters are equal. (7) The compensator. —
This must be adjusted to fulfil the second black
condition.
SCREEN. RULED (See " Half-tone Process "
and "Halt-tone Screen.")
SCREWS AND SCREWTHREADS (See
"Camera Screw" and "Mounts, Lens.")
SCULPTURE, PHOTO. (See "Photo-sculp-
ture.")
SCULPTURE, PHOTOGRAPHING
The principal points that require attention in
photographing sculpture are given under the
heading " Statuary, Photographing " ; but it
is desirable to give a hint in this place on the
photographing of sculptured panels. With most
of these panels, a direct front position is almost
imperative ; the panel must be regarded almost
as a picture and photographed in the same
manner. Care must be taken to get the outlines
of the panel perfectly rectangular, the comers
square and Oie opposite sides parallel. The
most simple method is given under the heading
" Paintings, Photographing." The front posi-
tion does not always show the relief so efiectively
as an oblique view, consequently, when possible,
the work should be done at the time of day
when the natural lighting gives the desired effect.
SECONDARY AXIS (See " Optical Axis.")
SECRET CAMERAS (See "Detective Cam-
era " and " Disguising the Camera.")
SEED LAC (See " Gums and Resins.")
SEL D'OR (See " Gold Hyposulphite.")
SELECTIVE SENSITISERS
A synonym for optical sensitisers, under which
heading they are described.
SELENIUM
Se. A non-metallic element. Atomic weight,
79. It is used in phototelegraphy.
SELF-DEVELOPING PLATES
Dry plates carrying the developer in or on the
film, or on the glass side, and requiring only to
have water applied for the developing action to
take place. Mx early form was that introduced
by Dr. BaecHandt, who soaked dry plates in a
solution containing salicylic acid and pyrogallic
acid. The systems by which the developer
Self-portraiture
472
Sensltometry
is in the form of a dried paste on the glass side
of the plate are far more satisfactory. Thomas
Bolas patented (in 1907) a dry developer, to be
applied to the glass side of the plate or used as
a separate sheet. In addition to claiming the
distribution of difierent portions of the developer
in difierent parts of the area, the use of hydroxyl-
amine and an ammonium salt is named, also the
use of acid sulphite, and the use of bicarbonate
as an alkali. The acid constituent (A) may con-
tain the reducing agent : —
Metol
Hydroquinone
Mhk sugar, matmite, or other
1 part
2 parts
sugar-like preservative
Sodium bisulphite .
Starch, partly boiled and partly
li »
in grains . . . .
6 ,,
and water in sufficient quantity to give a paint-
like consistency on a thorough incorporation or
grinding of the ingredients. Instead of metol
and hydroquinone, other reducing (developing)
agents may be employed. The alkaline accele-
rator (B) may contain the following ingredients : —
Sod. carbonate or bicarbonate . s parts
Gum arable . , . .1 part
and water in sufficient quantity to give a paint-
like consistency to the mixture upon grinding.
The inert or slightly acid separating material
(C) may contain the following ingredients : —
Sulphate of Ume or sulphate of
baryta . . . .4 parts
Gum arable . . . .1 part
and water as before.
SELF-PORTRAITURE
When there are no bright objects in the back-
ground and the duration of exposure is of little
or no importance, a small stop may be inserted
in the lens in order to make a comparatively
long exposure necessary. The operator may then
open the shutter or uncap the lens and take up
his position at a suitable spot previously arranged
opposite the camera, stay there while the ex-
posure is being completed, and then go back to
the camera and dose the lens. The brief period
during which the operator is not in position will
make no appreciable difference to the plate if
the stop used is small enough, the plate slow
enough, and the background dark enough.
Another and a better plan, suitable for outdoor
groups when the operator wishes to be included,
is to make the exposure through the agency of
black thread. Two lengths of black thread, long
enough to reach from the camera to the operator
should be taken. One is attached to the lens
cap (a shutter cannot be used), and the other is
tied to one corner of the focusing cloth, the latter
being folded on the top of the camera in such a
way as to be easily pulled over the lens. When
all is ready for the exposure the thread attached
to the cap is pulled, the cap then falls to the
ground and the exposure begins ; when suffi-
cient exposure has been given the thread at-
tached to the black focusing cloth is pulled
and the cloth falls in front of the lens ; the
operator then hastens back to the camera and
caps the lens.
SELF-TONING PAPERS
Printing-out gelatino-chloride emulsions con-
tainuig some salt of gold, which is reduced in the
fixing bath and thus tones the image and does
away with the necessity of separate toning.
Ashman and OfFord suggested this addition in
1885 ; but Bachrach, three years later, published
the fact that the addition of gold obviated sub-
sequent toning. Most of these papers require
merely fixing or immersion in a prehmuiary salt
bath to vary the tone obtained. In some
cases the gold is accompanied by lead or other
metallic salts, which doubtless play an import-
ant part in the toning of the image.
SELLA'S PRINTING PROCESS
A process published by M. V. J. Sella, of Biella,
in 1857. It was an "ink" process, in which
the salts of silver and gold were superseded by
salts of iron and chromium.
SEMITONE (Pr., Demiteinte : Ger., Halbton)
A half-tone. In photography, the shades in-
termediate between the Ughtest parts of the
picture (high lights) and the deepest shadows.
SENSITISED PAPER (Pr., Papier sensible;
Ger., Gesilbertes Papier)
An old term apphed to plain salted and albu-
menised paper after sensitising with silver
nitrate.
SENSITISERS (Pr., Sensibilsateur ; Ger., Sensi-
bilisatoren)
There are practically two classes of sensitisers,
the so-called chemical, and the optical sensitisers.
The former are generally halogen absorbers,
which increase the sensitiveness of the negative
emulsion or increase the intensity of the printed
out image. Por colour sensitisers, see " Colour
Sensitising."
SENSITISING
Rendering sensitive to light. Methods for
sensitising are given under the various processes,
as for example, blue-print, kallitype, carbon,
albumen, etc.
SENSITIVENESS OF PLATES AND
PAPERS
The question of the sensitiveness of plates is
dealt with under " Sensltometry." At present
there is no generally accepted method of testing
papers for their sensitiveness, the usual com-
mercial method being merely to give the ex-
posures to certain lights.
SENSITIVENESS, RESTORING (See
"Pogged Dry Plates, Restoring.")
SENSITOMETER
A device for testing the sensitiveness of plates
and paper, and described in the following
article.
SENSITOMETRY (Pr., Sensitometrie ; Ger.,
Empfindlichkeitsmessung)
Soon after the introduction of the gelatine dry
plate, it was usual to express the speed of the
emulsion as " x times," which meant that it was
X times the speed of a wet collodion plate. This
Sensitometry
473
Sensitometry
speed was no fixed quantity, and the expression
consequently meant but little. Wamerke intro-
duced a sensitometer, consisting of a. series of
numbered squares with, increasing quantities of
opaque pigment. The plate to be tested was
placed in contact with this, and an exposure
made to the light emanating from a tablet of
luminous paint, excited by burning magnesium
ribbon. After development and fixation the
last number visible was taken as the speed of
the plate. The chief objections to this method
were that practically no two numbered tablets
agreed, that the pigment possessed selective
spectral absorption, and that the luminosity of
the tablet varied considerably with the lapse of
time between its excitation and the exposure of
the plate. Various other methods were pro-
posed, but none found any practical use. In
1890, Hurter and Driffield published a series of
papers on the subject of speed determination,
and proposed a method of exposing a plate to
a series of lights of known intensities and
measuring the densities obtained on develop-
ment. This method has become very general in
Bngland, though possibly it is not strictly
adhered to by all its users. Notwithstanding
various attacks, the main principles of the
A. Chapman Jones
Plate Tester
B. Gauge for Height
of Candle Flame
H. and D. system, as it is briefly termed, remain
uncontroverted. On the Continent, another
system, known as Scheiner's, has been elab-
orated by Eder, and in this a rotating sector
wheel is used, the steps of which bear a ratio
of I : I'z/. After exposure, the last number
visible, when the negative is placed film down-
wards on white paper, is taken as the speed of the
plate.
Chapman Jones has introduced a modified
Wamerke tablet containing a series of twenty-
five graduated densities, a series of coloured
squares, and a strip of neutral grey, all five being
of approximately equal luminosity, and a series
of four squares passing a definite portion of the
spectrum ; finally, there is a square of a line
design, over whici is superposed a half-tone
negative. This " plate tester," A, is used with a
standard candle as the source of light, and is
useful for rough tests of both plates and print-
ing papers. Definitions of the leading terms
employed must here be given. " Opacity " is
the suppression or absorption of light by the
silver image. " Transparency " is tte remnant
of the original light which passes through the
negative image. " Density " is the relative quan-
tity of silver deposited per unit area. The exist-
ing confusion is well shown by the term " a
very dense negative," when really what is meant
is that the " opacities " of the silver deposited
are so great that they possess very little "trans-
parency " ; that is to say, the negative absorbs
the greater portion of the incident light. It is
true that the " denser " a negative the greater
the opacity, but it must not be forgotten that,
as defined above, density is the quantity of silver
deposited. Density is the logarithm of the
opacity ; thus, a negative which has an opacity
of 100 has a density of 2'oo, as this is the com-
mon logarithm of 100, and it has a transparency
of \h-
The usual mathematical expression of the
above facts is as follows, but in the following
pages, as far as possible, mathematics will be
exduded and everyday working instructions
given : —
Transparency, T ^
Intensity of light transmitted I _
Intensity of incident light lo
-^ .. - Intensity of incident light lo I.
upacity, u — jmgnsity of transmitted light "~ 1 ~ T
Density, D = -logio T = log,, O.
The last term is also frequently expressed as : —
D = - log. T = log, o,
Napierian, instead of common, logarithms being
used.
Hurter and Driffield pointed out that in a
perfect negative the opacities of the different
gradations were strictly proportional to the
light reflected by those portions of the subject
which they represented when the plate had
received correct exposure, and that a true repre-
sentation of the tones of the original is only
possible when the density or the quantity of silver
is proportional to the logarithm of the light in-
tensity. To use the H. and D. system correctly,
it is essential to have a standard light, an expos-
ing instrument, and a photometer or instrument
for measuring the densities.
The Standard Light. — The light adopted by
Hurter zind Driffield was the British Standard
candle, burning 120 grains of spermaceti wax
per hour. This candle gives satisfactory results
as regards the speeds of ordinary (non-colour
sensitive) plates for amateur use ; but the flame
is subject to fluctuations, and obviously will give
totally incorrect readings with colour-sensitive
plates, on accotmt of ttie spectral composition
of the light, this being very ydlow, or much richer
in yellow, orange, and red rays than is daylight.
If the candle is used for speed reading, it is always
advisable to expose with the plate to be tested
one of a known speed, then any variation of the
speed of the latter can be allowed for in cal-
culating the speed of the unknown plate. It is
important to see that the candle is burning regu-
larly at the base of the wick, with a well-formed
cup of wax, free from match-heads, bits of
charred wick, etc. The wick should bum over
at its top to the edge of the flame, the latter
being 45 mm. in height from that place where
the wick begins to blacken to the tip of the
flame. It is as well to make a steel metal gauge,
as shown at B, for measuring this height, and it is
also desirable to shield the candle flame from
draughts. As it must be kept at a constant
height, a retort stand with a slip arm to hold
the candle, or a sUding holder, must be provided.
Another standard light, more generally used
Sensitometry
474
Sensitometry
on the Continent, is the Hefner amyl-acetate
lamp, a small lamp which bums pure amyl-
acetate that gives a flame much like the candle
in spectral composition, and, therefore, open to
the same objections on this score as the standard
candle.
The most satisfactory standard light is acety-
lene, used under a pressure of about ^ oz. The
burner to be used is a Bray's " Elta," which
shows no tendency to carbonise, and in which
the gas escapes from two pinholes in the steatite
caps. These caps contain airholes. The rod-like
flames impinge against one another and produce
a brOliant flat flame of about i in. diameter.
Whereas in the candle the whole flame is used,
in the case of acetylene it is important to screen
ofE the margins and the tip of the flame as these
flicker considerably, and it is also necessary to
screen off the blue base of the flame. This can
be conveniently done by a Methven screen
or metal plate pierced with a square hole of
36 sq. mm. area. This screen should be as near
the name as possible (about 12, or not more
than 18 mm.), and the bottom of the aperture
should be sUghtly above the dark or blue area
of the flame, so that it is central with the whitest
and most luminous part of the flame. For exact
photometric investigations, the correct position
must be found by exposing a series of plates
and measuring the densities, but for practical
speed testing it wiU be sufficient if the eye, when
placed at the extreme edges of the dark-slide, can
see no trace of the tip, edges or base of the flame.
Renwick, of the Ilford Research Laboratory,
states that there is a variation in density over
the plate strips due to the variation in the
intensity of the light and the small area of the
flame exposed by the aperture. While this has
not been confirmed by any other writer, Sheppard
and Mees have confirmed the general fact that
such a burner is liable to variation, and have,
therefore, suggested a modification of the P^ry
cylindrical flame, obtained by means of a Bray
burner taking -25 ft. of acetylene per hour, and
constructed to give a cylindrical flame with the
admixture of air. The burner is enclosed by a
metal hood in which is an aperture -04 mm. and
a cone reaching from this to within ^ in. of the
flame itself, the latter being 35 mm. in height.
The correct distance between the standard
light and the sensitive surface should be i metre ;
if this is not adhered to a correction must be
made in estimating the intensity of the light
falling upon the plate. This correction, for vary-
ing distances is foimd from Schwarzschild's
formula and table, given below.
= (wYf
TABLE
OF CORRECTION FACTOR /.
G
D
400 cm.
200 cm.
roo cm.
50 cm.
40 cm.
30 cm.
0 cm.
t :;
12 ,,
16 „
0*989
0-989
0-989
0-988
0-986
0-992
0-991
0-989
0-986
0-982
I -000
0-997
o'ggo
0-979
0*962
l"or7
1-007
0-978
0-93+
0*879
I '023
1*009
0*965
0-899
0-818
i'337
l-ol
0935
0*829
0*712
D = the distance of the light, G = the distance
of any point of the plate x centimetres from
the perpendicular dra*wn through the centre of
the flame to the plate. A reference to and
explanation of this table will be found under
the description of the exposing instrument.
The experimenter must not overlook the
danger of the intensity of the light decreasing
as the gas supply and, consequently, the pressure
diminish, and he should take care that the
evolution of gas has ceased before exposure is
made. Another point is that when the carbide
receptacle is freshly charged, some air is always
introduced into the gas chamber, thus leading
to a decrease of luminosity of the flame. This
trouble may be overcome by generating a small
quantity of gas first and burning this, with the
water supply cut ofF, and then admitting more
water to the carbide till the bell is fully charged,
making the exposure when the generation of
the gas has ceased.
Although the acetylene light approximates
more nearly to daylight than the standard candle,
it is still too rich in red and orange rays, and it
should be screened down -with absorbent solu-
tions. The necessary dyes are gentian -violet,
acid green, mandarine orange and rose Bengal,
which can be obtained in conveniently small
quantities. Some pure copper acetate will also
be required.
The dyes can be most conveniently made up
into stock solutions as follow : —
A. Gentian violet
Distilled water to .
B. Acid green .
Distilled water to ,
C. Mandarine orange
Distilled water to
D. Rose Bengal
Distilled water to .
14 grs. 2 g.
16 oz. 1,000 ccs.
7 grs. I g.
16 oz. 1,000 ccs.
7 grs. I g.
16 oz. 1,000 ccs.
28 grs. 4 g.
16 oz. 1,000 ccs.
These stock solutions must be kept in the dark.
The actual filter or screen is made as foUows :
A solution
B
C
D
10 nuns.
10 „
10 „
10 „
I cc,
I ,.
I „
I
7J
Distilled water to 2 oz. 138 mins. or 100 ccs.
When mixed, this wiU not keep more than
24 hours, and it should be used in a cell 10 mm.
internal width.
The copper acetate solution is made as follows :
Pure copper acetate
Glacial acetic acid .
Distilled water to .
105 grs. 15 g.
35 mins. -5 g.
16 oz. 1,000 ccs.
This wiU keep indefinitely, and must be used
in a cell of 10 mm. internal width. It must
not be mixed with the aniline dyes, but used
in a separate cell.
The Exposure Instrument. — ^The instrument for
obtaining the series of graduated exposures con-
sists essentially of a sector wheel, 11 in. in
diameter, in which each sector is exactly half
the preceding one ; the angles should be : 1 80°,
90°, 45°, 22-5°, 11-25°, 5-625°, 2-8125°, 1-4062°
and -7031°- Obviously the 180° is made up of
the single quadrant below the centre and the
quadrant next above. These angles must be
accurately cut, an extremely difficult and costly
Sensitometry
475
Sensitometry
matter. The metal should be blackened and the
edges of the angles bevelled, so that the edge
of the bevel comes next the plate. The wheel is
mounted in a box so that it can rotate as close
as possible to the plate, and it will be found
more convenient in practice if the space between
the wheel and light is boxed in and the light
also enclosed so Qiat it can be used in a dark-
room. Such an arrangement obviates any pos-
sible source of error from light reflected from
the walls and ceiling of the room, and enables
one to attend to other matters whilst the plate
is exposing.
Diagrams C and D show an instniment made
by B. J. Wall, which may be taken as a guide.
The two dark-slides, d d, enable the experimenter
to expose four plates at once, using the halves
of quarter-plates, that is, strips of plates, measur-
ing 4i in. by if in. The light is placed central
with Si the axis on which the sector wheel
revolves. This introduces a small error, which
can be calculated from Schwarzschild's table
already given, but for practical speed testing this
may be neglected as it is less than the probable
error in reading the density. For accurate photo-
chemical work, the perpendicular from the centre
per minute the intermittency error is practically
negligible. The sector wheel may be driven
by hand, a small electric motor, a small water
turbine or hot-air gas-engine. Hiurter and Drif-
field used the treadle table of an ordinary sewing
machine ; but some mechanical arrangement
will be found most convenient, as it allows the
operator to attend to other matters.
To use the apparatus, attention should first
be paid to the light to see that it is burning
correctly, the sector wheel should then be set
in motion and the exposing shutter withdrawn.
For fast plates, an exposure of 40 candle-metre-
seconds will be sufficient as a rule, whilst for
slow plates 80 C.M.s. may be given. For lantern
plates this may be even doubled or quadrupled,
so as to obtain the characteristic curve of the
plate. Even with the largest sector, only half
the circle, or 180°, is used for the exposure, so
that no matter what exposure may be decided
upon, it must then be doubled ; in other words,
ignoring the intermittency error, if the actual
exposure is 80 sees, the effective exposure will
be only 40 sees., as half the time the plate is
covered by the opaque portion of the sector
wheel. If the candle is used, then we may give
ri
-L. M
^
'-H/ood
C and D. Wall's Exposure Instrument
of the flame should coincide with the centre of
the plate.
It will be found advisable to provide the dark-
slides with ;J-in. strips of black paper or thin
metal, along the two sides, so as to have two fog
strips, the use of which will be explained later.
The dark-sUdes should be made in the form of
a printing frame with solid back ; the ordinary
form may be used, but it rarely permits of one
plate being placed behind the other, as some-
times required. C and D are practically seU-
explanatory ; s is the sector wheel ; D D the
dark-slides ; M the Methven screen with circular
aperture ; and P the acetylene flame. Small
pieces of wood are fastened to the sides, top and
bottom of the box, inside, to prevent scattered
light reflections. The inside of the box must
be blackened. A is an aperture cut in the top
of the narrow portion of the box into which the
two liquid cells for screening the light are in-
serted. As the flame is so near the aperture in
the screen, this gets very hot, and it is advisable
to have the outer sleeve, into which the project-
ing piece of the lamp slides, lined with asbestos
cloth. E is an exposing door which, by means
of a milled head outside the case, can be raised
or lowered so as to admit or shut ofi the light at
will.
A series of intermittent exposures does not
produce the same eflect as the equivalent con-
tinuous exposure, but it has been shown by
Sheppard and Mees that it the wheel is not
driven at a greater speed than 100 revolutions
E, Grease-spot Photometer
actual seconds, but in the case of the screened
acetylene light, it is necessary to find by actual test
of a plate of known speed what is the equivalent
exposure. Thus, with the instrument as described
above, it has been found that an actual
exposure of 340 sees, gave exactly the same
result as an efiective exposure to a standard
candle of 40 sees.
For true speed reading the emulsion must be
coated on plate glass ; the plates should be
backed, and the strips to be tested should be
cut out of the middle of a whole-plate. The glass
generally used for plates is so uneven as to give
rise to considerable errors, and if not backed,
halation occurs ; the backing should be black
and not red.
The Photometer. — ^This instrument is used for
measuring the densities of the plates. The
simplest type, and the one used by Hiirter and
Driffield, was a modification of the Bunsen
grease-spot photometer ; its main fault is that
the two spots that have to be compared are not
contiguous. The instrument consists essentially
of a box with one side open and the edges splayed
out to protect the operator from the light, whilst
measuring the densities. B shows a plan. The
case may be made of wood, but those parts near
the lamps should be of asbestos millboard, inside
which should be two sheets of copper or zinc
perfectly plane and blackened, as should be the
whole of the inside of the box. At each end in
the centre of the sides is a hole 6 mm. in dia-
meter ; between these holes should be a plane
Sensitometry
476
Sensitometry
block of wood, with either a rack or a smooth
piece of metal on top ; and the small box shown
should be provided with a pinion or small rollers
so that it may run easily to and fro. In both
diaphragms should be placed either ground glass
or preferably opal, just behind the copper plate.
To the centre of the little box should be affixed
a pointer passing along a graduated scale,
fastened to the bed on which the box moves.
The little box is of light wood with two mirrors
at the back placed at a low angle, whilst between
them is the grease spot, which can be fixed to a
piece of stout card with a hole cut in it, or
between two thicknesses of card. Some instru-
ments are not provided with the lens and eye-
tube ; these are to be preferred, although far
better still is a low-angled bi-prism, which brings
the images of the spots into juxtaposition.
The making of a grease spot is by no means
an easy matter at first, but as the materials are
nothing but a hard carriage candle, a big darning
needle and a spirit flame or gas, plus the paper,
it is merely a question of practice to produce a
large number of spots, the best of which can then
be chosen. The paper should be thin, with a
matt surface, and not too hard, and it should
be cut into i-in. discs, which should then be
placed round the candle, the eye end of the
darning needle made hot and placed as nearly
as possible in the centre of the paper ; the heat
melts the wax, which is absorbed by the paper,
and forms a semi-translucent spot, preferably
not more than i mm. in diameter. Make a
number, and choose the best and most regular.
A very translucent spot enables one to read very
high densities, but it is not so sensitive. After
using the instrument for a short time, it wiU
soon be found whether the grease spot chosen
is satisfactory or not, for as the highest density
that is usually required is about 3-60 this should
be the limit of sensitiveness required. The
chosen spot should be placed between two thin
opaque cards, with a I-in. hole cut in them,
and the spot should occupy the centre of this
aperture. The cards may be slid into the little
box as shown at E, through the top. The box
should measure about 2 in. by if in., with J-in.
holes in the sides. These holes, the grease spot
and the holes in the sides of the photometer
box itself, must be absolutely axial one with
another.
At the left hand of the instrument is a couple
of weak brass dips, fastened to the side to hold
the negative to be measured against the aperture.
At this side, also, is a small door, on the inside
of which is a mirror that reflects the light on to the
scale. At the right hand of the instrument is a
circular plate pierced with openings which can
be rotated in front of the aperture exactly like
the old wheel diaphragms of lenses so as to
reduce the luminosity of the one light, as this
considerably faciUtates the readings.
With the grease spot photometer, the distance
between the two diaphragms at the end of the
scale bed must be 12 in. ; with the two Lummer-
Brodhun rhombs and the Martens heads,
described below, this distance must be increased
to 20 in. To mark the scale (preferably of ivory
or celluloid), the following formula is used : let
z = half the distance between the two dia-
phragms, D = the density, and x = the distance
the grease spot is shifted to obtain equality of
illumination, then
■'««e-^3
Example : let the distance between the two
idiaphragms = 20 ins., then z = 10, then d for
any distance, say 5-6 in., will be
log of 15-6 = I-I93I25
log of 4-4 = -643453
0-549672
2
1-099344
which is the density required.
In order to save calculatiofls, the following
table gives the distances and the corresponding
densities : —
Distance
Density
X 0-057
=
o-l
X 0-II4
=
0-2
X 0-171
=
0-3
X 0-226
^
0-4
X 0-280
^
0-5
X 0-332
=
0-6
X 0-382
=
0-7
X 0-430
=
0-8
X 0-476
=
0-9
Distance
Density
X 0-519
=
i-o
X 0560
=
I-I
X 0-599
:=
1-2
X 0-634
=
l'3
X 0-667
=
1-4
X 0-698
=
1-3
X 0-726
=
1-6
X 0-752
=
1-7
X 0-776
=
1-8
To use the table, z is merely the exact centre
of the scale, and if liiis is 6 in. or 10 in. from either
diaphragm, then the above distances must be
merely mtiltiplied by 6 or 10, and marked off
on the scale in the corresponding densities. Each
di-vision or density space should be further
divided into four equal parts, which enables one
to read the densities to every -25.
It has been assumed above that the centre
point is marked zero or o ; ob-viously, then, the
readings to the right -will be minus readings, and
those to the left plus readings. This leads to
trouble and confusion, and it is better to mark
the extreme right of the scale zero, and the
numbers -will then run up to 3-60, the centre being
1-8. This enables the densities to be read ofi
direct.
The diaphragms at each end of the photo-
meter box should be of equal diameter ; when
the hghts are equal the zero point will fall in
the centre. It is preferable, however, to reduce
the right-hand Ught by a diaphragm of smaller
diameter or by increasing the distance of the
hght. In any case, it is ad-visable to pro-vide
extra diaphragms on the right-hand side so as
to be able to reduce the hght here for reading
high densities. It will be found convenient to
reduce the Hght to densities of -5, i-o, and i'5
respectively. To find the diameter of the smaller
apertures, square the logarithm of the diameter
of the original aperture, deduct .5, i-o, and 1-5
respectivdy, and di-vide the remainder by 2, when
the quotients will be the logarithms of the
diameters of the new diaphragms. For instance,
suppose that the original diaphragms are 6 mm.
in diameter, then
6« = 36
log 36 = 1-556302
and 1-556302 —0-5 = 1-056302
1-056302 -j- 2 =0-528151
Sensitometry
477
Sensitometry
which is the logarithm of 3-374, the diameter of
the new diaphragm, which will reduce the
densities by 0-5. In exactly the same way we
find that the diameters for i-o and 1-5 would be
1-897 and 1-06 mm. In any case, it is advisable
F. Wedge
to test these diaphragms by actual readings, the
mean of six readings being taken.
Instead of circular apertures, rectangular ones
may be used, and a square of about -203 mm.
is convenient. As the density patches on the
plate measure approximately 2-5 x i cm., it is
obvious that the diaphragms may be consider-
ably larger than stated above, but it is convenient
to keep them small, as this enables one to shift
the plate about over the aperture and thus avoid
any local defect, such as a pinhole or black spot.
If rectangular apertures are used, then a strip
of metal, 10 in. long, with a wedge cut out as
shown at P, will be required. The wedge should
taper from j^ in. to a point, and this can be
marked with the densities according to the
following rule : —
D = log. of wedge length — distance from apex.
Par superior to the grease spot in accuracy of
reading are the photometer heads of I<ummer and
Brodhim and of Martens. The former is made
in two forms, one of which gives an image similar
to the grease spot G, the second kind being still
more sensitive, as, with experience, readings to
about 0-5 per cent, or even to 0-22 per cent, are
possible. Instead of the grease spot two right-
angled prisms are used (j and k in diagram H).
J has a small ring C C etched out, whilst the
central circle is left polished ; the other prism K
is placed in contact with J, and the passage of the
light is shown by the lines and arrows ; at D,
where there is optical contact, the light from the
source at r passes straight through the prism,
but at C, where it meets with a thin film of air,
it undergoes total reflection and forms the outer
circle, shown grey in G. Exactly in the same
G. Grease-spot
Image
H. Photometer Head
having two Right-angled
Prisms
way, the light from I, meets at c a film of air,
is reflected at right angles, and is lost in the
mounting of the prism, whilst the central beam
passes straight through to the eyepiece.
In the still more delicate instrument, the
ihomb, shown at y in diagram I, is used. The
light proceeds from two sources M and n; two
right-angled prisms are placed with their hypo-
thenuses together. On one of the prisms the
surfaces u, y, and € are etched to a matt
surface ; at p, S, and C the surfaces are left
polished, and are in optical contact. At G R
and G I, are two small plates of glass which reduce
the light about 8 per cent. The field, as seen in
the eyepiece, presents the appearance of z, and
if the intensity of the light on D B and B c is the
same, h r and H 1, are equally bright, and the
fields D R and D c are also equally bright but
stand out darker than the backgroimd. If, on
the other hand, the intensity on b C is greater
than on d b, the contrasts in the right half of the
field of view are increased and those in the left-
hand field are lowered. With both these heads,
the operator sees the field of view not at right
angles to the scale but at about an angle of 45°,
but the makers, Schmidt and Haensch, of Berlin,
supply a form of direct-vision head.
HlDrHlHrDlHr
I. Ltimmer & Brodhun J. Martens's Photometer
Photometer Head Head
Martens's photometer head, made by the same
firm, is shown in diagram form by J ; in this, the
light from the two sources i, and R falls upon two
plaster-of-paris screens Sj s^, and is thence
reflected to the two mirrors Mj Mj and the two
right-angled prisms Pi Pj. There is total reflec-
tion to the plano-convex lens F, to which is
cemented the bi-prism b, by which images are
brought into juxtaposition in the eyepiece E.
In the photometer as suggested by Hurter and
Liriffield two oil lamps with flat flames, fed from
a common oil receptade, were used, but unless
the lamps are outside the photometer room the
heat is too great to be comfortable. With elec-
tric light the trouble of the heat is more easily
avoided, but accurate readings cannot be ob-
tained with a lot of stray Ught about the room.
In any case the use of two separate lights intro-
duces an element of uncertainty through the
variation of the lights themselves, and it is better
to use one Ught, such as a 150 candle-power
electric or powerful incandescent gas, and reflect
it by means of mirrors through diaphragms as
Sensitometry
478
Sensitometry
shown at K, in which I, is the light, mm the
mirrors, and p the photometer.
A simple and ingenious photometer has been
devised by Chapman Jones, called by him an
opacity meter, and illustrated and described
Arrangement for Photometer with only
One Light
under its own heading. In this case the screen
is opal glass, against which the plate is clipped ;
the scale may also be in opacity logarithms or
densities. Another instrument, introduced by
P. F. Renwick, is used for measuring densities,
and is a simple form of comparison photometer,
in which a uniformly and strongly illuminated
area of fine ground glass is viewed through two
small square apertures close together in the front
of the instrument, one of which is covered by the
density to be measured, and the other by a sliding
wedge of neutral tinted glass compensated to give
a uniform field by a very thin wedge of the same
kind and angle. The two apertures are brought
into contact by means of an Albrecht rhomb.
Spectrophotometers are nmuerous and costly.
Briefly the light passes through two apertures,
the two beams split up into contiguous spectra,
and the luminosity of one reduced to that
passing through the density to be measured, by
means of Nicol prisms. An instrument that has
been highly recommended is the Martens's polar-
isation photometer or " absorptionsmesser,"
made by Schmidt and Haensch, which is shown
at Iv. The quality of the fields or the zero point
is first obtained by revolving the upper prism
A ; then the reading of the angle is taken, the
negative strip b is ttien placed on the bed on an
opal plate (not shown), A revolved till even illu-
mination is again obtained, and the reading
taken. The density is log tan ^e' - log tan * fl,
in which fl' is the angle with the negative plate
and 0 the angle without the negative. The
log tan can be obtained from any book of
mathematical tables.
Such calculations may seem formidable, but
they consist really of reading logarithms from an
ordinary book of mathematical tables, and the
application of the three simple rules of arithmetic.
Development of the Plate.- — ^The plate strips
having been exposed, the next step is their
development. Originally, Hurter and Driffield
suggested the use of ferrous oxalate as the
standard developer, but, recognising that this
was no longer in practical use, they adopted a
non-staining pyro-soda developer, and this
should be adopted now as the standard. The
formula is : —
PyrogaUol . . 56 grs. 8 g.
Sodium sulphite cryst. 280 „ 4° „
Sodium carb., pure . 280 „ 40 „
Distilled water to . 16 oz. 1,000 cos.
This win not keep as one solution, but it can be
easily prepared in two-solution form, the pyro
and sulphite being dissolved in half the water
and the carbonate in the remainder, and the two
mixed just before use. A constant temperature
must be maintained, and 65° P. (18° C.) may be
adopted. Not only the developer, but the dish,
the measures, and the plate itself, should be at
this temperature. It is possible to use a pro-
perly constructed thermostat, but equally satis-
factory results can be obtained by using a. zinc
or copper tank sufficiently large to contain dish,
measures, and developer. Diagrams M and N
represent a tank used by the author. The zinc
tank holds half a gallon of water ; the dish made
of copper is provided with projecting edges E,
which are turned over so as to fit loosely on the
edges of the tank. Sufficient room is provided
in the tank to allow of the measure and fie bottle
of developer being placed in it to warm up. The
water is heated to about 68° or 75° P., according
to the season of the year, and the dish and the
measures cool it down to 65° P. in about ten
minutes. After exposure, the plate is also placed
in the dish, covered with the opaque cover, and
left for two or three minutes to warm up. The
developer is flowed over the plate, the opaque
cover replaced, and the dish gently rocked.
There is not the sUghtest advantage in looking
at the plate, and the opaque cover prevents any
possible light fog. The duration of development
is a matter of choice ; if too short the resulting
densities are thin generally and difficult to
measure, whilst if too long the higher densities
are beyond the power of the photometer. For
the above pyro-soda developer four minutes will
be found to be about correct.
There is one point which is of considerable
practical importjuice, and that is the use of two
strips for speed determinations. Por this reason
it is strongly advised to cut the plate into two
lengthwise before exposure. A fixed frame can
be made with a guide for the diamond, and the
L. Martens's Polarisation Photometer
plate may be cut and put in the dark-slide and
exposed as one. This will obviously yield two
strips, the second of which should be developed
for double the time of the first ; that is, eight
minutes with pyro-soda. Of course, any other
developer may be adopted as the standard, but
then it is a question as to whether the system
Sensitometry
479
Sensitometry
can be correctly termed that of Hurter and
Driffield. It has been repeatedly stated that
certain developers will enable exposures to be
reduced to one-third, one-fourth, and so on ; this
is tantamount to saying that a particular
developer will treble, quadruple, or otherwise
increase the speed of the plate. This question
has been examined by Sheppard and Mees, and
they found that there were practically two
classes of plates on the market — one that gives
the same speed with aU developers, and the other
with which the speed is increased by using an
organic developer instead of ferrous oxalate.
They found that practically the second class of
plate showed an increase of speed with organic
developers over ferrous oxalate of 1-75 : i.
Whatever be the developer adopted, it is
important that no bromide be used.
As soon as development is finished the plate
should be thoroughly fixed in an acid fixing
bath, washed, immersed for a minute or two in
a 5 per cent, solution of hydrochloric acid, rinsed
under the tap, and the film gently rubbed with a
of the box or in its proper position and adjusted
till the fog strip is over the aperture. The fog
strip is that portion of the plate protected from
any light action by the opaque card at the edges
of the dark slide, and the reading of this is the
density due to the glass, the gelatine and any
fog inherent in the emulsion itself. Then the
greatest density should be read, and all the
others in turn, each being jotted down in a note-
book kept for the special purpose. For the sake
of convenience the decimal points may be
neglected whilst reading, as they can always be
inserted afterwards.
The following is an example of the reading of
a plate developed for three minutes with a metol-
hydroquinone developer at 65° P. (18° C.) : —
M. and N. Wall's Developing Tank
wet pledget of cotton wool and put away to dry.
As soon as dry the back of the glass should be
well cleaned with cotton-wool or a rag, and the
dividing lines between the densities marked with
a pen and ink, as this considerably facilitates the
adjustment of the strip in the photometer.
Reading the densities. — ^The first thing to do is
to caUbrate the photometer. For accurate read-
ing it is essential to work in a dark-room, and at
least five minutes should be allowed to elapse
before attempting to read so as to allow the retina
to recover from the fatigue caused by bright
light. To calibrate the photometer — that is to
say, to find the zero — the spots or patches formed
in the photometer box are compared, and the box
shifted to right or left tiU they are of equal
luminosity. At least three readings should be
taken or six for preference, and the mean of
these adopted.
The strip of plate should be thoroughly
warmed, as this prevents the condensation of
moisture on it, which is apt to occur if the heat
from the lamps is great. The plate should then
be slipped into the spring catch at the left hand
Plate A
Zero point, 'lo ; fog point,
•35 - -lo =
35 ; actual fog =
•25
True density =
Exposure C.M.S.
Reading
Reading— {zero -}-
fog = "as)
40
2-65
2-30
20
2'67
2-32
10
2-65
230
5
2'55
2'20
2'5
2'35
2'00
125
l-go
I'55
■625
i'45
1*10
•312
l'o5
■80
•156
■75
•40
Another plate gave the following readings :-
Plate B
Zero point, •15; fog point, ^30 ; actual fog =
•30 -•IS = -15.
True density =
Exposure C.MS.
Reading
Reading — [zero -f-
iog = -30)
40
2'8o
2'5o
20
242
2"I2
zo
I"90
i-6o
5
170
1-40
25
I'32
I '02
I'25
■98
■68
■625
•60
•30
•312
■40
"10
•155
■34
•04
A third plate gave the following : —
Plate C
Zero point, -10 ; fog point, -55 ; actual fog
•55 _ -lO = .45.
True density =
Exposure C.M.S.
Reading
Reading " {zero -f-
Sog = -55)
40
f95
1-40
20
i-go
i'35
10
177
I'22
5
i'57
I'02
2'5
i'39
•84
I'25
I'20
•65
■625
■85
■30
•312
•65
■10
•156
■59
■04
If it is impossible to obtain equality of the
fields with the highest densities, the luminosity
of the right-hand side can be reduced by bringing
Sensltometry
480
Sensitometry
one of the smaller diaphragms into position and
adding its value to the density reading. Thus,
if witii the largest supplementary diaphragm
the density is found to be 3-45, the real density
will be 3-45 + "5 (the value of the supplementary
diaphragm) = 3-95. It may be as well to point
out that the accuracy of such high density
readings as this is very doubtful. Having jotted
down the readings, first the zero point is deducted
from the fog, then the fog and zero are deducted
from all the readings in turn, and the true
densities thus found. The densities are then
plotted out on charts, and the points joined
up by holding a flexible rule along them and
drawing pencil lines. The charts {see O, P, Q, and
R) can be drawn on paper or scratched on a
Exposure in Candle Metre Seconds
^0-166 0312 0-625 125 2-5 5 10 20 W, 60 160 S20 640
y
--
/
A
/
/
/
/
/
/
V
/
''
^
O
/
^
a
/
y
/y
y
^
/
^c
i
-£
/
1
^
/
0
bottom of the chart, as shown in O by the dotted
lines ; this gives the " inertia " of the plate.
The " inertia " of the plate is its slowness, and
the speed of the plate is found by dividing 34
by the inertia. Frequently the inertia is ex-
pressed in logarithms, and is then called log I.
Turning to chart O, consider the three plates.
First with regard to a, the straight line portion
obviously lies between 2-5 and 0-3 12 c.m.s. or
candle-metre-seconds. The density corresponding
to 0-156 is too high, and this is the period of
under exposure. From 2-5 to 5 c.m.s. the curve
begins to flatten, and had the exposure been
increased it would have turned right down
again. This flattened portion from 2-5 to 40
C.M.S. is the period of over-exposure. The point
0156 0-312 0*25 125 2 5
10 20 40 6
0 l£
0 3
?0 &
0
?5
/
B/
V
A.
1-0
»5
/
/
/
/
/
V
/
/
~=-i
S
y
^m
^
/
01 2 3 4 5 7' ? 3 4 S 7 10 20 30 50 70 100 ZOO 500 lOOO
I 5 V I Z 3 4 5 7 10 20 30 50 70 too 200 500 IDOO
0(56 0312
0«5 125
25 5 10 20 40 flO t60 320 640
20
25
1-5
to
05
N'3
1
V
N-2
/
'/
N"l
/
/
//
y
/
i
'/y
«-?iw
1
/
0
234571 23457 10 20SOKI7DI00300 300 1000 ag i j 3
Q R
O, P, Q and R. Charts of Plate Densities, etc.
0H56 0312 0625 f25 2-5
5 10 20 40 BO
160
320 640
2-5
2-0
1-5
2-0
3 15
■
--
—
--
E3
■-^
'
- FO
y-i
^
1-0
-..
J-A
._.
X-
y\
/
/
0-5
/
0-5
/
/
/
cos
Jc
^
s^
^
/
^
B0
0
slate. The inertia scale is merely the log scale
of an ordinary slide rule repeated four times
instead of twice. At the points 0-156, 0-312,
0-625, i'25, etc., are drawn the vertical equi-
distant exposure lines, and the exposures can
be written at the top. The " density " and
" development factor " scales on the right and
left respectively are exactly similar, and the
distance from o to 1-0 should exactly correspond
with the length of the inertia scale from 10 to
100 or 100 to 1,000. From the 100 point on the
inertia scale draw the heavy line to i-o on the
development factor scale. Having marked the
densities corresponding to the exposures and
joined up the points by straight lines, the
characteristic curve of the plate is obtained. The
speed is found as follows : by means of a trans-
parent celluloid ruler or a piece of black thread
find that portion that lies on a straight line and
continue it tiU it cut the inertia scale at the
where the straight portion on being continued
cuts the inertia scale is 0-15, therefore the speed
of this plate was 34 -;- 0-15 = 226 H. and D.
In plate B there is a totally different char-
acter ; here the straight portion extends from
•625 to 40 C.M.S. As a matter of fact, it ex-
tended to 80 C.M.S., although this was not
charted. The inertia is obviously 0-36, and the
speed consequently 34 -^- 0-36 = 95 H. and D.
This would be an excellent landscape plate with
considerable latitude of exposure, as the straight
portion extends from -36 to 40 C.M.S., or the
range is i : iii. Plate A, on the other hand,
has only a range of i : 25.
Plate C is peculiar, as it will be seen that the
curve begins to fall off at 10 C.M.S. ; the highest
density is comparatively low, 1-40 for 40 C.M.S.,
yet the inertia is 0-15 and the speed therefore
226 H. and D.
It will be noted that the reading of plate A
By H. Essenhigh Corke, F.R.P.S.
FIRELIGHT EFFECT
16
Sensitometry
481
Sensitometry
at 10 c.M.s. -was I -60, obviously too low, as the
straight liae cuts at 176 ; here there is probably-
some little error in the plate coating which has
given this low reading. The dotted portion of
the curve is known as the " period of under-
exposure," the straight portion that of " correct
exposure," whilst the reverse or turning over of
the_ curve as in A (diagram O) is known as " the
period of over-exposure," the whole forming the
characteristic curve of the plate.
The latitude of a plate can be easily calculated
if the range of light intensities in a subject is
known. For instance, with a landscape the
range is usually about i : 30, and with plate B
the latitude would be therrfore iii h- 30 = 3-7,
so that it would be permissible to give an expo-
sure from I to 3J seconds and yet obtain a good
negative.
Sheppard and Mees have given a mathematical
expression and formula for finding the latitude
of the plate, which they define as its opacity for
blue violet light. They also suggest a much
simpler method, which is to expose another plate
of known inertia underneath tiie plate of which
it is desired to know the latitude, and measure
the apparent inertia ; the difference between the
known inertia and that obtained will be the
latitude of the plate.
It will be noted that on the right-hand side of
the chart O are three lines a, 6, c, drawn from
the 100 point of the inertia scale and parallel
with the straight portion of the curves A, b, and
C. When a line thus drawn coincides with the
line drawn from 100 to i, which is obviously at
an angle of 45°, the negative is correct as regards
the rendering of the tones of the subject. IE this
development factor or gamma A., as it is called,
is above i, as with plates A and B, the contrasts
of the subject are increased ; whereas if below, as
with C, the contrasts of the subject are reduced.
The development factor or A. is important, and
may be calculated in various ways, as will be
seen later.
It has already been advised that two strips
should be exposed and developed together, the
one for double the time of the other. This
enables the operator to determine whether the
plate contains free bromide, as this is sometimes
added to the emulsion by the mantifacturer,
either in the shape of potassium or ammonium
bromide or hydrobromic acid, to keep the plate
clean. Free bromide in the film or added to the
developer actually lowers the speed of the plate
with a given time of development. If, then, on
reading the second strip, developed for double
the time, it is found to have a different inertia,
the true speed of the plate can be found by chart-
ing the two readings and continuing the straight
portion of the curve of the strip developed for the
shorter time, which we will call A, to a point c
below the inertia scale p. C may be any con-
venient point. Then from c draw the ordinate
C D to the inertia scale and bisect this at E, con-
nect E with F the inertia of a, and having charted
B, the plate developed for double the time, con-
tinue the straight portion till it cuts E P at g ;
then an ordinate from g to the inertia scale gives
the true inertia of the plate. In P this operation
is shown, and the inertia of a = -46, that of b
= -29, whUst the true inertia is -iSs. Bromide
added to the developer increases the inertia in
31
the same way, though with continued develop-
ment the true inertia is obtained.
The duration of development may be fixed at
any convenient length, the only consideration
limiting it being the ease of reading the densities.
Prolonged development has no effect upon the
inertia or speed of the plate. The sole result of
shorter or longer development is the attaiiunent
of a lesser or greater development factor, pro-
vided the emulsion and developer contain no free
bromide. This is clearly seen from the accom-
panying table and chart Q, the former being
taken from an early issue of the Photo-Miniature
by Driffield.
z
2
3
4
5
Exposuri
C.M.S.
Density
Density
ratio
Opacity
Opacity
ratio
Strip No. I
developed
4 miQS.
1-25
5.0
.310
.520
.725
I.O
1.67
2-33
2.04
3-31
S-30
1.0
1.62
2.59
Strip No. 2
developed
8 mins.
1-25
2-5
5-0
•530
.905
t-235
1.0
1.70
2-33
3.38
8.03
17.18
1.0
2.37
5.08
Strip No. 3
developed
12 mins.
1.25
2-5
5.0
.695
1.X40
1.625
1.0
1.6+
2.33
4-95
13.80
42.17
1.0
2.78
8.51
In column i are the exposures, in column 2 the
densities, in column 3 the ratios between the
densities, whilst in column 4 are the opacities,
and in column 5 the ratios between the opacities.
As all the strips were exposed at once there is
no question of variation here, but varying the
length of development has produced densities
which vary very widely, the increase being as
much as 2 : 34. The densities given by Driffield
have been ciarted, and it wiU be at once seen
that the inertia obtained with all three strips
is the same, but the gammas are very different.
The fact of the inertias being the same proves
that prolonged development will not fetch
more out of a plate," and the variation of gamma
proves that by reducing or prolonging the time
of development the photographer is in a position
to alter the character of his prints by using a
higher or lower gamma. For instance, assuming
that a negative was developed to a gamma of
•7 as strip i, it is obvious that the negative
would be what is generally termed " thin," and
therefore probably most suitable for gaslight
paper. If it had a A = I'I4 as strip 2, then it
would be much denser, and probably suitable for
P.O. P. ; whereas if it had a A = 1-5 as No. 3, then
it would be dense and suitable for rapid bromide
paper. In the last case most probably the lower
tones — that is, the shadows — ^would be much
blocked up by the time the high lights were
sufficiently printed, whilst in the first case the
high lights would be printed out before the
shadows had obtained ."iufficient depth.
The Development Factor. — ^I'he development
factor or gamma has already been defined as the
degree of contrast in the negative. This is
dependent in part on the plate and also on the
Sensitometry
482
Sensitometry
duration of development. Gamma may be found
graphically as already described, or W. B. Fer-
guson's method may be adopted, this being to
miiltiply the means of the highest densities
by 3-3-
For instance, taking plate B (chart O), the
upper densities and differences are : —
Densities Differences
2-5o> 3.8^
2-12^ ,.«|
176:
I -40:
1-05
mean -3625
Then -3625 x 3^3 = i'207, which coincides with
that found graphically.
The gammas usually adopted in practice are
•8 for portraits, i-o for architecture, and 1-3 for
landscapes. To find the necessary time to
develop to any given gamma, plot out on a chart
the gammas obtained by developing the two
strips or by Ferguson's calculation, this chart
being exactly the same as our speed chart, only
the development factors are written on the left-
hand side and the time of development at the
bottom instead of the inertia scale {see R).
Suppose that we obtain for the A strip A = 7 with
three minutes' development, and for B A = i-2
with six minutes' development, plot these, and
draw a curve connecting these points with the
zero point {see R). Then, to find the necessary
time to obtain any given gamma, draw a straight
line from the required development factor and
another at right angles to it tiU it cuts the
time scale at the bottom, when, as wiU be seen
from R, the times would be 3-6 minutes for
y — ■$, 4-6 minutes for ■7 = 1, and 7 minutes
for 7 = 1-3.
A moment's consideration will show that there
must be a limit to the density obtainable on a
plate, and this is termed Dm, or gamma infinity
700 .
The Velocity Constant, or k. — The velocity of
development is the speed with which a plate
develops ; usually ferrous oxalate is used as
the developer for photochemical investigations,
but pyro-soda or other organic developer may
be used instead. The mathematical expression
for this factor is
I , DOO
or
, =Jlog, _2l_
In order to save calculation, Sheppard and Mees
have given a table (reproduced in the next
column) which enables k to be found with very
little trouble.
An example wiU make the use of this table
clear. Two strips are developed, the first say
for four minutes, and the second for double that
time — that is, eight minutes. The gammas are
found, as previously described, and assuming
them to be i'5 for the strip developed for the
shorter time and 2-1 for that developed for
double the time, then
;2-7 -i- 1.5 = 1-8
In the second column of the table, headed
12
A /or A
7;
A /of A
K
Ti
o'ooi in K
Ti
O'OOI in It
O-0O5
1-977
0-0050
0-205
1-358
o-ooiS
o-oio
952
0-0048
0-210
1-349
0-0016
0015
928
0-0050
0-215
I-34I
0-0018
0'020
903
0-0046
0-220
1-332
0*0016
0-025
880
0-0044
0-225
1-324
0-0016
0-030
858
0-0042
0-230
1-316
0-0016
0-035
837
0-0040
0-235
1-308
0-0014
0-040
817
0-0040
0-240
I -301
0-0014
0-045
797
0-0038
0-245
1-294
0-0016
0-050
778
0-0038
0*250
1-286
0*0016
0-055
759
0-0036
0-255
1-278
0-0014
0-060
741
0-0034
0-260
I-27I
0-0014
0-065
724
0-0034
0-265
1-264
0-0014
0-070
717
0-0032
0-270
1-257
0-0012
0-075
691
0-0032
0-275
1-251
0*0012
o-o8o
675
0-0030
0-280
1-245
0-0012
0-085
660
0-0032
0-285
1-239
0-0012
o-ogo
644
0-0032
0-290
1-233
0-0012
0-095
628
0-0032
0-295
1-227
0-0012
o-ioo
612
0-0032
0-300
1-221
o-ooio
0-105
596
0-0032
0-305
i-2r6
0-0012
o-iio
580
0-0030
0-310
1-210
O-OOIO
0-115
565
0-0028
0-315
1-205
O-OOIO
0-I20
551
0-0028
0-320
I -200
O-OOIO
0-125
537
0-0028
0-325
1-195
O'00o8
0-130
523
0-0026
0-330
1-191
O-OOIO
0-135
510
0-0028
0-335
1-186
0-0008
0-140
496
0-0024
0-340
1-182
0-0008
0-145
484
0-0024
0-345
1-178
0-0008
0-150
472
0-0024
0-350
1-174
O-OOIO
0-155
460
0-0024
0-355
1-169
0-0008
0-160
448
0-0023
0-360
1-165
0-0008
0-165
437
0-0022
0-365
l-l6l
0-0008
0-170
426
0-0020
0-370
I-I57
0-0006
0-175
415
0-0018
0-375
1-154
0-0008
O'iSo
405
0-0018
0-380
1-150
0-0006
0-185
396
0-0020
0-385
1-147
0-0008
o-igo
387
0-0020
0-390
1-143
0-0008
0-195
377
0-0018
0-395
1-139
0-0006
0-200
1-368
0-0020
0-400
I -1 36
0-0006
2? we find 1*40, and against this in column i
under k we find "180, but this is for 5 minutes.
. . (5 -i- 4) X -180 = -225 = K.
Column 3, headed A for A -ooi in k, is used
as follows : supposing <-^ = i-373. the nearest
number to this is 1-377, ^^^ A or tlie difference
= 1-377 — 1'373 = -004, then -004 -r- -0018,
from the third column = 2-2, therefore we take
the K of 1-377 and add -0022, thus —
•195 + -0022 = -197.
This table does not apply for any developer
with a "Watkins factor of over 15 ; if -yj is i*8
times greater than yj, two other strips must be
developed for twice as long as before.
We may now proceed to find yoo. The
formula for this is
-yoo ^
_ 7i_
72
K^l
I — e - "h
In order to save calculation, Sheppard and Mees
have given the table on the opposite page.
An example -will make the use of Oiis table
clear. The two strips having been read and
y, and y^ having been found, k is calculated
as just described, and we found in the case
assumed k = -225, then kI^ = *225 x 2 = -450,
in the second column headed i — e-«< against
this we find -3617, then
-=- -3617 =
yoo
1-5
4*14.
The higher the gamma infinity the more a plate
may be forced in development, and for very fast
Sensitometry
483
Sepia Paper
Kt
i-e-Kt
a for
o-ol in Kt
Kt
l-e-rt
A /or
0-01 in Kt
o-ooo
o-oooo
2-000
0*8647
1
0-025
0'02
■ 0-0095
2-025
0-8680
L 0-0013
0*050
0-046
2-050
0-8712
1
0075
0-073
2-075
0-8744
O'lOO
0-0952
0-1174
2-100
0-8776
0125
. 0-0086
2-125
0-8805
■ 0-0013
0-150
0-1387
2-150
0-8834
0-175
0-1600
2-175
0-8863
0-200
O-I8I3
2-200
0-8892
0-225
0-2082
. 0-0077
2-225
0-8919
. 0-00103
0-250
0-2252
2-250
0-8945
0-275
0-2422
2-275
0-8971
0-300
0-2592
2-300
0-8997
0-325
0-2769
■ 0-0071
2-325
0-9021
. 0-00096
0-350
0-2945
2-350
0-9045
0-375
O-3I2I
2-375
0-9069
0-400
0-3297
2-400
0-9093
0-425
0-3458
. 0*0064
2-425
0-9113
. 0-00086
0-450
0-3617
2-450
0-9135
0-475
0-3776
2-475
0-9157
0500
0-3935
2-500
0-9179
0-525
0-4085
■ 0-0057
2-525
0-9197
■ 0-00078
0-550
0-4234
2-550
0-9217
0-575
0-4373
2-575
0-9237
0-600
0-4512
2-600
0-9257
0-625
0-4641
0-0052
2-625
0-9274
. 0-00071
0-650
0-4772
2-650
0-9292
0-675
0-4903
2-675
0-9310
0-700
0-5034
2-700
0-9328
0-725
0-5158
■ 0-0047
2-725
0-9344
0-00064
0-750
0-5281
2-750
0-9360
0-775
0-5394
2-775
0-9376
0-Soo
0-5507
2-800
0-9392
0-825
0-850
0-5613
■ 0-0042
2-825
0-9408
. 0-00058
0-5714
2-850
0-9412
0-875
0-5827
2-875
0-9426
o-goo
0-5934
2-900
0-9450
0-925
0-6031
. 0-0038
2-925
0-9463
. 0-00032
0-950
0-6128
2-950
0-9476
0-975
0-6225
2-975
0-9489
I -000
0-6322
3-000
0-9502
1-025
0-6485
■ 0-0034
3-025
0-9513
0-00047
1-050
0-6547
3-050
0-9525
1-075
0-6609
3-075
0-9537
i-ioo
0-6671
3-100
0-9549
I-I25
0-6741
0-0032
3-125
0-9559
• 0-00043
I-I50
0-6830
3-150
0-9570
1-175
0-6909
3-175
0-9581
1-200
0-6988
3-200
0-9592
)
1-225
0-7059
■ 0-0029
3-225
0-9601
L 0-00039
1-250
0-7131
3-250
0-9611
f
1-275
0-7203
3-275
0-9621
I
1-300
0-7275
]
3-300
0-9631
)
1-325
0-7339
1 0-0026
3-325
0-9639
1 0-00036
1-350
0-7403
3-350
0-9648
1
1-375
0-7469
)
3-375
0-9657
)
1-400
0-7534
3-400
0-9666
1-425
0-7592
. 0-0024
3-425
0-9674
. 0-00032
1-450
0-7651
3-450
0-9682
1-475
0-7710
3-475
0-9690
1-500
0-7769
3-500
0-9698
1-525
0-7822
■ 0-0022
3*525
0*9706
. 0-00029
1-550
0-7875
3-550
0*9713
1-575
0-7928
3*575
0-9720
1-600
0-7981
3*600
0-9727
1-625
0-S029
. 0-0021
3-625
0-9732
. 0-00026
1-650
0-8077
3-650
0*9739
1-675
0-8125
3-675
0-9746
1-700
0-8173
3-700
0-9753
1,-725
1-750
0-8215
0-8259
0'00i7
3-725
3-750
09758
0-9764
, 0-00023
1-775
0-8303
3-775
0-9770
1-800
0-8347
3-800
0-9776
1 825
0-8387
■ 0-0016
3-825
0-9780
. 0-00022
1-850
0-8426
3-850
0-9786
1-875
0-8465
3-875
0-9792
1-900
0-8504
3-900
0-9798
1-925
0-8539
. 0-0014
3-925
0-9802
. 0-00019
1-950
0-8575
3*950
0-9807
1-975
0-86II
3-975
4*000
0-9812
0-9817
Extreme care must be used in employing the
foregoing tables for finding 700 , as a very small
error will make a considerable difference in the
result. Almost as satisfactory results may be
obtained by adding i per cent, of potassium
bromide to the developer and continuing develop-
ment for half an hour, and after reading the strip
finding -yoo graphically by the chart. The
quantity of bromide to be used depends upon the
plate, the important point is that the plate
should be as free from fog as possible, even with
the prolonged development. Should the develop-
ment— thirty minutes — be not long enough, this
■will be apparent from the inertia obtained from
this long development being less than for the
same plate without bromide, then the develop-
ment must be longer still. The effect of bromide
in the developer is at first to increase the inertia
and decrease 7, but with prolonged development
these effects disappear, and both the inertia and
7 are the same as if no bromide were used.
The Photometric Constant. — Hurter and Drif-
field proved that the density was directly pro-
portional to the amount of silver deposited, and
this has been termed the photomeliic constant
= P the quantity of silver in grammes per
100 square centimetres. Hurter and Driffield
foimd that this was = -oisi, Eder obtained
•0103, and Sheppard and Mees found P = -01031.
The Watkins and Wynne Plate Speeds. — Whilst
the Hurter and Driffield system is generally used
for plate testing, there are two other systems of
plate speeds which are used with the Watkins
and Wynne exposure meters, which are founded
upon purely arbitrary standards. As it is often
useful to know how to convert the one system
into the other, the following rules can be used : —
To convert —
H. and D speed Nos. into Watkins, multiply
by 50 and divide by 34; or practically
H. and D. x i^.
Watkins P Nos. into H. and D., divide by 50
and multiply by 34 ; or practically P No.
shutter work — such as focal plane work, where
practically the whole of the exposure falls in
the period of under-exposure— a plate with a
high 700 will give as good results as a very fast
plate.
Watkins J extract the
mmtipi-y Wy &A..
____—, 4? to^HT^ndTD^ extract the
squaitilooL anrjEnTfr^f 6^7-7.
In order to save trouble, the table on page 484
gives the inertias, the H. and D. Nos., and Wat-
kins and Wynne in parallel columns. The in-
ertias are those marked on the scale of the charts.
SEPARABLE LENS
A lens of which the front and back combina-
tions may be used independently, either alone
or in combination with other lenses. Rapid and
wide-angle rectilinears, Zeiss VIIo anastigmats,
Goerz double anastigmats, and DaUmeyer stig-
matics may be taken as types of this class ; while
the Cooke, Tessar, and Aldis lenses belong to the
non-separable class.
SEPIA BROMIDES (See " Sulphide Toning,"
" Blake - Smith Process," and " Alum-
'hypo' Toning.")
SEPIA PAPER
A printing paper coated with a compound
containing salts of silver and iron ; development
Sepia Platinotypes
484
Shapes of Photographs
INERTIAS AND COMPARATIVE PLATE SPEEDS
(See SENSITOMETRY)
Inertias
H. and D.
Speed
Walkins
P. No.
Wynne F.
No.
Inertias
H. and D.
Speed
Watkins
p. No.
Wynne F
No.
Inertias
H. and D.
Speed
Walkins
P. No.
Wynne F.
No.
34'0
i-o
1-4
7-7
4-2
8-1
n-9
21-9
G»6o
56-5
83-0
58-3
32-0
1-062
1-56
7-93
4-0
8-5
12-5
22-4
0-58
58-5
86-0
59-5
30-0
I-I3
1-66
8-2
3-8
8-9
l3-o8
23-0
0-36
61*0
89-7
6o-3
28-0
I-22S
1-8
8-5
3-6
9'4
13-8
23-6
0-34
63-0
92-6
61 -6
26-0
1-307
1-92
8-8
3-4
lo-o
14-7
24-3
0-32
IV^
96-3
63-0
24-0
1'35
1-98
8-9
3-2
10-6
15-6
25-0
0-30
68-0
loo-o
64-0
22'0 1
1-54
2-26
9-5
3-0
11-3
16-6
25-2
0-48
72-0
105-0
66-0
20*0
1-7
2-5
lo-o
2-9
11-7
17-2
26-3
0-46
74-0
109-0
67-0
19*0
1-79
2-6
10-3
2-8
12-2
17-9
26-9
0-44
77-0
II3-0
68-0
l8-0
1-88
2-76
IO-5
2-7
12-6
18-3
27-6
0-42
82-0
120-0
70-0
17-0
2-0
2-9
10-8
2-6
I3-I
19-2
27-9
0-40
85-0
125-0
71-5
l6-0
2-12
3-1
11-3
2-5
13-6
20-0
28-4
0-38
89-0
131-0
73-3
15-0
2-26
3-3
II-5
2-4
14-2
20-9
29-0
0-36
950
140-0
75-5
14-0
2-42
3-56
12-0
2-3
14-8
21-8
29-6
0-34
loo-o
147-3
77-6
13-0
2-63
3-86
12-3
2-2
15-5
22-8
30-3
0-32
103-0
I3I-0
78-8
I2-0
2-8
4-1
13-0
2-1
16-2
23-8
31-0
0-30
113-0
I66-0
82-5
II-O
3-r
4-5
13-5
2-0
17-0
25-0
31-7
0-29
II7-0
172-0
84-0
10*0
3-4
5-0
14-2
1-9
i7-g
26-3
32-3
0-28
1210
178-0
83-5
9-5
3-55
5-2
14-5
1-8
18-9
27-7
33-5
0-27
I26-0
185-0
87-3
90
3-7
5-4
14-8
1-7
20-0
29-4
34-7
0-26
1310
192-0
89-0
8-5
4-0
5-8
15-4
1-6
21-25
31-23
35-8
0-23
136-0
200-0
90-5
80
4-25
6-2
15-8
1-5
22-6
33-2
37-0 .
0-24
141-0
207-0
92-0
7-5
4-45
6-5
1 6-2
1-4
24-3
35-8
38-2
0-23
148-0
217-0
95-0
7-0
4-85
7-1
17-0
1-3
26-15
38-5
39-7
0-22
154-0
226-0
96-3
6-8
5-0
7-3
17-2
1-2
28-3
41-6
41-3
0-21
162-0
238-0
98-7
6-6
5-15
7-5
17-5
I-I
31-0
45-6
43-2
0-20
170-0
231-0
loo-o
6-4
5-30
7-8
^V^
1-0
34-0
50-0
45-25
0-19
179-0
263-0
104-0
6-2
5-47
8-0
l8-o
0-95
35-5
52-2
46-3
0-18
189-0
277-0
109-0
6-0
5-66
8-3
l8-3
0-90
37-7
55-5
47-7
0-17
20O-O
294-0
IIO-O
5-8
5-85
8-6
18-6
0-85
40-0
58-3
49-0
0-16
2I5-0
316-0
114-0
5-6
5-1
8-9
19-0
o-8o
42-5
62-5
51-8
0-15
227-0
334-0
II7-0
5-4
6-3
9-2
19-3
0-75
46-0
67-7
52-6
0-14
242*0
336-0
120-0
5-2
6-5
9-5
19-6
0-70
48-5
71-3
54-0
0-13
262-0
3850
123-0
5-0
6-8
10 -o
20-0
0-68
50-0
71-3
tj-0
0-12
283-0
4160
130-0
4-8
7-1
1-04
20-5
0-66
51-5
75-7
55-7
O-II
319-0
469-0
138-0
4-6
7-4
I -08
20-9
0-64
53-0
78-0
565
O-IO
340-0
500-0
143-0
4-4
7-7
x-xj
21-3
0-62
54-4
8o-o
57-2
being effected with plain water and fixing in a
weak " hypo " bath, toning being optional. The
finished prints are of a good sepia tone. The
Natnias process is recommended ; for this two
solutions for sensitising are required : —
A.
Green ferric am
monio-citrate
4 oz.
440 g.
Citric acid
I ,.
100 ccs
Distilled water
10 „
1,000 „
B.
Silver nitrate
I oz.
110 g.
Distilled water
4 „
400 CCS.
These are mixed together, made up to 20 oz.
or 2,000 CCS., and applied to the paper with a
Blanchard or Buckle brush, and then dried ; the
whole of the operations must be carried out in
the dark-room. A second coating is sometimes
advisable. The paper is printed in contact with
a negative in daylight in the usual way, but not
very deeply, because in the washing after print-
ing a slight intensifying action takes place. After
about five minutes' washing the print must be
fixed for one to two minutes in an 8 per cent,
solution of " hypo." The print is finally washed
for about twenty minutes and then dried. The
print previous to fixing is of an unpleasant yellow
colour, but the operation of fixing changes the
yellow colour to a good brown, such change being
due, it is thought, to slight sulphurisation. If
the fixed prints are not of a pleasing colour they
may be toned in an alkaline sulphocyanide bath
containing 1 gr. of gold chloride and 50 grs. of
ammonium sulphocyanide per 5 oz. of water.
SEPIA PLATINOTYPES, OR SEPIATYPE
(See " Platinotype Process.")
SERUM PROCESS
An early process (about 1856) for preparing
plain paper for printing. The paper was pre-
pared with serum of milk, then salted or sensi-
tised. The prints were of purple tone.
SHADING MEDIUM
A film of gelatine, bearing on its surface a
pattern of stipple or line in relief ; used in pro-
cess work, etc. This film is stretched tightly on
a wooden frame and backed with ceUulpid
varnish. The surface of the film is inked, and
the pattern can then be transferred to any part
of a plate or stone requiring shading with stipple
or line.
SHADOWGRAPHS
Silhouette photographs have been called
shadowgraphs, but the name has been more
generally applied to. X-ray photographs.
SHAPE, CUTTING (See " Cutting Shape.")
SHAPES OF PHOTOGRAPHS
There is a strong tendency to restrict the shape
of a photograph to some form of the rectangle,
although an oval, a circle, and even a lunette,
may be employed effectively at times. The
roimding of two corners to form a " dome," or
of four corners to form a " cushion," is still
resorted to at times, but it is rarely desirable,
and is probably a survival from the days when
lenses frequently left the comers of the plate
unexposed. The relation between the length
and breadth of a rectangle is of distinct import-
ance ; a narrow upright panel, for instance, often
Sharpness
485
Shutters
emphasises a suggestion of height. But the chief
consideration is that the shape shall include only
what is necessary to the making of the picture,
and it would be distinctly wrong to include
blank or iminteresting parts of the print simply
to attain a particular proportion in the resulting
rectangle.
SHARPNESS
The usual standard of sharpness, or critical
definition, is that a point shall be represented by
a circle not exceeding ^^ of an inch in diameter.
This standard is easily attained, and, indeed, is
far surpassed. Even at full working aperture
lenses of a certain type will give satisfactory
sharpness over the whole of the plate they are
intended to cover. The focal field being practic-
ally a plane, there is no loss of sharpness towards
the edges. On the other hand, lenses with a
curved focal field will only give general sharp-
ness of definition when a smaller stop is used.
To secure sharpness in every detail of the
image the aperture of the lens is reduced until a
satisfactory definition results. This may be
done either to counteract poor marginal defini-
tion, or to secure sharpness in objects situated
in different planes. It is desirable in certain
cases to vary the degree of sharpness in difierent
parts of the subject, the parts having the great-
est sharpness generally being emphasised thereby.
In other cases, sharpness is rather a drawback
to a pleasing rendering of a subject. To throw
the whole out of focus is not a satisfactory
method of modifying sharpness ; but there are
types of lenses with an adjustment by means of
which any required degree of softness or diffusion
may be secured. Objectionable sharpness may
be modified during printing by interposing be-
tween negative and paper one or more thick-
nesses of celluloid (clear or matt), or even by
printing from the glass side of the negative. In
enlarging, bolting silk is often used for a similar
purpose. {See also "Definition.")
SHEATHS
Flat metal cases to hold plates, nsed in
magazine cameras ; each exposed plate is caused
to fall into the bottom of the camera, leaving
the next one in position for exposure. (See also
"Magazine Camera.")
SHELLAC {See " Gums and Uesins.")
SHELLAC MOUNTANT {See " Mountants.")
SHELLAC VARNISH
A solution of shellac in alcohol is used in
process work as an acid resist for backing the
plates, or stopping out margins or other parts
to be protected from the et<iiing. For 4 oz. of
shellac about 6 oz. of methylated spirit is
required. Sometimes about 2 drms. of methyl
violet dye is added to colour the varnish. For-
mulae for shellac varnishes for negatives are
given under the heading "Varnishes."
SHINGLE MARKS
Defects met with in the wet-plate (collodion)
proces3, and caused by the presence of water in
the collodion, or by excessive coldness of the
sensitising bath.
SHOP FRONTS, PHOTOGRAPHING
Shop fronts are always difiScult subjects to
photograph, because of ttie many reflections. A
method often recommended is to have a black
cloth larger than the window, and to place
the lens through a hole in the cloth, the latter
being fixed or held in such a way as to stop all
reflections from the opposite side. This method,
however, is rarely possible, because of the large
size of some windows and the difficulty of arrang-
ing the cloth. The only practical and satis-
factory method is to choose a time of day when
the sun is not shining on the opposite buildings.
SHORTENING THE FOCUS {See "Focus
Adjuster" and "Supplementary Lenses.")
SHUTTERS iVi., Obturateurs ; Ger., Ver-
schliisse)
Mechanical devices for exposing the plate.
Their use is necessitated by the fact that expos-
ures shorter than one-quarter of a second cannot
be given by hand, nor even that without risk of
A. Roller-blind
Shutter
B. Diaphragm Shutter
shaking the camera. There are many kinds of
shutters, a convenient classification being that
which groups them into those working before
the lens, between the lens combinations, and
behind the lens, though this division is not rigid
since many before-the-lens shutters can be used
equally well behind. The earlier shutters, such
as the flap, drop, and combined drop and flap
shutters, belonged to the first class, and are
practically obsolete, excepting the first-named,
which is still found useful in studio work. The
drop shutter has been completely superseded by
the roUer-blind shutter A, in which a spring blind
with a central aperture is caused to pass before
the lens. The speed is varied by altering the
tension of the spring by means of a winding
knob, a given number of turns corresponding to
a given speed.
The focal plane shutter {which see) is also a
roller-blind shutter, but is placed close to the
plate. In this, not only can the spring tension
be altered, but provision is made for varying
the width of the slit or opening, thus giving a
greater range of speed. This shutter has a
higher efficiency, and is capable of greater
rapidity than any other type ; but is liable in
some cases to cause distortion of moving objects,
since the plate is exposed a portion at a time.
In the second class of shutters are included
Shutters, Efficiency of
486
Silhouettes
those known as diapliragm. shutters, which work
between the combinations of the lens usually by
the opening and closing of thin metal or vulcanite
plates. The speed is varied either by adjusting
the tension of a spring, by a pneumatic brake,
or by altering the size of the aperture. Such
shutters form part of the lens, as at B.
The rotary shutter, C, which may work either
C. Rotary Shutter
between or in front of the lens, consists of a
circular disc with an opening towards the side.
This is made to revolve by means of a spring,
the opening passing across the lens during the
revolution.
The behind-lens bellows studio shutter con-
sists of two semi-circular bellows, which open
silently from the centre when the pneumatic
ball is pressed, closing again as the latter is
released. A dip prevents the return of the air
when it is desired to keep the shutter open. (See
also " Pneumatic Release," and other headings.)
SHUTTERS, EFFICIENCY OF
The proportion between the length of the
exposure and the time during which the lens
is fully uncovered. Two shutters may give
exposures of the same rapidity, but of very
different efficiency. Thus, one may take up the
greater portion of the time in opening and shut-
ting, while the other is fully open for the best
part of the exposure. It thus results that with
the first shutter a longer exposure is required to
produce the same hght effect as the second.
The focal plane shutter is the most efficient,
since the whole of the light from the lens reaches
the plate.
SHUTTERS, INSTANTANEOUS {See "In-
stantaneous Shutter.")
SHUTTERS, TESTING
There are many different ways of testing
shutter speeds. One is to photograph a wheel
revolving at a known rate, and having at its
margin a white spot or bright metal disc. On
developing the negative, the spot or disc will
be found to have formed a curve on the plate,
and the length of this curve as compared with
the circumference of the image of the wheel,
divided into the time of revolution, gives the
speed of the shutter. This can readily be carried
out by setting a bicycle upside down and attach-
ing a small silvered disc or bright button to one
of the spokes close to the edge. The wheel is
now set revolving until the disc or button re-
appears regularly at one place at intervals of
exactly a second, the exposure being then made
in bright sunshine or by buxoing magnesium
ribbon. Then, if the curve on the resulting nega-
tive measures, say, one-tenth the circumference
of the image of the wheel, the exposure is obvi-
ously one-tenth of a second. For very rapid
exposures the wheel may be revolved at a faster
rate.
A bright spot or disc on a pendulum has also
been used, allowance having to be made for
the fact that the rate of swing is not uniform
throughout the beat. A pendulum-testing device
for use with a suitably graduated scale is on the
market. A. Lockett, in 1909, suggested the
employment of a bright ball on a conical pendu-
lum, which revolves in a circle at a regular rate.
There are numerous other methods, most of
which, however, call for special apparatus.
SIDE SWING
An arrangement whereby the camera back
may be indined in a sideways direction. This
adjustment is useful when photographing build-
ings or other objects that recede from the
camera. In such a case, one side of the picture
will be out of focus as compared with the other,
unless the lens is stopped down ; but by using
the side swing the definition is equalised, although
a sUght distortion is introduced.
SIDEBOTHAM'S PROCESS
A waxed paper process introduced by J. Side-
botham, of Manchester, in 1855.
SIDEREAL PHOTOGRAPHY
The photography of stars, the term " Sidereal "
being derived from a I/atiu word meaning a
star. The methods of photographing stars,
planets, nebulae, etc., are described under the
heading " Stars, Photographing."
SIDEROSTAT
An instrument used in astronomical photo-
graphy, photomicrography, spectrography, etc.,
and known also as a heliostat (which see).
SILHOUETTES (Fr., Silhouettes ; Ger., Schat-
tenbilder)
Black profile portraits (as A) showing outline
only and no details, so-called from the French-
man Etienue de Silhouette. They may be pro-
duced photographically, as shown in B. A white
sheet B is hung in an open doorway ; the room
A. SUhouett©
being darkened, the sitter D is posed in pro-
file in the room and against the sheet, the
camera E being in the room as shown. A short
exposure is given, and a strong developer used
in order to procure a negative showing the
black (dear glass in the negative) profile against
a perfectly white (black in the negative) back-
Silk, Photographs on
487
Silver Bath
ground. A longer exposure will produce faint
details, but these are not required in a true sil-
houette. At night, flashlight may be used be-
hind the sheet and the same effect produced. The
curve at the bottom of the silhouette picture is
obtained by painting oVer the bare glass on the
negative with opaque pigment or by covering it
with red or black paper. Pull-length figures
may also be taken.
Another and a widely used method of taking
silhouettes is shown in sketch C. Two dark
screens a are placed parallel to one another, and
a white background B is placed so as to catch
the light from the window C. The sitter D is
then placed between the screens so as not to
B OD
n^
B. and C. Methods of Producing Photographic
Silhouettes
catch the direct light from the window ; the
camera is placed at E, and a dark doth or cur-
tain is thrown over the screens so as to form
a tunnel. The sitter is in the shade, while a
brilliant light falls upon the background. Focus-
ing must be accurate in order that the outlines
of the figure may be perfectly sharp. Any
printing process may be used, but one giving a
black-and-white effect is best.
SILK, PHOTOGRAPHS ON {See " Fabrics,
Printing on.")
SILVER (Pr., Argent: Ger., Silber)
Ag. Atomic weight, 108. A white, compara-
tively soft metal, obtained from nimierous ores.
It is not attacked by weak acids, but dissolves
in cold nitric add and hot sulphuric add. It
forms a large number of salts, all of which are
more or less sensitive to light, and are the bases
of most printing processes and the sensitive
materials for negative work. Silver exists in
various states of fine powder, and can then be
either black or coloured.
SILVER ACETATE (Pr., AcUate d' argent ;
Ger., Silberacetat)
AgCjHaOj. Molecular weight, 167. Solubil-
ities, I in 100 water, insoluble in alcohol. It
is in the form of fine white powder or crystals,
obtained by adding an alkaline acetate to silver
nitrate solution or by dissolving silver carbonate
in gladal acetic add. It has been occasionally
used in printing-out papers, but it gives yellow-
ish grey images of low intensity, and its sensitive-
ness is only about one-fifteenth that of silver
chloride.
SILVER ACETO-NITRATE
A solution of silver nitrate containing gladal
acetic add, used in the old wet plate days.
SILVER ALBUMINATE (Pr., Albuminate
d' argent; Ger., Silber albuminat)
A very ill-defined compound of silver nitrate
and albumen, which was supposed to form one
of the sensitive compounds m the old sensitised
albumen paper.
SILVER AMMONIO-NITRATE (Pr., Am-
monio-nitrate d' argent ; Ger., Salpeter-
saures Silberoxydammoniak, or Silber-
oxydammoniak )
Synonym, ammonio-oxide of silver. AgNQj
2NH3. Molecular weight, 204. Solubilities,
very soluble in water and alcohol. It
takes the form of colourless needles, and is
obtained by mixing a solution of ammonia with
a silver nitrate solution and carefully evapora-
ting, but nearly always it is prepared in solu-
tion by adding ammonia to silver nitrate solution
till a clear solution is obtained ; at first, on the
addition of the ammonia, a blackish brown pre-
dpitate of silver oxide is formed, which dissolves
in excess of ammonia to form a dear solution. A
solution thus prepared is used for sensitising
plain paper, and also to form silver bromide in
emulsion making. According to the above
formula, two molecules of ammonia are required
for every molecule of silver nitrate, but it is
possible to obtain a clear solution with only
half the quantity of ammonia by dividing the
silver solution into two equal parts, to the one
adding enough ammonia solution to obtain a
dear solution, and then adding the other half
of the silver nitrate. The solution containing
the lesser quantity of ammonia gives emulsions
freer from fog, but usually of lower sensitiveness.
SILVER AMMONIO-CARBONATE(Pr.,^»w-
monio-carbonate d'argent ; Ger., Kohlen-
saures Silberoxydammoniak)
AgjCOj 4NH3 (ascribed to it by Bder). Mole-
cular weight, 229. Solubilities, soluble in water
and alcohol. It is not found in the solid form,
but always in solution, and is prepared by adding
a solution of ammonium carbonate to a silver
nitrate solution, when a yellow predpitate of
silver carbonate is first formed, which dissolves
in excess of the ammonium carbonate, carbonic
add being evolved. It is occasionally used in
emulsion making, particularly for slow, dean-
working emulsions.
SILVER AMMONIO-CITRATE (Pr., Am-
monia - citrate d'argent ; Ger., Citronen-
saures Silberoxydammoniak)
Solubilities, very soluble in water and alcohol.
It is prepared by adding citric acid to silver
nitrate solution, and then a solution of ammonia ;
a white, curdy predpitate of silver citrate first
forms which is soluble in excess of ammonia. It
is used in preparing slow, clean-working negative
and positive emulsions, and also for printing-
out emulsions.
SILVER BATH (Pr., Bain d'argent; Ger.,
Silberbad)
A solution of silver nitrate used for sensitising
wet collodion plates and albumenised and plain
papers, which is frequently designated " 48-
grain bath," " 60-grain bath," etc., this referring
to the number of grains of silver nitrate dissolved
Silver Bromide
488
Silver Fluoride
in I oz. of water. The following are typical
formulae : —
Silver Bath for Line Work
Silver nitrate . . 300 grs. 69 g.
Distilled water to . 10 oz. 1,000 ccs.
Potass, iodide sol. (8
grs. per oz.) . 7J mins. 1-56 „
Sod. carbonate crystals 15 grs. 3-45 g.
Silver Bath for Half Tones
Silver nitrate . . 350 grs. 80 g.
Other ingredients as above.
Dissolve the silver in one-fourth of the water,
add the iodide solution, and shake till the yellow
precipitate is dissolved, then add the carbonate
and shake well, and then the rest of the water.
Place the bath in a bright light for twenty-four
hours, filter, and add enough dUute nitric acid to
render acid, using methyl orange as an indicator.
Silver Bath for Albumen Paper
The silver bath for albumen paper is usually
made thus ; —
Silver nitrate . .350 grs. 80 g.
Citric acid . . 500 „ 114 ,,
Distilled water to . 10 oz. 1,000 ccs.
SILVER BROMIDE (Pr., Bromure d' argent;
Ger., Bromsilber)
Synonym, bromide of silver. AgBr. Mole-
cular weight, 188. Solubilities, practically in-
soluble in water, alcohol and ether, soluble in
ammonia, potassium cyanide and sodium hypo-
sulphite. It is a yellow amorphous powder, ob-
tained by adding any soluble bromide to silver
nitrate solution. For photographic purposes it is
always prepared in the presence of some vehicle
which holds it in suspension in the form of an
emulsion and prevents it from forming coarse
granules. If, as is usually the case, the bromide
is precipitated in the presence of ammonia, a
much more sensitive salt is obtained, and the
sensitiveness can be increased by digestion in the
warmth for some time or merely by allowing the
emulsion to stand. Under these conditions the
grain of the silver bromide probably increases
in size, and also the light which it absorbs alters
in character. Freshly prepared gelatino-bromide
emulsion is transparent and a deep ruby colour ;
by the action of ammonia or heat it becomes
more opaque, and the light transmitted changes
to orange, and by further ripening to yellow,
green, greenish blue, and blue, these dianges
being accompanied by increases in sensitiveness.
Silver bromide is the most light-sensitive silver
salt, but, unlike silver chloride, does not give rise
to dark-coloured products on prolonged exposure,
except in the presence of some halogen absorber
such as silver nitrate, potassium nitrite, or
metabisulphite. Its spectrum sensitiveness
varies with its method of preparation and degree
of ripening, but practically it may be considered
to extend from the ultra-violet to about F in
the bright blue, with the maximum about PJ G.
SILVER CARBONATE (Pr., Carbonate
d' argent ; Ger., Kohlensaures Silberoxyd)
AgjCOa. Molecular weight, 276. Solubilities,
insoluble in water and alcohol, soluble in potas-
sium cyanide, ammonia, and sodium hypo-
sulphite. It is a yellow granular powder, pre-
pared by adding an alkaline carbonate to silver
nitrate solution. Occasionally it is used in
printing-out and negative emulsions.
SILVER CHLORATE (Pr., Chlorate d' argent ;
Ger., Silberchlorat)
AgGOs. Molecular weight, 191 -5. Solubilities,
I in 20 water, insoluble in alcohol and ether. It
is a white granular powder or minute crystals
obtained by dissolving silver oxide or carbonate
in chloric acid. It cannot be made by adding a
chlorate to silver nitrate. Practically of no
photographic importance.
SILVER CHLORIDE (Pr., Chlorure d' argent;
Ger., Chlorsilber)
Sjmonym, chloride of silver. AgCl. Molecular
weight, 143-5. Solubilities, practically insoluble
in water, alcohol, and ether, soluble in ammonia,
potassium cyanide, and sodium hyposulphite.
It is a white granular powder, obtained by pre-
cipitation from silver nitrate by adding a soluble
chloride. It is used principally for printing-out
emulsions and positive development processes.
Red silver chloride (one of Carey Idea's " photo-
salts") is produced by acting on ordinary silver
chloride with a reducing agent.
SILVER CHROMATE {Tt., Chromated' argent ;
Ger., Silberchromai)
AgjCrO,. Molecular weight, 332. Solu-
bilities, insoluble in water, alcohol, and ether ;
soluble in ammonia and " hypo." It is in the
form of a red amorphous powder, obtained by
adding potassium chromate to silver nitrate
solution. The addition of a very small pro-
portion of this salt to a printing-out emulsion
reduces the gradation, and makes the paper more
suitable for thin, flat negatives.
SILVER CITRATE (Pr., Citrate d' argent; Ger.,
Silbercitrat, Ciironensaures Silberoxyd)
Synonym, citrate of silver. AgCsHsO,.
Molecular weight, 297. Solubilities, insoluble in
water, alcohol and ether, soluble in ammonia,
potassium cyanide and " hypo." It is a curdy,
white powder, obtained by adding an alkaline
citrate to silver nitrate solution ; practically but
little citrate is formed by using citric acid. It
is employed in printing-out emulsions.
SILVER CUTTINGS {See " Residues.")
SILVER CYANIDE (Pr., Cyanure d' argent ;
Ger., Silbercyanid)
AgCN. Molecular weight, 134. Solubilities,
insoluble in water, alcohol, and ether, soluble in
ammonia, potassium cyanide, and " hypo." It
is a white powder, obtained hy adding an alka-
line cyanide to silver nitrate solution ; it is the
blackening agent in Monckhoven's intensifier.
SILVER FLUORIDE (Pr., Fluorure d' argent ;
Ger., Silberfiuorid)
AgP4H20. Molecular weight, 199. Solu-
bilities, very soluble in water and tJcohol. It
takes the form of yellow conglomerate crystals,
obtained by dissolving silver oxide or carbonate
in hydrofluoric acid ; it cannot be made by
adding an alkaline fluoride to silver nitrate.
Silver Image
489
Silver Oxalate
SILVER IMAGE (Fr., Image d' argent ; Ger.,
Silberbild)
A term applied to negatives or positives pro-
duced by the action of light on a silver salt.
SILVER INTENSIFIER
The silver intensifier has the advantage that
the density is under control, and either little or
much intensification can be given. The film
should be hardened in a 10 per cent, solution of
formaline for three minutes and then washed in
water. Wellington's formula ( 1 889) is : —
A. Silver nitrate . 120 grs. 28 g.
Water (distilled) . 2 oz. 200 ccs.
B. Ammonium sulpho-
cyanide . . 240 grs. 56 g.
Water ... 3 oz. 300 ccs.
Add B to A, and keep in a dark place. The bottle
is shaken immediately before use, and some of
the liquid poured into a vessel. A strong
" hypo " solution is then added very slowly till
all but a trace of the precipitate has dissolved.
To each ounce of this solution 3 grs. of a 10 per
cent, stock solution of pyro (preserved with
sodium sulphite) and 4 mins. of liquor ammoniae
are added, and the solution poured upon the
plate and allowed to act until the desired density
is obtained. A few drops more of ammonia may
be added if the action is slow in beginning, but
too much will spoil the bath by precipitating the
silver. The plate is then refixed for ten minutes
in an ordinary " hypo " bath and then well
washed. As the intensifier contains " hypo," a
prolonged washing is not necessary after the first
fixing and previous to intensifying. Many modi-
fications of the above formida have appeared,
but all are much alike in the results they give.
Some workers recommend the rinsing of the
intensified plate in a bath of 6 mins. of hydro-
chloric acid and i oz. of water before re-fiidng,
using an alkaline fixing bath.
For Parmer's silver intensifier, solutions of
I oz. of silver nitrate in 12 oz. of distilled water
and f oz. of potassium bromide in 2 oz. of dis-
tilled water are mixed together, and the pre-
cipitate is removed, washed with water, and
stirred into a solution of 2 oz. of "hypo" in
6 oz. of water. In a few hours' time, filter and
make up to 16 oz. with distilled water. In this
immerse the negative for five minutes, and then
develop with ferrous oxalate or with a pyro-
silver bath, consisting of pyro, 4 grs. ; distilled
water, 2 oz. ; silver solution, 6o^mins. ; and 10 per
cent, solution of '880 ammonia, 30 mins.
Wellington's improved formula (191 1) is given
under the heading " Wellington's Silver Inten-
sifier." For Monckhoven's intensifier, see Under
its own heading.
SILVER IODIDE (Fr., lodure d' argent : Ger.,
lodsilber)
Agl. Molecular weight, 235. Solubilities,
practically insoluble in water, alcohol, and ether,
soluble in potassium cyanide, and " hypo." It
is obtained by adding a soluble iodide to silver
nitrate solution ; when precipitated in the pre-
sence of excess of alkaline iodide it is a pale
yellow powder, whilst with excess of silver nitrate
it is a deep orange, curdy precipitate ; the latter
darkens in light, whilst the former undergoes no
visible change. It is but very slightly soluble
in strong ammonia, i in 2,500 parts, but it is
readily soluble in potassium iodide solution,
forming a double salt AglKI, or Agl2KI,
both of which are decomposed by the addition
of water, depositing pale yellow powdery silver
iodide. It is also soluble in silver nitrate solu-
tion, forming the double salt 2AgN0,AgI,
which is more soluble in cold than in hot
solutions. A 10 per cent, solution of the nitrate
dissolves -053 per cent. Agl, an 8 per cent, solu-
tion -077 per cent., and alcoholic and ethereal
solutions dissolve more. The negative silver
bath for sensitising wet collodion plates should
always be saturated with silver iodide before use,
otherwise the iodide will be dissolved from the
film.
Silver iodide is chiefly employed for the wet-
plate process, and as an addition to gelatino-
bromide emulsions, in which it acts as a restrainer
of fog during digestion and produces greater
sensitiveness. It is usually mixed with the
alkaline bromide, and it is supposed to form a
double salt generally known as bromo-iodide of
silver, and this is confirmed by the fact that such
an emulsion only shows one maximum of sensi-
tiveness in the spectrum, whereas the two salts
separately emulsified and then mixed show two
distinct maxima.
SILVER LACTATE (Fr., Lactate d' argent;
Ger., Silberlactat, Milchsaures Silber)
AgCaHjO, HjO. Molecular weight, 215. It
is in the form of white crystals or powder,
obtained by dissolving silver carbonate in lactic
add. It is very rarely used, and then in printing-
out emulsions.
SILVER METER {See " Argentometer.")
SILVER NITRATE (Fr., Azotate d' argent ;
Ger., Silbernitrat, Salpetersaures Silber)
AgNOj. Molecular weight, 170. Solubilities,
I in I water, i in 26 alcohol, i in 5 boiling alcohol.
It is in the form of colourless rhombic plates, and
is obtained by direct solution of silver in nitric
acid or by dissolving the oxide or carbonate. It
is not in itself sensitive to light, but is readily
reduced to the metallic state in the presence of
organic matter, such as gelatine, paper, or the
skin. It is the salt from which are formed all
sensitive materials in photography in which
silver is used.
In process work, silver m'trate is sometimes
used for etching baths for steel, and the follow-
ing formula is recommended : — Alcohol 6 parts,
distilled water 6 parts, pure nitric acid i6-6 parts,
silver nitrate -83 part.
SILVER NITRITE (Fr., Azotite d^ argent ;
Ger., Salpetrigsaures Silber)
AgNOj. Molecular weight, 154. Solubilities,
I in 300 water. It is a crystalline white powder,
obtained by precipitation from silver nitrate by
an alkaline nitrite, and is of no photographic
importance.
SILVER OXALATE (Fr., Oxalate d' argent ;
Ger., Silberoxalat, Oxalsaures Silber)
AgjCjO,. Molecular weight, 304. Solubilities,
practicsJly insoluble in water and alcohol.
Silver Oxide
490
Silver Salts
soluble in nitric acid. It is a white crystalline
powder, obtained by adding an alkaline oxalate
to silver nitrate. It has been suggested for print-
ing-out emulsions, but is rarely used.
SILVER OXIDE (Pr., Oxyde d' argent: Ger.,
Silheroxyd)
AgjO. Molecular weight, 232. Solubilities,
practically insoluble in water, alcohol, and ether.
It is a heavy, brownish-black powder, obtained
by precipitation from silver nitrate by a caustic
alkali, and is practically of no importance
photographically.
SILVER PHOSPHATE (Pr., Phosphate
d'argent ; Ger., Silberphosphat)
Synonym, normal silver orthophosphate.
AgaPO^. Molecular weight, 419. Solubilities,
insoluble in water, alcohol, and ether, soluble
in organic acids, ammonia, potassium cyanide,
and " hypo." It is used for printing-out emul-
sions, and gives an extremely long scale of grada-
tion— that is, very soft flat prints from strong
negatives. It occurs as a heavy yellow powder
and can be prepared by adding phosphoric acid to
silver nitrate or by using ordinary sodium phos-
phate (Naj HPO4) ; the reaction that takes place is
3AgNOs -I- Na^HPOi = AgaPOj H- 2NaN03 -t-
HNO5. The resulting liquid contains free nitric
acid, which dissolves some of the silver phos-
phate.
SILVER POISONING
AH silver salts are more or less poisonous
when taken internally, and the antidotes are
table-salt or any soluble chloride followed by
emetics and mucilaginous drinks, or white of
egg and milk, and the use of the stomach pump.
SILVER PRINTS
A generic term, including all prints of which
the image is metallic silver, such as plain or
salted paper, coUodio-chloride, gelatino-chloride,
bromide and gaslight and kalUtype prints.
SILVER PROCESSES
AU processes or methods in which silver is
used.
SILVER RESIDUES (See " Residues.")
SILVER SALTS
A description of the individual silver salts Is
given under their respective headings. Prac-
tically all the silver ssdts are sensitive to light
either per se or in contact with organic matter.
Marktajtiner Tumeretscher compUed the follow-
ing table, which gives an extremely useful out-
line of the sensitiveness of the various salts and
the intensity of the printed-out image. He used
a Vogel photometer, exposed the paper for an
equal time, took the last visible number as the
speed, silver chloride on paper being set as 100.
SILVER
SALTS : TURNERETSCHER'S
TABLE OF SENSITIVENESSES
ETC.
I. — ^WiTH Excess of Silver
II.— With Excess of Salt
Name and
chemical formula
A.~Without
ammonia juming
■B.—With
ammonia fuming
A.— Without
ammonia fuming
B.—With
ammonia fuming
Remarks
(sohtbility)
^8
Colour
and intensity
of
the same
1
Colour
and intensity
of
the same
^1
II
Colour
and intensity
of
the same
s 1
1^
Colour
and intensity
of
the same
1. Silver chloride,
AgCl
(insoluble)
100
Blue black;
very intense
roo
Blue black;
more intense
than without
fuming
80
Violet ; very
intense
200
Violet ; very
intense
Although very in-
tense with ex-
cess of salt, yet
less than with
excess of silver
2. Silver bromide,
AgBr
(insoluble)
700
Bluish grey ;
not intense
900
Bluish grey ;
not intense
250
Bluish grey ;
not intense
300
Bluish grey ;
not intense
Scarcely more in-
tense with than
without ammo-
nia fuming
3. Silver iodide,
Agl
(insoluble)
300
Greenish grey ;
not intense
450
Reddish grey ;
not intense
40
Yellowish grey;
not intense
75
Yellowish grey;
not intense
Fuming scarcely
increases the in-
traisity
4. Silver chloride
freed from ex-
cess of silver
by washing be-
fore exposure
95
Slightly red-
dish violet ;
very intense
100
Slightly red-
dish violet ;
very intense
Less intense than
normal paper ;
scarcely more
intense with
5. Silver chloride,
w^hed as in 4,
then floated on
a solution of
potass, nitrite
80
Near the nor-
mal paper in
intensity
130
Equal to the
normal paper
Prepared accord-
ing to Abney's
process
6. Silver chloride,
washed as in
4, then floated
on sodium sul-
phite solution
100
Violet ; very
intense
100
Violet ; very
intense
Does not quite
equal the in-
tensity of the
normal paper,
but much more
intense than
washed paper.
491
SILVER SALTS: TURNERETSCHER'S TABLE OF SENSITIVENESSES, ETC,
— continued
I.— With Excess of Silver
II.— With Excess or Salt
Name and
chemical formula .
(solubUHy)
K.—WiOumt
ammonia fuming
ammonia fuming
fi..— Without
ammonia fuming
B.—With
ammonia fuming
Remarks
1!
CoUmt
and intensity
of
the same
II
Colour
and intensity
of
the same
Colour
and intensity
of
the same
Colour
and intensity
, °^
the same
7. Silver nitrate,
AgNOa (on
paper)
6
Reddish ; not
intense
8
Reddish ; not
intense
Silver nitrate
does not darken
alone, only in
the presence of
organic matter
8. Silver albumin-
ate witliout
silver nitrate
13
Red; sUghtly
intense
30
Bluish ; slight-
ly intense
Prepared by float-
ing paper on
whipped albu-
men, then on
AgNOa
9. Silver chloride al-
bumen paper,
freshly sensi-
tised
50
Purple brown ;
vary intense
60
Purple brown ;
very intense
So-called " Rosa-
brilliant " paper
was used
lo. Preserved com-
mercial silver
chloride albu-
men paper
70
Purple brown ;
wery intense
80
Purple brown ;
very intense
zr, Gelatino-bromide
dry plate
600
Greenish grey ;
not intense
12. Silver formate,
H— COOAg
The sensitised
paper darkened
even in an abso-
lutely dark
room
13. Silver acetate,
CH3— COOAg
(1 : 97)
6
Yellowish grey
slightly in-
tense
20
Reddish grey;
tolerably in-
tense
4
Yellowish grey;
not intense
15
Reddish grey;
slightly in-
tense
14. Silver propion-
ate,
CHs— CHjf-COOAg
(1 : 119)
6
Red brown;
slightly in-
tense
10
Yellow brown;
slightly in-
tense
7
Red brown ;
slightly in-
15
Yellow brown ;
slightly in-
tense
15. Normal silver
butyrate,
CHs(CH2)2COOAg
(I : 200)
8
Reddish yel-
low; moder-
ately intense
22
Red brown ;
mod er ate ly
intense
10
Reddish grey ;
mod er ate ly
intense
20
Grey brown ;
mod er ate ly
intense
Colour more in-
tense than with
the isobutyrate
16. Silver isobutyr-
ate,
<CH3)2— CH— COOAf
(r : 108)
7
Yellowish red ;
not intense
18
Brownish ;
sUghtly in-
tense
6
Reddish
b r 0 sv n ;
slightly in-
tense
18
Red brown ;
slightly in-
tense
Colour somewhat
less intense than
with the normal
salt
17. Silver valerianate
(CHa^HCH^
(r : 540)
8
Violet brown ;
mod er ate ly
intense
14
Reddish grey ;
tolerably
intense
14
Reddish grey ;
mod er ate ly
intense
30
Grey brown ;
mod er ate ly
intense
18. Silver caproate,
{CHshCmcrfda-
(soluble with great
dieaculty)
9
Grey ; moder-
ately intense
15
Grey ; moder-
ately intense
14
Reddish brown
tolerably
intense
24
Grey; moder-
ately intense
19. Silver heptylate,
CH3(CH2) .COOAg
(soluble with
difficulty)
10
Brownish vio-
let ; tolerablj
intense
14
Grey violet ;
tolerably
intense
14
Brown violet ;
tolerably
intense
16
Grey brown ;
intense
20. Silver octylate,
CH3(CHa).COOAg
(scarcely soluble)
12
Grey; slightly
intense
5
Grey ; not in-
tense
17
Reddish
brown ; tol-
erably intensf
6
Grey brown ;
slightly in-
tense
SI. Silver pelargon-
ate,
CHs(CH3)7COOAg
(insoluble in cold
water)
25
First red, then
grey ; toler-
ably intense
30
Grey ; tolerablj
ably intense
20
First red, then
grey ; toler-
ably intense
25
Brown ; toler-
ably intense
492
SILVER SALTS : TURNERETSCHER'S TABLE OF SENSITIVENESSES. ETC.
— continued
I.— With Excess of Silver
II.— With Excess of Salt
Name and
chemical formula
A— Without
ammonia fuming
B.—wm
ammonia fuming
A.— Without
ammonia fuming
B.—With
ammonia fuming
Remarks
(solubthly)
ss
Colour
and intensity
of
the same
if
It
Colour
and intensity
of
the satne
if
II
Colour
and intensity
of
the same
£ ■
1^
Colour
and intensity
of
the same
22. Silver caproate.
CHs(CH2)8COOAg
(insoluble)
5
Brown violet ;
slightly in-
tense
6
Reddish grey ;
not intense
14
Reddish
brown ; toler-
ably intense
18
Reddish grey;
tolerably in-
tense
The paper re-
mained white
for several weeks
when kept in the
dark
23. Silver palmitate,
CH3(CH2)„COOAg
(insoluble)
5
Yellowish ; not
intense
6
Yellowish grey;
not intense
3
Yellowish ; not
intense
8
Yellowish grey;
not intense
The salt solu-
tion was used
•^ normal
24, Silver stearate,
CH3{CH2)i6COOAg
(insoluble)
U
Grey ; not in-
tense
22
Grey ; not in-
tense
In one whole day*s
exposure the
paper turns vel-
vet brown ; so-
lution of the
salt i normal
25. Silver cerotate,
CH3(CH2)25COOAg
(insoluble)
z
Yellowish grey,
slightly in-
tense
5
Yellowish;
slightly in-
tense
2
Yellowish ; not
intense
5
Yellowish ; not
intense
The salt solution
was used -^^
normal
26. Silver oleate,
CisHasCOOAg
10
Reddish grey;
slightly in-
tense
zz
Greenish grey ;
slightly in-
tense
9
Reddish grey :
slightly in-
tense
6
Grey; slightly
intense
The salt solution
was used i nor-
mal
27. Silver glycollate.
CH20H.COOAg
(soluble with
difficulty)
6
Yellow red ;
tolerably in-
tense
IZ
Brownish;
slightly in-
tense
4
Yellowish grey ;
not intense
7
Brownish ; not
intense
28. Silver lactate,
CHsCHOHCOOAg
(I : 20)
8
Yellowish red ;
tolerably in-
tense
z6
Yellow red ;
tolerably in-
tense
17
Rusty yellow ;
tolerably in-
tense
18
Grey ; toler-
ably intense
On account of the
insolubility of
the salt alcohol
was used to pre-
pare the paper
2^. Silver paralac-
tate,
CHsCHOHCOOAg
7
Yellowish Kd ;
tolerably in-
tense
17
Yellow red ;
tolerably in-
tense
17
Rusty yellow
to brown;
tolerably in-
tense
17
Grey brown ;
tolerably in-
tense
The paper pre-
pared with ex-
cess of salt was
rather more in-
tense than with
excess of silver
30. Silver oxalate,
COOAg— COOAg
(insoluble)
2
Reddish ; not
intense
80
Red brown ;
very intense
20
Dark brown ;
intense
70
Dark brown ;
very intense
31. Silver malonate,
CH20H(COOAg)2
(soluble with
difficulty)
+
Reddish grey ;
slightly in-
tense
8
Grey ; toler-
ably in-
tense
5
Reddish yel-
low : slightly
intense
13
Jeddish brown ;
tolerably in-
tense
32. Silver malate,
CjHsOHfCOOAg)^
(soluble in hot water)
2
Red brown ;
slightly in-
tense
z8
Grey brown ;
intense
7
Red brown ;
intense
13
Red brown ;
very intense
33. Silver tartrate,
(CHOH>2(COOAg)2
(soluble with
difficulty)
7
Red brown ;
intense
X7
Red brown ;
intense
6
Reddish brown;
tolerably in-
tense
24
Red brown ;
very intense
34. Silver citrate,
CsHBOyAg
(soluble in boiling
water)
15
Grey brown ;
mod er ate ly
intense
18
Red brown ;
intense
6
Brown ; moder-
ately intense
12
Grey brown ;
intense
35. Silver hippurate,
f.„ ^ NHC7H5O
■^"2 < COOAg
13
Rusty brown;
tolerably in-
tense
24
Grey brown ;
tolerably in-
tense
z6
Eusty brown;
tolerably In-
tense
50
Grey brown ;
tolerably in-
tense
Silver Stains
493
Silverware, Photographing
SILVER STAINS
Dark brown or red stains wluch appear on
negatives during or after printing upon P.O. P.
or other paper containing soluble silver salts,
either the paper or the negative being damp.
To prevent them the negative should be var-
nished. To remove them, imm.erse the negative
in a solution of 20 grs. of potassium iodide in
I oz. of water for ten minutes, rinse thoroughly,
and transfer to a solution of 30 grs. of potassium
cyanide. Dab the stains with a tuft of cotton-
wool soaked in the solution until they disappear,
when the negative should be rinsed thoroughly
and dried. (See also " Stains, Removing.")
SILVER SUBBROMIDE, SUBCHLORIDE.
ETC. {See "Silver Subhaloids.")
SILVER SUBHALOIDS
Chemists have usually considered that the
action of light upon the silver haloids was the
splitting off of a molecule of the halogen and the
formation of a salt with consequent lower pro-
portion of halogen, which may be represented by
the formula, 2Aga = AgjCl -f a or 4Aga =
AgjCl, + Clg. They named the new compounds
subhaloids. For many years the existence of such
subsalts was denied, because the actual existence
of silver suboxide could not be definitely proved.
In 1 89 1 Guntz was able to prepare the sub-
fluoride AgjF or AgiFj by heatmg silver fluoride
AgF in a sealed tube at a temperature not
above 194° P. with finely divided silver and also
by electrolysis of a saturated solution of silver
fluoride, using silver electrodes. By treatment
of this salt, a yellow crystalline powder, with
steam he was able to prepare the suboxide
AgjO, and Weltzien prepared a silver hydroxide
Ag4(OH)j by treating it with hydrogen peroxide.
Prom the subfluoride Guntz also prepared the
subchloride by passing dry hydrochloric add gas
over it, or by treating it with the volatile chlor-
ides of carbon, siUcon, and phosphorus, etc. The
subchloride varies in colour from deep violet red
to violet black, and when heated it spUts up into
ordinary silver chloride and metallic silver
potassium cyanide; and sodium hyposulphite
produces a similar reaction with the solution of
the chloride. Silver subiodide was also prepared
by Guntz by the action of hydrogen iodide. The
actual formation of these subhaloids is a strong
argument in favour of the subhaloid theory of
the latent image {which see). The subbromide
may be prepared in the same way as the sub-
chloride, or by treating the subfluoride with
phosphorus tribromide (Heyer). Liippo-Cramer
claims to have prepared a subbromide, AgiBr,, by
treating mercurous bromide with silver nitrate.
SILVER SULPHATE (Fr., Sulfate d' argent :
Ger., Silbersulfat, Schwefelsaures Silber-
oxyd)
■A-gaS04. Molecular weight, 312. Solubility,
•58 in 100 water. White crystals obtained by
mixing concentrated solutions of silver nitrate
and sodium sulphate.
SILVER SULPHIDE (Pr. Sulfure d' argent ;
Ger., Silbersulfid)
AgjS. Molecular weight, 248. Solubilities,,
insoluble in water and alcohol. It is a brownish-
black powder, and is obtained by mixing an
alkaline sulphide with silver nitrate solution. It
is also obtained when liver of sulphur is added
to spent fixing baths, and is supposed to form
the brown or sepia image in sulphide toned
bromides.
SILVER SULPHOCYANIDE (Pr., Sulfocyan-
ure d' argent ; Ger., Silber^hodanat)
AgCNS. Molecular weight, 166. Solubilities,
very soluble in water. Yellowish white crystals
obtained by adding silver nitrate to an alkaline
sulphocyanide. It is of no photographic import-
ance.
SILVER TARTRATE C^., Tartrate d' argent ;
Ger., Silbertartrat, Weinsteinsaures Silber)
AgjC^HjO,. Molecular weight, 364. Solu-
biUties, sUghtly soluble in water. It is a fine,
white powder, obtained by adding silver nitrate
to an alkaline tartrate. It is used in printing-
out emulsions.
SILVER TESTER {See " Argentometer.")
SILVER WASHINGS {See " Residues.")
SILVERLINE PROCESS
A French process of line engraving. A zinc
plate was coated with an etching ground, a
drawing scratched through with a needle point,
and the lines etched deeply. The resist was
then cleaned off, and the lines filled in with soft
solder consisting of a mixture of bismuth, tin,
and lead. The solder was melted by heating
the plate with buttons of solder on it, and rub-
bing the molten solder in the lines with a rag.
The surface was polished and the plate again
etched in nitric acid, which attacked the zinc
without touching the solder, and thus the lines
were left in reUef .
SILVERWARE. PHOTOGRAPHING
The task of rendering silver as silver is a
difficult one, and the secret of success lies in the
lighting and the use of backed plates. The
operator should remember that the angle of
reflection is always equal to the angle of inci-
dence ; thus, at whatever angle the light falls
on a reflective surface, it is reflected back at the
same angle. It wiU therefore be obvious that,
if the silver object be illuminated by a strong
front hght, the reflections will come back into
the lens. The most suitable angle at which the
strongest light should reach the bright objects
is one of about 45° ; then the reflections will
be well away from the directioti of the camera.
The shadow sides will be rather dark as com-
pared with the bright high lights, but this will
be modified by using a reflector, which may be
a sheet of white cardboard.
If the silver objects can be treated to prevent
reflections, the task of getting a satisfactory
photograph of them becomes easy. Many
methods have been advocated for dulling the
surfaces. One of the best is to hold the silver
over a piece of burning magnesium ribbon, the
white smoke from which will deposit upon the
silver ; the magnesium can easily be removed.
A method frequently adopted is to dab the sur-
faces with putty, but t\as is rather messy and
Similigravure
494
Sizes of Plates and Papers
troublesome to clean ofi. A better plan is to
place a piece of ice in each vessel ; this causes
the metal to cool rapidly, and if there is
moisture in the atmosphere, as upon a wet or
damp day, dew will soon deposit upon it ; in
exceptionally dry weather the cold metal could
be sprayed, using water in an ordinary scent
sprayer, or could be steamed.
Any lettering on the articles can be brought
out by arranging the light and the reflector,
or the lettering may be filled up with black
printers' ink, which can be quickly cleaned out
with benzole or turpentine after the negative
has been made.
Exposures should be full in order to soften the
contrasts, as under-exposure would mean brighter
and glaring high lights and black shadows. The
developer used— say, metol or rodinal — should
bring out the details in the shadows before the
high lights become too strong.
SIMILIGRAVURE
A French name for the half-tone process.
SIMPSONTYPE
A printing process — the coUodio-chloride —
discovered by George Wharton Simpson, in
which silver chloride contained ia collodion was
employed (published 1864). The original formula
was : A. Silver nitrate f oz. and distilled water
f oz. ; warm gently vmtil dissolved, and add
5 oz. of alcohol. B. Calcium chloride, 160 grs. ;
absolute alcohol, 5 oz. C. Citric acid 160 grs.,
absolute alcohol 5 oz. Take 40 oz. of plain
collodion of medium density and add to it
solution A, a little at a time, with considerable
shaking. This may be done in daylight, but the
following operations must be carried out in the
dark-room or by weak artificial light. Next add
B and C in the manner described for A. The
emulsion is applied to glass, opal or paper.
G. W. Simpson was for many years editor of the
Photographic News ; he died in i88o.
SINGLE LENS
The so-called landscape lens ; an achromatic
meniscus, composed of flint and crown glass.
When cameras are listed with " achromatic "
lens, a single lens is usually meant, not a rapid
rectilinear.
SINGLE TRANSFER
The method of working the carbon process by
transferring the film from the paper on which
it is printed to a second paper which forms its
final support.
SINKS {See "Developing Bench or Sink.")
SINOP PROCESS
A simplified method of collotype printing, in-
vented by Pousin, of Rheims. Plates are sold
ready coated with an emulsion, which is believed
to be gelatine containing a merourous salt. These
plates, which keep indefinitely, are sensitised by
bathing in a potassium bichromate solution.
They are dried and exposed under a negative,
then washed to remove the unaltered bichromate,
soaked in glycerine, the surplus moisture re-
moved, and the plate inked up with a gelatine
roller and greasy ink. Impressions on paper are
then pulled off in an ordinary letter-copying
press.
{See " Proportional Scales and
SIZEOMETER
Rules.")
SIZES OF PLATES AND PAPERS
The accompanying tables give the sizes and
diagonals of British and Continental plates
and of films, and sizes of drawing papers and
of mounts. It should be remembered thai
Continental dark-slides are to the sizes given,
the plates being made from i to i-J-mm. smaHei
so as to fit. In Great Britain plates are made
to the sizes stated, and there is an allowance in
the dark-sUde.
The diagonals of plates are often referred to
when condensers for enlarging are being con-
sidered, as a suitable condenser should have a
diameter equal to the diagonal of the plate.
Thus, a half -plate negative needs a condenser at
least 8 in. in diameter, in order to cover the
corners of the negative.
BRITISH PLATES
CONTINENTAI, PLATES
■BUMS
Dimensions
Diagonals
Dimensions
Diagonals
Dimgnsions
Diagonals
In.
Cm.
In.
Cm.
In.
Cm.
In.
Cm.
In.
Cm.
Jn.
Cm.
3i X 2i
8-9 X 6-3
4i
10-9
1-5 X 1-5
4 X 4
2-25
5-7
2 X li
5 X 3-8
2i
6-3
3i X 3i
8-3 X 8-3
4S
II-7
1-77 X 2-36
4iX 6
2'9
7-5
2i X li
5-7 X 3-8
2i
6-Q
(Lantern plate)
2-56 X 3-5
6i X 8-9
4-6
ii*i
2i X 2i
5-7 X 5-7
3i
8-1
4i X 3i
(Quarter-plate)
10-8 X 8-3
51
IO-6
3-54 X 4-7
9 X 12
5-9
14-9
2iX I
6-3 X 4-2
3
6-9
3-54 X 7-o8
9 X 18
7-9
20-0
2iX 3i
5-7 X 8-3
3H
10*0
5, X 4
12-8 X lo-l
^1
r6*2
4-3 X 5-90
II X 15
7-3
i8-6
4iX2
10-8 X 6-3
4H
22-5
5i X 3J
14-0 X 8-9
6i
i6-6
4-7 X 6-29
12 X 16
7-9
20-1
3iX 3
8-9 X 8-9
5
12-6
(Post card)
4-7 X 7-87
12 X 20
9*2
23'3
4i X 3i
10-8 X 8-3
5l
10-6
6i X 4i
l6-5 X 10-7
7i
r9-6
5-1 X 7-o8
13 X 18
8-7
22-1
5iX3i
14-0 X 8-3
6i
l6-2
(Double
5-9 X 8-26
15 X 21
10-2
26
5 X4
12-8 X lOT
6
l6-2
quarter)
7-o8 X 9-45
18 X 24
II-9
30-1
6iX4i
l6-5 X 10-7
7
19-6
8-26 X 10-63
21 X 27
13-5
34-2
7 X 5
17-8 X 12-7
8
21-9
6i X 4i
I6-S X 12-0
8,V
20-4
9-45 X II-8
24 X 30
15-3
39
six 2i
8-3 X 5-7
3 *
10
(Half-plate)
3iX4i
8-9 X 1-77
5
14-6
6i X 3i
ITS. X 8-2
7i
19-0
9 X 34
22-8 X 8-9
9
24-5
(Stereoscopic)
and six larger sizes, 24 X 36
cm..
7X5
17-8 X 12-7
8f
21-9
27 X 33 cm., 30 X 40 cm., 36
X 48
8i X 6i
21-6 X l6-5
loH
27-1
cm., 40 X 50 cm,, and 50 X 60
cm.
tWhole-plate)
10 X 8
25-3 X 20-3
t2j
32-7
and larger
Sizing
49S
Sketch Effects
Sensitised Papers
Sensitive papers may be had cut up to almost
any size, from about 2^ by ij in. to 21 by 25 in.,
rectangular, square, or circular. The full sizes
of complete sheets vary somewhat, but the fol-
lowing may be taken as the average : —
Bromide and gaslight paper. — Rolls, 10 and
25 ft. long ; IS, 20, 22, 25, 30, and 40 in. wide.
P.O.P.— Sheets, 24^ by 17 in. Rolls, 25 ft.
long and 12 and 25 in. wide.
Platinotype. — Sheets, 26 by 20 in.
Carbon. — In " bands "12 ft. long, 30 in. wide.
Ferro-prussiate. — Rolls, 32 ft. long, 30 and
40 in. wide.
Drawing Papers
Demy
Royal
Cartridge .
Double crown
Imperial .
Double demy
Double elephant
Antiquarian
22
X
17 in.
2-)
X
20 ..
2b
X
21 M
30
X
20 „
10
X
22 „
35
X
22 „
40
X
27 „
53
X
31 ..
In.
Cm.
Brttish Mounts —
Midget
lA X 2
3-3 X 5-7
C. de V
2x4
6
^ X lo-"^
Cabinet
...
6i X 4i
l6-5 X 10-8
/
6J X 10
17-3 X 2'i-4
Imperial
i
and
and
1.
7J X 9f
20
X 25-1
Promenade
...
8i X 4
21
X IO-I6
Boudoir
8i X 5i
21-
5 X 14
/
I
13 X 7i
33-0 X 19
Panel
and
and
8i X 4
21
X 10-16
Stereoscopic
...
7 X 3i
17-7 X 8-9
Royal
...
loi X 5i
27
X I'!
Large Panel
...
roi X 17
26-7 X 43-1
Grand Panel
23 X I3i
58-
4 X 34-9
Victoria Midget ...
2f X li
6
X 3-8
Cabinet Midget ...
211 X li
6-8 X 4-4
Promenade Midget
3 X It
7-9 X 4-1
Boudoir Midget ...
3i X 2
8-6 X 5-08
Panel Midget ...
4i X li
10-
5X 4-4
Continental Modsts—
Carte Mignonnette
If X 2-3
3-5 X 6
Carte de Visite ...
2i X 4i
6-
3 X 10-5
Carte Malvern ...
3-1 X 6i
8
X 16-5
Carte Victoria ...
3-1 X 5
8
X 12-6
Carte Album
4-3 X 6i
II
X 16-5
Carte Cabinet ...
4-7 X 6-2
12
X 16
Carte Promenade
3-9 X 4-7
10
X 12
Carte Paris Portrait
5i X 8-66
13-3 X 22
i
3-5 X 4-7
9
X 12
Carte Amateur ...
{
5-1 1 X 7-o8
5-9 X 8-26
13
15
X 18
X 21
I
7-o8 X 9-4
18
X 24
Carte Artiste ...
7-8 X IO-2
20
X 26
Carte American ...
...
7-4 X 12-9
19
X 33
Carte Family
9-05 X II-4
8-2 X 13-3
23
22
X 29
X 34
Carte Excelsior ...
10-2 X 12-5
9-8 X 14-9
26
25
X32
X38
Carte Panel
11-02 X 14-9
28
X38
11-02 X 17-7
28
X 45
Carte Royal
14-9 X l8-8
14-9 X 21-6
38
38
X 48
X 55
Carte Portrait-Nature
18-8 X 22-8
18-8 X 23-6
48
48
X58
X 60
SIZING
Raw papers generally need to be sized before
sensitising, because the size fills up the pores and
keeps the image on the surface ; in some cases,
also, it increases the sensitiveness. As a general
rule, sizing improves any raw paper. The sizes
most used are arrowroot and gelatine, and the
paper can be floated on one of these or brushed
100 grs.
25 g-
20 „
5„
10 oz.
1,000 CCS
50 grs.
25 g.
10 oz.
1,000 CCS
15 grs.
7-5 g.
2 oz.
220 CCS.
over with the substance. In the case of gelatine
the paper may be wholly immersed.
A rrowroot. — Of the many formulae known, that
due to Duchochois is as follows : —
Arrowroot
Glucose .
Water .
Mix the arrpwroot and glucose with a little cold
water, add the remainder hot, and boil up the
whole in a porcelain dish. Cool, skim and strain
through muslin before use. The above is suit-
able for the iron printing processes, namely, blue
print, kallitype, etc. Other formulae are given
under separate headings.
Gelatine. — The following is suitable for print
ing with iron salts : —
Hard gelatine
Water .
Alum
Alcohol (pure)
Soak the gelatine in about 9 oz. of the water for
about an hour, heat until dissolved, dissolve the
alum in the remaining water, add to the gelatine,
and lastly the alcohol. After coating, dry for
three minutes and coat again. For plain silver
paper, dissolve 5 grs. of gelatine in 10 oz. of
water, by aid of heat, and then dissolve therein
60 grs. of ammonium chloride. Immerse twice
as above.
Gum Arabic. — For iron papers, prepare a weak
solution of gum arable (5 or 6 grs. to the oz. of
water), and brush over the paper.
Resin, Iceland moss, and agar-agar are also
used.
SKETCH EFFECTS
A term applied to pictures in which a part is
photographic, and the remainder hand-work with
pendl, crayon, etc. The usual plan is to work
up the picture and then to copy and print dupli-
cates. Sometimes the sketch efiects are obtained
by using platinotype or bromide paper, and
developing only that part of the image desired
by brushing on a developer mixed with glycerine.
The usual plan is to make a print upon rough
bromide paper, and to brush over any parts that
are to be reduced with a " hypo "-ferricyanide
or other reducer. The work calls for great care,
and the print must be frequently rinsed in water
and finally washed. It may be found easier to
have the print half dry when brushing the
reducer round delicate outlines, as the face, for
example ; but the methods employed depend
upon the worker's skill. When portraits are
taken specially for sketch effects a white back-
ground should be used. Sketch effects needing
no pencil work are largely produced on platino-
type paper owing to the facility with which such
prints can be developed in parts with the ordinary
platinotype developer mixed with glycerine, but
bromide prints may, of course, be developed in
a similar way. The objection to bromide paper
for direct sketch effects by development is that
the image is not faintly visible after printing, as
it is upon platinum paper ; but any part of the
image may be reduced at a later stage.
The " hypo "-ferricyanide reducer is rather
apt to stain, and the following will be found to-
be more serviceable : —
Skiagram
496
Snapshots
A
Iodine, resublimed
i oz.
55 g-
Potassium iodide
I „
IIO„
Water
4 „
400 CCS
B
Potassium cyanide
I oz.
nog.
Water
4 >,
400 CCS
Two-tMrds fill a saucer with water, add a few
drops of the A solution until the water is of a
deep sherry colour, and then add just enough
of the B solution to decolorise. Apply this with
a tuft of cotton-wool, the work being done near
to running water so that the reducer may be
washed off quickly ; the reducer leaves the paper
white if allowed to act long enough. Reducers
cannot be used for platinotype paper.
SKIAGRAM
A radiograph, or X-ray photograph.
SKIAGRAPHY
Radiography, or X-ray photography.
SKIN, EFFECTS OF CHEMICALS UPON
A few photographic chemicals in common use
have a harmful effect upon the skin, as explained
under separate headings. {See, for example,
" Bichromate Disease," " Hygiene in Photo-
graphy," " Metol," " Poisons and their Anti-
dotes," etc.)
SKY NEGATIVES (Se^ " Ooud Negatives.")
SKY. PRINTING IN (See " Clouds, Printing
in.")
SKY SHADE
Commonly a hinged flap attached to the top
of the lens hood, and used to screen the lens
from the too bright light of the sky, and from
the sun if present. It permits of the sky portion
of the negative being so shaded that both fore-
ground and sky are correctly exposed on the
same negative.
SKY SHUTTER
This has the same purpose as the foreground
shutter {which see).
SLIDE CARRIER
A bag or case to carry the dark-sUdes. Usually
it is of leather lined with velvet or baize and
fastening with straps or by a lock and key.
Loose lined partitions are often provided to
prevent the slides rubbing against each other.
Sometimes there is also a pocket for the lens
or lenses. Generally, however, both slides and
lenj are carried in the same bag as the camera.
Also a name given to the plate carrier.
SLIDE, DARK- {See " Dark-sUde.")
SLIDE, LANTERN {See " Lantern SUdes.")
SLIDE RULE, PHOTOGRAPHIC (Pr., mgle
mobile photographique , Ger., Photograpk-
isches Rechen-lineal)
An instrument invented by A. Lockett, and
shown at the Royal Photographic Society's
Exhibition of 1909. It consists of a graduated
right angle with a pivoted rule that may be
made to move diagonally over it. By its use
many photographic and optical calculations are
quickly and automatically carried out, as, for
instance, ascertaining measurements of objects
from photographs ; finding the conjugate foci
for enlarging, copying, or reducing with a given
lens ; determining the length of studio necessary
for portraiture with a stated objective; dis-
covering the focal length obtained by combining
two lenses, etc.
SLIP-IN MOUNTS
A mount composed of two boards, the upper
having a cut-out opening, fastened together by
the edges on three sides, while the fourth side
is open to admit of a print being slipped in and
adjusted in position behind the opening. This
kind of mount is suitable only for glazed prints,
or such as will lie quite flat. As no mountant
is required, the gloss of the surface of a glazed
print is imaffected. The mounts are mad.e in
standard sizes, and do not, therefore, admit of
any trimming down of the print. As it is possible
for the print to shift in the mount, it is well,
when it is properly adjusted, to apply a ^ touch
of adhesive to two points on one edge of the
print, and rub it down so that it adheres
to the back board. This may be done by means
of a knife slipped in at the opening through
which the print was passed.
SMOKE BOX
A form of flash lamp for burning magnesium
ribbon, and recommended by B. Seymour. The
bottom of a box is replaced with a sheet of glass
covered with white tissue-paper ; this, in use,
is the front of the box, as illustrated. The lid
is lunged, as shown. Holes are cut at the base
Smoke Box
for ventilation, and the inner side of the top of the
box is lined with tinplate and fitted with a hook
or other device for holding the ribbon. The lid
or door is closed immediately the ribbon is
lighted, and the smoke box held in the hand
and moved about as desired. Afterwards, the
box can be taken out of doors and the smoke
allowed to escape.
SNAPSHOTS
A common term designating so-called " instan-
taneous " exposures made with a camera held in
the hand. Unfortunately, it suggests a random
and unconsidered operation into which a large
element of chance enters ; whereas the mere
fact that the actual exposure given was a short
one does not imply that no thought, study, or
observation was devoted to the subject. More-
over, the possibility of taking " snapshots " has
Snow and Frost Photography 497 Snow and Frost Photography
aSorded the keeu-eyed photographer number-
less opportunities of recordii;g transient effects
and arrangements which would otherwise have
been missed. It is to be hoped that the word
" snapshot " will either be replaced by a more
appropriate one, or will speedily live down the un-
fortunate significance it acquired in early days.
Absurd as it may seem, the notion is by no
means obsolete that because a shutter will work
at a certain high speed it will give a satisfactory
result at that speed in all circumstances. This
is a serious mistake, but a not uncommon one.
In any given case there is a certain requisite
exposure that can only be widely departed from
to the detriment of the result. In the early days
of so-called snapshot work the commonest fault
was under-exposure. Since that time, however,
there has been a tremendous increase in the
sensitiveness of plates ; lenses have been made
with larger working apertures ; and shutters
have been improved in design and efficiency ;
and yet there are still occasions when the " snap-
shot " is necessarily under-exposed — either the
lighting demanded a longer exposure than could
be safely given in the hand, or an unduly short
exposure had to be given on account of rapid
movement in the subject. It is only in such
cases that the development of snapshots differs
from the normal. Harshness in the result is what
has to be guarded against. The use in such
circumstances of, say, a strong hydroquinone
developer would probably result in dense, clogged
high lights and shadow masses void of detail.
Potassium bromide or other restrainer should be
avoided, the developer should be well diluted,
and plenty of time given to the developing ac-
tion. While, of course, no possible alteration of
developer can compensate for absence of effec-
tive light action, all the developable detail in
the shadows shoiUd be secured. This may result
in too great density in the high lights, but this
may be modified afterwards with practically no
detriment to the softer shadow detail, by the use
of such a selective reducer as ammonium per-
sulphate, or by mechanical reduction with
Baskett's reducer or methylated spirit. The
printing paper chosen should have been specially
made to give softness of gradation from negatives
of undue harshness. {See also " Focal Plane
Shutter," "Hand Camera, Work with," and
"Instantaneous Photography.")
SNOW AND HOAR FROST PHOTO-
GRAPHY
The characteristic of average snow views is
the unusual degree of light contrast. Freshly
fallen snow in direct sunlight causes the whitest
of paper to appear grey by comparison. Thus,
in a snow scene the tree- trunks, buildings, etc.,
appear much darker than usual, and should the
photographer be led to under-expose he will get
an inky blackness in the shadows and an intense
whiteness in the snow. A broad expanse of
freshly fallen and unbroken snow can rarely, if
ever, be efEectively photographed. The sparkling
snow cannot be properly interpreted by white
paper. In composing a snow view, spottiness
and patchiness must be guarded against and
special attention paid to the foreground. Plain
freshly fallen snow rarely makes an interesting
foreground, but tree stumps, gates, farm imple-
32
ments, etc., under a mantle of snow are often of
great pictorial value, and cart-wheel ruts and
lines of footprints will be found to serve admir-
ably in breaking up a foreground ; it is an old
dodge to select the view-point and then to make
a line of footprints to suit the composition of the
desired picture. Of the greatest importance is
the lighting. While a flat, dull sky with no sun
may suit some subjects, more effective results
are obtained in sunlight, and more particularly
when the sun is near the horizon ; it will be
obvious, then, that the best-lighted effects are
obtained in the early morning and in the after-
noon. The low lighting breaks up broad ex-
panses of level and white snow, and causes foot-
prints, ruts, etc., in the foregroimd to stand out
more prominently.
Either ordinary or isochromatic plates may
be used, and they must be well backed, because
of the risk of halation. Isochromatic plates used
with a yellow screen may sometimes be of advan-
tage, because of the frequent yellowness of
winter light, and because a blue sky may be
interpreted dark, so bringing out any hoar frost
or snow effects on trees standing against the sky.
Many of the snow-scene photographs taken in
the Alps have black skies, owing to the use of a
deep yellow ("many times") screen. The ex-
posures are not much shorter than for ordinary
views, because generally there are deep shadows
in the scene, and under-exposure would cause
these to be almost clear glass in the negative,
and any attempt to force development for the
purpose of bringing out detail would ruin the
soft effect. An under-exposed negative of a
snow-scene is practically useless, and it is better
to expose fully and to get all detail possible in
the shadows. Details are more important than
density. The latter can be added to a negative,
but details cannot. An exposure meter of the
Watkins type may be used with success ; it is
held 12 or 15 in. from the body and turned
towards the sky, but not in such a way that
direct sunlight falls upon it. For an open scene
the exposure so estimated may be divided by
three or four ; but when there are many trees
or other deep shadows, the exposure may be
increased up to the full time given by the meter.
With careless development the delicate grada-
tion and detail in the snow is likely to be blocked
up and rendered unprintable. Mrs. Aubrey I,e
Blond, who has had a long experience in snow
and ice photography, uses a metol-hydroquinone
developer. She pours it into two half-pint
bottles, one labelled " Old " and the other " New."
The former is used over and over again for
developing, and as it becomes used up it is kept
full by adding from the new solution. The
method is economical and gives excellent results.
Sir W. Abney recommends beginning with —
Ammonia . . .30 mins. 6 ccs.
Potass, or amm. bromide . sogrs. 12 g.
Pyro . . . • I >. •24,,
Water . . . . 10 oz. 1,000 ccs.
Allow this to act until all detail is out, and
finish with —
Ammonia
Bromide
Pyro
Water .
30 mms. 6
8ogrs. 19
40 „ 9-5
10 oz. 1,000
ccs.
Soap
498
Sodium Chloride
SOAP (Fr., Savon ; Ger., Seife)
Soap is used as a lubricant when burnishing
prints. Hofbauer has stated that the addition
of Castile soap to a pyro developer prevents fog
in cases where excessive alkali is used. A solu-
tion of 100 grs. of the soap in 10 oz. of water is
used instead of plain water when making up
the developer.
A good soap should always be used for wash-
ing the hands after working with such chemicals
as amidol, metol, potassium bichromate, etc.
SODA, ALUM (See "Alum.")
SODA, CAUSTIC {See " Sodium Hydrate.")
SODA SALTPETRE {See " Sodium Nitrate.")
SODIUM ACETATE (Pr., Acetate de sonde ;
Ger., Essigsaures Natron)
Synonym, acetate of soda. NaCaHjOj 3H2O.
Molecular weight, 1 36. Solubilities, i in i water,
I in 23 alcohol. Obtained by neutralisation of
acetic acid with sodium carbonate or hydrate.
Colourless transparent efflorescent crystals. It
is used prindpaUy in the gold toning bath.
Twice-fused sodium acetate is also occasion-
ally used ; it has a slight alkaline reaction which
makes the toning bath act more quickly, and at
the same time the double-fusing destroys any
organic impurities, such as sodium formate, etc.,
which tend to reduce the gold.
SODIUM BIBORATE {See "Sodium Borate.")
SODIUM BICARBONATE (Fr., Bicarbonate de
sonde; Ger., Doppelt Kohlensaures Natron)
Synonyms, monosodic carbonate, acid sodium
carbonate, NaHCOj. Molecular weight, 84.
Solubility, 1 in 11 -3 water, insoluble in alcohol.
It takes the form of rhombic tabular crystals or
fine white powder, obtained by passing a stream
of carbonic add gas through a solution of car-
bonate of soda. Occasionally it is used in gold
toning, but it must not be confounded with
sodium carbonate.
SODIUM BICHROMATE (Pr., Bichromate de
soude ; Ger., Doppelt Chromsaures Natron)
Sjmonyms, dichromate of soda, add sodium
chromate. NajCr^O, 2H2O. Molecular weight,
298. Solubilities, i in i water, insoluble in
alcohol. It consists of red deliquescent crys-
talline fragments, obtained in a similar manner
to the potassium salt, and used for the same
purposes, ito parts of sodium bichromate will
replace i part of the potassium salt.
In process work, this salt has been suggested as
a substitute for the potassium and ammonium
salts in sensitising, but it has no advantages ;
indeed, its deliquescence is a disadvantage.
SODIUM BISULPHITE (Pr.,B»i«;^te(foiOM(fo ;
Ger., Saures Schwefligsaures Natron,
Natrium Bisulfit)
Synonym, add sulphite of soda. NaHSO,.
Molecular weight, 104. Solubilities, I in 3-5
water, i in 70 alcohol. It is a white, crystalline
powder or prismatic crystals, with faint sulphur-
ous odour, obtained by passing sulphurous add
gas through a solution of carbonate of soda.
It is used for acidtdating fixing baths and
solutions of sodium sulphite, and for preserving
stock solutions of developers.
A thick, yellow liquid, known as bisulphite or
acid sulphite lye, ozone bleach (Pr., Bisulfite lye ;
Ger., Sulfitlauge), which is a saturated solution
or sodium bisulphite, is obtainable commerdally.
This can be made as follows : —
Sodium sulphite
Warm distilled water
10 oz.
20 ,.
55° g-
1,000 CCS.
87-5 CCS.
Dissolve, and add slowly when cold-
Sulphuric add . . if oz.
SODIUM BORATE (Fr., Borate de soude ; Ger.,
Borax, Bor saures N air on)
Sjmonyms, borax, sodium tetraborate, pyro-
borate, biborate, tincal or tinkal. Na2B407
10H2O. Molecular weight, 382. Solubilities,
1 in 17 cold, I in '5 boiling water, insoluble in
alcohol, very soluble in glycerine. It is in the
form of hard, white crystals or powder, ob-
tained from the native borax or neutralisation
of native boric add. It is used prindpally in
gold toning and as an accelerator with eikon-
ogen and hydroquinone developers.
SODIUM BROMIDE (Fr., Bromure de soude ;
Ger., Bromnatrium)
Synonyms, bromide of soda or sodium. NaBr.
Molecular weight, 103. It is a white crystalline
powder, which readily absorbs moisture from
the air without deliquescing, and cakes into a
hard, semi-translucent mass. It is obtained in
the same way as the potassium salt, and it is
occasionally used in emulsion making, but its
hygroscopic qualities render it less certain than
the potassium and ammonium salts.
SODIUM CARBONATE (Fr., Carbonate de
soude : Ger., Soda, Kohlensaures Natron,
Natriumcarbonat)
Synonyms, soda, washing soda, carbonate of
soda. f'NajCOs loHjO. Molecular weight, 286.
Solubilities, i in i-6 water, insoluble in alcohol.
It is in the form of large prismatic crystals or
fine white powder, obtained on a large scale by
converting salt into sodium sulphate, and then
decomposing the latter by roasting with lime-
stone and coal. It is the favourite alkali for
development.
Washing soda is an impure variety which con-
tains variable quantities of water, sodium sul-
phate, and other impurities.
An anhydrous s^t (Fr., Carbonate de soude
anhydre : Ger., Kohlensaures N air on Wasserfrei),
NajCOs, molecular weight 106, is obtained as
a fiie white powder by heating the ordinary car-
bonate. Practically 37 parts of the anhydrous
salt are equal to 100 of the ordinary soda.
SODIUM CHLORIDE (Pr. Chlorure de soude.
Selmarin ; Ger., Chlornatrium, Sal Gemmis)
Synonyms, muriate or chloride of soda, salt,
common or table-salt. NaQ. Molecular weight,
58-5. Solubilities, i in 27 water, almost insoluble
in alcohol. It is a fine white crystalline powder
or transparent crystals, obtained native or by
purification from sea water. It is used to pre-
pare chloride emulsions and as a weaker restraiaer
than the alkaline bromides in developers.
Sodium Chloroplatinate
SODIUM CHLOROPLATINATE (Fr., Chloro-
platinate de sonde, Chlorure double de
sodium etde platine : Ger., Natrium-platin-
chlorid)
Pta.aNaaeHjO or PtajNa6HjO. Mole-
cular weight, 560-4. Solubilities, soluble ia water
and alcohol. It is a yellow crystalline powder,
obtained by adding sodium chloride to platinum
chloride. It is used in the platinotjrpe process
to produce greater contrast in the prints.
SODIUM CITRATE (Fr., Citrate desoude ; Ger.,
Citronensaures Natron)
Synonym, citrate of soda, neutral citrate of
soda. 2Na3C,H50, 11H2O. Molecular weight,
714. Solubilities, 1 in i-i water, slightly soluble
in alcohol. It is a white crystalline or granular
powder, obtained by neutralising citric acid with
sodium carbonate. It is used as a preservative
for albumen paper, to form sUver citrate in
printing-out emulsions and as a restrainer in
developers.
In consequence of its deliquescent nature it
is best prepared in solution by adding about
266 grs. or g. of sodium carbonate to 162 grs.
or g. of citnc acid in solution; the result will
be 480 grs. or g. of sodium citrate ; about
3 oz. or 1,440 ccs. of water should be used,
and the total bulk made up to 4 oz. or
1,920 CCS., when the solution will be 25 per
cent. A little salicylic add will prevent it from
growing mouldy.
SODIUM FLUORIDE (Fr., Fluorure de soude ;
Ger., Natrium Fluorid)
Synonym, fluoride of soda. NaF. Molecular
weight, 42. Solubilities, i in 23 water. It takes
the form of dear lustrous crystals or white
powder, obtained by neutralising hydrofluoric
add with carbonate of soda. It is used like the
potassium salt to strip the film from gelatine
negatives.
SODIUM FORMATE (Fr., Formiate de soude ;
Ger., Ameisensaures Natrium)
Synonym, formiate of soda. NaCHOj HaO.
Molecular weight, 86. It is a white deliquescent
crystalline powder, obtained by neutralising
formic acid with soda. It has been suggested
as an ingredient in the platinum and gold toning
baths.
SODIUM HYDRATE (Fr., Soude caustique ;
Ger., Aetznatron)
Synonyms, caustic soda, sodium hydroxide.
NaOH. Molecular weight, 40. Solubilities, i in
1*62 water, soluble in alcohol. It is poisonous,
the antidote being water, followed by lemon or
lime juice and milk or oil. It usually occurs in
white sticks or lumps obtained by decomposing
sodium carbonate with lime. It is used as an
accelerator in development. It should be kept
in bottles with rubber or paraffin stoppers, and
should not be handled with the fingers.
SODIUM HYPOCHLORITE (Fr., Eau de
Javelle ; Ger., Javellesche Lauge.)
Synonyms, eau de Javelle, Labarraque's solu-
tion, chlorinated solution of soda, ozone bleach.
It is a liquid possessing a strong chlorine odour,
containing sodium hypochlorite, salt, and car-
499
Sodium Hyposulphite
bonate of soda, obtained by decomposing bleach-
ing powder with sodium carbonate : —
Sodium carbonate . i oz. no g.
Bleaching powder . 320 grs. 73 „
Water to . . . 4 oz. 400 ccs.
Shake thoroughly, allow to stand for an hour,
and filter. It is used to remove stains from
negatives and destroy the last traces of " hypo."
SODIUM HYPOSULPHITE (Fr., Hyposulfite
de soude ; Ger., Fixirnatron, Unterschweflig-
saures Natron)
Synonyms, " hypo," sodium thiosulphate,
hyposulphite of soda. NajSaO, 5H,0. Molecular
weight, 248. Solubilities, i in -65 water, insolu-
ble in alcohol. It is in the form of white trans-
parent crystals, obtained by various processes on a
large scale, in which sodium sulphite is the start-
ing point. Its chief use is as a fixing agent for
negative and positive work.
SODIUM HYPOSULPHITE, TESTING FOR
The water in which negatives, etc., are being
washed after fixing is often tested to ascertain
whether " hypo " is present ; that is to say,
whether the negatives, etc., have been washed
long enough to remove all the " hypo." The best
method of so doing is to use the following solu-
tion : —
Potassium carbonate
Potassium permanganate
Distilled water
S grs. ig.
10 oz. 1,000 ccs.
A few drops of this pinkish-purple liquid added
to a sample of the washing water will turn green
when " hypo " is present ; the smaller the pro-
portion of hypo " in the water, the longer the
change takes ; and if there are very slight traces
present, the change will be to blue, not green.
The water to be tested should be the last the
negatives or prints have been washed in, and
prrferably that which has been standing still
for about ten minutes with the negatives therein ;
take the water as much as possible from the
bottom of the tank.
For the starch iodide test, powder and boil a
piece of starch about the size of a pea in two
or three drams of water until a dear solution is
obtained ; add one drop of a tincture of iodine
(iodine dissolved in alcohol), which will produce
a dark blue colour. Fill one test tube with distilled
water, and another with the water to be tested,
and add to each tube one drop of the solution.
If any " hypo " be present, the blue coloiir will
disappear. The tubes should be warmed slightly
and examined side by side against white paper,
as the test is very delicate.
The Bannon or silver test is to let a negative
or print drain into a test tube, then heat the
drainings, and add a few drops of a. silver
nitrate solution. A black predpitate will be
formed if xtrffffo P^^t of " hypo " is present,
while a smaller amount will give a yellowish
precipitate.
A rough and ready test is to taste the drainings ;
the sweeter the taste the more " hypo " present.
For the zinc and sulphuric add test, dilute the
acid to twice its bulk with water ; put some zinc
into a flask, with the washing water, and add
the dilute add. If " hypo " is present, sul-
Sodium Iodide
500
Sodium Sulphide
phuretted hydrogen is produced, as demonstrated
by holding over the flask a piece of blotting-
paper moistened with a solution of lead acetate,
which will be blackened. Chromic acid also gives
u test ; about 4 grs. are dissolved in 5 oz. of
water, and a few drops of sulphuric acid added.
If on adding the wasmng water a greenish cloud
appears, " hypo " is present. Potassium ferri-
cyanide in a weak solution and ferric chloride
in a stronger solution, mixed in equal propor-
tions and added to the washing water, gives a
greenish colour if " hypo " is present.
SODIUM IODIDE (Pr., lodure de sonde ; Ger.,
lodnatrium)
Sjmonym, iodide of soda. Nal. Molecular
weight, 150. Solubilities, i in -5. water, i in 3
alcohol. It is in the form of white crystalline
powder or cubical crystals. Very rarely used
in place of the other iodides in consequence of
its deliquescent nature.
SODIUM NITRATE {Ft^Azoiate desoude ; Ger.,
Salpetersaures Natron)
Synonym, cubic. Chili, or soda nitre or salt-
petre. NaNOj. Molecular weight, 85. Solu-
bilities, I in i-i water, i in 100 alcohol. It takes
the form of colourless rhombohedral crystals,
obtained native. It is rarely used in photo-
graphy, though it is stated to give a rich brownish
black tone to developed silver images.
SODIUM NITRITE (Pr., Azotite desoude; Get.,
Salpetrigsaures Natron)
Synonym, nitrite of soda. NaNOj. Molecular
weight, 69. Solubilities, i in 1-4 water, slightly
soluble in alcohol. It is in the form of white
opaque sticks or colourless crystals, prepared by
fusing the nitrate or neutralising nitrous acid.
Occasionally used to obtain a permanent stand-
ard photometer paper and in the diazotype pro-
cess. It must not be confounded with the
nitrate.
SODIUM NITROPRUSSIDE (Pr., Nitroprus-
siate de sonde ; Ger., Nitroprussidnatrium)
Synonym, sodium nitroprussiate. Na2Fe(CN)5
(NO) 2HjO. Molecular weight, 298. Solubilities,
I in 2-5 water, soluble in alcohol. It is in the
form of deep ruby red transparent crystals,
obtained by the action of nitric acid on potassium
ferricyanide. It is one of the most light-sensi-
tive iron salts, and is occasionally used for iron
printing and photometric work.
SODIUM OXALATE (Pr. Oxalate de sonde ;
Ger., Oxalsaures Natron)
Synonym, oxalate of soda. Na2C204. Molecular
weight, 134. Solubilities, i in 33 water, insoluble
in alcohol. It is a white crystalline powder,
obtained in the same way as the corresponding
potassium salt. It is rarely used, on account of
its low solubility, but is occasionally employed
in the platinotype process.
SODIUM PERSULPHATE (Pr., Persulphate de
sonde ; Ger., Ueberschwefelsaures Natrium)
Na^SaOs- Molecular weight, 238. Soluble in
water. It is a white crystalline powder, obtained
like the corresponding potassium salt, and used
for the same purposes.
SODIUM PHOSPHATE (Pr., Phosphate de
soude ; Ger., Phosphorsaures Natron)
Synonyms, phosphate of soda, disodiujn ortho-
phosphate. Na^HPOi 12H2O. Molecular weight,
358. Solubilities, i in 67 water, insoluble in
alcohol. It takes the form of colourless trans-
parent crystals or white granular powder,
obtained by treating calcium phosphate with
carbonate of soda. It is used in the gold toning
bath.
SODIUM PYROBORATE (See " Sodium Bor-
ate.")
SODIUM SILICATE (Pr., Silicate de soude :
Ger., Natronwasserglas)
Synonyms, soluble glass, soda water-glass.
NajSiOj + Aq. It is in the form of white to
bluish grey hard flat pieces, obtained in the same
manner as the corresponding potassium salt and
used for the same purposes. It is also met with
commercially as a syrupy yellowish liquid con-
taining 20 per cent, silica and 10 per cent. soda.
In process work, sodium siUcate is used either
alone or in combination with albumen or other
ingredients as a substratum to make the gelatine
film hold better on the collotype printing plate.
The substratum may consist of water 3I oz.,
gelatine 46 grs., sodium silicate \ oz., chrome
alum, 8 grs. The silicate is added after the other
ingredients are mixed and dissolved.
SODIUM SULPHANTIMONIATE (Pr. Snlfo-
antimoniate de soude, Sel de Schlippe ; Ger.,
Schlippesche Salz)
Sjmonyms, Schlippe's salt, sodium thio-
antimonate. NajSbSi gHjO. Molecular weight,
479. Solubility, i in 3 water. It is in the form
of large colourless or yellow crystals, obtained
by boiling milk of Ume, sulphide of antimony,
and carbonate of soda. It is used to tone
bromide prints and for darkening negatives
after mercurial bleaching. It is rapidly de-
composed by absorption of carbonic acid from
the air.
SODIUM SULPHATE (Pr., Sulfate de soude ;
Ger., Schwefelsaures Natron)
Synonym, Glauber's salt. NajSOj loHjO.
Molecular weight, 322. Solubilities, i in 3 water,
insoluble in alcohol. It is in the form of colour-
less eflSorescent crystals, obtained as a by-product
in the salt cake process. It is used to prepare
barium sulphate.
SODIUM SULPHIDE (Pr., Sulfure de soude ,
Ger., Natriumsttlfid)
Synonym, sulphide of soda. NajS 9H2O.
Molecular weight, 240. Solubility, soluble in
water. It consists of colourless, transparent,
dehquescent crystals, obtained by fusing sodium
carbonate with sulphur. It is used for sulphide
or sepia toning of bromide prints. It should not
be kept near any sensitive materials, and the
bottle should be well stoppered.
In process work, a 5 per cent, solution of
sodium sulphide is used as a blackener in the
intensification of wet collodion negatives, in
preference to the ammonium sulphide. Being a
dry salt, it is more portable and convenient to
handle.
Sodium Sulphite
■^01
Solutions, Concentrated
SODIUM SULPHITE (Pr., Sulfite de soude ;
Ger., Natriumsulfid)
Synonym, sulphite of soda. NajSOj 7HaO.
Molecular weight, 252. Solubilities, i in 2-2
water, slightly soluble in alcohol. It takes the
form of colourless crystals or powder, obtained
by passing sulphurous acid gas over damp
sodium carbonate. The crystals are efflorescent
and are readily oxidised to sulphate. It is an
energetic absorbent of oxygen, and is therefore
used to preserve developing agents ; the efflor-
esced salt should not be used for this purpose,
as it is a weaker preservative, and the sulphate
acts as a restrainer.
The anhydrous salt — (Pr., Sulfite de soude anhy-
dri ; Ger., Wasserfrei Natriumsulfid), NajSOj;
molecular weight, 126; solubility, i in 4 water —
occurs as a fine white powder, and is prepared
by heating the crystaUiue sulphite to 212° P.
One part of the anhydrous salt is equal to 2
parts of the crystalline.
SODIUM TARTRATE (Pr., Tartrate de soude ;
Ger., Weinsaures Natron)
NajC^HjO, 2H,0. Molecular weight, 230. It
consists of white crystals, obtained by neutralis-
ing tartaric acid with sodium carbonate or
hydrate. Occasionally it is used in printing-out
emulsions.
SODIUM THIOSULPHATE (See "Sodium
Hyposulphite.")
SODIUM TRIBASIC PHOSPHATE (Pr.,
Phosphate tribasique de soude : Ger., Drei-
basisch Phosphorsaures Natron)
Synonsrm, tribasic phosphate of soda, normal
sodium or trisodic orthophosphate. NajPOj
I2H20. Molecular weight, 380. Solubilities, i
in 5-1 water, insoluble in alcohol. It consists of
large, six-sided, colourless crystals, obtained by
adding caustic soda to sodium phosphate. It
has been suggested by Lumidre as a substitute
for the caustic and carbonate alkalis in devel-
opers, but has not found general use. Add
453 gis- 01^ g- °^ sodium phosphate to 51 grs.
or g. of caustic soda, both in solution, and
make the total bulk to 10 oz. or 4,800 ccs.,
and the result will be a 10 per cent, solution
of the tribasic salt.
SODIUM TUNGSTATE (Pr., Tungstate de
soude: Ger., Wolframsaures Natron)
Synonyms, tungstate of soda, sodium wol-
fran;ate. Na,,W,20u 28HjO. Solubilities, i in 4
water, insoluble in alcohol. It takes the form of
transparent tabular crystals, prepared by fusing
wolframite with sodium carbonate. It is used
in gold toning.
SODIUM VANADATE (Pr., Vanadate de
soude; Ger., Natriumvanadat)
Synon3nn, sodium ortho vanadate. NajVOj.
Molecular weight, 184. Soluble in water. It is
a white crysttdline powder, which is rarely used,
but which has been suggested to increase con-
trast in printing-out emulsions.
SOFTNESS
A term generally used to indicate an abund-
ance of middle tones without loss of detail in
either the high lights or the shadows. The ab-
sence of softness means harshness ; its exagger-
ation produces flatness. Under-exposure and
over-development will give the former; over-
exposure and under-developmeat the latter.
The selection of special printing papers aids in
securmg a bright result from a soft negative, or
a soft result from a hard negative, as the case
may be.
SOL LAMP
A lamp in which vaporised methylated spirit
is burnt in an incandescent mantle. The spirit
is contained in a reservoir, which may be raised
or lowered on an upright rod to adjust the pres-
sure, a bend in the supply tube being carried
over the burner so that the spirit continues to
be vaporised once the lamp is alight. To start
the lamp, a band of asbestos soaked in spirit is
placed below the burner and ignited. The lamp
is suitable for enlarging and for use in the optical
lantern.
SOLAR CAMERA (Pr., Chambre solaire, Cham-
bre d hiliostat ; Ger., Solar Kamera, Son-
nenkamera)
An apparatus for enlarging by the direct rays
of the sun, now practically obsolete. There were
two forms, one resembling an ordinary daylight
enlarging camera, while the other had, in addi-
tion, a condenser in front of the negative to
concentrate the rays. Sometimes a heliostat
was used to keep the sun's rays constantly
directed on the condenser.
SOLAR ENLARGING
Sometimes referred to as solar printing.
Enlarging with the solar camera, that is, by
sunlight.
SOLAR PHOTOGRAPHY (See "Sun,
Photographing the.")
SOLAR SPECTRUM (See "Spectrum,Solar.")
SOLARISATION
A term with many photographic meanings.
It is synonymous with reversal (which see), and
it is also applied to halation and to bronzing.
SOLUBILITIES
The table on pages 502-505 gives a list of
the chief photographic chemicals, with formulas,
molecular weights, and solubilities in cold and
hot water. For other information, consult
articles under separate headings.
SOLUBLE GLASS (See " Potassium Silicate "
and "Sodium Silicate.")
SOLUTIONS, CONCENTRATED
Solutions made up of a greater strength than
that required for use ; developers, for example,
to which water is added before use. They are
often confused with " saturated solutions,"
which, indeed, are concentrated solutions, al-
though a concentrated solution need not be
saturated. Concentrated solutions keep better
than those diluted to working strength, and
almost any photographic solution can be made
up in a concentrated form simply by using less
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2 » «3
Solutions, Making up
506
Spanish Combined Bath
water than is required for the working strength,
and adding water at the time of use. Take any
one solution " ready-for-use " formula. Assume
that it includes 10 oz. of water. To prepare a
concentrated solution, use only 5 oz. of water,
when, of course, a bottle half the size can be
utilised. When required for use dilute with an
equal bulk of water.
SOLUTIONS, MAKING UP
The method of making up photographic solu-
tions should not be a haphazard one. The salts,
in making up a stock solution, for example,
must not be all placed in a dry bottle and the
water added, for this conduces to slow and often
incomplete solution. Another important point
is the quantity of water used. In the majority
of the formulae given in this work the quantity
of solvent is, where possible, given so as to make
a total bulk of either 10 or 20 oz., or 1,000 ccs.
Take any formula, such, for instance, as a de-
veloper containing —
Pyro .
I oz.
50 g.
Sodium sulphite
• 4 „
220,,
Citric acid
I ,,
55 .,
Distilled water to .
• 20 „
1,000 CCS
If the solids were weighed out and 20 oz. or
1,000 ccs. of water added, the total bulk would
be more than 20 oz. or 1,000 ccs., and unless the
total bulk were measured it would be impossible
to determine the exact quantity of solution to
use for a given weight of pyro. The correct
method is to dissolve the solids in about three-
fourths of the total bulk of water, and then add
sufficient water to make the given quantity.
Again, in making developers, it is advisable to
dissolve the preservative, the sulphite or meta-
bisulphite, first and then add the developing
agent, except in the case of metol, which should
always be dissolved first. When there are several
salts given, it is usual in photographic formulae
to dissolve them in the order in which they are
given, and it is preferable always to use warm
or hot water and dissolve each salt separately.
In nearly all cases there is considerable lowering
of the temperature when salts are dissolved,
hence the value of hot water, for most salts are
more soluble in hot than in cold water. As all
solutions are of greater specific gravity or heavier
than the solvents, it is not a good plan to place
the salts in a bottle, fill up with water, and allow
to stand, as the bottom of the liquid becomes a
saturated solution, whilst the top may be nearly
pure water. An excellent method is to use linen
or muslin bags containing the salts and suspend
them from the top of the bottle or jug, when the
solution of the salts rapidly sinks to the bottom,
its place being taken by fresh water or weaker
solution ; this method has the advantage, too,
of straining out any dirt or foreign matter from
the solution. The precautions given under the
heading " Water " should also be noted.
In a 10 per cent, solution, 10 parts by measure
contain i part of the dissolved substance.
The rough-and-ready method of mixing together
I oz. of the salt and 9 oz. of water does not make
a true 10 per cent, solution. Ten fluid otmces
contain 4,800 fluid grs., and should therefore
contain 480 grs. of the salt. Chemicals are
always sold by avoirdupois weight, i oz. of
which contains 437J grs., the apothecaries*
ounce consisting of 480 grs. The former and
lighter ounce therefore needs less water than the
latter in order to make a true 10 per cent, solu-
tion ; but, happily, the difference is not so
much as to make a very great difference in the
working powers of solutions. The correct way to
make a 10 per cent, solution is to place the
I oz. (avoirdupois, as bought) of chemical in a
measure or bottle, and make up to a total bulk
with water, of 9 oz. 55 mins. (9 oz. i drm. is near
enough). Ten mins. of such a solution will con-
tain I gr. of the dissolved chemical.
Solutions are not always made up in the 10
per cent, strength. When the proportion in a
formula is given as a percentage, the number of
grains of solid per ounce of liquid can be obtained
by multiplying the percentage figure by 4 and
adding to the result its tenth part. Thus 5 per
cent. = 5 X 4 = 20; -fg X 20 = 2; 20 -^ 2
= 22 ; that is, 5 per cent. = 22 grs. per ounce,
(approx.). The following table, compiled by
C. C. Sherrard, shows at a glance the exact com-
position of "per cent." and "part" solutions,
made by simple multiplication : —
Strength of
Solution
1 per cent.
2 per cent.
3 per cent.
4 per cent.
5 per cent,
ro per cent.
15 per cent.
20 per cent.
25 per cent.
40 per cent.
8^«
is
Grs,
♦•557
9-114
13-671
18-228
22-785
45-57
68-355
91-14
113-925
182-28
Strength of
Solution
in
1,000 . .
in
500
in
400
in
300 . .
in
200
in
100 . .
in
50 . . .
in
25 .
in
10 . . .
in
5 ■ • •
til
"as
Grs.
•«57
■9114
1-139
1-519
2-2785
4-557
9-114
18-228
45-570
91-14
SOLUTIONS, SATURATED {See "Satur-
ated Solution.")
SOLUTIONS, STOCK {See " Solutions, Mak-
ing up.")
SOLUTIONS, SUPER-SATURATED {See
" Super-saturated Solutions.")
SOLUTIONS, TEMPERATURE OF {See
" Temperatures.")
SPANISH COMBINED BATH
A combined toning and fixing bath for gelatino-
chloride paper, said to have been invented by
a Spanish expert, but closely resembling other
combined baUis. It gives rich tones on prints
from good negatives, and the formula, as gener-
ally published, is as follows : —
" Hypo " .
2| oz.
300 g.
Am. sulphocyanide
75 grs.
19 „
Sub. acetate of lead
50 „
12-5 „
Lead nitrate
IS „
3-75 .,
Citric acid
15 „
3-75 „
Alum
SO „
12-5 „
Water
9 oz.
1,000 ccs
Specific Gravity
507
Spectrography
Dissolve in hot water, stand a few days, filter, and
add:—
Gold chloride
Water
S
grs.
oz.
1-25 g.
no CCS.
SPECIFIC GRAVITY (Fr., Pesanteur spici-
fique, Densiii; Ger., Spezifisches Gewicht)
Synonym, density. The weight of a certain
bulk of a soUd or Uquid compared with that of
the same bulk of water ; in the case of gases,
hydrogen is the standard. Thus, a certain
measure of water is found to have a weight of
3 lb. ; the same measure of mercury is found to
have a weight of 40-8 lb; then ^— - = 13-6,
which is the specific gravity of mercury. Den-
sities of solutions are commonly measured with
the hydrometer (which see), there being, as a
rule, a relation between specific gravities and
hydrometer degrees.
SPECTACLE LENSES
Simple lenses consisting of only one piece of
glass, and occasionally used in photography.
Owing to their being non-achromatic, tiieir
■chemical and visual foci do not coincide,
and, after focusing, the distance between
lens and plate is decreased by ^ to j>j of
an inch when photographing normal objects ;
in portraiture, copying, etc., the correction
needs to be greater.
SPECTACLES, MONOCHROMATIC
Spectacles or monocles, usually of blue glass,
used for judging the appearance of the view to be
photographed. Seen through blue glass, the
colours in the view are toned down or obliterated,
and one gets a better idea of how the picture
will be represented in the monochrome print.
A blue focusing (ground-glass) screen gives the
same effect. (See also " Stereoscopic Spectacles.")
SPECTROGRAPHY (Fr., Spectrophotographie;
Ger., Spekirophotographie)
Any spectroscope may be converted into a
spectrograph or camera for photographing the
spectrum by attaching to the telescope a camera
instead of an eyepiece. The simplest form is
that in which a direct-vision spectroscope is used,
and it may be either an ordinary camera or
merely an oblong box to the front of which the
spectroscope is attached, whilst the back car-
ries the dark-slide for the plate. The usual eye-
piece lens must be removed, and care should be
taken that no part of the mount cuts off the spec-
trum. No lens need be used, and the length of
the spectrum is then solely dependent on the
extension of the camera. If a lens is used, then
the lines wiU be sharper. A shows the simple
box form without lens ; F is the box, d the direct-
vision prism, B the slit, a the condenser, and E
the milled head for focusing the collimator lens.
B shows the form with lens d behind the prisms ;
H is an outer tube that prevents stray light
having access to the camera, K is the groove
for the dark-slide, and E a central screw, on
which the back can be swung to any angle and
then fixed by the screw F ; 6 is a short length of
bellows.
When using the direct-vision spectroscope, the
line that passes straight through is generally
the D line ; therefore the spectroscope must
be placed above the centre of the plate, other-
wise the violet end will not be included. With
the spectrograph without lens, the length and
width of the spectrum are dependent solely on
the extension of the camera.
In the ordinary single or two-prism spectro-
scope the telescope should be entirely replaced by
a light camera, and it is advisable to cover
over the prism table and the lenses so that no
light has access to the plate but through the
slit ; otherwise general fogging of the plate
will ensue.
It is convenient to take a series of negatives
on one plate, and this can be done by small
sliding shutters in front of the slit, but more
conveniently by providing a slit, say, of one inch
width, in the back of the camera and arranging
for the dark-slide to be shifted in its grooves
so that three or four contiguous spectra may
be obtained by merely shifting the plate. Witii
all prismatic spectrographs it is essential to
arrange for the swinging of the plane of the
plate ; that is, for putting the violet end nearer
the lens than the red. If the spectroscope is
always to be used with the same prisms and
lenses, then this can be done once for all; other-
wise slots and screws must be provided as shown
in diagram B.
One great disadvantage of the prismatic
spectrograph is the uneven dispersion, the red
being cramped together and the blue and violet
more extended. On the other hand, this may
be an advantage in photographing very faint
absorptions or sensitising action in the red if
mere qualitative and not quantitative results are
desired. This unequal dispersion is well shown in
C and D ; the former represents the spectrum
produced by a diffraction grating and the
latter a spectrum of equal length and disper-
sion produced by a prism.
With all glass there is more or less absorption
of the ultra-violet, and with heavy flint glasses
with great dispersion this may even extend into
the visible violet. Quartz, calcite, and fluorite
are very transparent to this region, and must
be used both for prisms and lenses if photo-
graphy of the ultra-violet is to be attempted.
Undoubtedly the concave grating which requires
no lens is most useful for this region. Practic-
ally, ordinary glass may be considered not to
transmit beyond X 3,400 when a thickness of
about ^ in. is used. Another disadvantage with
the prismatic spectrograph is that the lines are
curved with the convex side towards the red,
due to the fact that only those rays which pass
through the centre of the sUt can pass through
a plane perpendicular to the refracting edge of
the prism, which is usually called the principal
plane.
Diffraction-grating spectrographs are far more
satisfactory for all photographic work, especially
now that the excellent celluloid replicas can be
obtained so cheaply. The principle of the direct-
vision spectroscope is described elsewhere, and
the same arrangement may be used for the spec-
trograph. A section of such an instrument,
designed by TaUent, is shown at E, in which
S is the slit, c the collimator lens, d the grating
cemented to a narrow angle prism which
refracts the central white beam to w into a small
Spectrography
508
Spectrography
pocket of blackened wood ; 1, is the camera
lens, and P the dark-slide. The lenses are single
landscape lenses, and their foci or that of the
camera lens will depend upon the length of the
spectrum desired. A lens of 14I in. will give a
spectrum of about 4 in. in length between
X 3,500 and X 8,000. The slit must be placed
at the equivalent focus of the collimator lens,
and all parts except just the grating aperture
should be blocked out and the interior of the
camera lined with black velvet or blackened to
prevent reflections.
If it is not desired to use a prism grating, then
obviously the plate must not be in a straight
line with the grating, but at the angle of diffrac-
tion. This may be calcixlated as follows: The
I inch =
b
b
•03937043
I
.03937043
•00175292
X 14490
The correct position of the plate may also be
found by supporting the collimator lens on a
block of wood, or temporarily attaching it to
a card and placing the slit at its equivalent focus
close to a strong light ; then, on inserting the
grating close behind the lens, the first order sipec-
trum will be seen on each side of the white image
of the slit, and the distance from this will, of
course, give the angle between the axial line and
the grating. The grating may be placed at
fp%
A
01®®!
4
E
H ' ^
.^a.
F. Calculating Angle of
Diffraction
B. Spectrograph, with Slot and Screw
Attachments
In diagrams C and D, the letter
references are as follow : —
3, brown ; r, red ; (», orange ; oy^ orange yel-
low ; y, yellow ; y£^, yellow green ; ^, green ;
d£^f blue green; 6, blue; ^zf, blue violet; »,
violet ; I, lavender
E. Tallent's Diffraction-grating
Spectrograph
A a B C
'Q{,jtm-^ii-L^
E b
A. Box-form Spectre-
graph Camera
C and D. Spectra produced by Diffraction Grating and Prism
respectively
spectra formed by a diffraction grating lie on
each side of the central white image, and to find
the distance of the first wave-length or the angle
of difiraction let P represent a spectroscope in
which b is the grating space — that is, the width
of one ruling and the adjacent space — and e the
angle of deviation. What we wish to deter-
mine is either e, or the length of A B, then
taking -0003340 mm. as the first wave-length
which it is desired to find the position of —
A B = sin e = -0003340 -i- b
and assuming that 6 = -001752, we have —
sin e = -0003340 -5- -001752 = -1906 = 11°
practically.
The grating space, or 6, is found very easily,
thus : Assuming that we have a grating with
14,490 lines to the inch, then —
right angles to the collimator lens, or preferably
so that its plane cuts the angle between the
axes of the collimator and camera lens — that is,
so that the angles of incidence and diffraction-
are equal.
For a plane metal or reflection grating the
arrangement shown for this {see " Spectroscope ")
may be adopted, replacing the telescope by a
camera, and fixing the collimator and camera at
an angle of 45°, the grating being mounted on
a revolving table.
Excellent replicas, cemented to sections of con-
vex lenses so as to form concave gratings, being
now obtainable, it may be as well to give Eder's
method for mounting concave gratings for spec-
trography. The idea is to keep the slit position
constant, which is a great convenience when
using a heliostat or fixed source of artificial
light, H in G. The camera moves round a
Spectrography
point G ; the slit s, which is joined to the tube
T, always moves along s G ; the plate p moves
on the arc p" p p'", which is struck from the
centre G ; the slit s is joined by a rod s b c to c,
which is the centre of the distance p g, G being
the grating. It is obvious then that as the
plate is moved round the arc p" p p"' the slit
and the grating also move. The central point
of the grating must be exactly over the point g,
and the slit s must be exactly over the point
s, at which the rod is joined to T. T is a collap-
sible tube, which can be shortened or lengthened
as it approaches or recedes along s G.
When diffraction spectra are used, the spectra
are not isolated, but overlap ; and this over-
lapping follows the law \^ = 2X» = jX' =
4 X» = 5 \s, in which X*, X», X^, etc., are the
wave-lengths in the first, second, third, etc.,
orders. This overlap is shown in the following
table, taking X 6,000 in the first order : —
First order spectrum 6,000
Second „ „ 3,000 6,000
Tliird „ „ 1,500 4,000 6,000
Fourth „ „ 3,000 4,500 6,000
^ifth „ „ 3,600 4,800
ovxih „ „ 3_ooo 4,000
509
Spectrography
G. Use of Heliostat in Spectrography
For visual work this overlap is of no moment
when using the first order only, because the eye
is not sensitive to the ultra-violet ; but in spec-
trography this overlapping may be very trouble-
some, particularly when dealing with the ex-
treme red, for if we take the limit set by the
absorption of the glass as X 3,400, as that which
would act on the plate, this line would coincide
with X 6,800 in the first order, and therefore
the farther we proceed with the red the more
active will be the ultra-violet of the second
order, and thus totally erroneous condusions
may be drawn from the results.
This superposition of the second order can
always be seen in negatives when using day-
light, the electric arc, or magnesium ribbon ;
so that it is as well to use some absorbent
material between the light source and the plate.
This may be either in front of the slit or, prefer-
ably, in front of the plate itself. In the former
position there may be used a cell containing a
solution of aesculin or filter yellow K, or a
gelatine screen stained with the above. For a
screen in contact with the plate it is advisable
to coat a sheet of thin patent plate with a 5
per cent, solution of gelatine, and when dry to
stain up about half of the plate ; that is, up to
about where the D lines fall, with filter yellow
K or dianil orange G. The screen should then
be placed in contact with a plate and a long
exposure given to the arc or magnesium ribbon
to see that it does absorb the whole of the ultra-
violet.
It may also be found convenient to fix per-
manently in the dark-slide a scale either of wave-
A
A
/
' 7594
/
7000
Li 6706
• 6I-2'
.
/
1667
B
/
1
I6»
6600
Li ei02
- 6I-0
Na6B90'
.
/
60*3
0
/
6890
/
6600
ThB345
- 37-6
/
6270
E
/
.6000
/
k66J
_F
■ •aa-e'
•
/
/
4600
/
4308
Q
/
-
4000
/
3968g
3933fR
/
4<lO0 fiOjOO eOOO TOOO 8000
H. Interpolation Chart
lengths or one merely divided into known divi-
sions, and excellent glass scales 10 mm. in length
and divided into tnillimetres can be obtained
commercially. With such a scale, which is
impressed on the plate at each exposure, it is
easy to calculate with approximate accuracy the
wave-length of any line or the limits of an
absorption band, etc. For instance, having
determined that the distance between Hj and C
is exactly 90 mm., we have only to divide d X
— that is, their difference in wave-length — by
90 to find the number of wave-lengths to a
millimetre, thus —
C X 6563 — H X 3968 = 2595
■■■2595 -f- 90 = 28^8 wave-lengths per millimetre,
so that if an unknown line was found 10^5 mm.
from H, its approximate wave-length would be
3968 -)- (28^8 X 10-5) = 4270-4.
Obviously, this method is but approximate, but
it is useful when studying absorption spectra
or the sensitiveness of a plate.
To construct a wave-length scale, the easiest
method is that suggested by A. J. Newton
1 .... 1 ... 1 .... 1, ... 1 1 .... 1 .... 1
7000'
6000' 6000 4000 '
Waun Lengths in Tenth Metree
H ■*
0 3.
■ ' aboo
I. Wave-length Scale.
(Penrose's Pictorial Annual, 1905-6, p. 81), but
it requires an arc lamp, though the lines may be
obtained by the metiiod described under the
heading " Wave - lengths." Narrow the slit
down so that the D lines are divided ; then, using
Spectrometer
510
Spectroscope
a panchromatic plate, photograph the lithium
sodium, thallium, and blue strontium line. A
sheet of plain glass should be placed in the dark-
slide to represent the scale plate which will sub-
sequently be fixed there. For the lithium lines
use a deep red screen in front of the slit and give
about two minutes' exposure ; then with a yellow
or green screen obtain the thallium line, and
finally the blue strontium line without a screen.
After development, measure accurately the
distance between the lines and make an inter-
polation chart with the wave-lengths as abscissae
[see H) and the distance of the lines as ordinates,
and draw the curve or straight line. It is
advisable to increase the actual distances by
some unit, say lo, all through. Then mark the
wave - lengths in whole numbers, starting at
\ 3,500 and going up to X 7,500 or higher. The
result will be as shown in H. Prom this draw
an enlarged diagram, with the distances marked
as at I, and then copy this in an ordinary camera
down to the required size. Prom this negative
make a positive by contact, and cement it into
the dark -slide so that the D lines coincide
exactly with those marked on the scale.
In photographing the spectrum for any pur-
pose whatever, one must take into account the
various factors incident to each region. For
the ultra-violet, as has been pointed out, we
must discard glass or use a concave grating.
For the infra-red, glass is transparent enough
probably for as far as the beginner is likely to
want it. For the ultra-violet and the visible
spectrum up to about X 5,000 any ordinary plate
may be used ; but it is in dealing with the
other half of the spectrum up to about X 7,000
that one has to use special colour-sensitive
plates. For green and blue-green, acridine
orange NO is the best sensitiser, though this
region may be well recorded on any commercial
erythrosine or isochromatic plate provided a long
exposure be given or absorbing screen used.
The erythrosine plate will also record to about
X 6,000, but beyond this one must use a pan-
chromatic plate, sensitised with orthochrome T,
pinaverdol, pinachrome, or homocol. For the
extreme red — that is, from about X 6,400 to X 6,800
— pinacyanol is the best dye ; whilst for X 7,000
to X 7,200 dicyanine is the most satisfactory.
The method of preparing these plates is described
elsewhere.
The plates must have a black backing. As
regards the exposure but little help can be
given, and in developing care should be taken
not to prolong the duration too much, as other-
wise fine faint lines may be easily buried.
SPECTROMETER (Fr., SpectromHre : Ger.,
Spehtrometer)
A spectroscope in which the prism or grating
is mounted on a table, which is graduated into
degrees and minutes so that the deviation of
any line may be read.
SPECTRO-PHOTOGRAPHY (See " Spectro-
graphy.")
SPECTRO - PHOTOMETER (Fr., Spectro-
photomHre ; Ger., Spektropkotometer)
An instrument by means of which the lumi-
nosity of various regions of two spectra can be
directly compared. Various forms have been
suggested.
There is, first, the double - slit photometer of
Vierorot, in which the lights to be compared fall
on the slit, the two halves of which can be
opened or closed, and thence passed through
a prism, to appear at the eyepiece as adjacent
spectra; they are compared by opening and
closing the one slit which transmits the light
to be measured, whilst that transmitting the
standard light is kept constant. The eyepiece
of the telescope is provided with sliding shutters
which enable one to limit the field of view to the
particular region under examination. The
disadvantage of this method is that the two
spectra are not of equal purity, and therefore not
of the same colour, this being an inherent defect
in the use of two slits of different widths.
Lummer and Brodhun introduced a photo-
meter with two collimators at right angles to one
another, the lights being brought into juxta-
position by means of a Lummer-Brodhun rhomb
and thence dispersed. The reduction of one of
the lights is produced by rotating sectors.
Polarising photometers have been devised by
Glan, Crova, Hiifner, Konig, Glazebrook, etc.
Their principle is that the lights are received
through two contiguous slits, then pass through
the dispersing medium, a Wollaston prism, and
are brought into juxtaposition by a biprism,
thence reaching the eyepiece, which is fitted with
an analyser. This method also has its faults,
and is really only strictly correct when mono-
chromatic spectrum rays are used.
SPECTROSCOPE (Fr., Spectroscope: Ger.,
Spektroskop)
An instrument designed for seeing a spectrum
and consisting essentially of three parts— the
slit, the dispersing medium, and the observing
telescope. The latter is essential if it is desired
to see the spectrum uncontaminated by white
light, though it is possible to see a spectrum in
any ordinary room with no more apparatus than
an opaque card with a slit in it and the dispers-
ing medium. If, for instance, a slit about i in.
long and J in. wide is cut in an opaque card about
12 in. long and 6 in. wide, and this card is placed
A. Spectroscope
on the cross-bar of a window, a fairly pure
spectrum can be seen by going to the other side
of the room and examining the slit through the
dispersing medium held dose to the eye. A
complete spectroscope is shown at A, in which
C is the collimator, consisting of a slit s at the
focus of the lens I ; P is the prism, or dispersing
medium ; and P the telescope which receives the
refracted and dispersed beam. A third tele-
scope is sometimes provided which throws a
numbered scale on to the second face of the
prism, whence it is reflected to the telescope and
the eyepiece.
The slit is usually made of metal, and con-
sists of two plates, one of which may be fixed
and the other movable, the latter being actuated
Spectroscope
511
Spectroscope
by a micrometer screw so that its distance from
the fixed jaw may be varied at will. In purchas-
ing a slit, stipulation should- be made that the
jaws are of platinoid, a hard white alloy which
does not readily tarnish. It is advisable also to
have what is known as a symmetrical slit — that
is, one in which both jaws are moved simultan-
eously by one screw. For very accurate wave-
length determination this is important, as it is
the centre of the line which is measured, and
with a symmetrical slit this is constant, whereas
with an unsymmetrical slit the spectral line
widens on one side. On the other hand, it is quite
possible to obtain wave-length readings, of suf-
ficient accuracy for ail ordinary work, with a
sUt having only one movablej jaw if the edge
of the spectrum line that coincides with the
fixed jaw is taken for measurement. It is neces-
sary that the jaws of the slit be bevelled with
the bevel inside, and that the bevel be blackened,
as this prevents reflection of the Ught. The
jaws must be parallel and without any side slip,
and parallelism of the jaws can be easily tested
by opening the slit, then gradually closing it
down till the aperture entirdy disappears. This
it should do throughout its entire length simul-
taneously. The edges of the jaws are easily
damaged, and therefore the slit should never be
screwed up roughly or too tightly. As the slit
for normal work is extremely narrow, dust
particles are very apt to lodge between them
and give rise to dust lines, wbich are longi-
tudinal black lines running throughout the
length of the spectrum. These dust liies, whilst
delSacting from the appearance of the spectrum,
are convenient in one way, as they prove whether
the sUt is parallel to the edge of the prism or
the ruling of the grating, as 3 parallelism exists
the lines are parallel to the edges of the spec-
trum. To dean a slit from dust partides a
soft wood match stick should be cut to a fine
bevd or chisd shape, and, the jaws being
opened, the match should be inserted and the
jaws dosed till just gripping the wood, and then
the match should be moved up and down and
the jaws again opened and the match removed.
When chemicals or solutions are burnt or vola-
tilised by a spark dose to the slit, it is apt to
get splashed with partides of the salt ; it is
advisable then to use a condenser, whidi enables
the spark to be worked some distance from the
slit and focuses the image on the slit, or a thin
microscopic cover glass may be temporarily
placed in front of the slit.
Frequently a slit is provided with draw
plates which cover parts of the sUt, thus enabling
two or more contiguous spectra to be photo-
graphed.
The dimensions of the slit depend upon the
aperture of the collimator lens and the prism or
grating, and it may be taken as a safe rule that
the dear aperture of the slit should not be less
than one-third the diameter of the lens. To
some slits is also fitted a piece of metal with a
wedge-shaped aperture cut in it ; this is used
to limit the size of the spectrum, and is an
advantage for spectrography, as it enables one
to narrow the width oi the spectrum and thus
prevents the diffusion of stray light. In most
spectroscopes the aperture of the slit is narrowed
by an internal diaphragm, which prevents scat-
tered light reaching the coUimator lens. It is
usual, too, for the slit to be mounted on a focus-
ing tube, but for spectrography it is just as
well to determine once for all the accurate dis-
tance of the slit from the collimator lens, and
fix it so ; and this does not at all interfere with
the use of the instrument for visual work. The
focal length of the collimator lens is merely a
question of convenience, though naturally there
are certain theoretical considerations that
govern this. The rays from the slit are parallel-
ised by the coUimator lens, and we may calcu-
late the breadth of the slit image as formed by
the telescope or camera lens thus : let j = the
height or length of the slit, / = the focus of the
collimator lens, F = the focus of the telescope
or camera lens, and S = the image formed by
the latter, then —
P
S = s X J
For instance, suppose the length of the slit =
12 mm., the collimator lens focus = 250 mm.,
and the camera lens focus = 500 mm., then —
o 500
S = 12 X - — = 24 mm.
250 ^
whidi will be the breadth of the slit image or
spectrum.
It is essential that the collimator lens be
achromatic, and that the slit be exactly at its
equivalent focus. If these two points be not
aftended to, the aberrations of the lens come
into play, and critical sharpness of the spectrum
lines is impossible. The method of adjusting the
slit and collimator for visual work is very simple.
Assuming that the telescope eyepiece is fitted
with cross wires or spider Imes, these should be
sharply focused and then the telescope focused
for a very distant object, such as a church spire
or tree. Then, without altering the tdescope
focus, swing it into line with the collimator lens,
removing lie dispersing medium, and obtain a
sharp image of the slit by racking it nearer to
or from the collimator lens. It is important, too,
that the slit should be central with the axes of
the collimator and tdescope lenses. This can
be determined by placing an opaque card with
a small central hole over the slit and seeing
whether the image of this hole falls in the centre
of the collimator lens and the eyepiece.
The prism usually supplied with spectroscopes
has a refracting angle erf 60°, and it is important
that it should be levd and with the refracting
edge paralld with the slit. Should the slit not
be paralld with the refracting edge, it will be
found that the Praunhof er lines are not exactly
at right angles to the length of the spectrum.
As a rvde, it will be found that the slit tube can
be revolved so that this f aidt can be easily reme-
died. Should the spectrum not entirdy fill the
eyepiece — that is to say, if the height of the
slit be reduced so that the spectrum is seen
only as a narrow stripe across the field of view —
the non-parallelism of the slit and prism edge
can also be seen by the width of the spectrum
decreasing or increasing as the slit is turned
one way or the other.
The dimensions of the prisms should be such
that they will entirely take up the beam of
paralld light from the collimator. The height
must therefore be equal to the diameter of the
Spectroscope
SI2
Spectroscope
collimator lens, but the length must be greater
This can be shown mathematically to be :
h
fj 1- l>.^ sin
calling I = the length, h = the height, and fi =
the index of refraction, then for a 60° prism and
B. Direct-vision Spectroscope
an index of refraction of 1-5 and a height of
2 in. this becomes :
h 2
I
^/■-^-v-^'
3-02 in.
The telescope should, like the collimator,
have an achromatic lens, and should be of the
same dimensions, and is generally of the same
focus. The eyepiece is usually that known as
a Ramsden, in which two plano-convex lenses
are placed with their convex surfaces towards
one another, the distance between them being
about two-thirds of the focal length of one of
them. This is frequently provided with cross
wires or spider lines, which are used for measur-
ing the position of a line. There are many dif-
ferent forms of eyepieces, some being provided
with a bright metallic point, on to which the
light is reflected from the outside by a small
mirror. In others, such as the Gauss, a line of
light is reflected by a piece of silvered glass.
Micrometer eyepieces are also sometimes used,
in which a micrometer screw moves a plate or
wire across the spectrum, the amount of travel
being read off on a divided drumhead or scale.
These eyepieces are uSed for the measurement
of wave-lengths, but visual measurement has
been almost entirely superseded by the spectro-
graphic method.
A very convenient accessory to the eyepiece is
two sliding shutters, which can be pushed in from
either side, thus enabling one to limit the field
of view and cut out a brilliant line which might
otherwise overpower a close, faint one. There
are two other accessories often fitted, but which,
except for rough visual measurement, are of
little practical value. The first is the com-
parison prism, which is a small reflection prism
that can be swung over half the slit, the advan-
tage being that one can compare two light
C. and D. Three-prism and Five-prism
Trains for Spectroscope
souxces, for instance daylight, which may be
admitted to the slit in a straight line, and a
vacuum tube or cell filled with coloured fluid,
which can be placed at right angles to the axis
of the collimator. The other accessory is a scale
of lines, which is projected from the last face of
the prism into the eyepiece.
For rough visual work it is usual to emplby
direct-vision spectroscopes, and these are fitted
with three or five prisms placed base to apex,
the glass being so chosen that whereas the
deviation of the D line, for instance, by the one
set of prisms is counteracted by the others, so
that it emerges in a straight line, the other
colours are spread out on either side of it.
The usual form of the direct-vision spectroscope
is shown at B, in which S is the slit, b the colli-
mator lens, P the train of prisms. The distance
between the sUt and collimator lens is adjust-
able by sliding the whole tube A out. Fre-
quently a lens is placed at the aperture B for an
eyepiece. An extra fitting, C, carrying at one
end a condensing lens, r,, which can be focused
on to the slit by sliding the tube, is a great
advantage, as it Umits the hght received by the
slit to that which it is desired to examine. Occa-
sionally a comparison prism and photographed
number scale are also fitted. C and D show
respectively three-prism and five-prism trains.
For the critical examination of a spectrum it
is advisable that the line or region under examina-
tion should pass through the prism at the angle
of minimum deviation. Unless a special form,
or, as it is usually called, an auto-coUimating
E. Auto-collimating Spectroscope
spectroscope, be used, it would be necessary to
adjust the prism for this position for every line.
Several such instruments can be obtained com-
mercially, but a simple form, which is not diffi-
cult to fit to any spectroscope, is shown at E.
To the prism table is fastened a slotted brass
rod, D, a continuation of which just bisects the
refracting angle of the prism P, when this is
placed at the angle of minimum deviation for
the D line. C is the collimator and F the tele-
scope, and to their ends are fastened two thin
brass rods, A E and B E, which, when the posi-
tion of minimum deviation is found, are joined
together by a pin, E. Then any movement of the
telescope also moves the collimator and prism
into the position of minimum deviation.
A spectroscope fitted with a diffraction grat-
ing is much to be preferred for most purposes,
because the spectrum is normal ; that is to say,
the distances apart of the rays of different
colours are arranged according to their wave-
length. On the other hand, as the prismatic
spectrum is more brilUant, the prism is to be
preferred for very faint spectra.
All the parts of the details given above for
the prismatic spectroscope apply to that made
with a diffraction grating or replica, and the
same precautions have to be observed to ensure
parallelism between the slit and the rulings of
the grating, and the plan {see E) may be taken
as the plan of a diffraction-grating spectroscope
if the prism be removed and replaced by a
transmission grating.
Spectrum
S13
Spectrum, Solar
With a plain reflection grating it is obvious
that we cannot see through the metal, but we
see the spectrum reflected from its surface, so
that, although we may use the same stand, the
collimator and telescope are arranged as at P,
G. Mounting a
Concave Grating
Reflection-grating
Spectroscope
in which C is the collimator, s the slit, T the
telescope, E the eyepiece, and G the grating.
Direct-vision grating spectroscopes are also
made, but in this case (as at H) the grating G
is cemented to a prism p of narrow angle, which
throws the central white beam w out of the field
of view. S is the slit, i, the lens, and E the eye-
piece. For all advanced work the concave
grating is most generally used, and it has the
great advantage that no lenses are required, for
the metal, being cast and polished to a spherical
form, acts like a concave mirror and forms an
image without the aid of lenses. The particu-
lar method of mounting concave gratings is
rather beyond the scope of this work, but the
principles involved may be given. In diagram
G, let A B be a circle struck from the centre c :
G is the grating. It is obvious that G is an arc
of the circle of which c G is the radius. Now it
was proved by Rowland that if a light source —
which is, of course, the sht — and the grating be
placed on the circumference of a circle G a c J3,
L Q
6
H. Direct-vision Grating Spectroscope
which has as diameter the radius of curvature
of the grating, then the image of the slit wotUd
also be formed on this circumference. There-
fore it would only be necessary to place an eye-
piece at the point where the image is formed
to see the spectrum.
SPECTRUM (Pr., Spectre ; Ger., Spektrum)
A ribbon or band of colours formed when a
narrow beam of heterogeneous light traverses
a dispersing medium such as a prism or diffrac-
tion grating.
SPECTRUM ANALYSIS (Fr, Analyse spec-
trale ; Ger., Spektral-analyse)
The analysis of a substance by burning or
otherwise raising it to the point of incandescence,
as, for instance, by the electric current, and then
examining the hght by a spectroscope. As all
substances give characteristic spectra, with
bright Unes always of the same wave-length, it
is possible to tell what substances are burning
33
or incandescent. Spectrum analysis is only
qualitative and not quantitative ; that is to say,
the elements present can be named, but the
quantities in which they exist in the substance
under examination cannot be stated.
SPECTRUM CURVE (Fr., Courbe spectrale ;
Ger., Spektruni-Krummung)
The curve obtained by photographing the
spectrum on a sensitive surface, which, by the
deposit of metallic silver or alteration of colour,
indicates the coloiirs to which the substance used
is sensitive.
SPECTRUM HELIOGRAPH {See "Helio-
graph.")
SPECTRUM, LUMINOSITY OF
The first examination of a spectrum at once
shows to the veriest tyro that the luminosity of
the colours varies enormously. The following
table gives the generally accepted distribution
of the colours and the visual luminosity of the
various regions of the solar spectrum.
Wave
Length X
Lumin-
Quantity
Colour
of light, the
Of the
Of the
osity
total being
colour
limits of
— 1,000
(i/i
the colour
Red . .
663
625
8
91
Orange . .
610
5oo
76
147
Yellow and )
Yellow-green j
575
550
100
396
Green and 1
Blue-green )
526
490
64
303
Bright blue I
and Indigo J
472
12
38
450
7
13
Blue-violet
440
430
Violet . .
420
4
12
Note that the above table applies only to the
solar spectrum as regards the last two columns,
and that the figures in these would difier for
almost every light source.
SPECTRUM, PHOTOGRAPHING THE {See
" Spectrography.")
SPECTRUM, SOLAR (Fr., Spectre solaire ;
Ger., Sonnenspektrum)
The spectrum given by direct or reflected sun-
light. As has been pointed out {see " Fraun-
hofer Lines "), the solar spectrum is crossed by
numerous dark lines of g?:eater or less breadth
and intensity, and the discovery of the actual
cause of these Unes is ascribed to Kirschofi in
1859. He enunciated three laws, which prac-
tically explain the formation of all spectra : he
said (a) that a substance when excited by some
means tends to emit definite rays, the length
of the wave depending upon the substance and
its temperature ; (6) a substance also exerts a
definite absorption, which is a maximum for the
rays it emits ; {c) the ratio between the emis-
sive and absorptive power is constant for all
Spectrum, Virtual
substances at the same temperature. The first
two laws explain the occurrence of the Praun-
hofer lines in the solar spectrum.
SPECTRUM, VIRTUAL (Pr., Spectre virtuel:
Get., Virtuell Spektrum)
A term applied to any spectrum seen through
a prism or grating, and which is not formed by
the aid of lenses.
SPEED INDICATOR (Pr. Indicateur de vitesse ;
Get., Geschwindigkeitsmesser)
An appliance patented by the Thornton-
Pickard Company for use with their roller-blind
shutters. It consists of a dial marked with the
different speeds, and having a pointer so geared
as to move in accordance with the tension of the
spring blind. The indicator shows at a glance
the speed at which the shutter is set.
SPEEDS. PLATE {See " Sensitometry.")
SPERM CANDLE (See " Sensitometry," sub-
heading "The Standard Light.")
SPHERICAL ABERRATION
The failure of a lens having a spherical surface
to bring all the rays transmitted through it to
a focus in one plane, so that when the margins
of the image are in focus the centre is dififused.
When the rays passing through the margin of
the lens are brought to a focus nearer the lens
than are the rays transmitted through the
centre, the spherical aberration is said to be
positive ; when the contrary is the case, it is
said to be negative. The flatter the surface
of the lens which receives parallel rays from
an object, the worse is the aberration. It is
remedied by the use of a diaphragm or stop,
but as this reduces the amount of light the
lens manufacturer largely overcomes the trouble
in another way ; he combines two lenses, the
one showing positive and the other negative
aberration.
SPIKE OIL (Pr., Essence d'aspic ; Ger.,
Spikol or Lavendelol)
Synonym, oil of spike lavender. It is a pale
yellowish volatile oil with fragrant lavender
odour obtained from the leaves and tops of
Lavendula spica. It is used in some varnishes.
In process work, this oil is given in several
formulse as an addition to bitumen solution. It
prevents the film drying brittle.
SPILLER'S REDUCER {See "Copper Chlo-
ride.")
SPINTHARISCOPE
Sir William Crookes's instrument for demon-
strating the action of radium upon a fluorescent
screen.
SPIRIT OF HARTSHORN {See " Ammonia.")
SPIRIT LAMPS (Pr., Lampes d'alcool ; Ger.,
Spirituslampen)
Spirit lamps of different kinds are used for
various photographic purposes, as in heating
burnishers and solutions, warming negatives
prior to varnishing, etc. They all consist essenti-
514 Splroscope and Spirograph
ally of a reservoir for the spirit, having an
earthenware or metal tube in which is placed a
loose cotton wick. The flame given xs hot and
non-luminous.
SPIRIT LAMP, INCANDESCENT (Pr.,
Lumidre d'alcool d incandescence ; Ger.,
Spiritus Gliihlicht)
A lamp in which a mantle coated with rare
earths is rendered incandescent by vaporised and
ignited methylated spirit. Such lamps are
obtainable in various patterns for use m optical
and enlarging lanterns. A typical model is
shown at A. In this, the spirit, contained m the
Two Types of Incandescent Spirit I^imp
chamber R, is volatilised by means of the small
spirit flame s, placed below it, the height of
which is adjusted to a nicety by rack and pinion,
thus controlling the pressure of the combustible
vapour. The lamp can be brought into full
action in a few minutes, and yields a light of 300
candle-power for a couple of hours. In another
type of lamp, B, the spirit flows from a reservoir,
E, along a tube filled with asbestos. To start the
lamp, an asbestos fork, F, is moistened with
spirit and lighted, the heat vaporising the spirit
in the tube and causing the vapour to flow up
the bend and down the narrower tube at the side
to the burner, where it ignites. Once started,
the heat of the incandescent mantle keeps up the
supply of vapour, while the pressure may be
increased at will by means of the rubber bulb G.
{See also "Sol Lamp.")
SPIRIT LEVEL {See " Camera Level.")
SPIRIT PHOTOGRAPHY {See " Psychic Pho-
tography.")
SPIRIT OF SALT (See "Hydrochloric Acid.")
SPIRIT OF WINE {See "Alcohol.")
SPIRITUS GLONOINI
Nitro-glycerine in a i per cent, alcoholic
solution, and so named in the American Pharma-
copoeia. J . Vansant has recommended it as an
accelerator for use with pyro.
SPIROSCOPE AND SPIROGRAPH
The former is the mechanical and optical
apparatus used for viewing or projecting kine-
matograph pictures of microscopic size, the
images of which are borne by a disc known by
the second of the above terms. It is the inven'
tion of Theodore Brown and Charles Urban.
Spitzertype
S15
Spotting Prints
SPITZERTYPE
E. Spitzer's method of making process blocks.
No details have been published, but the results
seem to suggest that the basis of the process
is the reticulation of the gelatine film on the
lines of the Pretsch and D^as processes.
SPLASHES AND DROPS. PHOTOGRAPHY
OF
The photographs of splashes taken by A. M.
Worthington, F.R.S., and R. S. Cole, M.A., and
shown at the Royal Institution in 1894, were
obtained by allowing a drop to fall in absolute
darkness, and illuminating it at any desired
stage by a Leyden jar discharge taking place
between magnesium terminals. The following
description is due to Photography. The spark
was produced at the focus of a deep, silvered
watch glass G {see diagram), subtending an angle
of nearly 180°, and was brought very near to
the place of impact. A single quartz spectacle
Cleetromefer
Darb-room
O C
Arrangement for Photographing Splashes
lens, J, was substituted for the usual lens of the
camera, H, and thus the absorption of photo-
graphic rays by glass was avoided. The diagram
shows the arrangement of the apparatus. Simul-
taneously with tiie drop, a metal timing sphere,
D, was allowed to fall between two other insulated
spheres connected to the inner coats of two large
oppositely charged Leyden jars, B B, standing on
the same badly conducting table. C C indicate
paraffin blocks. Prom the outer coats of the
jars, wires E and F led into the dark-room, and
there terminated in a spark-gap between mag-
nesium terminals at the focus of a small concave
mirror, consisting of a silvered watch glass. The
Wimshurst maclnne, a, was turned till the lower
ball of the rough electrometer shown was lifted
up and struck a glass plate ; then the sphere
was liberated by tossing up by hand the remote
end of the light, horizontal, pivoted rod which
supported it. This broke the contact of crossed
wires beneath the rod, cut off the current from
the electro-magnet N in the dark-room, allowing
an indiarubber catapult, M, to toss up one end of a
similar horizontal lever, at whose other end the
drop I, had been supported, without adhesion, on
a smoked watch glass. By this means sphere and
drop were left in mid-air, free to f aU at the same
instant. The sphere, in its fall, discharged the
inner coats of the two Leyden jars, and this pro-
duced a simultaneous discharge at the spark-
gap between the outer coatings, thus illununat-
ing the plate k. The timing of the spark was
effected by adjusting the height of fall of the
timing sphere by sliding the liberating apparatus
up or down the vertical supporting rod. (See
also " Bullets in Flight, Photographing.")
SPONGE BRUSH
The Buckle brush, described under the head-
ing " Brushes."
SPOT CUTTER
An appliance for cutting number labels or
white spots for lantern slides. The numbers are
supplied printed on paper strips, and when one
is required a strip is paid into a slot in the
cutter till the required number is under a circular
aperture. On turning a handle at the bottom
of the cutter the number is cut cleanly out in
the form of a round disc. The advantage is that
it is much easier to cut out the numbers in
rotation as required than to hunt for them in
a boxful of loose labels.
SPOT. FLARE (See " Flare Spot.")
SPOTS ON PRINTS (See "Black Spots,"
"Dust Spots," etc.)
SPOTTING MEDIUM
A term sometimes given to the medium
applied to a negative to allow spotting, etc., to
be done, and sometimes to the material with
which the spotting is carried out. For the
former, see " Retouching " ; for the latter, see
" Spotting Negatives " and " Spotting Prints."
SPOTTING NEGATIVES
For spotting, a negative should be placed on
a retouching desk in front of a window, and a
sheet of white paper used as a reflector. For
small spots, finely pointed lead-pencils form the
best means of removal. Those marked HH, H,
and H B will be best, the hardest being used for
the smallest spots. Precision of touch is neces-
sary, and the use of a magnifying glass is very
desirable. It is essential ttat a touch be given
with the pencil accurately on the spot ; there
is a risk of pencilling on the film round the spot,
and so aggravating the defect. It is better to
leave the spot slightly visible as a grey rather
than attempt to remove it too thoroughly. It
may show as a strong white spot on the print
if worked too much. When spots are large, the
pencil will frequently fail to be effective. In
that case water-colour, applied with a brush or
a fine mapping pen, will be better. The most
suitable colour is either lamp-black or ivory-
black, used in a very thin solution, so that it is
grey rather than black. In many cases spots
may be difficult to remove without showing on
the print. The only course to adopt is to obliter-
ate them thoroughly, so that they show as white
spots on the print, and then touch them out on
the print as described under the headiag " Spot-
ting Prints."
SPOTTING PRINTS
Bromide prints, platinotypes apd carbon prints
should be spotted, when required, with water-
colour applied with a finely pointed brush; or
a lead-pencil, h b, may be used for matt bromide
Sprinkler
Si6
Stains, Removing
prints if they are not toned. Lamp-black water-
colour will be the most suitable for black
platinotypes, carbons and untoned bromides ;
while sepia and Vandyke brown mixed in various
proportions will allow any tint of brown carbon,
bromide or platinotype to be matched. For
glossy or semi-glossy bromide or silver prints a
little gum may be added to the colour for spotting,
and neutral tint and crimson lake added to the
stock of colours will provide material for match-
ing the tones of silver prints. No medium is
necessary as a general rule, but occasionally the
surface of a gelatine priut will repel the colour.
In that case, a very little prepared oxgall should
be added to the mixed colour ; it may be
obtained at an artists' colourman's. Spotting
should be done after the prints are mounted.
SPRINKLER (Pr., Aspersoir : Ger., Spren-
kelnder)
A rose spray used for washing negatives and
prints, and attached either to the end of a
rubber tube connected with the water tap, or
to a swing arm on the tap itself. A form of
sprinkler is also made containing a filter in
addition, to screw on any ordinary tap. Another
kind of sprinkler consists of a metal tube like an
inverted T, the horizontal arm of which is closed
at the ends and pierced with a row of holes,
while the end of the upright portion is connected
to a rubber tube leading to the water supply.
Also the name given to any appliance for
sprinkling or spraying the floors of dark-rooms
and other photographic workrooms, to lay the
dust.
SQUEEGEE (Pr., Rdcleur ; Get., Gummiquet-
sche)
An appliance used for pressing wet prints into
close contact with plate glass or ferrotype sheets
when glazing ; for rubbing prints down when
mounting ; and for various other purposes which
require Sie application of pressure or call for
the expression of moisture. There are two forms.
Flat Squeegee
Roller Squeegee
The flat squeegee. A, consists of a strip of thick
flexible rubber moim.ted in a wooden handle,
and is used by drawing it to and fro across the
print. It is sometimes used to remove splashes
of water and solution from the developing
bench, etc. In the roller squeegee, B, a movable
rubber roller is attached to a handle, the method
of use being obvious. A pattern with two
rollers is also made.
SQUEEGEE PAD
An accessory for glazing or matting prints.
It consists of a sheet of celluJoid, either glossy
or matt, placed between two covers of india-
rubber cloth, which are fastened to it by one
edge only. The prints are spread on the cellu-
loid, film side down, and the indiarubber cloth
laid over them, a squeegee being then applied
iu the usual manner. Both sides of the celluloid
can be used. The rubber covers are then turned
back and the celluloid sheet with the prints is
hung up by means of a hook or pin passed
through the edges of the covers. When dry, the
prints fall off with a glazed or matt surface.
SQUEEGEE PLATE
A name for the pulp slab [which see). It is also
applied to ferrotype plates and enamelled metal
plates resembling them, employed in glazing
prints.
STAGE PHOTOGRAPHY (See "Theatrical
and Kinematograph Photography.")
STAIN REMOVERS
Acid solutions (usually hydrochloric and
citric, combined with alum and sometimes with
other substances) are used for clearing away
stains caused by developers, particularly the
pyrogallic acid developer. To 4 oz. of a saturated
solution of common alum may be added i drm.
of hydrochloric add ; there are many other
formulse. Chapman Jones has stated that acid
stain removers are founded on wrong principles ;
the alum hardens the film and retards the wash-
ing away of stains, and the acid acts by lightening
the colour of the stain, which, however, is
rendered insoluble and is consequently &ced
in the film. More satisfactory methods will
be found described under the heading "Stains,
Removing."
STAINS, REMOVING
Stains on Hands. — Pyro and some other de-
velopers stain the fingers by prolonged use ; care
must be taken to avoid putting the fingers in solu-
tions, excepting when absolutely necessary. Any
tendency to staining may be entirely obviated
by rinsing the fingers and immersing them for
a few seconds in an acid fixing-bath immediately
after putting them in the developer. Rinsing and
drying must follow at once. An acid fixing-bath
or a solution of potassium meta-bisulphite will
also remove stains of permanganate and many
other photographic substances. It is a good plan
to bathe the hands in hot water and then, before
drying, rub glycerine into them.
Stains in Intensification. — Stains should not
arise if the negative is in good condition and if all
the previous work.has been carried out correctly.
Yellow stains that may appear during mercurial
intensification are due solely to imperfect fix-
ing of the negative. Insufficient washing after
fixing will also cause staining. There is no
method of removing these stains. In intensi-
fying by silver, Wellington's method, surface
staining may occur if the operation is very pro-
longed, the cause being the same as in a long or
forced development. These stains may be easily
removed by methylated spirit applied as directed
under the heading " Reducing Negatives by
Mechanical Means," or they may be treated by
thiocarbamide or the " hypo " and ferricyanide
solution.
Stale Plates
S17
Stars, Photographing
Stains on Negatives. — ^When negatives show
staiumg after development and fixing, the char-
acter of the stain will always indicate the cause
and the cure. Iridescent markings round the
edges of a negative are almost always caused by
using old plates, especially if the plates have
been kept under bad conditions or forced in
development. They may be removed by means
of thiocarbamide or by methylated spirit applied
with friction. Surface stains, semi-iridescent,
with rainbow-coloured markings, are sometimes
seen on negatives otherwise perfect. These are
due to scum on the developer, caused either by
nsing the same solution for several plates in
succession, or by mixing the developer in a
measure without rinsing after previous use. A
weak thiocarbamide solution will remove these
stains almost instantly. A weak " hypo " and
ferricyanide reducer will also remove them in a
few seconds.
Stains on Prints. — Silver prints show yellowish-
brown stains, semi - iridescent, if the surfaces
cling to the dish or to another print during the
first few seconds of washing in plain water before
toning. These stains are most frequently attri-
buted to " hypo," but they are in reality silver
stains. There is no method of removing them
satisfactorily. Similar stains may develop during
fixing, or in the first washing water after fixing,
if the prints are allowed to cling together ; and
they cannot be removed satisfactorily. Platino-
type prints may develop yellow stains after wash-
ing and drying if the clearing has been imper-
fectly or carelessly performed. It is difficult to
remove these stains without injuring the print ;
the best treatment is a strong solution of hydro-
chloric add, I part of pure acid to 10 or 12 of
water. Two or three successive baths of acid
may be used, the prints being afterwards washed
well. Prints on bromide or gaslight papers may
be stained from the same causes as given under
the sub-heading above, " Stains on Negatives."
The treatment is the same, excepting that solu-
tions about one-fourth of the strength are used.
STALE PLATES
Stale plates are distinguished after develop-
ment and fixing by an iridescent or fogged
edging round them ; but there is no satisfactory
method of telling whether a plate is stale pre-
vious to exposure and development. The deterio-
ration of plates is caused more by an unsuitable
atmosphere than by the mere lapse of time. When
plates are known to be stale, a special restrainer,
as follows, may be used with them : —
Potassium bromide . . 2 grs. -46 g.
Potassium bichromate . 2 „ -46 „
Water . . . . i oz. 1,000 ccs.
Double the normal exposure will not harm very
stale plates. When about to develop, take
enough water to cover the plate and mix with
it 30 drops of the special restrainer given above.
Plow the mixture over the plate and rock for a
minute or two ; in a measure have ready any
ordinary developer (not containing ammonia),
and pour off' the restrainer into the developer
and return the whole to the plate and develop
in the usual way ; add more restrainer if fog
appears. If the plates are exceptionally bad, a
single drop of sulphuric add may be added.
Development as above is very slow and the
results hard, that is to say, very contrasty ;
thus, stale plates are useful for certain kinds of
copying. The older the plates, the longer should
be the exposure and the greater the quantity
of restrainer used, and, of course, the harder
the result.
STAMP PHOTOGRAPHS
Stamp Photographs.")
(See " Postage
STAND, CAMERA (See " Camera Stand,"
"Step-ladder Stand," etc.)
STAND DEVELOPMENT (See " Development.
Stand.")
STANNOTYPE
A modification (1881) of the Woodburytype
process, also invented by W. B. Woodbury. In-
stead of forcing the gelatine into a block of soft
type metal by great pressure to make the matrix,
the relief, made of bichromated gelatine, is faced
with tin-foil.
STANNOUS CHLORIDE (See "Tin Chloride.")
STARCH (Pr., Amidon : Ger., Starke)
CoHioOj. A substance prepared from wheat,
rice, Indian com, potatoes, etc., and met with
in ihs form of lumps or powder. Its prindpal
photographic use is as a mountant. A variety
of starch is arrowroot, which gives an almost
dear solution when boiled, in which form it is
used as a size for photographic papers, ordinary
starch being sometimes used for the same pur-
pose. Starch, when heated to about 400° P.
(204° C), is converted into dextrine.
STARCH MOUNTANT (5ee "Mountants.")
STARS, PHOTOGRAPHING
The various methods of photographing stars
are so numerous that the most important of
them will be best treated under special headings,
as noted below. In general the science of
astrophotography may be divided into two main
dasses, depending on whether the photographic
camera is stationary, or is moved either by
hand or dockwork so that the apparent motion
of the stars across the field is neutralised.
Astrophotography with Stationary Camera. —
There are numerous subjects with which valuable
results may be obtained with no extra apparatus
beyond an ordinary camera. Suppose the
photographer wishes to prepare for himself an
accurate chart of a certain constellation of
stars. AH that is necessary is to direct the
camera, either by means of the tripod sliding
legs or by some form of tilting table, to the
middle of the constellation. The plates em-
ployed should be of the most rapid variety
obtainable, and preferably panchromatic or uni-
formly colour-sensitive. When all is quite rigid,
give an exposure of, say, ten or fifteen minutes
with the largest stop available. On developing
the plate a series of arcs of drcles having different
densities wiU be seen. These are the " trails " of
the stars which were projected on the plate,
the movement being due to the earth's rotation
past the star during the exposure. Obviously,
then, the length of the lines will depend on the
Stars, Photographing
Si8
Stars, Photographing
length of exposure. If, now, the beginning or
ending of every star trail is marked with a.
small dot of Indian ink, of the same diameter
as its corresponding line trail, the resulting
series of dots will show as a star map. If the
accompanying lines are found to be confusing,
it is quite simple to trace the dots on tracing
paper or cloth, when a star map will be obtained
wluch may be placed in front of a small box
containing a lamp. This contrivance wiU be
found of great help to anyone wishing to teach
the forms of the constellations, as the illuminated
stars may be easily seen by a number of people
at the same time.
Numerous other methods of utilising photo-
graphs obtained by fixed cameras will doubtless
occur to the worker. For example, at the times
of the year when it is known tiat a shower of
meteors is expected, the camera may be directed
to the proper position and left open for some
time in the hope of a meteor flashing across the
field of the lens. Many interesting pictures of
these remarkable celestial visitors have been
thus recorded. {See also " Meteor Photo-
graphy.")
Astrophoiography with Moving Cameras. — When
it is desired to obtain accurate charts of the
sky, the camera must be so mounted that by
means of suitable clockwork the stars may be
kept exactly on the same portions of the photo-
graphic plate throughout the exposure. The
motion of the stars from east to west across the
sky is at such a rate that a complete circuit of
the heavens is made once in 24 hours. If the
direction of motion be carefully examined, it
wiU be found that all the stars travel in circles
parallel to the equator, so that to follow them
we must employ what is called an equatorial
mounting ; this consists of an arrangement
whereby the axis of rotation can be tilted with
respect to the horizon, until at any given place
it is exactly parallel to the earth's axis. When
this is accurately adjusted and the clockwork
rated properly, it will be possible to obtkin
star photographs with any desired length of
exposure.
With the apparatus above described it becomes
possible to employ very powerful cameras, both
as to aperture and focal length, so as to record
stars so faint that they have never been seen
by the im aided eye. The telescopic star cameras
used in this way are of two kinds, depending on
whether a refracting or reflecting system is used
to give the image. The largest refracting lens
telescope existing is that made for the Paris
Exhibition of 1900, with a lens of 50 in. aperture
and 180 ft. focal length. This is not in use,
however, owing to the great expense of
working.
The largest lens in actual use is that at the
Yerkes Observatory, near Chicago, which has
an aperture of 40 in. and a focal length of about
60 ft. Numerous reflecting telescopes are in
use. The two largest now being used for photo-
graphy are 60 in. in diameter ; one, made by
the late Dr. A. A. Common, is now at Harvard
College Observatory, U.S.A. ; the other, made
by G. W. Ritchey, is at the Solar Observatory,
Pasadena, California. This last is probably the
most powerful telescope the world has ever
known, and the resulting photographs are of
wonderful clearness and beauty. Many re-
searches are being made with this 60 in. reflector
which are quite beyond the scope of any other
instrument, such as large scale photographs of
the spectra of stars and planets, measurements
of the velocities of stars in space, etc.
One of the greatest applications of the equa-
torially mounted star camera has been the
" International Photographic Chart of the Sky,"
a co-operative scheme shared by all the nations
of the world. This was inaugurated at Paris
in 1887, when a congress of the world's astro-
nomers resolved to prepare a photographic
chart of the heavens, showing stars down to the
fourteenth magnitude. This was to be supple-
mented by a second series of plates of short
exposure, for a catalogue of stars down to the
eleventh magnitude. The standard instrument
was a twin refracting telescope — a photographic
camera of 1 3 in. aperture and 1 1 ft. focal length,
attached to a visual guiding telescope of 11 in.
aperture. Each photographic plate covers about
four square degrees of the sky. This magnificent
work is now being brought to a successful
conclusion, and the publication of the charts
is well advanced.
A task of such magnitude is obviously not
applicable to the detection of rapid changes in
the positions or brightness of the stars. To
provide information for this purpose Pickering,
at Harvard College Observatory, has arranged
for a complete photographic survey of the sky
with a short focus camera. Copies of this work
are obtainable, and it will be repeated at con-
venient intervals, so that a definite check will
be possible on any changes in the positions or
magnitudes of the stars.
For charting very condensed areas, such as
the Milky Way, in which it is important to
obtain a record of the general aggregation of
the stars, the most successful meUiod is that
adopted by Barnard, who used at the Lick and
Yerkes Observatories a small lantern lens of
2 in. aperture and 5 in. focal length. An
apparatus of this type gives exquisite pictures
of the star groupings when used with an
efficient equatorial mounting.
Photography is now used for systematically
recording the brilliancy of stars. This is done
by obtaining photographs with the plate slightly
displaced from the true focus for parallel rays,
so that the image of each star shows as a small
round disc instead of a very tiny point. A
series of standard density squares from a standard
light source are impressed on the plates before
exposure to the sky ; it is therefore possible by
measuring these density squares and the star
discs to obtain accurate values of the relative
brightness of the stars.
Planet Photography. — ^This is so much beyond
the reach of the ordinary photographer that it
is only suitable here to give a short outline of
the results obtained by the photographic
astronomer provided with the very special
equipment necessary for the purpose.
The first successful attempts to obtain pictures
of the planets showing the details of their
surface markings were made by Gould, at
Cordoba, in 1879, on the planet Mars, and by
Dr. Common in the same year on Jupiter. The
earliest satisfactory photographs of Uie wonder-
Stars, Photographing
519
Stars, Photographing
ful planet Saturn, with his accompanying
system of rings, were obtained by M. M. Henri,
at the Paris Observatory, in 1885.
Mars has always proved a fascinating object
on account of its being our nearest celestial
neighbour after the moon, and, further, it is
thought that the conditions of its surface are
somewhat similar to our own — that is, there
seems good reason for beUeving that land and
water are present in separated masses as on
our earth, and the presence of ice is also very
probable. The photographs of Mars show very
clearly that the surface of the planet is irregularly
divided into dusky and light patches, and at
the two diametrically opposite points corre-
sponding to the axes of rotation, there are small
oval patches of intensely white material, which
are generally considered to be the snow caps
at the extremities of the poles of the planet,
corresponding to our Arctic and Antarctic
regions of perpetual ice and snow. This view
is rendered more feasible by the further fact
that these white polar caps are found to vary
regularly in extent, getting smaller and smaller
as the summer season on the planet approaches,
and gradually increasing again on the advent
of the Martian winter.
Some of the most beautiful photographs of
Mars have been taken by Professor Lowell
with his telescope of 24 in. aperture, at Arizona,
on an elevated plateau well up out of the lower
strata of our atmosphere. He has also succeeded
in photographing several of the peculiar thread-
like markings called " canals," which have
caused so much controversy among astronomers
during the last twenty years.
Excellent photographs have also been taken
by Barnard at the Yerkes Observatory, and by
Hale at the Mount Wilson Observatory. The
general equipment is the same, and consists of
the largest and most perfect telescope that the
observer can command ; to this is applied the
highest power magnifier that the objective
and atmospheric conditions will stand, and also
photographic plates of special rapidity and
colour sensitiveness. The atmospheric condi-
tions vary so rapidly that for such objects as
planets it is usual to arrange the plate holder
as a repeating back, fitted to take a great number
of pictaires at short intervals on the same plate,
so that the few times of best definition may
perhaps be caught among a great number of
mediocre ones.
Jupiter, although not productive of such
great discussion, offers many features for which
the application of photography is eminently
suitable. This planet is apparently clothed in
clouds, and these are arranged in broad belts
parallel to the planet's equator, showing as
bands of alternately light and dark material
on the photographs. In one of them there is a
remarkable feature called the " Great Red
Spot," a large oval patch of ruddy colour which
has been visible now for many years. It is
hoped that large scale pictures of this pheno-
menon may definitely decide the relation of its
drift among the surrounding cloud belts, and
later, possibly, its true character.
Saturn is the furthermost of the planets
of the solar system of which satisfactory
photographs have been obtained. Numerous
excellent pictures have recently been taken at
the Lowell Observatory, showing most minute
detaU on the cloud belts and the surface of the
rings.
Uranus and Neptune, the two outermost
planets, have been often photographed, but
their images so far have only been small discs
without definite surface detail.
The minor planets are a closely associated
swarm of small bodies revolving round the
sun in orbits between Mars and Jupiter. The
majority of them are so small as usually to be
unobservable even with the largest telescopes,
and they have nearly all been discovered by
means of their trails on photographic plates
exposed for long periods to the sky. The early
part of this work was done by moving the
telescopic camera at the same rate as the earth's
rotation, so that each photograph showed all
the stars as minute bright points. If then an
object was foimd showing an elongated image,
and it was decided to be a real marking, it was
assigned a provisional number as a new planet,
and after full confirmation on subsequent
photographs n name would be given to it.
Lately an ingenious method has been devised
to permit of the discovery of small planets
being recorded which, if left to trail, would be
too faint to give any perceptible image. Suffi-
cient is now known of the general motions of
this belt of small planets to allow of their probable
velocity in any region of their orbit being fairly
accurately calculated. The camera is then set
to travel at this velocity, instead of at the
earth's velocity as before. This means that
the little planet will now be able to accumulate
its hght on the image on the plate, and it will
thus show up as a small round point among the
surrounding stars represented by short elongated
trails. The plates used should be of the fastest
emulsion available, consistent with a fine grain.
NebulcB Photography. — This branch of photo-
graphic astronomy is almost beyond the reach
of the camera alone. There are only one or
two nebulae which can be photographed with
rapid exposures, and then only on a very small
scale, scarcely repaying the trouble which may
be taken. With a small expenditure, however,
a very serviceable driving mechanism may be
obtained or constructed by the observer, and
then very interesting pictures of the chief
nebulae may be photographed without any greater
difficulty than is experienced in taking high-
power telephotographs. The focal length of
lens to be selected depends to some extent on
the object selected for experiment. Thus the ne-
bulae of Orion, Andromeda, the Magellanic Cloud,
the Pleiades, and other objects of considerable
extent give very beautiful pictures with cameras
of quite moderate focal lengths, say from
1 2 to 30 in. Naturally on such objects the lens
should be of the largest relative aperture possible,
as then the exposure necessary will be the
minimum, and the chances of disturbance during
the operation reduced as far as possible. The
range of gradation is so great that the utmost
care sho^d be taken with the development,
a moderately dilute solution of any of the
standard formulae being suitable. All plates
should be thickly backed, otherwise the star
images distributed over the region will be so
Statuary, Photographing
520
Stereoscope
expanded as to detract seriously from the value
of the picture.
The famous Orion, or " Pish Mouth," nebula
was first satisfactorily portrayed by photo-
graphy by Draper, in 1880. Later magnificent
pictures were obtained by Dr. Common in
1883, at Ealing, with a large silvered glass
reflector, 36- in. in diameter, which he had
himself entirely constructed. With further
advances in the rapidity of photographic plates
and perfection of apparatus it was possible to
delineate greater and fainter extensions, and
also by employing iustruments of enormous
length the fine detailed structure was for the
first time brought to our knowledge. The
greatest advances of recent years were made
by Keeler, at the Lick Observatory, California,
and Ritchey, at the Yerkes Observatory, near
Chicago. The former made an extensive survey
of the class of nebulae whose structure is dis-
tinctly spiral, and published an atlas of beautiful
reproductions of the most important. Ritchey
has more specially aimed at obtaiuing specially
large-scale pictures of the principal nebulae,
showing the wonderful relationships existing
between the cloud-like wisps and the star
aggregations with which they are apparently
associated. The study of these pictures is of
the greatest importance.
STATUARY, PHOTOGRAPHING
Statuary should always be photographed in
a light as softly diffused as possible in order to
secure roundness and softness ; but in order
to secure contrast it is necessary that the
direction of the lighting should be from one
side, and sufficiently pronounced to give shadows
and relief. In most cases a point of view
towards one side will be the most satisfactory,
and this should be the opposite side to that
from which the light is coming. Occasionally,
however, a full front view must be taken. A
dark background, which will show as a dark
grey in the print, should be used when possible,
though in many cases the photographer will
have very little choice. In outdoor statuary,
dark foliage at a distance from the group wiU
form a good background, and direct sunshine
must be avoided. When a suitable background
cannot be obtained, double-printing should be
adopted.
A good method of determining the exposure
for groups of statuary is by means of a meter,
the meter being held close to the statuary and
facing the camera. Using lens aperture //16
and a plate 200 H. and D., the exposure for a
single figure or small group of white statuary,
not more than 5 ft. or 6 ft. high, will be one- tenth
of the time that the meter requires to match its
standard tint if a Wynne meter is used, and
one-twentieth for a Watkins. Por bronze or
dark figures, one-fifth of the Wynne meter
time, and one-tenth of the Watkins, should be
given. Large groups, 10 ft. or 12 ft. high, will
require half these exposures.
STELLAR PHOTOGRAPHY {See "Stars,
Photographing.' ' )
STENOPAIC PHOTOGRAPHY
Synonymous with pinhole photography.
STEP-LADDER STAND
A type of camera stand, largely used in Prance
for street views, etc., when it is desirable to have
the camera in a position above the heads of the
spectators or pedestrians The type most widely
Step-ladder Stand
used consists of a step ladder of a convenient
height to the top of which is hinged a table
upon which the camera is screwed, the table
and camera being adjusted by means of strut B.
STEREOPTICON
The American name for the optical lantern.
STEREOPHOTODUPLICON
An arrangement for taking stereoscopic
photographs, invented by Theodore Brown and
described under "Stereoscopic Photography."
STEREOSCOPE (Pr., SUrioscope ; Ger., Stereo-
skop)
An optical instrument for uniting into one
image two plane representations as seen by
each eye separately, and giving to them the
appearance of relief and solidity. The subject
of binocular vision was studied by various optical
writers who have flourished since the time of
Galen. Baptista Porta, one of the most
eminent of them, repeats, in his work " On
Refraction," the propositions of Euclid on the
vision of a sphere with one and both eyes.
Leonardo da Vinci referred to the dis-
similarity of the pictures seen by each eye as
the reason why " a painting can never show a
A. Diagram Illustrating Stereoscopic Relief
relievo equal to that of the natural objects,
unless these be viewed at a distance and with
a single eye," which he thus demonstrates. If
an object, c (in diagram A), be viewed by a
single eye at A, all objects in the space belund
it — included, as it were, in a shadow E C F, cast
by a candle at A — are invisible to that eye;
but when the other eye at B is opened, part
of these objects become visible to it, those only
Stereoscope
S2I
Stereoscope
being hid from both eyes that are included, as it
were, in the double shadow c d cast by two lights
at A and b, and terminated in d ; the angular
space E D G, beyond D, is always visible to both
eyes. The hidden space c D is so much shorter
as the object c is smaller and nearer to the eyes.
Elliot was the first to construct a stereoscope ;
but as it was devoid of lenses, the coalescing of
the two pictures depended upon a somewhat
scope," the fundamental principle of which
forms the basis of all modem instruments. He
conceived the idea that if prisms or sections of
complete lenses were used to divert the rays
commg from two pictures placed side by side,
so that their images were thrown to a common
centre, the evils of reflection obtaining in all
reflecting instruments would be altogether dis-
missed. Diagram D shows his instrument, a
o
1. R
C. Wheatstone's
Stereoscope
6 6
L R L R L R
D.Brewster's E. Brown's " Blocket " F. Prism
Stereoscope Stereoscope Stereoscope
unnatoral accommodation of the eyes. In a
box, F {see diagram B), he made apertures, D and
E, and at the opposite end a single aperture c.
The pictures to be combined were placed at a
distance behind the box, with the picture
belonging to the left eye at B, and the picture
belonging to the right eye at A. On placing the
eyes at i, R their axes crossed at c, and then, by
a slight effort in focal accommodation to A B,
the two pictures a and b were seen combined
and presented the desired illusion. Only persons
possessing the power to accommodate the
focus of the eyes to a remote plane whilst
G. Bates's Improvement on the Holmes
Stereoscope
their axes were converged to a nearer plane,
could obtain the desired result. Wheatstone's
" Reflecting Stereoscope " (C) proved to be the
first practical stereoscope. Two plane mirrors
MM, set at an angle of 45°, reflect the stereo-
scopic pictures A and b into the eyes at z, and
R, so that the combined result is seen somewhere
in the direction of o. The mirrors are fixed, but
the distance between a and b is made adjustable
by a screw, threaded (left and right) at each end.
Sir David Brewste?, who appears to have been
investigating stereoscopic phenomena at the
same time as Wheatstone, devised what is
known as the " Refracting or Lenticular Stereo-
and b represent the pictures ; d and E are a
pair of prisms fitted to a suitable framework
and with their thinner edges turned towards
each other. On placing the eyes at i, R, the
pictiures A B are seen at a common point c, and
stereoscopic solidity and relief results. Brewster
soon found that the use of sections of convex
lenses effected the necessary refraction, and at
the same time provided magnifiers. The best-
known form of Brewster's Lenticular Stereoscope
is that of a tapering box, with the lenses at one
end, and at the other a groove for the reception
of the pictures. The box contains further a
ground-glass panel at the back, so that when
transparencies are under observation they are
viewed by transmitted light ; while for opaque
pictures, the box is fitted with a reflector hinged
at the top.
Dr. Oliver Wendell Holmes, of America, in
1 861, invented a form somewhat like that
illustrated at G, but without the sliding view-
holder, the latter improvement being added by
Joseph L. Bates, of Boston, in 1864. The
design shown at G has become universal. There
are some persons, however, who experience
considerable difficulty in seeing stereoscopic
views properly with this dass of instrument,
the reason generally being that the pupillary
centres of their eyes are not close enough together
or far enough apart to suit the index of refrac-
tion and magnification of the lenses of the
particular stereoscope in use. To obviate this
diflS-culty, stereoscopes have been designed with
means for varying the separation of the lenses,
Baird's Lothian stereoscope being a good
example of this type of instrument ; the proper
distance for the pictures in relation to the
lenses is arrived at by sliding the view-holder
along parallel carrying tubes, the latter being
detachable so that the instrument may be used
for the examination of stereoscopic prints
mounted in albums.
Stereoscopic Camera
522
Stereoscopic Photography
Theodore Brown's " Blocket " instrument (see
E) is probably the smallest stereoscope.
It is based on the laws of reflection, and
acts as follows : — Let the pictures be repre-
sented as situated at A B, the eyes of the
observer at i, and R, and the optical part at E.
The left eye i, sees its picture by direct vision
from I, to A. Inside the small casing E two
mirrors are fixed facing each other, but not
quite parallel. The right eye R sees in the
mirror c an image of the picture B by reflection
from mirror d, and, by a suitable adjustment
in the relative angles of these two mirrors, B
is superimposed upon A, where stereoscopic
fusion takes place. If a prism of the shape of
the space between the mirrors c and D is sub-
stituted for the mirrors and the casing is dis-
pensed with, a prism stereoscope (shown at P)
is the result, and the light will be acted upon
precisely in the same manner and with the
same result.
STEREOSCOPIC CAMERA {See "Stereo-
scopic Photography.")
STEREOSCOPIC PHOTOGRAPHY
The invention of the stereoscope being prior
to the discovery of photography, the first
pictures for this instrument consisted of line
drawings. With the advent of photography,
the stereoscope became increasingly popular, as
this discovery provided the means of repro-
ducing the minutest details of a subject binocu-
larly with absolute precision. To secure a
photographic slide for the stereoscope, it is
necessary that two distinct photographs of the
subject be taken from standpoints corresponding
to the positions of the two eyes, and that these
photographs be mounted side by side. If the
subject is still-life, the two pictures may be
taken by successive exposures, moving the
camera between them a distance of 2f in. to
3 in. To facilitate the operation, various con-
trivances have been devised, an example of
which is shown at A, in which A is a slab of
wood having attached to its upper surface two
narrower strips B c linked together at D parallel-
rule fashion. B is fixed to the base A, while C
G jIV] K Hf--; L
in plan a camera tumable on its axis at j.
If the dark-slide, holding a plate, is furnished
with an opaque card just half the size of the
plate itself and loose enough to be shaken from
one end of the dark-slide to the other without
opening the slide, the two photographs of one
subject may be obtained on a single plate. The
picture for the right eye is secured with the
camera in the position indicated in full line,
covering the field between A B, half the plate
only at H being at first exposed. The dark-
slide is then closed and withdrawn from the
camera for the purpose of shaking the opaque
card from G to H ; it is re-inserted in the camera
and the shutter drawn out so that the portion
of the plate at G may now be exposed. Before
uncapping the lens, however, the camera is
turned slightly from left to right, so that it
covers the field between CD. A stereoscopic
I M vl N
A. Arrangement for Stereoscopic Photography
with Single Camera
is free to swing. The camera to be used is
secured to c and rests lightly on B. With the
camera in the position indicated at K i, M N,
the first exposure is made, which will give the
picture belonging to the right eye. The strip
C carrying the camera is now moved so that the
camera occupies the position indicated at
G H 1 J, when the second (left eye) picture is
taken. Another method of stereo-photography
with a single camera and by successive exposures
is Indicated in diagram B, in which E represents
<2^^>J
_L'
'.F
B. Another Arrangement
for Stereoscopic Photo-
graphy with Single
Camera
C. Brown's
Stereophoto-
dupUcon
pair of images will thus be impressed upon one
plate. Further, if the operation be carried out
in the order indicated no transposition of the
finished prints will be required. Stereo-photo-
graphy by the successive exposures and displace-
ment system, whilst being useful for stUl-life or
fixed subjects, cannot be adopted with success in
cases where movement of any part of the subject
is likely to occur, or when the illumination of
the subject is liable to alter. The most perfect
results for the stereoscope can only be obtained
when the two images are received upon the
plate simultaneously. It is not, however,
impossible to do this with a single-lens camera.
For example, in Brown's stereophoto-duplicon
(C) there is a chamber forming a supplementary
extension of an ordinary camera. In the
chamber are placed four mirrors as at D E H G.
Let A B represent the subject to be photographed.
Taking the centre ray, the light coming from C
strikes the surface of the two outermost mirrors
D G, is reflected to E h, thence through the lens
Stereoscopic Photography
523
Stereoscopic Projection
J to the plate i F at the back of the camera.
Images from the binocular angle are thus secured
simultaneously on one plate and at one exposure,
and as the light crosses before reaching the
plate the pictures are taken so that the negative
yields a pair ready transposed for immediate
inspection in the stereoscope.
A modification of the apparatus just described
is that of the so-called stereoscopic transmitter,
in which only two mirrors are employed, set at
an angle to each other and placed at an angle
of about 45° in relation to the axis of the lens
of an ordinary camera. Transposition of the
images takes place before the light reaches the
sensitive plate. The mirrors are surface-silvered
and of the kind used in reflex cameras.
The ideal apparatus for stereoscopic photo-
graphy consists of a camera furnished with a
pair of carefully matched achromatic and recti-
linear lenses of 5 in. to 6 in. focal length duly
corrected for spherical aberration. The distance
between two such lenses should be adjustable,
so that for near subjects their separation may
be reduced to 2 in., or for remote subjects
increased to 3 in. or 3^ in. The mechanism
controlling the opening and closing of the two
shutter apertures should be such as to ensure
absolutely synchronous working. I,enses of a
shorter focal length than 5 in. are unsuitable
for stereoscopic work, as they appear to give
an exaggerated perspective which is especially
noticeable in architectural subjects. Again,
too great a separation of the lenses on a stereo-
scopic camera induces abnormal relief in the
stereoscope, besides making it difficult for the
two pictures to be seen blended together at
all planes in the composition.
The actual practice of stereoscopic photo-
graphy, once the principle has been grasped, is
simple. Bxposure and development are as
usual, taking great care, however, when the
two images are on separate plates, to obtain
results as uniform as possible. Hand-work on
the negative is not desirable, and, indeed, will
militate against success. It is only in the
transposition of the prints that there is any
difficulty. It has already been shown that by
«ome methods of stereoscopic photography,
transposition of the prints is not necessary.
Again, it is possible to cut the negative and to
"transpose the halves in a special printing frame
so that the print obtained is suitable for use
without alteration ; but in the case of photo-
graphs taken in two-lens cameras, and when
the negative is not cut before printing, the
following procedure will be necessary : Lay
the print face downwards, and lightly mark
the edges of the print so that the sequence of
the images can be recognised at a later stage.
Assume that, as the print lies face down, the
image on the left is No. i, and that on the right
No. 2. Carefully trim, leaving on the right of
the right-hand print J in. more of the picture
than appears on the left-hand print ; in the same
way leave on the left of the left-hand print
i in. more of the picture than appears on the
right-hand print. Next sever the two images
and mount the prints, being careful to place
them about -J in. apart. Looking at the face
side of the prints. No. i wUl be on the left
and No. 2 on the right.
STEREOSCOPIC PROJECTION
The projection of a pair of stereoscopic
pictures in such a manner that each eye of the
observer shall see but one image, the one belong-
ing to it. In 1 841 Dove showed that if one
of a pair of stereoscopic pictures is outlined in
blue on a white ground, and the other element
.b"
6 5
A. D' Almeida's System of Stereoscopic Projection
in red, the two being approximately superposed
upon the same sheet, a spectator furnished
with red and blue glasses will see the outlines
as a single solid image. In demonstrating this
fact Dove obviously foreshadowed the work of
Ducos du Hauron. {See " Anaglyph.") De la
Blanchdre and Claudet, some years later, at-
tempted to eliminate the use of the spectacles.
J. Ch. D' Almeida, in his communication
(1858) to the French Academy of Sciences,
described how he placed in the course of the
luminous rays two coloured glasses (red and
green) ; the observer views the projections
through glasses of similar colours, the fusion
being seen as a black and white combination
in stereoscopic relief. D'Almeida's system is
shown at A. A represents the green image on
the lantern screen, and B the red image ; the
O 6
(- R L R
B and C. Drouin's and Moessard's Systems of
Stereoscopic Projection
former is blotted out with the green spectacle
glass B*, so that the right eye R sees only the
red image B. Likewise, the red image is blotted
out by the red glass a^, so that the left eye i,
sees only the green picture A. Many modem
experimenters have modified the above system.
It has been suggested that, instead of using two
separate projections, similar results may be
obtained by making a composite slide and pro-
jecting the same by a single lantern.
Stereoscopic Projection
524
Stereoscopic Spectacles
B' Almeida also invented the eclipse system
in which a perforated shutter rotates in front
of side-by-side lanterns. Another form of
eclipse system, but of small practical value,
consists in using a box apparatus similar to
Blliot's stereoscope.
There are numerous ways in which stereoscopic
elements when projected side by side upon a
screen may be united so as to produce the
desired results. Drouin, of France, suggested
the system shown at B. The stereoscopic
elements C D being projected by a lantern, D is
seen by the right eye, R, direct, and C by reflection
in the prism. The light emanating from c
impinges at B, is deflected to A and thence to
the left eye i,. The left eye, therefore, sees
the image of C, superposed on the image D,
where unison takes place and stereoscopic
effect results.
Moessard used two prisms, mounted opera-
glass fashion. C shows an arrangement by
which a single mirror M suffices to superpose a
second image of the necessary pair upon its
complement image D. Two lanterns A B are
sed to project their respective elements upon
lantern screens, c D. The observer, with his
eyes situated at L R, sees one element, D, by
&
€Z?-
\OVi-^P<'
D. Anderson's System of Stereoscopic Projection
direct vision, and the companion element, c,
by reflection in the mirror, stereoscopic relief
resulting. There is a number of similar systems.
In 1890, Anderson, of Birmingham, invented
stereoscopic lantern projection by means of
polarised light. Two lanterns project the
elements in superposition upon the screen s, in
diagram D. Before each lantern is a polariser
p p'. The picture received by the screen is
thus formed of two polarised pictures ; for
instance, one in a vertical, and the other in a
horizontal position. The observer looking at
the composite picture through analysers A A*,
placed before his eyes, E ES will see with each
eye its proper element, and fusion results. The
fact that light is lost in polarisation and depolari-
sation somewhat discounted Anderson's method ;
but to rectify matters a flexible screen having
a metallic reflecting surface was introduced, and
this also had the merit of preventing depolari-
sation apart from the analysers. Anderson
also constructed his polarisers and analysers
of bundles of thin glass, like the microscopic
cover glass, and set at about the polarising
angle. The glasses iu the bundles are not set
quite parallel to each other ; otherwise Hi-
defined images would result, owing to disturbing
reflections. Many of the systems above described
are obviously applicable to the kinematograph,
and, indeed, almost all have been tried with
varying success.
Direct Stereoscopic Projection. — AH the fore-
going systems may be termed indirect methods
of stereoscopic projection, inasmuch that in
every case the final results are observed after
looking through coloiired glasses, prisms, mirrors,
shutters or other devices ; but as long as inter-
mediate agencies are necessary, stereoscopic
relief upon the lantern screen will remain com-
mercially impracticable. The only systems of
direct stereoscopic lantern and kinematograph
projection have been evolved by Theodore
Brown. One applies to ordinary lanterns and
the other to the kinematograph. The former
consists of a special carrier furnished with a
plurality of glass slides or films carrying different
sections of one subject in panoramic order and
with varying speeds according to the supposed
distance of each plane in the composition of
the subject depicted. Remote mountains are
depicted on one glass or rollable film ; the
middle distant objects (ships) on a second
one; and foreground objects (trees, etc.) on a
third. The mechanism of the carrier through
which the three glasses are caused to slide hori-
zontally is such that the first has hardly any
movement, the second moderate movement,
and the third quick movement. On the screen,
and before the mechanism is set working, the
composition appears as an ordinary picture •
but on operating, and thus impartmg the
panoramic and varying movements, the observer
at once perceives a depth of perspective, such as
is apparent in any ordinary stereoscope. The
fast-moving foreground appears decidedly at
a near plane, the sea and ships at a distance
beyond the foreground, and, finally, the remote
mountains at a great distance away. With this
impression comes the sense of actual space
between foreground and background. In com-
plicated subjects as many as six distinct layers
of rollable films have been introduced.
In Brown's direct system as applied to kine-
matographs, there are four chief modes of pro-
cedure : ( I ) Placing the subject on a rotatable
stand revolved synchronously with the working
of the taking camera ; (2) Causing the camera
to circumscribe the subject, by making the
former travel round the subject at a speed
regulated by the working of the camera ;
(3) Using the camera on a special tripod head,
designed to give an oscillation to the camera
whilst in operation ; and (4) Taking the subject
in a continuous panoramic direction, at a speed
of operating according to the movement of the
vehicle carrying the camera.
STEREOSCOPIC SPECTACLES
Spectacles at one time largely used tor viewing
stereoscopic prints. They are even now used
for viewing stereoscopic photographs in books
and at times when the prints cannot be placed
in a stereoscope. The earliest form of stereo-
scopic spectacles was made by Duboscq, of Paris,
about 1852. Later he introduced spectacles
which were actually skeleton box stereoscopes.
John Parker, in the late 'fifties of the last century,
made spectacles which were worn on the nose,
but were encumbered with a division plate 01
blind on the bridge.
Stereoscopic Vision
52s
Stoppers, Removing Fixed
/!
;E
\l
Stereoscopic spectacles of a different kind are
used for inspecting anaglyphs. {See " Anaglypho-
scope.")
STEREOSCOPIC VISION
A term used in reference to the power to see
stereoscopic images coalesced without the aid
of any instrument whatsoever. Briefly, it
consists in directing the eyes' axes to a remote
plane whilst accommodating their focus to a
near plane. As this operation involves strain
and considerable practice before it can be
successfully accomplished, various suggestions
have been made to assist the observer to train
his eyes in the acquisition of this power. Prob-
ably the most successful method of acquiring
the power to see stereographs stereoscopically
without an optical instrument is the following : —
Referring to the diagram, cut a
strip 1 in. wide out of both the
right- and left-hand prints of a
stereogram. The portions se-
lected should show remote as well
as near objects, and the foremost
object should occupy the centre
position in each strip. Obtain
a piece of cardboard (preferably
dead black) if in. wide and about
6 in. high ; bend this at right
angles in the centre, so that half
may lie flat on a table, while the
other half wiU stand erect.
Place the two strips of view at
A B, side by side, supported at
the back, and at a distance of
about 3 ft. from them place
the cardboard E. I/Ower the
eyes l,R so that they are just
above the level of the table top
and at a distance from E of
about 7 in., and in such a position that the left
eye I. sees only the strip A, and the right eye R
sees only the strip B, each eye being prevented
from seeing the other strip by the shutter card E.
As the two corresponding points in the views
A and B have a separation only of 1 in. instead
of 2|- in. or 3 in. as in ordinary stereoscopic
slides, the eyes are easily made to diverge
their axes to this slight extent ; and the result
is the two pictures combine and stereoscopic
relief results. Having succeeded in coalescing
A and B in this position, their separation may
be gradually increased, until corresponding
points reach 2f in. This done, ordinary full-
sized views may be substituted for A B, and
when by practice in this manner the observer
has learnt the secret of muscular control of the
axes of the eyes, he may dispense with the
cardboard.
STERRY'S PROCESS
A process of obtaining soft bromide prints
from very hard negatives, introduced by John
Sterry. The exposed paper is immersed for about
a minute in a ^ per cent, solution of potassium
bichromate, washed and developed in the usual
way, double the customary time being necessary.
It will be found that the shadows retain much
gradation. The colour of the image is not in-
terfered with, and the process is also available
for lantern plates.
00
L R
Diagram Illus-
trating Stereo-
scopic Vision
STIGMATIC LENS
A lens free from astigmatism (fully described
under its own heading). In addition, it is free
from chromatic and spherical aberration.
STIGMA TYPE
A process of producing pictures by setting up
type characters consisting of dots, squares, etc.,
forming a sort of half-tone image ; introduced
by Carl Pasol Pflege, in Vienna, in 1868.
STIPPLE (Pr., Pointillage : Ger., Punktierung)
In retouching, working-up enlargements, etc.,
the covering of surfaces or filling-in pf spots and
imperfections with small points or dots, whether
applied by pencil, brush, or crayon. The opera-
tion is known as stippling, and the dotted or
grained work, however produced, as the stipple.
(See " Retouching.")
In process work and lithography, " stipple " is
a style of shading produced by making dots with
a fine brush in a regular geometrical pattern,
usually in small curves. By varying the size
and spacing of the dots, great variety of light
and shade is produced. Copper- and steel-plate
engravers produce a similar stipple by means of
a needle-point penetrating an etching ground.
Process workers usually obtain their stipples
ready made on copper plates, from which trans-
fers are taken, or by means of shading mediums
STIPPLETTE
A method of quickly and mechanically imi-
tating the effect of sable brush stippUng and
hatcWng, introduced by T. S. Bruce, of Hamp-
stead, in 1906.
STOCK SOLUTIONS {See "Solutions, Making
up.")
STONE, PRINTING ON {See " Marble, Photo-
graphs on.")
STOPPERS, REMOVING FIXED
Prevention being better than cure, both necks
and stoppers of glass bottles should be lubricated
with tallow, vaseline, etc. The various methods
of removing stoppers have been summarised as
follows: — "(i) Press the stopper (longways) in
one direction with the thumb (grasping the
bottle with the fingers of the same hand) ; now
with the other hand hold a chisel or file by the
iron part and tap the opposite end of the stopper
in the contrary direction to which you are press-
ing it. (2) Place the stopper in or under a clamp
— as that of a carpenter's bench— first wrapping
something soft round it, as a piece of leather or
wool. Considerable leverage can thus be obtained,
but it must not be used to too great an extent
or the stopper will snap off. (3) A substitute
for the wooden clamp is the use of a key whose
handle is just large enough to go over the
wrapped-up stopper. These three may be termed
the mechanical methods. The use of heat is
also very effective in expanding the neck of the
bottle. For this purpose we may (4) invert the
bottle and dip stopper and neck into a saucepan
of hot water. A string should be tied roimd the
stopper or it may drop out and the contents of
the bottle be lost. (5) Rotate the neck of the
bottle rapidly in the flame of a Bunsen burner.
Stopping-down
526 Studio Design and Construction
This is a very effective method, but requires care.
(6) Take one turn of a stout piece of string round
the neck, and then by means of the two ends
saw the string rapidly backwards and forwards.
The heat produced by friction will cause the
neck to expand."
Stoppers may become fixed owing to the
evaporation of their contents, the solid matter
crystallising between the neck and the stopper.
The remedy is to pour some of the solvent used
to make the solution round the stopper and
renew as may be necessary, giving it time to
work its way between stopper and neck.
STOPPING-DOWN
The use of a smaller stop to decrease the
aperture of a lens with the object of improving
the depth of focus or definition, of reducing
spherical aberration to a negligible quantity, etc.
{See "Diaphragms.") Stopping-down directly
affects the duration of exposure, as explained
under the heading " Exposure Tables."
STOPPING-OUT {See " Blocking-out.")
STOPPING-OUT VARNISH
A black or coloured shellac or asphalt varnish
or lacquer used by process etchers for stopping-
out the portions of plates which have been
sufficiently etched, so that these parts are pro-
tected wlulst the remaining portions can be re-
etched.
STOPS {See "Diaphragms.")
STRESS MARKS
Synonymous with abrasion marks {which see).
STRIPPING FILMS {See " Film Stripping.")
STRONTIUM BROMIDE (Pr., Bromure de
strontium ; Ger., Strontiumhromid)
Synonym, bromide of strontia. SrSr^ 6HjO.
Molecular weight, 355'S. Solubility, i in i water ;
I in 30 alcohol. It is in the form of small colour-
less crystals, obtained by neutralising hydro-
bromic acid with strontium hydrate or carbonate.
Occasionally it is used in collodion emulsions.
The anhydrous salt, SrEr^, molecular weight
247-5, occurs as a. white and very hygroscopic
powder.
STRONTIUM CHLORIDE (Fr., Chlorure de
strontium ; Ger., Strontiumchlorid)
Synonym, chloride of strontia. SrClj 6HjO.
Molecular weight, 266-5. Solubilities, 1 in 1-33
water ; slightly soluble in alcohol. It occurs as
white needles, obtained in a similar manner to
the bromide, and it is used for making chloride
emulsions.
The anhydrous salt, SrClj, molecular weight
158-5, also occurs as a white powder; solubili-
ties, I in I -96 water, slightly soluble in alcohol.
STRONTIUM IODIDE (Pr., lodure de stron-
tium ; Ger., Strontiumiodid).
Synonym, iodide of strontia. Srl^ 6HjO.
Molecular weight, 449. Solubilities, i in -56,
water ; soluble in alcohol and ether. It is a
yellowish granular powder, prepared like the
bromide. It is used the same as the bromide.
The anhydrous salt has the formula Srl^.
Molecular weight, 233-5.
STUDIO CAMERA (Pr., Chambre d' atelier ;
Ger., Atelier Kamera)
The studio camera requires to be substantially
made, rigidity and strength being here of primary
importance, while portability is of secondary
importance. It should have a swing back, a
rising and falling front, and, if possible, a long
bellows extension for use in copying. The
illustration shows a typical studio camera and
stand. It is furnished with a rack and pinion at
both front and back, so that the camera can be
racked backward or forward at either end. Each
end has a draw-out extension in addition. Ex-
tending supports beneath the bellows prevent
Studio Camera
" sagging." The top of the stand has a tilting
table worked by an Archimedean screw operating
on an eccentric block, while for raising or lower-
ing the camera a screw cog movement is pro-
vided. The dark-slide has a roller shutter, and
is fitted with carriers for the smaller sizes of
plates. Some workers prefer to have the focusing
screen and dark-slide running side by side in
grooved rails at the back of the camera, as then
the ground glass may instantly be pushed out
of the way after focusing and the slide simul-
taneously brought into position. Such ar,
arrangement is often provided in connection
with the repeating back.
STUDIO DESIGN AND CONSTRUCTION
The studio, or " glass-house," as it was origin
ally called, or " gallery " or " operating room,"
as it is more generally termed in America, has,
from the first days of photography, received a
great amount of attention, and been the subject
of much theory and experiment. The earliest
illustration of the kind of place used for portrait-
ture in the days of the daguerreotype process is
to be found in a drawing by George Cruikshank,
which appeared in the Omnibus of 1844, and
which shows an apparently semidrcular room,
Studio Design and Construction 5^7 Studio Design and Construction
With the sitter placed on a high platform at the
Central point of the diameter to bring him close
to the completely glazed roof from which he
received a flood of all-round top lighting. Modi-
fications of this form of studio naturally came
in with the advent of the wet collodion process,
one of the earliest and most notable of these
being the original " tunnel " studio, A, of Monk-
hoven, so called from the tunnel or unlighted
portion in which the camera was placed. The
idea of this was partly that the operator might
be able to focus without the use of a cloth, and
partly that the eye of the sitter, who was still
illuminated by strong top front light, might have
the pupil less contracted by the latter when he
was looking into a dark space. It was also
thought that a more " restful " expression would
thereby be obtained, but the opposite effect was
often produced ; and with other improvements,
of which the first was the side lighting shown in
the diagram, the origitial tunnel form fell into
disuse and is now used for cop3ring only.
One of the first studios constructed with side
lighting was that of Col. Stuart Wortley {see B).
The sloping front light was of clear glass, and
that at the side of corrugated glass to 7 ft. from
the ground, thence to the roof being of clear
glass. It had two sets of blinds, one opaque
and one transparent, and was thus the prototype
of the modem system of lighting. The next step
towards the more modem forms of studio may
be said to be the celebrated one of Rejlander,
who brought artistic knowledge to bear upon
his photographic work, and designed his studio
to get the efiects he desired. As shown at C,
the erection took more the ridge-roofed form,
which later came entirely into use ; it had
side, top, and front lights ; all the spaces indi-
cated in the diagram were of clear glass, though
those in the gable ends at least were usually
covered with semi-transparent blinds, being used
to give some amount of diffused Ughting on to
the shadow side of the sitter. A later studio
was that of T. R. Williams {see D), and this,
having had to be made simply by replacing a
sohd roof by a glazed one at his premises in
Regent Street, I,ondon, had an unavoidable
south aspect ; the difficulties of the direct sun-
light illumination were got over partly by work-
ing diagonally across the apartment as shown,
and partly by the use of no less than three sets
of blinds, one over the other, the outer ones
being of dark blue calico, the next of thick white
calico, and the inner of thin jaconet muslin. In
spite of all these difficulties of working, the
finest photographic work as regards lighting and
modelling, produced up to its date, was done in
this studio by its clever user.
Another later and, indeed, almost modem,
south-lit studio was that of Valentine Blanchard
(E), in which the difficulties of direct sunlight
were got over by the use of a movable trans-
lucent screen, as shown on the plan and section,
and the use of partly obscured glass in the
portions indicated by shading in the diagram.
Diagrams P to H show the three principal forms
of studio now in use. These are drawn in section,
and all to the same scale, to facilitate compari-
son, the glazed portions being shown by thin
lines and the opaque portions of the walls and
roof by thick ones. In the first place, all three
studios have been drawn to an equal width of
15 ft., but in the " lean-to " and " single slant "
types narrower and wider designs have been
also respectively indicated to illustrate the
greater suitability of the former to narrow
studios, and of the latter to wide ones. In the
lean-to diagram two roofs of varying pitch are
also shown, one at an angle of 30°, and the other
at that of 45°, in the latter of which cases it may
be noted that the roof becomes rather long and
somewhat costly, a defect which, however, might
be reduced by making the upper portion a flat,
which, in positions in which it is readily acces-
sible, might be utiUsed for printing, etc. The roof
is, of course, shorter in the case of the pitch of
30°, but it then has the disadvantage that snow
would lie more easily upon it, and that the
incidence of the hght upon the sitter is made
sUghtly more vertical than in the case of the
steeper roof. This question of pitch also depends
largely on the position of the studio and its
surroundings, and in these diagrams it has been
assumed that the glazed sides of the studios are
facing due north, which is, theoretically, the
ideal position, though in practice it is generally
better to make a studio, if possible, face a little
to the east of north, in order that the sun may
be off it earlier in the day. The roof pitch is also
governed by the fact that the maximum midday
altitude of the sun in summer is a little more
than 60° above the horizon, and that, therefore,
unless the pitch of the roof approaches that
angle in steepness, the sun will shine over the
ridge into the apartment at that time. This is
shown in the diagrams P, G and H by the dotted
lines to the left. In the case of a lean-to studio,
however, it may be assumed that that form
would not be chosen unless there was already
some structure in existence for it to be built
against, and that it would, therefore, be prob-
ably protected from the south, in which case
the roof might be kept flatter in pitch. The
lean-to form of roof is best suited for studios of
from 10 ft. to 15 ft. in width, which are protected
by other buildings on the south side, and for
which a pitch of 45° for the roof is, therefore,
very suitable.
The ridge form has the advantages that it is
easy of construction by the ordinary builder ;
that almost any width can be covered by it ;
that it gives plenty of headroom for the easy
moving about of backgrounds (the square in
each diagram represents an 8-f t. stretched back-
ground), and that its roof may be made almost
of any patch desired. That in the diagram is
at an angle of 45°, in which case, however, imless
erected in a sheltered position, it would require
a sun-screen on the ridge, at least, at midsummer.
By making the slope of the roof 60°, and putting
a flat on ttie top, this could be avoided, and the
size of the roof be kept down, but in that case
the " single slant " form, as shown in the last
diagram, would be preferable. One of the defects
of both the lean-to and the ridge forms of a
roof is, that as ordinarily constructed, it is
frequently necessary to make the wall plate at
the eaves of such dimensions that it becomes a
positive obstmction to the light, cutting it in two,
and so producing a double high-light in the eye
of the sitter which has to be either taken out
by the use of the knife on the negative or by
Studio Design and Construction 5^8 Studio Design and Construction
that of tlie brush on the print. In those two
forms of studio, also, there is the necessity of
having two complete sets of bUnds, which when
both dark and light ones are used, as is most
generally desirable, involves a great complica-
tion of cords, wires, and pulleys, to distract the
attention of the operator. Per these reasons and
others, the single slant form of studio has of late
obtained. Of course, like most other things, tlie
single slant studio is not absolutely perfect, it
being sometimes not easy to get quite all the
top light required, and, unless it is wide enough
for one to work across it, it is not altogether a
good studio for copying ; yet for a fairly wide
design, in which case there is also obviously more
head room, it is a capital form for general portrait
A. Monkhoven's "Tunnel"
Studio
'Sa
D. "Williams's Studio
03
flo
E. Blanchard's Studio
H. Single-slant Studio
PLAN
B. Wortley's Studio
F. Lean-to Studio
G. Ridge-form Studio
years come more and more into favour, and
with it, when roofed to an angle of 60°, the
direct rays of the sun are excluded ; there is no
trouble with snow or leakage ; the glass is easily
cleaned both inside and out ; and with opaque
blinds pulling down from the top and up from
the bottom, on spring rollers, and a series of
transparent ones running on horizontal wires
within, all varieties of lighting can be easily
work, and is generally considered the best and
most modem form of construction.
With regard to the diagrams P, G and H, it
may be noted that the dotted lines to the right
enclose between themselves and the base or
ground line, an angle which may be subtended
by adjacent buildings without the latter obstruct-
ing much, if any, of the lighting of the studio
itself. In neither of the forms of studio shown
By (the late) Col. J. Gale
SNOW AND HOAR FROST PHOTOGRAPHY
18
Studio Design and Construction 5^9
Studio Portraiture
is it necessary to carry the side lighting down to
within less than 3 ft. from the floor, and in most
single slant designs 4 ft. 6 in. will be found quite
sufficient. Neither in any studio, unless it be
very short indeed, is it necessary to carry the
side of top light right to the ends, from 3 ft. to
5 ft. at the extremities being preferably built
solid to admit of the shading of backgrounds
and the getting of a dark atmospheric space
behind the sitter when required.
The length of the studio may be anything from
20 ft. to 35 ft., less being too short for the use
of ordinary portrait lenses for full length figures,
and a greater amoimt being of not much real
practical use. A good amount of width is, how-
ever, always an advantage. A very fairly pro-
portioned studio is one in which the widtii is
rather more than haU the length. As regards
height it must be remembered that all tie rods
and similar obstructions must be at least 9 ft.
from the ground to allow of the movement of
strained backgrounds beneath them ; also that
as the intensity of light decreases in the ratio
of the square of the distance from the source,
a very high studio may have a disadvantage in
that respect.
The glazed portion of the studio should be
executed in one of the many forms of patent
glazing without putty which are now on the
market. Clear glass is desirable in most positions,
as transmitting most light, but if the situation
is overlooked, or necessarily of such an aspect
as to receive the direct rays of the sun, some
kind of obscured glass may be used, the varieties
known as rolled and fluted plate being those
which stop the least amount of light.
In planning a studio, the entrance doors and
those of the diessing-room and dark-room should,
i£ possible, be kept in the unhghted side so as
not to intMfere with the use of both ends, which
may with advantage be fitted up as permanent
fixed backgroimds, with plain or papered walls,
Lincrusta or other reUef work, panelling, tapes-
try, or whatever form of artistic decoration,
suitable for backgrounds, that the taste of the
designer may suggest. In the matter of studio
decoration generally, light and pleasant tints,
such as warm and ddiicate greys and greens, may
be recommended, but heavy and sombre colours
should be avoided as absorbing light ; strong
reds and yellow are unsuitable on account of the
non-actinic character of the light reflected from
them.
A good smooth floor is, of course, a necessity
to facilitate the easy movement of cameras,
furniture and backgroimds, and if a stained and
polished or parquet floor is not attainable, the
best covering for an ordinary one is good inlaid
linoleum, on which a few good rugs will produce
a pleasing effect. D- B.
Studio Blinds. — The amount and direction of
the light admitted to the studio is usually regu-
lated by means of spring-roller blinds, of dark-
blue or dark-green lining. It is advisable to
have a doub'e set for all the glazed portion of the
studio, overlapping after the manner shown in
the illustration. One set, a a, should draw from
top to bottom in the ordinary way, while the
other, B B, is arranged to pull up from bottom
to top by cords passed over piileys, pp, and
carried down again, the free ends being then
34
fastened to brass hooks, h h. The number of
blinds required will depend on the size of the
glazed portion, which need not be of very large
extent. They should not be too wide, or the
lighting will be less under control ; about 2 ft.
is a convenient width. Where there is a good
unobstructed light, white calico blinds are
frequently fitted underneath the dark ones, to
secure any desired degree of softening. Many
workers prefer, instead of this, to have loose
white muslin curtains running on wires behind
or in front of the dark blinds; while another
alternative is to paste white tissue paper on the
glass, or to glaze the studio with ground glass.
The last two methods have the disadvantage
that they may obstruct too much Ught on dull
days. When it is not desired to incur the
expense of blinds, dark curtains made to nm on
wires or rods may be substituted.
Greenhouse as Studio. — Generally, a greenhouse
is glazed on two, three, or four sides, and pro-
bably down to within 1 ft. or so of the ground,
thus admitting hght all around the figure. It
«
^^^MSssSfe«*y simS|!i^^iiiSv&^
Studio Blinds.
is necessary to block out all unnecessary light
by gluing Willesden waterproof paper, or similar
material, on the inside of the glass. The choice
of aspect depends on whether the studio is to
be used most frequently in the morning or in
the afternoon ; if the former, choose a western
aspect, and if the latter, an eastern aspect. If
the studio is likely to be used at any time, heavy
opaque blinds should be provided for each side ;
or one set of bUnds may be made to do duty for
either side as required by simply changing over
the cord. The opaque blinds and the interior
of the studio may be painted a Ught grey colour.
Spring blinds are best for the roof, and two sets
will be required, each bHnd being about 2 ft.
across ; one set shoidd be of a dark blue (not
a green-blue material), and one set of white
calico. To regulate the hght from the side, dark
blue blinds on small brass rings, suspended from
a wire, can be used.
STUDIO PORTRAITURE
The chief considerations in portraiture are
dealt with under that main heading, but there
remain a few special points in studio work that
should be mentioned. The conditions of light
Stumping
530
Sulphide Toning
ing in a studio allow of numerous effects that
are quite impossible in ordinary rooms. The
large amount of available light should be con-
trollable by bUnds, and when the sitter enters
the studio the top Ught should always be ob-
scured. Otherwise the glare will be found to be
too strong for most people, producing a screwing
ap of the eyes, thus giving a false expression ;
whereas, by having a subdued light when the
model enters, one is able to study features under
more normal conditions, and to arrange the pose
before letting in bright light. Having attamed
the desired position, the light is arranged by
opening the blinds where required. In this way
it is much easier to notice the different effects of
light and shade than by having the full amount
of light open and gradually cutting it off. The
photographer must cultivate the art of making
the sitter feel at ease in the studio, it being im-
possible to obtain a. successful portrait if there
is a feeling of constraint. Avoid the appear-
ance of all unnecessary appliances ; make the
studio appear as much like an ordinary room as
possible, with interesting pictures, books, plants,
etc., to divert the sitter's attention from any
idea that he is in some strange place. Have
everything ready and at hand that may be re-
quired.
STUMPING
The application of powdered colour to a photo-
graphic print or enlargement by means of a
paper or leather stump, or with a finger-tip,
the print being first prepared by rubbing with
very fine pumice powder
SUBMARINE PHOTOGRAPHY
This is an application of photography which,
probably on account of the very special appar-
atus, and the great difficulties encountered, has
received but little attention. Attempts have
been made from time to time, and with varying
success, to photograph the bottom of large rock-
pools and shallow lagoons, by connecting the
camera with a tube of large diameter, pointed
downwards through the water. A special raft
having a well in its centre, to carry the downward-
pointing photographic apparatus, has been used
with success ; the shadow cast by the raft cuts
off all sky reflections. By working at sunrise
and an hour or so before sunset, a kind of oblique
lighting was obtained which gave very pleasing
results, the exposures varying from -sVth of a
second to two seconds, according to the depth of
water, lighting, etc. Green-sensitive orthochro-
matic plates were found to yield the best results,
the greenish yellow tint, caused by the oblique
rays of the sun passing through the sea-water,
acting as a kind of natural compensating filter.
The actinic value of light decreases very rapidly
with increasing depth of water, so that some
means of artificial illumination soon becomes
necessary. This at once presents many diffi-
culties, as special apparatus to hold the illu-
minant becomes necessary, and is rather costly
to construct, owing to the perfect fitting necessary
to make every part water-tight. Heavy plate
glass must be used for the window of the illu-
minant box, and the box itself must be well
weighted to insure its sinking to the bottom on
an even keel. The box must be fairly large, so
as to permit of a good sized window, and also
a fuU charge of magnesium powder being used.
The best results will be obtained by using two
such illuminant boxes, sunk one on each side
and slightly in advance of the camera, which
also must be enclosed in a water-tight, glass-
fronted, weighted box. Both the camera shutter
release and the ignition of the magnesium flash
can be worked by electrical switches. One
trouble which may spoil many exposures is the
condensation of moisture on the inner surface of
the glass front of the box carrying the camera,
due to warm moist air within the box. The glass
should be very carefully cleaned, the box kept
as cool as possible, and ff there is great variation
between the temperature of the air and the floor
of the sea, a small quantity of calcium chloride
may be placed in the box at the moment of
closing it. This wUl be found to act as a pre-
ventive of condensation. P. M-D.
SUBSTITUTION PROCESS {See "Ceramic
Process.")
SUBSTRATUM (Fr., Substratum ; Get., Unter-
guss)
A solution, generally of gelatine and chrome
alum, poured over a plate or other support to
cause the sensitive film to adhere to its support.
A dilute solution of sodium silicate (1 in 300)
has also been used for this purpose, but it is by
no means a safe remedy, as its alkaline nature is
apt to act on the emulsion. Diluted albumen
and a decoction of glasswort (Fr., Percepierre ,
Ger., Glaskraut) have also been suggested. The
chrome gelatine solution is prepared as follows : —
Gelatine
Distilled water to
37 grs. 4-25 g.
20 oz. 1 ,000 CCS.
Allow to soak for an hour, melt by the aid of a
water bath, and add —
Chrome alum (2% sol.) . 185 mins. 19 ccs.
This should be applied freely to the plate, and
the latter then set up to drain and dry.
SUGAR IN GELATINE
Ordinary sugar is occasionally added to
gelatine solutions, particularly for the carbon
process, to render it more soluble and to prevent
spontaneous insolubilisation after sensitising.
Its action is purely mechanical, as it dissolves
out in water.
SUGAR OF LEAD (See " Lead Acetate.")
SUGAR OF MILK
Synonyms, lactose and milk sugar. CjaHj^Oii.
It is prepared from milk by coagulating the
proteid and evaporating the whey to a syrup,
when crude sugar of milk will crystaUise out ;
it is then recrystaUised, when it forms white
rhombic crystals. It is used chiefly in the
preparation of dry powder developers.
SULPHIDE TONING
Bromides. — Success depends on the use of a
fresh developer for each print, full development,
drying after fixing and before toning, and
thorough bleaching to a light colour.
Two stock solutions should be prepared, each
of which will keep indefinitely.
Sulphide Toning
531
Sulphuret of Ammonia
Bleaching Solution A
Potassium femcyanide i oz.
Potassium bromide . ij „
Water to . . • 9i „
Bleaching Solution B
Mercuric chloride . 120 grs.
Potassium bromide .120 „
Water to . . .10 oz.
The table shows the number of parts of these
solutions and of water required to produce a
variety of tones : —
no g.
165 „
925 CCS.
28 g.
28 „
1000 CCS.
Rich
Colder
Deep
Brown-
Pure
brown
brannx
brown
black
black
Bleach.
sol.
A
I
I
i
I
i
Bleach.
sol.
B
—
I
I
2
2
Water
•
II
lO
lOj
13
9i
After bleaching thoroughly, the print must
be washed ; in addition, an acid bath must
be used whenever the working solution contains
solution B. The acid bath is hydrochloric
add 30 mins., water about 6 oz. ; its object
is to prevent the combination of the mercury
with the gelatine. The print should be taken
from the bleaching solution, washed in about
three changes of water, and then immersed in
the acid solution for two or three minutes. A
second and third add bath should be used,
and then the print washed again for about
twenty minutes in several changes of water.
When the toner for pure black is used for
bleaching, the print is intensified considerably,
and allowance must be made in printing. There
is also a slight strengthening when using the
solutions for deep brown and brown-black.
When suffidentiy washed after bleaching, the
prints should be treated with the sulphide
solution. Prepare a stock solution of 520 grs. of
sodium sulphide in 10 oz. of boiling water, stor-
ing it in a screw-stoppered bottle. The working
solution is 40 mins. of the stock solution in
suflident water to make i oz. This should
be used once, and then thrown away.
Fine red and red-brown tones can be obtained
by substituting a stock solution of i oz. of
sodium sulphantimoniate (Schlippe's salt) and
i oz. of sodium carbonate in suffident water to
make 9J oz.
The prints are bleached in : —
Bleaching solution A . .1 part
Water 11 parts
Wash for half an hour, and immerse in one of
the following mixtures : —
Red
chalk
Red-
brown
Warm
brown
Sod. sulphantimoniate sol.
Sodium sulphide sol.
Water ....
I
n
2
i
2
i
24
The prints shotdd be washed thoroughly for
about half an hour, and then dried. Bleaching
solution B — the mercuric solution — must not
be used with sodium sulphantimoniate.
P.O.P. — Many attempts have been made to
introduce a method of toning P.O.P. by the
sulphide process, but they have not been suffi-
cientiy successful to render the process suitable
for ordinary working.
SULPHIDING (See " Sulphide Toning.")
SULPHITE (Pr., Sulfite ; Get., Sulfit)
A salt formed by the replacement of the
hydrogen in sulphurous add, HjSO,, by a metal,
as, for example, in sodium sulphite, NajSOj.
SULPHOCYANIDE POISONING
The question as to whether the sulpho-
cyanides of ammonium and sodium are poisonous
or not has been a matter of controversy. Dr.
Heffter, of I<eipzig, in 1896, took several doses
of sulphocyanides without feeling any ill effects.
On the other hand, it should be said there is
the oft-quoted case of a Cambridge lady who,
in 1894, was poisoned by taking less than 5 grs.,
the doctor stating that 3 grs. were suffident
to cause death. Dr. Leo Baekeland stated at
the time that "it is a ridiculous mistake to
think that the sulphocyanides are poisonous.
There is certainly a confusion here with
cyanide, which is really one of the most powerful
poisons known." In any case, the admission
of ammonixmi sulphocyanide, either by itself or
in a gold toning bath, into cuts or sores upon
the hand causes much trouble, and it is better
in aU cases to treat it as if it were a. poison.
SULPHO-PYROGALLOL {See "Berkeley's
Sulpho-pyrogallol." )
SULPHUR (Fr., Soufre ; Ger., Schwefel)
Synonym, brimstone. S. Atomic weight, 32.
A non-metallic element, occurring native in
many parts of the world. It is a brittie solid,
lemon-yellow in colour, and tasteless. Solu-
bihties, insoluble in water ; soluble in carbon
disulphide, turpentine, benzol, and slightly in
warm alcohol. The sublimed sulphur (flowers of
sulphur) is the purest commerdal form.
SULPHUR DIOXIDE (See "Sulphurous Acid.")
SULPHUR TONING
A method of toning in which free sulphur
compounds are used. Bromide prints may be
immersed in a hot solution of alum and " hypo,"
and silver prints, deeply printed, in an add
" hypo " bath. In the second case, the result
is fugitive. It will be noted that these are
combined toning and fixing methods.
Sulphur toning is frequently an accidental
effect. In some forms of the combined toning
and fixing baths, if the bath is overworked and
the gold becomes exhausted, toning will still
continue, the change in colour being due to
the deposition, of sulphur on the silver image.
Sulphur prints are liable to discolour, deteriorate
and fade.
SULPHURATED POTASH (See " Potassium
Sulphide.")
SULPHURET OF AMMONIA (See " Ammo-
nium Sulphide.")
Sulphuret of Carbon
532
Super-saturated Solutions
SULPHURET OF CARBON {See "Carbon
Bisulphide.")
SULPHURETTED HYDROGEN {See "Hy-
drogen Sulphide.")
SULPHURIC ACID (Fr., Acide sulfurique ;
Ger., Schwefel Sdure)
Ssmonym, oil of vitriol. HjSOj. A heavy,
oily, colourless liquid ; specific gravity, i -84
(=98 per cent. HjSOj by weight). It is
intensely corrosive and chars all organic matter
it touches. It is used to acidify some developers,
and occasionally with chrome alum as an
addition to the " hypo " fixing bath. Great
caution is necessary when mixing solutions
with sulphuric acid, and the latter should be
added slowly to the water, etc., not the water
to the acid.
In process work, this add is not much used,
but it forms with potassium bichromate a good
pickle for cleaning glass, and with chromic
acid a cleaning bath for copper etching, the
latter solution being also good for matting a
copper plate. In electrotjrping, sulphuric acid
is largely used in making up the copper deposit-
ing bath.
SULPHURIC ETHER {See " Hther.")
SULPHUROUS ACID (Fr., Acide sulfur eux :
Ger., Schweftige Sdure)
Synonyms, solution of sulphur dioxide or
sulphurous anhydride, hydric sulphite. H2SO3,
or more correctly, SOj -I- HjO. Solubilities,
miscible with water and alcohol. It is a colour-
less liquid smelling strongly of sulphur dioxide,
and containing about 6 per cent, of SO2. Mole-
cular weight, 82. It is obtained by deoxidising
sulphuric acid with copper or mercury, or by
burning pyrites. It is used as a preservative
and to acidify the fixing bath.
SULPHUROUS ANHYDRIDE {See "Sul-
phurous Acid.")
SUN, PHOTOGRAPHING THE
Very Uttle interest attaches to photographs
of the sun taken with cameras fitted with lenses
of ordinary focal lengths, but good results may be
obtained by means of medium or high-power
telephoto equipments. If the equivalent focal
length is sufficient to give an image about i in.
or more in diameter, the photographs would
probably be of value for scientific records of the
phenomena taking place on the sun's surface.
In the case of the photographer merely wishing
to obtain a chance record, there is no necessity
for providing any mounting, or, in fact, any
accessories beyond some means of holding the
camera steadily in the direction of the sun, and
an exposure shutter giving the most rapid expo-
sure it is possible to make. Use any good brand
of slow plates, preferably of the fine-grain
variety, and develop with a rather hard deve-
loper, as in most cases over-exposure will be
experienced in spite of the rapid shutter.
If records of more perfect astronomical value
are desired, the only difference will be an improve-
ment of the mounting of the camera, to allow of
repeated exposures without constant readjust-
ment of the image, and for large-scale work an
increase of the aperture and focal length of the
lens system employed. In most, cases an equa-
torial mounting will be found necessary, with
clock-driven mechanism adjusted to the solar
rate of movement. Por the telephoto camera,
however, either a positive or a negative secondary
magnifier may be employed, the actual system
chosen depending on the choice of the operator.
Both methods are in constant use, and give
practically equally good results, although, of
course, the positive magnifier makes the appa-
ratus more cumbersome. With such cameras the
photographs will show simply the white round
disc of the sun, with, at times, groups of dusky
spots showing in belts across the middle regions.
By means of a special spectroscopic attachment,
ciled the spectroheliograph, it is now possible
to screen off all light from the plate, except that
of one particular colour, and on photographs
thus taken it is found that certain patches of the
surface are rendered much more prominent than
on the ordinary pictures in integrated suidight.
Instruments of this type are now installed at all
the chief observatories of the world.
(For notes on the phenomena to be photo-
graphed round the sun on special occasions, see
under the headings " Corona Photography," and
"Eclipses, Photographing.")
SUNNING-DOWN
Any part of a P.O.P. print that is white or too
light and devoid of detail may be toned to a
pale grey by sunning-down. A shield is cut and
laid over the parts of the print that it is desired
to protect, the print being put in a printing
frame under a piece of plain glass.
SUNSET EFFECTS
Although the beauty of a sunset effect is
so largely dependent on colour, the mono-
chromatic rendering by photography is fre-
quently charming and suggestive. The technical
difficulties are, however, often very considerable.
The light, although visually brilliant, is more
or less non-actinic, and an exposure that is
ample for the sky itself is far from sufficient
for the rest of the subject. The discrepancy is
not so great in the case of the sea as in the
case, say, of a wooded landscape, or when there
are dark foreground objects. Hence some of the
most successful results are those showing the
sun setting over the water. As the light at
sunset is frequently rich in yellow and red,
rather than blue, rays, the use of an ortho-
chromatic plate, or, preferably, a panchromatic
plate, is advisable. Under-exposure may pro-
duce greater contrasts in the sky, but it deprives
the rest of the picture of that subdued luminosity
which is one of the charms of sunset.
Sunrises are similar in character and effect
to sunsets, but do not receive nearly the same
amount of attention from photographers.
SUPER-SATURATED SOLUTIONS
Over - saturated solutions; those overcharged
with the salt. A saturated solution of mercuric
chloride in plain water may, for example,
be made to take up more of tie salt by adding
hydrochloric acid. The use of such solutions is
not recommended in photography.
Supplementary Exposure
533
Swing Back
SUPPLEMENTARY EXPOSURE {See
"Auxiliary Exposure.")
SUPPLEMENTARY LENSES
Lenses employed to increase the usefulness
of other lenses by altering the focal length.
Derogy issued a portrait lens fitted with two
supplementary lenses, one being positive and
the other negative. J. Traill Taylor developed
the idea by fitting a series of lenses upon a
slide or wheel which was placed between the
lenses of a rapid rectilinear. Later, supple-
mentary lenses were used on many hand cameras
to take the place of a focusing adjustment ;
the Kodak portrait attachment is an example.
Achromatised supplementary lenses for por-
traiture, copying, distant and wide-angle work
are sold under the name of " planiscopes." When
a lens is set to its infinity focus and a supple-
mentary lens is fitted dose in front of it, an
object placed at a distance equal to the focal
length of the supplementary lens will be sharply
defined upon the screen. Thus a spectacle
lens of 40 in. focal length will enable an object
at that distance to be photographed without
focusing or additional camera extension.
SUPPLEMENTARY LIGHTING
AuxUiary exposures have been referred to as
supplementary lighting, but the term more
correctly refers to the system of casting addi-
tional light upon the subject by means of
reflectors, mirrors, or magnesium light, in
addition to daylight. Magnesiimi ribbon or
powder is largely used for lighting up dark
comers of interiors, etc. In interior work,
such as crypts, the burning of a few inches of
magnesium behind a pillar or other object helps
exposure considerably. A mirror can be used
in a similar way ; it should be held in the path
of the sun's rays, which are reflected by the
mirror on to the darker parts of the view, the
mirror being kept on the move and, of course,
out of the field of view. Mirrors are of the
greatest service for supplementary lighting
when copying in picture galleries.
SWEATING OF THE SCREEN
In working the half-tone process with wet
collodion or collodion emulsion, especially in
winter time, considerable trouble is met with
owing to the condensation of moisture on the
screen — commonly known as " sweating." The
remedy is to warm the screen, or to rub over it a
trace of glycerine, or coat it with a thin film of
gelatine J oz., acetic acid ^ oz., warm water 20 oz.
SWELLED GELATINE PROCESS
Before zinc and copper etching were fully
developed this process was largely worked,
but it was roundabout and uncertain. A thick
glass plate was coated with a thick layer of
bichromated gelatine, and after being dried
was exposed under a line negative. The plate
was then placed in a dish of clean cool water,
when the swelling began immediately. The
parts of the gelatine film not acted upon by
light absorbed water and swelled up. The
exposed parts remained at their original level.
When the relief was thought to be sufficient,
the plate was removed to a hardening bath of
chrome alum, citric acid, and water. Whilst
still moist, a plaster cast was taken from the
gelatine relief, and when this was dry it formed
a matrix for a wax mould for electrotjrping.
If a stereotype was required a second cast had
to be made from the first, as the latter was in
relief lines, which would have produced an
intaglio result in the stereotype. The process
is full of difficulty and uncertainty, and the
operations take a long time.
SWING BACK (Pr., Bascule ; Ger., Bewegliche
Visirscheibe)
An adjustment by means of which the camera
back may be inclined towards or away from the
lens. The simplest form of swing back is merely
hinged at the bottom to the baseboard, but it is
preferable to have it pivoted at the centre. The
swing back is used when the camera has to be
tilted to include the top of a high building. , In
such a case, the upright lines of the building
would be shown converging towards the top, as
Use of the Swing Back
SUTTON, THOMAS
Died, 1875. An active photographic experi-
menter from 1856 to 1872. Founder and editor
of Photographic Notes, and the inventor of
a panoramic camera. In 1862 he invented a
plan for giving paper a coating of indiarubber
dissolved in benzole, before albumenising. In
1859 he invented a fluid lens.
SWANTYPE
A half-tone process devised by J. W. Swan,
and difiering from the ordinary halt-tone process
only in the manipulation of screens and stops.
if the building were falling over backwards. By
bringing the swing back into operation, as at
A, so that the focusing screen is parallel with the
building, the lines are rendered vertical. The
tilting of the lens with regard to the plate neces-
sitates the use of a small stop, and it is better
to avoid inclining the camera if the same result
can be obtained by using the rising front.
Another employment of the swing back is when
objects at different distances are required to be
equally sharp without stopping-down, as, for
instance, the knees and hands as well as the
head of a sitter in portraiture, or the foreground
Swing Front
534
Szczepanik's Process
and middle distance of a landscape. Near objects
are always brouglit to a focus farther from the
lens than distant ones, as shown at B, where the
foreground of the picture is seen to be focused
at F, beyond the position of the ground-glass
screen s, when the distance D is sharp, whSe if
the near foreground is in good definition the
distance is thrown out of focus. By inclining
the swing back outwards, as at C, both fore-
groimd and distance are in focus at once. This
method of equalising the focus must be used
cautiously, as it has the defect of introducing
a slight distortion. Some cameras are provided
also with a side-swing, the camera being then
said to have a double swing back.
SWING FRONT (Fr., Planchette d bascule:
Ger., Bewegliches Objektivbrett)
An adjustment in which the camera front is
hinged to the baseboard frame, or is pivoted at
its own centre, so that the lens may be swung
upward, or downward. The principal advantage
is that high buildings may be included on the
plate without having to tilt the camera. It is
necessary to keep the back vertical, and some
stopping-down of the lens is usually required,
for which reason it is preferable whenever pos-
sible to employ the rising front movement instead,
as this enables the lens to be used at a larger
aperture. The use of the swing front has the
same effect as that obtained by tilting the
camera and using the swing back, but the lens
is not so easily kept with its axis falling on
the middle of the plate. Many field cameras
have a swing adjustment to both back and front.
SYMBOLS (See " Element " and " Solu-
bilities.")
SYMMETRICAL LENS
A lens in which the two combinations have
similar curves and balance one another.
SYMPATHETIC PHOTOGRAPHS
A plain piece of paper is coated with a lo per
cent, solution of gelatine, dried, floated upon
n lo per cent, solution of potassium bichromate,
and dried in the dark. The paper is exposed
under a positive, say an unmounted lantern
slide. The print, with the image showing very
faintly, is then immersed in a lo per cent,
solution of cobalt chloride, when the parts not
acted upon by light will absorb the solution.
The print is then washed and dried. A faint
image will be seen, and this will change colour
according to the condition of the atmosphere.
When the weather is fine aijid dry or heat is
appUed to the print, the picture will be of a
pretty blue colour, but when damp the colour
will change and the picture almost disappear.
(See also " Barometer, Photographic")
By the Stone method the image is composed,
as above, of gelatine rendered insoluble upon
unsized paper ; when the paper is dipped in
water the image appears by reason of those
portions of the picture having no gelatine
upon them becoming comparatively trans-
parent ; as the picture dries the image dis-
appears. Stone's sensitive solution was : Water,
5 oz. ; gelatine, J oz. ; potassium bichromate,
24 grs. Unsized paper was coated with this
(warm), dried in the dark, printed under a
negative, and soaked in warm water.
SYNCHROMIE
A four-colour printing process in which all
the colours are printed at one impression,
invented by Vittorio Turati, of Milan. A
mosaic of pigment colour was formed on the
bed of the printing machine, and, the surface
being damped, impressions were taken off on
to paper.
SYNTHETIC GUM {See " Arabin Gum-
bichromate Process.")
SYNTHOL
A trade name for a developer in powder form,
a hydrochloride of diamido-orcinol. C5H(CHs)
(OHs)(NHaHa)j,. It is said to be obtained
from various plants, the mother substance
being orcin. It is very soluble in water and can
be used in conjunction with sodium sulphite
without an alkali, like amidol. A working
formula is : —
Sodium sulphite .
, 300 grs.
68 g.
Potassium bromide
5 „
i-i ,.
Synthol
• 30 „
6-8 „
Water
. 10 oz.
1,000 CCS.
SYPHON (Fr., Siphon ; Ger., Heber, Siphon)
An appliance for drawing off water or other
liquid from a vessel without disturbing the latter.
A simple syphon may be made with a bent lead
pipe, one end of which is longer than the other.
The short arm is corked and the tube filled with
water, the long arm being then also corked. The
short end of the pipe is introduced in the vessel
and the cork removed ; then on taking out the
other cork the syphon will commence to work, the
liquid in the vessel rising up the tube and dis-
charging. Another convenient device is a short
lengUi of rubber tubing with spring clips for the
ends. Some sj^phons are provided with an ad-
ditional tube joined near the end of the long arm ;
by its means, the liquid is drawn over the bend
by suction.
SZCZEPANIK'S PHOTO-WEAVING PRO-
CESS
Jan Szczepanik invented an ingenious method
of producing the cards for the Jacquard loom
by photographic means. His method is based
on the half-tone process, and consisted in the
use of a series of special ruled screens and
variously shaped diaphragms which produced
a negative in square dots something like a.
design for crewel work. This negative was
printed by means of sensitised fish-glue on to a
zinc plate, the image being developed, so that
the dots were isolated, with spaces of bare zinc
around them, and in some parts there were no
dots at all, as the light and shade of the picture
demanded. The plate was then put into an
electrical apparatus, so arranged that a tracer
point passed in lines over the plate, the point
alternately making and breaking contact as
it passed from the enamel film dot to bare
metal. Thus an electrical current was inter-
mittently transmitted to a Jacquard punching
machine, the keys of which were operated by
the current.
TABLET CRUSHER
An appliance for pulverising " tabloid " and
other compressed chemicals, and consisting of
a round metal receptacle, in which fits a peculiar
form of stopper which may be used as a pestle.
The " tabloid " is placed in the receptacle and
reduced to powder by working the stopper.
"TABLOIDS"
A proprietary name (registered in 1884) for
compressed chemicals made by the successors
of Brockendon, who, in 1842, originated com-
pressed chemicals in the shape of bi-convex
discs. They contain chemicals in correct and
known quantities, and need simply to be dis-
solved in the required amount of water to make
a working solution. There are many other forms
and makes of compressed chemicals.
TACHYSCOPE (Fr., Tachyscope ; Ger., Tachy-
skop)
A form of zoetrope invented by Ottomar
Anschiitz, of Lissa, and used to reconstruct the
appearance of motion from animal photographs
taken in series. It consisted of a shallow
cylinder into which a bent strip of photographs
was inserted. The strip was pierced with up-
right narrow slits between the photographs,
the number of slits corresponding with that of
the pictures. The advantage was that a variable
number of photographs might be used to form
a series, whereas with the zoetrope the nimiber
must always correspond with the slits in the
fixed side. Anschiitz also invented an electrical
tachyscope.
TALBOT, HENRY FOX
Bom 1800, died September 17, 1877. Retired
from public life in 1834 to devote his whole
time to scientific work. While sketching at
Lake Como with WoUaston's camera lucida in
October, 1833, he was struck with the idea of
fixing images produced by that instrument, and
six years of steady work at the problem followed.
He was to some extent successful, and on
January 31, 1839, he read before Uie Royal
Society a paper on the process, which he called
" Photogenic Drawing " ; this paper was after
wards published in the Philosophical Maga-
zine. Prof. Faraday exhibited at the Royal
Institution on January 25, 1839, a collection
of Fox Talbot's "photogenic drawings," which
were produced solely by the action of light, and
at the same time described the process (which
see, under the heading " Photogenic Drawing ").
Daguerre was experimenting at the same time,
and published his results in 1 8 39, but the methods
of the two men were different, that of Pox
Talbot giving an image on paper, whereas that
of Daguerre produced an image upon a polished
silver surface. The calotype process, often
called the talbotype process, was patented by
Fox Talbot on February 8, 1841, and was the
subject of the third British photographic patent.
Fox Talbot in 1843 patented the use of a hot
solution of sodium hyposulphite for making the
pictures of his process winter and more per-
manent ; Sir John Herschel had suggested it in
1 8 19, and again advocated its use in 1843. In
1843 Fox Talbot took his process to Paris, and
in the following year (1844) began to publish his
famous work " The Pencil of Nature." After the
introduction of the Archer collodion process in
1 85 1, he devised a modification of it by which
shorter exposures were possible. A year later
he invented a process of engraving upon steel
plates by means of photography, and in 1854
he introduced albumen to give a gloss to the
surface of paper on which photographs were
printed. The calotype (or talbotype) process
of making negatives upon paper was largely
used by amateurs of the period, it being less
costly and troublesome than the daguerreotype
process, which was preferred by the profes-
sional portraitists.
Talbot was the first to describe the use of
line and network screens for the purpose of
breaking up the image into dots, and for this
purpose he made use of crepe, silk gauze, muslin,
and lines ruled on glass. He did not realise,
however, the idea of optical formation of the
dot in the negative as now practised.
TALBOTYPE (See " Calotype, or Talbotype,
Process.")
TALC (See " Chalk, French.")
TANK DEVELOPMENT (See " Development,
Stand.")
TANK, WASHING (See "Washing Tank.")
TANNIC ACID (See "Tannin.")
TANNIN (Fr., Acide tannique ; Ger., Gerh-
sdure, Gerbstoff, Tannin)
Synonym, tannic or digallic acid. CuHioOj.
Molecular weight, 322. Solubilities, 1 in i
water, i in -6 alcohol. A lustrous, faintiy yellow
amorphous powder extracted from gall nuts and
all kinds of bark. It has been recommended as
a hardening agent for prints, but it forms an
insoluble compound with gelatine which darkens
in light.
In process work, tannin is sometimes used as
an ingredient in the etching solution for collotype
plates, with the object of hardening the gelatine
film. A strong solution is sometimes applied
locally to make certain parts take the ink. It
has also been used for writing tities and other
lettering on collotype plates, the parts to which
535
Tannin Process
S36
Telephotography
the tannin ink was applied printing black. The
addition of tannin to the chromated gelatine
before coating the plate has been recommended
for making the film more durable and lasting.
TANNIN PROCESS (Pr., ProadS tannin,
Proc6d& Russell ; Ger., Tannin Prozess)
A dry collodion process invented by Major
Russell, in which a preservative bath of tannin
was used. The plate was coated with a sub-
stratum of gelatine and then with iodised col-
lodion, after which it was sensitised for five
minutes in a silver nitrate bath, and then well
washed. The preservative was a filtered solu-
tion of 15 grs. of tannin to each ounce of dis-
tilled water. This was poured on and oflE the
plate several times, throwing away the first
portion, the plate being then stood up to dry
in the dark-room. Plates prepared in this way
were ready for use when dry, and would keep
some time.
TANNING PRINTS
Tannin has been recommended for hardening
gelatine negatives and prints, a typical formula
being : —
Tannin . . . 4J grs. i g.
Sodium chloride . 45 ,, 10 „
Alutu (saturated sol.) 405 mins. 85 ccs.
Water . . . lo oz. 1,000 „
The tannin and sodium chloride (common salt)
are first dissolved, and the saturated alum solu"
tion added, the mixture being filtered or de-
canted. The prints are immersed for a few
minutes and well washed. It has been stated
that prints hardened with tannin become yellow
after a time ; whether this is so or not, the
method has no advantage over the use of for-
maline or chrome alum. (See also " Hardeners "
and "Pixing-hardening Baths.")
TARTAR, SALT OF {See " Potassium Car-
bonate.")
TARTARIC ACID CBi., Acide tartarique : Ger.,
Weinsdure)
C^HeO, or (CH)2(OH)2 (COOH),. Molecular
weight, 150. Solubilities, i in -75 water, i
in 3 alcohol, i in 250 ether. It is in the form of
colourless transparent rhombic crystals obtained
from argol or crude potassium bitartrate, de-
posited during the fermentation of wines. It is
used as a preservative for sensitised papers and
in printing-out emulsions.
TAUPENOT'S PROCESS
A collodio-albumen process invented in 1855
by Dr. J. M. Taupenot, a French scientist. It
was largely used for the production of stereo-
scopic teansparencies, and was a rival process
to the albumen process used by Perrier, the
details of the latter being kept secret.
TAYLOR, J. TRAILL
Born 1B27 ; died 1895. An authority on
photographic optics and editor of the British
Journal of Photography from 1864 to 1879 and
1886 until his death. He was a watchmaker by
trade, but as a youth practised the daguerreotype
process, and during his long residence in Edin-
burgh came into contact with Brewster, Pox
Talbot, Ponton, and many other photographic
and scientific celebrities. His first association
with photographic journalism was in 1856. In
i860 he delivered a lecture before the Royal
Scottish Society of Arts on " The Use of the
Optical Lantern in Photography," on which
occasion photographic lantern slides were pub-
licly exhibited for the first time. Between 1880
and 1885 he edited an American photographic
journal, the Photographic Times.
TEA PROCESS
In an obsolete process tea was used as a pre-
servative or organifier for collodion plates.
Por other preservatives, see " CoSee Process."
TEA-TRAY LANDSCAPES
Landscapes built up in a miniature form upon
a tea-tray, a branch of work with which the
names of Newton Gibson and W. Perry Barrin-
ger are connected. Snowscapes and desert
scenes are the easiest to produce, sugar, flour
and sand being used to build up the scenes. Trees
may be made out of small sprigs of foliage,
asparagus, etc., and miniature china figures,
animals, etc., included. Properly lighted and
skilfully photographed, effective pictures may
be produced in this way.
TELAUTOGRAPH (See "Photo- telegraphy.")
TELECTROGRAPH (See " Photo-telegraphy.")
TELECTROSCOPE
An early form of instrument for the electrical
transmission of photographs ; invented by
Szczepanik and Kleinberg, in 1898.
TELEGRAPH, PHOTOGRAPHS BY (See
" Photo-telegraphy.")
TELEMETER (See "Distance Meter.")
TELEPHOTO LENS (Fr., Lentille telephoto-
graphique; Ger., Teleobjektiv)
A lens giving a. high magnification com-
pared with ordinary lenses used with the same
extension of camera. The earliest commercial
telephoto lens was made by Thomas R. Dall-
meyer in 1891, and consisted of a single positive
lens, somewhat like a telescope object glass, and
a triple cemented negative lens of high power.
In consequence of the low intensity and high
magnification thus obtained, the telephoto lens
was suitable only for a very limited class of
subjects, and it was not until a moderate power
combination with a maximum intensity of about
fig was introduced that telephotography became
general. Negative attachments for use with
existing rectilinears and anastigmats were then
issued, and finally the Adon lens, a complete
telephoto lens of small size and weight, removed
the last difficulties connected with this branch
of work. Excellent telephoto lenses are now made
by a number of makers. (See also " Telephoto-
graphy" and "Bis-telar.")
TELEPHOTOGRAPHY (Pr., TUiphotogr aphis)
The photography of distant objects by means
of lenses giving high magnification compared
Telephotography
537
Temperatures
with ordinary lenses used with the same exten-
sion of the camera. A telephoto lens is, in fact,
a long-focus lens requiring but a short camera
extension ; it has not a definite or fixed focal
length like other lenses, and it may be so adjusted
as to give a sharp image at any extension of the
camera, provided that the extension is not less
than the focus of the positive lens which forms
part of the telephoto lens.
The combination of lenses which forms the
telephoto system consists of an ordinary photo-
graphic lens, preferably a rapid anastigmat,
called the positive element ; and a negative
lens, so arranged that its distance from the posi-
tive lens may be varied by means of a rack and
pinion on the lens mount. The distance from
the positive to the negative element and the
distance from the negative lens to the sensi-
tive plate are variable, the former being deter-
mined by the latter, and on these distances
depends the degree of magnification ; or, in
other words, the proportionate size of the
image compared with the size of the image
yielded by the positive lens alone.
Unless the positive lens can work at //8,
focusing and fiie arrangement of the picture
become very difficult. The value of the aperture
of the positive lens is reduced by the negative
element in direct proportion to the magnifica-
tion ; consequently, with a magnification of
four times, //8 becomes //32.
For ordinary work, the focus of the negative
lens should be about half that of the positive.
If great magnification is required for special
work, the focus of the negative lens should be
stiU less. This short-focus negative lens has the
disadvantage of reducing the covering power of
the positive lens, and this is a serious but
unavoidable objection to the telephoto lens
system.
Although the focal length is lengthened, the
area covered by the lens is reduced very con-
siderably ; but, with a given combination of
lenses, the greater the magnification, the greater
will be the covering power. It is very desirable
that the focus of the negative element should
be known, as it provides a definite basis for
ascertaining the degree of magnification. Ernest
Marriage gives the following simple nile for find-
ing the magnification when the focus of the
negative lens is known : After focusing, divide
the distance from the negative lens to the focus-
ing screen by the focus of the negative element,
and add i to the result. Example. — A nega-
tive lens of 4 in. focal length is used, and, when
the image is sharply focused, the negative lens
is 8 in. distant from the focusing screen. What
is the degree of magnification ?
— = 2; 2-1-1=3 times.
4
Many telephoto lenses have a scale of magnifi-
cations engraved on the moimt, so that, when the
image is sharply focused, the degree of magnifica-
tion can be read off from the position of the
indicator on the scale.
The working value of the stop can be ascer-
tained by multiplying the value of the Mertuie
in the positive lens by the degree of magmfication.
Thus with a magnification of three diameters,
//8 becomes //24; and with a magnification of
four times, //ii-3 becomes about //45.
The size of the image increases with the exten-
sion of the camera, so that it is a very simple
matter to secure any size that may be desired.
If the image when first focused is too small,
the extension of the camera should be increased,
and then the subject re-focused by the rack
and pinion on the lens mount. If it is too large,
decrease the camera extension and re-focus.
Attention has been directed to the fact that
the covering capacity of the telephoto lens is
very small ; consequently, the use of the rising
front becomes an impossibility, as the plate would
show dark comers. Tilting the camera is neces-
sary for all subjects which would require the
rising front when using an ordinary lens ; and
when the tilting becomes excessive, as in photo-
graphing architectural details at a considerable
height from the ground, it is not practicable to
set the camera back vertical owing to the im-
possibility of securing good definition through-
out when the plate is at such an angle to the
axis of the lens.
An objection to many telephotographs is the
very slight perspective effect obtained. It is the
extreme opposite to the exaggerated effect some-
times produced by a wide-angle lens, but at
times it is quite as pronounced and as unnatural.
Two difficulties that become serious when
working with a telephoto lens for distant sub-
jects are haziness in the atmosphere, which
renders it impossible to secure clear detail, and
wind, even a slight breeze introducing serious
vibration with the long camera extension.
TELEPHOTOSCOPy OR TELE-ELECTRO-
SCOP Y {See " Photo-telegraphy.")
TELESCOPIC TRIPOD (See "Camera
Stand.")
TEMPERATURES
Most of the solutions for ordinary photographic
work should be used at a temperature of 65° F.
(18° C), or as near that as possible. Solutions
for developing and fixing negatives and bromide
prints, toning and fixing silver prints, toning
bromide prints, and intensifying and reducing,
should aU be kept as nearly as possible to this
standard temperature. In cold weather the
dishes should be warmed before beginning any
operation. The developing solution for cold-bath
platinotjrpe should not be used cooler than 65°
p. or warmer than 90° P. (32° C). The stand-
ard temperature for developing carbon prints is
from 100° to 1 10° P. (38° to 43° C).
The temperature of developers influences the
time of development considerably. A nor-
mal Azol solution, for example, will, with a
given plate and used at a temperature of 40°,
develop a plate in 21 minutes, whereas if used
at 90° development would be complete in 3^
minutes. The intermediate temperatures and
times are :— 45°, i/i ^^^- '> 5°°. H min. ;
EC" i2i- min. ; 60°, io|- min. ; 65°, 8J mm.;
yo°\ 7 min. ; 75°, 6 min. ; 80°, 5i min. ; and
85° 4J min.
Developer, fixer, and washing water should be
of practically the same temperature, more par-
ticularly when bromide paper is used ; other-
wise blisters and other troubles may occur. If
such is not possible, the change should be gradual.
Temporary Support
538
Theatrical Photography
TEMPORARY SUPPORT
This is used in carbon printing for the double
transfer process ; known also as a " flexible
support." Its purpose is to hold the carbon
film during development, etc., until ready for
the second transfer to the final support. The
flexible temporary support is a paper coated with
a mixture of lac and gelatine that has been
rendered quite insoluble ; and, after coating,
the paper is rolled under heavy pressure, so as
to present a fine, smooth, and semi-glossy siu:-
face. The temporary support is prepared for
use by rubbing over with a waxing solution
(white wax dissolved in turpentine) ; after
allowing two or three hours for the turpentine
to evaporate, the support is ready for use in
exactly the same manner as single transfer
paper. After the flexible support has been
soaked for a few minutes in water, the exposed
print is squeegeed to the prepared surface ; and
after development, washing and drying, a piece
of double transfer paper is squeegeed to the
print. When thoroughly dry, the double transfer
paper holding the film firmly may be pulled away
from the temporary support, the sirrface of
which is left quite clean. Before using again
the flexible temporary support requires re-
waxing. When using this support a longer im-
mersion in the alum bath is necessary than for
ordinary single transfer paper.
In addition to the flexible temporary support
com.monly used in the carbon process, a piece of
matt-surfaced opal glass is sometimes used when
it is desired to obtain prints with a matt surface
instead of the semi-gloss imparted by the flexible
paper support. Tins opal glass is prepared by
waxing, and it is used in exactly the same manner
as the flexible support.
TENT, DEVELOPING {See "Developing
Tent.")
TEREBENTHENE
A rarely used synonym for turpentine.
TERTIARY COLOURS (Pr., Couleurs ter-
tiares ; Ger., Tertiare Farben)
A term usually applied to colours saddened or
lowered in luminosity by the admixture of black
or grey.
TERTIARY SPECTRUM (Fr., Spectre ter-
tiare : Ger., Tertiare Spektrum)
The small residual colours of the spectrum left
outstanding when the secondary spectrum is
corrected in lenses. That is to say, an ordinary
lens is corrected for two colours, and the out-
standing spectrum is known as the secondary
spectrum ; if three colours are corrected, the
outstanding spectrum is known as the tertiary
spectrum.
TEST PAPER (Pr., Papier rSactif; Ger.,
Reagens Papier)
Bibulous paper immersed in various solutions
and dried, used for testing the acidity or alka-
linity, etc., of liquids. Various kinds, such as
azolitmin, brazilin, congo red, dahlia, hsema-
toxylin, etc., are used by chemists, but those
principally used by photographers are litmus,
methyl orange, phenol-phthalein, and cochineal.
The following table gives the resultant colours
in the various solutions : —
Cochineal
Litmus . .
Methyl orange
Phenol-phtha-
lein . . .
Acid
Yellow .
Bright red
Red . .
Colourless
Alkaline
Reddish vio-
let
Blue . . .
Yellow-brown
Intense red .
In the presence
of carbon di-
oxide (car-
bonic acid)
Not affected
Reddish pur-
ple
Not affected
Useless
TEXTILES, PHOTOGRAPHS ON (See
"Fabrics, Printing on.")
TEXTURE (Pr., Tissure ; Ger., Gefiige, Textur)
The natural depiction of different surfaces
or materials in a photograph, which is then
said to have good textures, or textural ren-
dering.
THAMES COLOUR PLATE
A screen-plate patented by C. I,. Pinlay, in
1906, and consisting of contiguous red and green
circles with blue-violet interspaces, so small that
there are 70,000 colour patches to the square inch.
It is supplied either coated with an emulsion or
for use with separate panchromatic plates. A
compensating yellow filter of stained gelatine is
inserted between the lens combinations, and the
plate, loaded in darkness, is exposed glass side
to the lens. It is developed in darkness for
exactly five minutes in ordinary temperature,
using hydroquinone with caustic potash. The
plate is then washed for one minute and placed
in the reversing solution : Potassium bichro-
mate, I oz., or 80 CCS. ; water, 10 oz., or 800 ccs.,
sulphuric acid, i drm., or 10 ccs. After a few
seconds, the dish is taken into daylight and
watched until a positive is seen on holding the
plate up to the light. After well washing under
the tap, the plate is re-developed till a little
denser than required, washed for one minute,
and fixed in " hypo," finally washing well, and
when dry binding up with a cover-glass. If
separate plates and screens are used, the plate
is developed by itself, afterwards registering
with the screen.
THEATRICAL AND KINEMATOGRAPH
PHOTOGRAPHY
Theatrical Photography. — ^The usual plan of
taking photographs in a theatre is to employ
flashlight, elaborate arrangements and a large
battery of lamps, combined with the usual stage
lights, being necessary in most cases. The
invention, in 1901, of the Griin fluid lens, work-
ing at an aperture of f/2-$, enabled well-exposed
negatives of stage scenes during a performance
to be obtained in one-quarter of a second's ex-
posmre, and pictures of actresses, etc., in their
dressing-rooms, with five seconds' exposure.
Under very favourable circtunstances even
shorter exposures were given ; at the London
Alhambra, for example, excellently exposed
negatives were taken from the stalls with an
exposure of -^ second without the knowledge of
the performers. Rapid but not specially pre-
pared plates were used in conjunction with the
Theatrical Photography
539
Theatrical Photography
Griin lens. Aithur Payne considers that no
" ordinary " plate, however fast, can equal for
such work, by artificial light, a plate specially
bathed in the manner described below. The
speed of these special plates varies from 500 to
550 H. and D. According to Arthur Payne's
article in the British Journal of Photography
(July 6, 1906), clean working plates of medium
speed were bathed in the following : — A stock
solution of orthochrom T dye is made by dis-
solving I g. in i,cx3o CCS. of alcohol (90 per
cent.), and 4 cos. of this, together with 3 ccs. of
liquor amjuonise, are added to 200 ccs. of dis-
tilled water. This solution is filtered and used
at a temperature of 60° to 65° P. (15-5° to 18° C).
It must be made up as required, as it can be used
only once. The plates are immersed for three
minutes, care being taken to rock the dish and
avoid air-beUs. The solution is then poured
away and the plates washed in running water
for three minutes and dried. The plates are
now extremely sensitive to yellowish light, and
therefore the bathing, washing, and drying must
be carried out in darkness or in the safest
of ruby lights. The plates should be used as
soon as possible after they are dry. The de-
velopment of these plates is as usual, except that
it is best to use the developer at a temperature
of about 75° F. (about 24° C). Most of the
organic developers probably give equally good
results with these plates, but bromide or other
restrainer m.ust not be used, and they must be
of maximum strength, so that when used a
slight fog appears over the whole of the plate.
Edinol is found to give one of the best kinds of
negatives, fairly free from grain, which will bear
enlarging up to five or six diameters.
The plates treated as described above were
used with success by many workers, but Mr.
Payne discovered later that a i in 50,000 solution
of pinacyanol, used instead of orthochrom T,
gave increased sensitiveness and made the plates
more sensitive to red than to blue. The gain in
speed by yellow light is considerable when pina-
cyanol is used ; indeed, when a stage is iUu-
minated by yellow light, only focal plane shutter
exposures of ^ to ^ second are possible with
a lens working at f/3. In manipulating the
plates, darkness is best, or a very weak green
" safe ■• light.
In the majority of cases negatives of theatrical
photographs will be foimd very thin, although
possibly full of detail. Dr. Griin advocated
intensification with uranium, but Arthur Payne
advises printing upon gaslight paper, or the
making of a contrasty transparency upon a
photo-mechanical plate in the camera, enlarging
the image about two diameters, and from this
positive making an enlarged negative in the
camera ; by obtaining as much contrast as pos-
sible in the enlarged negative and printing upon
gaslight paper, the contrast in the final print
will probably be all that is required.
Photographically, stage lighting may be di-
vided into two classes : diffused lighting, when
the whole of the stage is fairly equally fiooded
with light ; and focused arc lamps or lime lights
when the light is concentrated upon one part of
the stage or upon the principal actor in the
scene. These effects are used independently and
together, and the photographer should try to
select a moment when the subject is illuminated
by both focused and diffused lighting ; although
the strong, bright lighting resulting from the use
of focused arcs alone produces interesting effects,
which photograph easily and well. Occasionally
some pretty effects may be obtained from the
wings on tiie stage, more especially when the
figure is lit by focused arcs, but permission to
use a camera in the wings during a performance
is rarely given. Arthur Payne believes that the
best position to work from, on the stage itself,
is obtained by sitting upon a chair, this resulting
in a low point of view, on the O.P. side of the
stage — that is, on the right-hand side as the
audience see it. The reason for selecting this
side is to avoid obstructing the officials, who are
generally on the " prompt " side in the execu-
tion of their duties. The stage appears to be
brighter, by contrast with the darkened theatre,
than is actually the case, but Mr. Payne says
this difficulty may be overcome by observing
the amount of light which is reflected from the
stage into the auditorium ; in this manner
fluctuations in the light may be followed with
ease. It may be accepted as a general rule that
the longest possible exposure should be given
on aU occasions, for it is mUikely that the photo-
grapher will ever meet with over-exposure,
except under extreme conditions, as stage
lighting usually gives heavy shadows.
Kinematograph Photography. — This involves
similar lighting conditions to those necessary in
ordinary photography. Excepting in the case of
stage scenes and make-ups," the operator of
the kinematograph camera does not know many
moments in advance what is going to happen
next. A crowd of people may, perchance, uu-
consdously group themselves into a most desir-
able arrangement, but the chances are they will
not. An devated position should be chosen, so
that possible obstructions, such as people passing
close to the lens, and, therefore, out of focus,
are avoided. The direction of the Ught, especi-
ally at noon, should be obUque and coming from
the back of the operator, either from his right
or left ; direct front lighting should be avoided.
Ideal illumination occurs when the sky is thinly
overcast, with plenty of light sifting through the
douds. Critical definition, a full range of tone
values, and exact speed with even motion, are
the three chief points to be aimed at. The first
point relates to choice and management of the
lens and the adjustment of the shutter aperture ;
the second relates to the Ught and afterwards to
proper development ; and the third to the correct
operating of the mechanism. The handle must
be turned at the rate of two revolutions per
second, and its speed must be regular through-
out the operation, irrespective of all else.
" Make-ups " and stage subjects afford oppor-
tunities of arrangements not possible with topical
or street scenes. The questions of lighting and
optical conditions remam the same. Stages on
which motion-picture plots are executed are
generally on the tops of houses, so that as the
sun alters its position, there are no shadows of
surrounding buildings cast upon the scene ; but
the house-top studio is not to be preferred to a
good open space on the ground level. The pro-
fessional's stage is built on the revolving prindple,
so that the direction of the Ughting can be kept
Theatrical Photography
S40
Thiocarbamide
constant throughout the day. The amateur is
not likely to want to take more than two or three
subjects in one day, and these he can arrange for
when the lighting is at its best.
When the camera has been set up on a
rock-steady support, the field covered by the
lens should be marked out on the floor of the
stage by means of white tape or chalk lines, as an
indication to the actors. The time limit for the
actions in each section is arrived at by rehearsing
the play, whilst the operator turns the handle of
his machine at the recognised speed ; the camera
need not be loaded, providing it is fitted with a
speed-indicator. It is the work of the stage
manager to watch the acting and to decide upon
the question of elimination. AU superfluous
action is cut out, not only to reduce expense, but
to crystallise the plot. No action is introduced
that can be assumed to happen, and only such
natural motions are allowed as will render the
subject intelligible to the average mind.
Trick and Make-up Subjects. — Motion-picture
photography lends itself to trickery and make-
believe more than any other branch of the picture-
making art. In subjects where human beings are
represented as passing through great peril, the
stop-camera method is resorted to. Thus, an
actual person acts the part up to the safe stage ;
the camera is then stopped, and a dummy sub-
stitute provided, made up to represent the
original. In like manner, when inanimate objects
are made to move without apparent human
control — such, for instance, as a knife cutting by
itself a loaf of bread ; cups and saucers collecting
themselves into a heap ; and so on — the photo-
grapher takes one or two pictures, stops, the
articles are moved to the second position in their
progress of movement, the camera again operated
for the space of one or two pictures and again
stopped, the articles moved to their third position,
and so on through the entire series of pictures.
The process naturally takes a long time to accom-
plish, but the results are often well worth the
trouble expended. Some cameras are fitted with
means whereby the operator may ensure expos-
ing only one picture space at a time, and an
assistant generally carries out the work of alter-
ing the positions of the objects after each expo-
sure. If a camera has its shutter aperture so
adjusted that sufficient exposure is obtained
whilst operating at less than the normal speed
of sixteen exposures per second, a subject moving
normally will appear to be moving swiftly when
projected upon the screen ; the opposite holds
good when the camera is operated abnormally
quick.
Stationary subjects, such as a man's face, may
be represented as increasing in magnitude by
causing the camera to travel towards the subject
during operation. Likewise, diminution of ob-
jects may be produced by taking the camera
away from the subject during operation. This
diminishing and growing magnitude effect inci-
dentally creates the illusion of an approaching or
receding subject. Hence, a train represented on
the screen as approaching, appears by its ever-
increasing size, to rush almost off the sheet into
the auditorium.
To give the effect of a balloon rising or falling,
or a flying machine travelling in space, roUable
backgrounds, on which are depicted distant land
and clouds, are placed behind the scene and
operated. The rollers on which such back-
grounds are wound are fitted to supports capable
of universal movement in one plane. If a balloon
or any other object is to be represented as
ascending, the background is wound from top
roller to bottom, passing downwards, or in an
opposite direction to that in which the balloon is
supposed to be moving. If a flying machine is
represented as travelling from left to right, the
background is moved in panoramic order from
right to left.
Many other effects are produced by what is
known as composite printmg, in which process
masking is resorted to and tie print made by
exposure in contact with two, three or more
separate negative films in succession, according
to the complexity of the subject to be produced.
Dissolving effects are produced as described
under the heading " Dissolving-views." Under
the heading " Aerial Screen " is explained one
method of producing " ghost effects " in kine-
matography.
THEATROGRAPH
A lantern projection apparatus for displaying
a series of photographic pictures, invented by
R. W. Paul, in 1896.
THERMO DEVELOPMENT (See "Develop-
ment, Thermo.")
THERMOMETER
A temperature measurer; there are three
thermometer systems in more or less common
use, namely, Fahrenheit, Reaumur and Celsius,
the latter being best known as Centigrade. The
Fahrenheit system, invented in 17 14, is the
most widely used in England; the Centigrade
system, invented in 1740, abroad; while the
Reaumur system, invented 1731, was in use
in Russia. It is a simple matter to convert
one to another. To convert —
Centigrade into Fahrenheit, multiply by 9,
divide by 5, and add 32 ;
Fahrenheit into Centigrade, subtract 32,
multiply by 5, and divide by 9 ;
Centigrade into Reaumur, multiply by 4 and
divide by 5 ;
Reaumur into Centigrade, multiply by 5 and
divide by 4 ;
Fahrenheit into Reaumur, subtract 32, multi-
ply by 4, and divide by 9 ;
Reaumur into Fahrenheit, multiply by 9,
divide by 4, and add 32.
THERMO REGULATOR (See "Mercury
Thermo Regulator.")
THINNING SOLUTION
A mixture of equal parts of ether and alcohol
used for thinning collodion which has become
thickened by evaporation, or which has been
made up with too great a proportion of pyro-
xyline.
THIOCARBAMIDE (Fr., Sulfo-urie, sulfocarh-
amide; Ger., Thiocarbamid, Sulfoharnstoff}
Synonyms, sulphourea, thiourea. CS(NHj)j.
Molecular weight, 76. Solubilities, i in 1 1 water,
very soluble in alcohol and ether. White
Thiosinamine 54'
lustrous crystals obtained by heating ammonium
sulphocyanide for two hours at a temperature
of 322° P. (161° C), when the ammonium salt
is converted without loss or gain into its isomeric
molecular compound thiocarbamide. Water-
house suggested it as an addition to the eikonogen
developer to obtain reversal by direct exposure,
and it is also used for toning with gold. The
most satisfactory formula for this is the following,
first suggested by Helain : —
Gold chloride (i %
sol.) . . . 120 mins. 25 ccs.
Add—
Thiocarbamide (2 %
sol.) . . . 65-71 mins. i3'5-iS ccs.
till the precipitate first formed is redissolved,
then add —
Three-colour Photography
24 grs.
10 oz.
5-5 g.
1,000 ccs.
Citric acid
Distilled water to
And finally —
Salt . . .48 grs. II g.
The prints should be rather deeply printed,
and immersed in a lo per cent, solution of salt
prior to toning. This bath is economical, and
free from any tendency to double tones. This
carbamide is used also for clearing yellow stains.
THIOSINAMINE (Fr., Sulfophenylurie ; Ger.,
Thiosinamin, A llylstilfoharnstoff)
Synonyms, allyl sulphocarbamide, allyl sul-
phourea, allyl thiourea, rhodaUine. CS(NH2)
NHC3H5. Molecular weight, Ii6. Solubilities,
slightly soluble in water, easily soluble in
alcohol and ether. It is in the form of
colourless crystals with faint garlic odoiir, ob-
tained by the action of ammonia and alcohol
on allyl sulphocyanate (mustard oil). It has
been suggested as a fixing agent, but its solvent
powers are very poor compared with " hypo,"
and its price is high.
THIOUREA (See "Thiocarbamide.")
THOUGHT PHOTOGRAPHY
Many of the " spirit " photographers have
claimed to be able to photograph thought. In
the Review of Reviews for Apnl, 1893, W. T.
Stead suggested that additional experiments
should be tried to obtain psychic pictures
without the agency of the camera, and in the
following July an experiment was tried and
recorded by Andrew Glendinning. A female
medium and clairvoyante held between the palms
of her hands an unexposed dry plate enclosed
in a dark-slide. The plate was afterwards
developed, when the picture of a child appeared
upon it. Unfortunately, it is impossible to
■discover what was the subject of the lady's
thoughts. It is recorded that Prof. Jordan, in
1896, placed seven men in front of his camera
and asked each one to think of a cat ; they did
so, and the resulting photograph was " a collec-
tive psychical image which is none other than
the astr^ cat in its real essence." Dr. Baraduc,
of the Paris Soci6te de Medecine, has stated
that by concentrating his mind on a definite
object so as to visualise distinctly a picture
thereof, the image was impressed on a dry
plate. Several other experiments have been
made in the direction indicated, but no properly
authenticated result of any importance has
been obtained. Many of the so-called thought
pictures that have been exhibited require an
immense amount of imagination to distinguish
any image upon them.
THREE-COLOUR PHOTOGRAPHY
This particular branch of photography is,
with the exception of the diffraction and Lipp-
mann's processes, practically the basis of all
colour photography. It is based on the theory
that by the use of three colours only aU the
colours of nature can be simulated, either by
the use of three lights — red, green, and blue-
violet — when optical synthesis is used, or by
the aid of three pigments — ^red, yellow and blue
— when the subtractive process is employed on
paper or glass.
The first idea of this process was enunciated
by Clerk-Maxwell in a lecture before the Royal
Institution, in 1861.
Henry CoUen, the miniature painter to Queen
Victoria, writing to the British Journal of
Photography (1865, p. 547), threw out a sug-
gestion, which, although theoretically incorrect,
shows that he certainly conceived the idea, and
apparently in ignorance of Clerk-MaxweU's sug-
gestions.
Ducos du Hauron sent, in 1862, a letter to a
M. Lelut, member of the Acad^mie de Medecine
et Sciences, in which he describes the principles
of three-colour work, and though, like Cohen's,
they were erroneous, still they are of suf&dent
interest to warrant inclusion : —
" Physical Solution of the Problem of Repro-
ducing Colours hy Photography. — The method
which I propose is based on the principle that
the simple colours are reduced to three — ^red,
yellow, and blue — the combinations of which in
different proportions give us the infinite variety
of shades which we see in nature. One may
now say that analysis of the solar spectrum by
means of a glass which only passes one colour
has proved that red exists in all parts of the
spectrum, and the like for yellow and blue,
and that one is forced to admit that the solar
spectrum is formed of three superposed spectra
having their maxima of intensity at different
points. Thus one might consider a picture
which represents nature as composed of three
pictures superimposed, the one red, the second
yellow and the third blue. The result of this
would be that if one could obtain separately
these three images by photography and then
reunite them in one, one wovUd obtain an
image of nature with all the tints that it
contains."
Here also the theory of colour selection is
erroneous, and founded on Brewster's theory,
but the above note proves that Du Hauron
had really conceived the idea of three-colour
work independently of Clerk-Maxwell.
Du Hauron goes on to describe the use of
three filters of deep red, deep yellow, and deep
blue, and gives a sketch of a chromoscope by
means of wtich the three positives could be
seen visually, and even suggests a stereoscopic
chromoscope. In November, 1868, Du Hauron
took out a French patent for three-colour
Three-colour Photography
S42
Time Exposures
work, and here he used red, green and violet
filters, thus falling into line with modem
practice. In 1865, Baron Rausonnet, of
Vienna, attempted to produce three-colour
photo-lithographs, but failed to obtain any
result, and gave up the idea. In 1867, Charles
Cros, a Frenchman, had quite independently
been working on the same problem, and in
1869 published his ideas. Ctos utilised the
principle of monochromatic illumination of his
subject, but he did not follow up the subject
quite so energetically as Du Hauron, who was
the first actually to produce a three-colour
print. It was only after the discovery of the
principle of orthochromatising that three-colour
work made any advances. It is impossible to
give a complete historical sketch of the subject,
but the above includes reference to the first
workers on the subject.
The commonly accepted theory of three-
colour work is that the filters and plates must
be so adjusted as to give a reproduction in
black — that is, in metallic silver — of the three
sensation curves according to Clerk-Maxwell,
but the requirements of the printing inks, or
the projection colours, necessitate modifications ;
and the generally accepted practice now is that
the three filters should have a sUght overlap,
as follows : The red filter should transmit
from \ 7,000 to \ 5,800 ; the green from \ 6,000
to \ 4,600 ; and the blue from \ 5,000 to
K 4,000 ; and equal density should be obtained
under each filter.
There is occasionally some little misunder-
standing about the printing inks and the pro-
jection colours, but this can be cleared up by
a very simple explanation. If a black-and-
white drawing is photographed, it is obvious
that the whites will give the density in the
negative, whilst the black, which is the colour
in which it is wished to print, gives the shadows,
or bare glass, so that obviously we print in
the colour that does not act. In projecting a
transparency from the negative we should
project by white hght ; therefore we should
project by the colour that did act on the
negative. DeaUng thus with a coloured sub-
ject, we use a red screen that cuts out the
blue, and therefore print from this negative
in the colour that does not act on the negative,
namely, blue ; using a green screen we cut
out the red, and therefore print in red ; and
with a blue screen, which cuts out the yellow,
we print in yellow. For projection, as stated
above, we project by the hght by which the
negatives were taken and, therefore, project the
transparency taken through the red screen by
red light, that taken by the green screen by
green light, and that taken by blue by blue
light.
Theoretically, there should be, of course,
correspondence between the light cut out by
the screens and the hght reflected by the inks,
but here there is generally a departure from
theory, as the theoretically correct inks are not
sufficiently permanent to light.
Three-colour work may be divided into
photomechanical printing ; the superposition of
dyed films or pigments, as in the carbon process,
in which the principle of subtractive colour
mixture is made use of ; and the optical
synthesis methods, such as the chromoscope,
three-colour projection, and screen-plate pro-
cesses. The production of filters for this work
is treated of under the heading of " Colour
Screen or Filter." It is far better to use a
panchromatic plate for all three exposures, as
the gradations are then more likely to be the
same, which may not be the case when plates
sensitised for each particular section of the
spectrum are employed. In no case should the
negatives be harsh, but rather tending towards
softness. With correct filters adjusted to the
plate with which they are to be used and correct
exposure, hand work on the negatives — except
for the retouching of pure mechanical defects —
should be avoided, as no one can tell from
looking at a subject exactly how much of
any one of the three printing colours is con-
tained in any colour of the original.
Pinatype is a three-colour process invented by
Dr. Konig, in 1905. Three negatives are first
obtained Qirough red, green and blue filters, and
from these transparencies are made. Special
gelatinised plates, sensitised with potassium bi-
chromate, are exposed under the positives and
washed, being then soaked in blue, red and
yellow dyes respectively, which are absorbed by
the soft or image portions only. The three plates
are pressed in turn in contact with moistened
gelatinised paper, which takes up the dye ; a
photograph, or strictly, print, in colours results.
THREE-COLOUR WORK
A term generally applied more particularly to
process work and printing in three colours, as
distinct from purely photographic methods,
which come under the heading of three-colour
photography.
THYMOL
An antiseptic obtained from certain volatile
vegetable oils, and used as a preservative in
mountants.
TIME DEVELOPMENT {See "Development
Factorial," " Development, Thermo," and
"Development, Time.")
TIME EXPOSURES
Exposures sufficiently long to be given by
hand, the duration being determined by closing
the lens at will, as distinguished from " instan-
taneous " exposures, or those that must be given
automatically by a mechanical contrivance. A
time exposure may be of any duration from a
quarter or half of a second up to several hours.
If very long, the lens cap will form the most con-
venient method of uncovering and covering the
lens, but for exposures up to eight or ten seconds
a mechanical shutter is preferable, as when this is
employed the photographer can watch moving
foliage or any subject that requires care in
seizing the opportunity for making the exposure,
and, without touching or looking at the camera,
can release the shutter at the critical moment,
thus ensuring exposure under the best conditions.
If foliage should move or any other accidental
necessity arise, he can at once dose the shutter,
if the exposure is nearly completed, and secure
a negative that shows absence of movement. In
long time exposures it may frequently become
Tin, Blackening
543
Tone
necessary to give several short exposures to make
up the total time. The photographer should
acquire the art of capping and uncapping the
lens without imparting a tremor to the camera.
For timing exposures, there is nothing better
than a chronometer or a watch with a seconds
hand. One exposure meter is fitted with a
chain which swings to and fro in a given time
and is approximately correct. Counting is fairly
satisfactory if one has learnt to count always at
the same speed, but a second is longer than the
average worker imagines, and considerable prac-
tice is necessary before one can count wiOiout
a watch with safety. A common plan is to count
in a normal manner, as follows : " One little
second," " two little seconds," " three little
seconds," and so on, practising this until each
sentence takes one second to repeat. For longer
exposures, both for camera and dark-room work,
a watch or a, special dark-room clock is to be
preferred.
TIN, BLACKENING {See " Blackening Appa-
ratus.")
TIN CHLORIDE (Pr., Chlorure d'itain ; Ger.,
Stannochlorid)
Synonym, tin protochloride or dichloride, tin
salt, stannous chloride. SnClj 2H,0. Molecular
weight, 225. Solubilities, i in i"5 water, soluble
in alcohol. It takes the form of white crystals,
obtained by the action of hydrochloric acid on
tin. It has been suggested for blackening nega-
tives after bleaching with mercuric chloride, but
it presents no particular advantage. Helain's
formula is : —
Tartaric acid.
Tin chloride .
Distilled water to
96 grs. 22 g
96 „ 22,,
10 OZ. 1,000 CCS.
TINCAL, OR TINKAL {See "Sodium Borate.")
TINCTURE OF IODINE (Se« "Iodine.")
TINFOIL (Pr., &tain en feuille, Feuille d'itain;
Ger., BlatUinn, Stanniol)
An alloy of lead and tin rolled out into thin
sheets. The thinnest variety is used for masking
negatives, especially in collotype printing, so as
to secure clean white margins. Woodbury used
tinfoil in his Stannotype process.
A process of using tmfoU instead of paper as
a base for photo-lithographic transfers was
worked out by Captain ManteU, at the Royal
Engineers' Military School, Chatham, its advan-
tage being freedom from expansion when the
transfer is damped.
TINT BLOCKS (Pr., CUchis d, teinte; Ger.,
Ton-platten)
A process block is sometimes printed on a tint
ground imitating the effect of an India tint
mount ; this ground is printed from a " tint
block." Sometimes an etched block is used in
half-tone work to give a preliminary printing in
a lighter tint of ink than the main block. This
blods is termed a tint block.
TINT PLATES
Copper plates engraved with a mechanical
stipple or fine ruling for the purpose of pulling
transfers therefrom. Lithographers and process
workers use them for applying a tint to some
part of an illustration that has to be shaded
or darkened in colour. Tint plates have now
been almost entirely superseded by shading
mediums.
TINTED PRINTS
Printing papers with coloured supports are
articles of commerce, as, for example, cream
bromide papers and self-toning papers, and pink
and mauve P.O.P. Other and much higher and
pronounced colours are also supplied. It is a
common practice to use white papers and to
stain with dyes or tea and cofEee.
TINTOMETER
An instrument for measuring and, as it were,
analysing the colour in solids and liquids ; in-
vented by J. W. Lovibond about 1887. The
object is placed at one end of the instrument ;
from a graded series of standards, made of
coloured glasses, numbered according to their
depth of colour, the colour of the object is
matched. Por investigation work, three colour
scales are employed (red, yellow and blue), and
the glass slips are graded in colour from plain
glass to maximum intensity. The instrument
itself consists of a double, parallel-sided tube,
having at one end an eyepiece and at the other
the viewing apertures.
TINTYPE {See "Ferrotype Process.")
TISSUE {See " Carbon Tissue.")
TISSUE NEGATIVES
In an early type of roll film, the sensitive
emulsion was spread upon paper and stripped
off after being developed and fixed.
TITHONOTYPE, OR TITHNOTYPE (Pr.,
Tithonotype ; Ger., Tithonotypie)
A process for obtaining metallic copies of
daguerreotypes by electrotypy, discovered by
J. W. Draper, of New York. The daguerreotype
was gilded, and left exposed to the air for a few
days. The back and edges were next varnished,
and copper was electro-deposited upon the
daguerretoype image, this taking from twelve
to twenty hours. If the work had been done
properly, the tithonotype was readily detached
without injury to the original, of which it formed
a perfect copy. Duplicates could be made from
the tithonotype if required.
TITLING NEGATIVES AND PRINTS {See
"Lettering Negatives and Prints.")
TOBACCO PRESERVATIVE
One of the many preservatives or organifiers
introduced before the days of gelatine dry plates
for keeping collodion plates in a good condition
for a few days. The formula was : Water, i oz. ;
gum arable, 10 grs. ; tobacco, 20 grs. The mix-
ture was boiled and filtered, then coated upon a
sensitive plate.
TONE
A term that is applied in two distinct ways.
It is used in the same sense as in painting, etching,
Tone Blocks
544
Toning Bromide Prints
drawing and kindred arts, to signify the degree
of depth of any mass of greys, such a mass being
described as a " light " or " dark " tone, a
" delicate " tone, etc. A picture is said to be
" light " in tone when there are few dark masses,
or it is " dark " in tone when the heavy or dark
masses preponderate.
" Tone " also indicates the actual colour of a
print, brown and red colours being termed
" warm " tones, and purple and black colours,
" cold " tones.
Light tones are called high, and dark ones low.
The more a picture inclines to whites and light
greys (or other colour) the higher it is in tone ;
the heavier and darker it is, the lower it is in
tone. (See also " Key.")
" Half-tones " are the shades of colour between
black and white, a half-tone image being an
image in which the haU-tones have been broken
up into dots ; in contrast with which an ordinary
photograph is said to be of " continuous tone."
TONE BLOCKS
Half-tone blocks are often referred to as
" tone blocks."
TONING (Pr., Virage; Ger., Tonen, Schonen.)
The operation of changing the colour of a
photographic image by changing its com-
position or depositing another metal. Toning
is almost exclusively employed for modifying
the silver images on printing-out, bromide, and
gaslight papers. It is sometimes adopted in
lantern sUde making. Details of the processes
are given under other headings.
TONING BATHS FOR SILVER PRINTS
A toning bath suitable for almost every
brand of gelatine and collodion printing-out
paper is : —
Am. sulphocyanide 12 grs. 4-5 g.
Gold chloride . i gr. '27 „
Water . . . 5-6 oz. 830-1,000 ccs.
Pull working details are given in the article
on " Toning P.O.P."
The following toning baths work admirably
with some brands of P.O.P. : —
Sodium phosphate
Gold chloride
Water .
Sodium formate
Gold chloride
Water .
20 grs.
I gr-
6 oz.
15 grs.
I gr-
6 oz.
7-5 g-
•37 „
1,000 ccs.
5 '6 g.
■37 „
1,000 ccs.
The sodium phosphate and the following
baths are all suitable for albumenised paper : —
Sodium acetate . 30 grs. 10 g.
Gold chloride . i gr. "3 „
Water . . . 7 oz. 1,000 ccs.
This bath should be mixed at least ten hours
Tjefore required for use.
Sodium bicarbonate 4 grs. V2 g.
Gold chloride . i „ '3 „
Water . . . 7 oz. 1,000 ccs.
Other formula are given under the headings
" Borax Toning," " c3doride of Lime Toning
Bath," " Bennett's Toning Bath for P.O.P.," etc.
TONING BROMIDE PRINTS
There are various methods of toning bromide
prints; the most satisfactory being those that
produce various shades of brown-black and
cold and warm brown, although red tones are
very suitable for flower studies and portraits of
children, etc. Green and blue tones are the least
desirable. In monochrome work it is rarely
desirable to imitate the colour of the subject.
In all toning processes, the method of pro-
ducing the print considerably influences the
final colour and quality. A strong, rich print
is essential for securing rich tones, and a strong
print cannot be obtained from a weak, flat
negative. Prom a good negative, a strong print
can only be obtained by correct exposure and
full development ; over-exposure and short
development yield a print that will never tone
to a rich colour ; the result is always weak and
poor. Another source of imperfect results in
toning is the very common practice of using
one quantity of developer for several prints.
Those developed last will invariably give weak
and poor colours when toned. Fresh developer
should be used for every print, excepting
small prints,f or which, relatively, a large quantity
of solution is employed. For these, two prints
may be developed in succession in one quantity
of solution, but this should be the limit.
Thorough fixation is essential to success in
toning bromide prints; thorough washing is
often equally important. Bromide prints should
always be dried after fixing and washing before
toning ; with some processes this affects the
colour very materially.
Copper Toning. — Very delicate red tones,
red-chalk, or rather sanguine, can be obtained
by toning with copper. For the formulae, see
" Copper Toning."
Platinum Toning. — Good sepia tones may be
obtained by this method, which is fully described
under a separate heading.
Vanadium Toning. — A good green tone can
be obtained by this process. (See " Vanadium
Toning." )
Ifon Toning. — Rich blue tones are obtained
by iron toning ; the bath should be prepared
by adding each ingredient in the same order as
in the formula : —
Ferric am.-citrate .
3 grs.
•62 g.
Pot. ferricyanide .
3 ,.
•62,,
Nitric acid
6 mins
1-2 CCS
Water .
8 oz.
800 „
The print tones rapidly in this solution to a
rich blue ; it requires washing in various changes
of water until the whites lose the stain acquired
during toning, and become quite pure. It is
better to prolong the washing a little beyond
the visible clearing. The permanency of prints
toned either by iron or vanadium is doubtful.
"Hypo "-alum Toning, — A method of sulphide
toning by means of a solution of "hypo" and
alum. The colour is a purple-brown, and the
results are thoroughly permanent. Working
details are given under the heading of " Alum-
'hypo' Toning."
Sulphide Toning. — A process of toning by the
use of a. solution of sodium sulphide which is
in every respect the most satisfactory method
of toning bromide prints. Very rich, pure
Toning, Double
545
Toning, Systematic
brown colours are obtained, the process is
simple and certain, and the prints after toning
are quite permanent. The process, one of
combined toning and intensification, is fully
described under Qxe heading " Sulphide Toning."
TONING, DOUBLE {See " Double Toning.")
TONING AFTER FIXING
A method that has been recommended on
account of the occasional loss of tone in the
fixing bath after toning. Success depends, as in
all toning processes, upon the quality of the
print.- Prints intended for fixing before toning
should be deeply printed, fixed, well washed,
and then toned in the ordinary sulphocyanide
and gold toner. With some papers, a more
satisfactory system is to immerse the fixed and
washed prints in a solution of i oz. of formaline
in 9 oz. of water. The toning bath is then used
just warm and kept warm while in use.
TONING AND FIXING COMBINED
A bath very frequently employed for toning
and fixing silver prints at one operation. It is
not merely the obvious saving of time and
trouble that has rendered it a favourite method
with many workers, but rather the great advan-
tage that the tone or colour of the prints remains
the same after finishing as when taken from the
toning bath. In separate toning and fixing,
the colour obtained by toning is frequently
considerably modified by the subsequent fixing.
A serious objection to the combined bath is
that prints may be toned to the desired colour
before they are properly fixed, and subsequent
fading is the inevitable result. Or the bath may
contain sulphur, and the tones may be due to
this substance rather than to gold, and this also
produces prints which will deteriorate quickly.
These objections may be entirely obviated by
adopting a suitable formula, preferably one that
contains neither acid nor alum ; keeping stock
solutions from which the bath may be prepared
when required ; mixing sufficient solution for
the prints that are to be toned, and throwing
away the mixed solution after using it once.
Using a combined bath many times in succession
is one of the most frequent causes of want of
permanence. A reliable formula and method
of working will be found under the heading
" Bennett's Toning Bath for P.O.P."
TONING LANTERN SLIDES
Lantern slides may be toned by any of the
methods given for bromide prints. Some of the
toning methods intensify as well as change the
colour of the slide— the sulphide, for example —
and somewhat destroy the transparency of the
image. Copper toning produces attractive red
tones, with transparency and delicate quality.
{See "Toning Bromide Prints.") The most
satisfactory warm and cool brown tones are those
produced by development.
TONING PLATINOTYPE PRINTS (See
" Platinotype Process.")
TONING P.O.P.
Of the two methods of toning and fixing prints
on printing-out silver papers, one is to tone first
35
and afterwards fix, and the other is to tone and
fix at one operation, the second method saving
much time and trouble, while capable of producing
quite as good results. It is described under the
heading " Toning and Fixing Combined."
For separate toning and fixing, the prints
require first to be washed for about twenty to
thirty minutes in several changes of water ;
the first two changes should be made as quickly
as possible, care being exercised to prevent
the prints from clinging together. To prepare
the toning bath, two solutions are necessary : —
A. Am. sulphocyanide . 520 grs. 120 g.
Water to . . 10 oz. 1,000 ccs.
B. Gold chloride . . 15 grs. 3'S g.
Water to • • 3i oz. 375 ccs.
To prepare the toning bath, take 2 drms. of A,
add 5 oz. of water, and then add slowly 2 drms.
of B ; in ten minutes the bath will be ready for
use. It will be sufficient for four whole-plate
prints or sixteen quarter-plates. A proportionate
quantity should be prepared for any other
number of prints, allowing always J drm. each
of A and B, and ij oz. of water for each whole-
plate print. The prints to be toned are placed
in the solution and continuously turned over by
lifting the lowest print and placing it on top
until the desired colour is reached. They are
then rinsed in two or three changes of water and
fixed for fifteen minutes in the following :
ijoz. 165 g.
5 mins. I cc.
ID oz. 1,000 ccs.
Sodium hyposulphite
Liquor ammoniee .
Water
Take care to ensure free access of the solution
to the surfaces of the prints, and to prevent them
from clinging together. After fixing, wash the
prints, in water frequently changed, for from
one to two hours.
An additional method of toning P.O.P. is by
means of platinum. The most satisfactory
manner of working is by first toning with gold,
preferably by the sulphocyanide bath, then,
after a short washing, toning with platinum,
washing again, and fixing.
An alternative plan is to use a self-toning
paper, by which the operation of gold toning is
avoided, and then the prints are washed, toned
simply with platinum, washed and fixed. Or
the prints may be toned first with platinum
and then finished in a combined gold toning and
fixing bath.
Formulae for platinum toning baths are given
under the heading " Platinum Toning " ; another
is: —
Potassium chloroplatinite i gr. -25 g.
Sodium chloride . . 10 grs. 2-5 „
Citric acid . . • 10 „ 2-5 ,,
Water
. 5-6 oz. 500-600 ccs.
Whatever method of toning is adopted, only
sufficient of the working solution should be pre-
pared for the prints to be toned ; it should be
used once, and then thrown away.
TONING, SULPHIDE {See "Sulphide Ton-
ing.")
TONING, SYSTEMATIC
A process of toning by which the exact amoimt
of gold, etc., is used, the solution being thrown
Toning without Gold, etc.
546
Transferred Light Action
away after use. W. J. Wilson was (in 1894) one
of tlae first to publish working details. The
amount of gold chloride required to tone safely
and thoroughly may be taken as from ij to if
grs. for each sheet of paper 24J in. by 17 in.,
dark or heavy prints requiring more gold than
lightly printed ones. Taking ij grs. as a fair
average (equivalent to -6 gr. per i sq. ft.), the
following bath may be made up : —
Ammonium sulpho-
cyanide . . 12 grs. 2'3 g.
Gold chloride . . i ,, -2 ,,
Water . . . 12 oz. 1,000 cos.
Twenty-four minims of this bath will tone i sq.
in. of P.O. P. print, or the bath may be used
in the following proportions : —
Inches Sq. Ins. Oz. Drs.
One whole sheet 24J X 17 ^ 416.5 requires 21 o
One piece . . . 15 X 13 = 180 „ 90
„ . . 12 X 10 = 120 „ 60
„ . . 10 X 8 ^ 80 „ 4 <^
8i X 6J = 55.25 „ 2 6i
„ . . . 6J X 4i = 30-87 •> 14
6 X 4i = 26 „ I 2i
4i X 3i = 13-81 „ 06
The above bath is weaker than that originally
advocated by W. J. Wilson.
TONING WITHOUT GOLD OR PLATI-
NUM
One of the most popular of the "no gold"
baths is the following, which gives rich tones
from warm brown to purple. The results are
fairly permanent, and the process is widely
used for prints required as rough proofs or those
which it is not desired to keep for any length
of time : —
Sodium hyposulphite
. 2 oz.
220 g.
Lead acetate
. i„
28,,
Water (hot) .
• 10 „
1,000 CCS.
The bath is ready for use when cold. A dense
precipitate is formed and the solution needs to
be decanted. The prints are printed more deeply
than usual, and are not washed previous to im-
mersion, but well washed afterwards.
TOUCH PAPER
Slow-burning paper strips used for firing a
flash-light mixture, which is piled up on one
end of the strip and the other ignited. The time
taken for burning depends upon the length of
the strip, 2 in. or 3 in. being usually enough.
The paper is made by soaking blotting-paper
in a solution of saltpetre in water, drying, and
cutting into strips about |- in. wide. Another
recipe is as follows : Finely powder separately
equal parts by weight of antimony sulphide
and potassium chlorate, mix together, and add
enough sheUac, dissolved in alcohol (ordinary
French polish answers well) to make a thick
cream. Spread this evenly upon paper, allow
to dry naturally, and cut up for use.
TRACING PAPER (Fr., Papier d calquer ;
Ger., Papier zum Durchzeichnen)
This paper has been recommended for use on
the glass side of a negative for the purpose of
working upon or for retarding printing. Some
of the French tracing " papers " are actually
papier glad, which consists of isinglass. Ordinary
thin paper may be made translucent by coating
with thin dammar varnish and allowing to dry ;
another substance is bleached beeswax dissolved
in alcohol and ether. A translucent paper suit-
able for use with colours mixed with spirit is
made by coating paper with bleached shellac 3
parts, mastic i part, strong alcohol 20 parts.
In lithography, several varieties of transfer
tracing paper are used for making drawings in
lithographic writing or drawing ink. These
tracing papers have a gelatine surface to render
it possible to transfer the ink when the paper is
damped and pressed down to stone or metal.
TRACINGS, PRINTING FROM
Tracings made by engineers, architects, etc.,
are easily duplicated by photographic printing,
the iron printing processes being widely used
because of their simplicity and cheapness. See
under the following headings : Blue-print
Process " (white lines on a blue ground), " Pellet
Process " (blue lines on a white ground), " Ferro-
gallic Process " (black lines on a white ground),
" Kallitype " (brown lines on a white ground),
" Ordoverax " (black ink lines on a white
ground), etc.
TRAGACANTH {See " Gums and Resins.")
TRANSFER PAPERS
Single transfer paper and final support for
double transfer are used in the carbon process
{which see).
In process work and lithography, numerous
kinds of transfer papers are used, some for
making original drawings upon and others for
retransferring impressions from existing stones
to plates bearing designs on them. Tracing
transfer and writing transfer papers are for
making original designs upon with pen or brush
and lithographic ink. Scotch transfer, India
transfer, and re-transfer papers are for re-
transferring designs. Grained transfer papers are
for making drawings upon with lithographic
crayons. Photo-litho transfer paper is for sensi-
tising with potassium bichromate to print under
a negative. Decalcomanie transfer paper is for
transferring designs to porcelain for vitrifying.
TRANSFEROTYPE
A special kind of bromide paper, widely used
many years ago. It was prepared on one side
with soluble gelatine and with a specially har-
dened sensitive emulsion. The wet bromide
print was squeegeed, face down, on the support
where it was intended to remain. Hot water was
poured on the back of the print, which melted
the soluble gelatine and released the paper,
leaving the image on the support.
The term is now used rather loosely to describe
transferred pictures by other processes.
TRANSFERRED LIGHT ACTION ON
DRY PLATES
It has often been stated that when an ex-
posed and undeveloped plate is packed in con-
tact with an unexposed plate, film to film, the
light action wiU be transferred. Experiments
made with Enghsh dry plates have proved that
even after ten years' contact no appreciable
light action has been transferred. There is a
Transferring Films
547
Trimming Knife
difference of opinion on the subject, but the pho-
tographer can easily test the matter for himself.
TRANSFERRING FILMS FROM NEGA-
TIVES {See "Cracked Negatives.")
TRANSIT BOXES
Boxes specially designed for sending nega-
tives, lantern slides, etc., by post or rail. For
negatives, wooden boxes lined with felt or
rubber are best. Various kinds of transit boxes
are described under the headings " Box,
Lantem-sUde," and " Packing Negatives for
Post."
TRANSLUCENT PAPER {See " Paper Nega-
tives " and " Tracing Paper.")
PHOTOGRAPHS
{See " Photo-tele-
TRICHROM EMULSION
A collodion emulsion sensitised with dyes
for the purpose of making the selective negatives
for three-colour printing. The emulsion is either
panchromatised or issued with three different
sensitisers, which can be added to the emulsion
just before use, and which sensitise it respec-
tively for red, green, and violet.
TRICHROMATIC PHOTOGRAPHY {See
"Three-colour Photography.")
TRICK PHOTOGRAPHY
Photography lends itself to the production
of a variety of " trick " effects, which may be
classified as: (i) Those produced by dividing
the exposure and making alterations in the
subject during those times when the lens is
covered {see, for example, " Boubles," " Treble
Photographs," " Psychic Photography," " Thea-
trical and Kinematograph Photography," etc.) ;
(2) those produced by manipulations in print-
ing, as by the methods described under the
heading, " Combination Printing " ; (3) those
produced by chemical manipulations (see, for
example, " Magic Photographs ").
TRICOLOUR PHOTOGRAPHY {See " Three-
colour Photography.")
TRIHYDROXYBENZENE
Synonym, trihydric phenols. Three isomeric
compounds, all possessing the same formula,
C,H,(OH)3, but differing in constitution. They
are interesting because pyrogallol or pyro is one
of them, and their graphic formulse may be re-
presented as follows : —
c-OH
c— OH
C— OH
C— OH
C— OH OH— C
HC/
C— OH HCV
TRANSMISSION OF
ELECTRICALLY
graphy.")
TRANSMITTER, STEREOSCOPIC {See
' ' Stereoscopic Photography ." )
TRANSPARENCIES, CARBON
Transparent positives made by the carbon
process. A special tissue for the purpose con-
tains more colour than the tissues for paper
prints, and requires from three to five times the
exposure necessary for an ordinary print. The
exposed tissue is squeegeed to, and developed
on, a sheet of glass previously coated with
a thin solution of bichromated gelatine, and
the remaining work resembles that described for
single transfer prints under the heading
"Carbon Process."
Glass plates (old negatives cleaned) may be
prepared by coating thinly with a solution of —
Gelatine . . .60 grs. 14 g.
Potassium bichromate 3 „ 7 „
Water . . .10 oz. 1,000 ccs.
and, after drying, exposing to daylight to harden
the coating. The gelatine must be soaked in
cold water for an hour, and then dissolved by
heat, the bichromate, dissolved separately in a
little water, being added to the gelatine. Pre-
pared glasses may be purchased when obtaining
the transparency tissue.
TRANSPARENCY (Pr., Transparence; Ger.,
Transparent, Durchsichtigheit)
A term commonly applied to lantern slides
or other positives on glass. {See also "Window
Transparencies." )
TREBLE PHOTOGRAPHS
Trick photographs in which a person is shown
in three different positions in the same negative.
They are produced in much the same way as
doubles {which see), the best method being to
use a black background and give three separate
and equal exposures, taking care that the three
images do not overlap.
TRIAMIDOPHENOL (Pr. and Ger., Tri- TRIMMER {See "Print Trimmer.")
amidophenol)
C,HjOH(NH2), 3Ha. Molecular weight
248-5. It is in the form of white needles, and
has been recommended as a developer, but it
is not much used.
CH
Pyrogallol
1-2-3 Trihydroxy-
faeozeae
\C— OH
;cH
1-3-5 Trihydroxy-
benzene
C— OH
Hydroxyhydro-
quinone
1-2-4 Trihydroxy-
benzene
It will be noted that the hydroxyl groups (OH3)
are in different positions in the benzene ring,
their positions beiug shown by the numbers
1-2-3, etc., in the second line of the titles. In
each case one hydroxyl group has replaced one
hydrogen atom.
TRIMETHYLAMINE (Pr., Trimithylamine ;
Ger., Trimethylamin)
(CHa)aN. Molecular weight, 59. A colour-
less gas obtained by the action of ammonia on
methyl iodide. A 10 per cent, aqueous solution
has been suggested as the accelerator for deve-
lopment, but its most unpleasant smell renders
it of small practical use. It was employed in
the Russian developer {which see).
TRIMMING KNIFE (Pr., Canif i decouper ;
Ger., Beschneidemesser)
The knife used in trimming photographic
prints and enlargements previous to mounting.
Trimming Prints
548 Tropics, Photography in the
Many workers prefer a good penknife to the
many patterns of knives made especially for the
purpose. The average type of trimming knife
is represented by A and B ; C resembles a sur-
geon's scalpel, and is useful for many other
purposes, such as mount-cutting, retouching,
etc. D is a wheel trimmer, which, with due
Five Types of Trimming Knives
care, may be employed for trimming wet prints
as well as dry ; while E is a trimming nib, use-
ful for cutting circular and oval prints, and in-
tended for insertion into an ordinary pen-
holder. Trimming knives should be sharpened
at intervals by rubbing on a fine oil-stone. The
trimming machine, or " print trimmer " (which
see), is likely to supersede the knife.
TRIMMING PRINTS
Prints are trimmed, or cut down, partly to
get rid of bare or rough edges, and partly to cut
away those outside parts of the picture that
are not required. A good method of deciding
just how much of a print should be retained is
to cut two L-shaped pieces of cardboard and
adjust those on the print so that they form
a rectangle including just the portion required.
This is marked with pencil and the print trimmed
accordingly.
The actual cutting may be accomplished with
no more elaborate apparatus than a sharp knife,
a steel straight-edge, and a sheet of glass or zinc
to cut upon. In addition, a T-square or set-
square must be used to secure accurate right
angles. Although prints are generally trimmed
dry, it is sometimes required to cut them while
wet, and for this purpose a wheel trimmer must
be used.
Trimming is greatly facilitated by employing
one of the many machines made for the purpose.
These usually take the form of a rectangular
board with a guillotine blade working along
one edge (see " Print Trimmer "). They are gener-
ally fitted with a scaled rule to assist in cutting to
given dimensions. Rectangularity is of course
secured automatically. Other apparatus is
made for cutting circular prints of different
diameters. Cutting shapes are also made, par-
ticularly for ovals.
Quite apart from the mechanical trimming of
prints, much judgment and taste is demanded
in deciding just how much of a print shall be
cut away to secure the best result. There should
be no hesitation in sacrificing all that hinders,
rather than helps, the proportion, composition,
and concentration of the subject. However care-
fully arranged on the plate, few prints do not
gain by judicious subsequent pruning.
TRI-NITRO-PHENOL
Synonyms, carbazotic add, picric acid.
C,Hjs (NOj)jOH. Molecular weight, 229. It is
obtained by dropping carbolic acid into nitric
acid, and its salts are explosive. It is in the
form of yellow crystals, which are very bitter to
the taste. It is used principally as a dye.
TRIOXYMETHYLENE (See "Paraformalde-
hyde.")
TRIPLET LENS
A lens consisting of three separate combinations.
TRIPOD (See "Camera Stand.")
TRIPOD HOLDER OR SUPPORT _
An arrangement to prevent the legs of the
tripod slipping on pohshed floors, stone pave-
ments, etc. Perhaps the simplest way of secur-
ing this end is to have a wooden triangle, as
shown at A, with holes bored at the angles at
which the points of the tripod legs may be
inserted. This is often useful in architectural
photography, or when it is desired to use a field
Tripod Holders or Supports
camera in an ordinary room for portraiture or
copying. A more portable application of this
idea consists of three wooden arms hinged
together to fold up when not in use, and having
holes at the ends. Slotted brass plates are also
made which are hinged at one end to the legs
of the tripod, as shown at B, a clamping screw
being passed through the three slots and tightened
up when the tripod is suitably adjusted.
TRIPOLI (Pr., Tripoli; Ger., Tripolith)
A siliceous pulverulent earth used for cleaning
glass, generally mixed with alcohol and ammonia.
TRITURATION (Pr., Trituration: Ger., Zer-
pultierung)
The rubbing up of a powder or other substance
in a mortar.
TROPICS, PHOTOGRAPHY IN THE
Light, flimsy cameras cannot withstand the
effect of tropical heat for long, the shutters of
Trough, Etching
549
Twin-lens Camera
the dark -slides refusing to open and dose and
the woodwork generally going wrong. The
camera should be well made of thoroughly
seasoned mahogany, brass-boimd for preference ;
waterproof glue should be used, or the bellows
should be attached by means of brass strips.
Cloth bellows are more immune from insect
attacks than those of leather. Rustless metal
fittings are better than those of wood. Plates
shotdd be packed in oiled paper, tinfoil, or in
soldered tin-plate cases. Developers may be
carried in concentrated form. The risk of melt-
ing the wet film during development must be
guarded against, hardening with formaline being
advisable. Plates should be dried out of the
reach of insects. As regards the developer,
the use of a more stable alkali than sodium
carbonate is recommended by experienced
travellers, and the diamidophenol and metol-
hydroquinone developers are often advocated.
TROUGH, ETCHING
A shallow tray of earthenware or pitch-lined
wood for the purpose of etching zinc and copper
plates. The ends are usually covered over for a
few inches to prevent the solution splashing
over when the teay is rocked. The troughs are
sometimes mounted on a m.achine for mechanic-
ally rocking them.
TUBE, CROOKES' (See " Crookes' Tube.")
TUBE. FOCUS {See "Crookes" Tube.")
TULOL
A developing compound introduced by Dr.
Iviesegang, of Diisseldorf, in 1899. It was a green
pulpy mass put up in collapsible tubes. When
required for use i part was dissolved in 50
parts of water.
TURMERIC (Pr., Curcuma ; Ger., Kufkuma,
Gelbwurzel)
Synonyms, curcuma, Indian safiron. It is the
rhizome of Curcuma longa, obtained from tropical
climates. It has been used for making yellow
screens and in orthochromatic collodion, but
has fallen into disuse. An alcoholic tincture of
turmeric is used to stain bibulous paper for a
test paper, which turns a reddish brown coloiir
with alkaline earths, a brown colour with boric
add, and a bright sulphur yellow with other
adds.
TURNBULL'S BLUE (Fr., Bleu de Turnbull ;
Ger., Turnbullschzes Blau)
A bright blue ferrocyanide of iron, Fe5(CN)i„
formed by the action of potassium ferricyanide
on a ferrous salt and forming the image in the
iron printing process when the print is developed
with ferricyanide.
TURNTABLE (Pr., Table tournante ; Ger.,
Drehscheibe)
An arrangement permitting a field camera
to be turned round in any direction on the
tripod, to which it is directly attached. As illus-
trated, it consists of a brass ring let into the
camera baseboard, in which revolves a second
ring having projecting eyes to fit the pegs on
the tripod legs. A milled-head screw is provided
to damp the turntable in any position. The ad-
vantages of the turntable, in addition to the
ease with which the camera may be pointed as
desired, are that there is no loose tripod head to
carry or screw to get mislaid, while the hole in
the baseboard allows it to fold over the lens
and shutter, so that a more portable construc-
Tumtable
tion of the camera becomes possible. Greater
rigidity is said to be obtainable with a turn-
table than with the ordinary tripod head, though
some workers dispute this.
In process work, a turntable is generally a
feature on the camera stand used for copying,
its object being to turn the camera sideways
when the prism is used, and to turn it parallel to
the length of the stand for direct work.
TURNTABLE TRIPOD TOP
A tripod head furnished with a revolving plat-
form. It differs from the turntable proper in
being attached to the stand itself instead of to
the camera.
TURPENTINE (Pr., Tirebenthine ; Ger.,
Terpentin)
A colourless volatile liquid obtained by dis-
tillation from an oily resinous substance ex-
tracted from various pine and fir trees. " Spirit "
and " oil " of turpentine, and " turps," are
identical. Rectified turpentine is a purer variety.
Venice turpentine is an exudation from the
larch, and occurs in the form of a honey-like
product, very sticky and tenadous, and smelling
of turpentine. Canada balsam is a similar pro-
duct.
In process work, turpentine has numerous
uses. Rectified turpentine is used for develop-
ing bitumen prints, and for thinning the transfer
ink used for inking up albumen prints. Commer-
dal turpentine is largely used for deaning the
ink off slabs, rollers, blocks, etc.
TWADDEL HYDROMETER (See "Hydro-
meter.")
TWIN-LENS CAMERA
A hand-camera with a full-size finder, having
a lens of the same focal length as is used for
taking the photograph. The image is reflected
by a fixed mirror inclined at an angle of 45° to
a horizontal screen, and may be focused right
up to the moment of exposure. Though bulkier
than the reflex, the twin-lens camera has the
advantage that the image is always in view.
u
ULLMANINE
A white water-colour pigment much favoured
by retouchers of photographs for reproduction.
It works well with the aerograph, photographs
white, and does not change colour.
ULTRA-VIOLET RAYS {Fr., Rayons ultra-
violets : Ger., Ultraviolette Strahlen)
A region of the spectrum lying beyond the
visible violet, the commencement of which is
sometimes known as the lavender rays. The
research in this region of the spectrum has been
much facilitated by the fact that the haloids of
silver are extremely sensitive to it, and one has
but to use a spectrograph fitted with quartz
lenses and Iceland spar prisms to obtain a
spectrogram of the same. Most of the work on
the ultra-violet, however, is done with concave
reflection gratings, which, forming a real image
without the aid of lenses, introduce no absorp-
tive medium. The farthest yet reached by
photographic means is A i,i8i by Victor Schu-
mann using a quartz spectrograph with silver
iodide deposited on glass with but very little
gelatine as binding agent and with the plate and
spectrograph exhausted of air, as he found that
both gelatine and air were rather strong absorb-
ents of the extreme ultra-violet. Ordinary glass
does not transmit beyond about \ 3,400.
In the ultra-violet lies the region of the greatest
photochemical action, and as has been pointed
out in the description of the diffraction grating
there is always an overlapping of the ultra-violet
of the one order on the red of the preceding one,
and therefore in spectrographic work this must
be looked for and absorbed by the use of yellow
filters. In ordinary photography, if anything
like correct colour rendering is required also, the
ultra-violet must be absorbed, for it is obvious
that, as we do not see this region, any action on
the plate would give a false rendering of the
colour. Eder has given the following interesting
table which shows the relative action of the
ultra-violet rays in
Effect 0!
visible
spectrum
Effect oj
ultro
violet
I. — Silver bromide with development —
(a) The photographic effect of dayUght
(reflected from white paper) is com-
posed of
(6) Photographic eflfect of magoesimn
light (from white paper)
(c) Argand gas burner (from white paper)
II. — Silver chloride with development —
The photographic effect of daylight (re-
flected from white paper) is composed
of
62%
30%
80%
i^%
38 %■
70%
20 %
98-99%
When using artificial lights such as the electric
arc, the mercury vapour lamp, and magnesium
ribbon, it may be considered that the bulk of the
photochemical action lies in the ultra - violet.
The practical absorbents of the viltra-violet are
sesculine and filter yellow K.
UNAL
Rodinal in powder form requiring to be mixed
with water to make a developer ready for use.
THEORY {See " Wave-
UNDULATORY
lengths.")
U.S. (UNIFORM STANDARD) STOPS (See
" Diaphragms.")
UNIT OF LIGHT (Pr., Etalon photometrique ;
Ger., Lichteinheit)
Different units have been adopted by various
countries. The British standard is a spermaceti
candle burning about 120 grs. per hour ; the height
of the flame from where the wick begins to char
to the top of the flame should be 45 mm., and
the top of the vdck should turn over towards the
edge of the flame. The candle should be Ut at
COMPARISON OF LIGHT STANDARDS (SCHAUJVl).
Hefner
Lamp
H.K.
Bougie
decimale
and British
standard
candles
German
standard
candle
= D.V.K.
Carcel
Lamp
10 c.-p.
Pentane
Lamp
VioUe's
unit
Hefner lamp.
Bougie decimale and \
British standard V
candle . . )
I
I-I4
0-877
I
0-833
0-950
0-0936
O-I06
0-0909
0-104
0-0439
0-05
German candle
I -20
1-05
I
O-III
0-109
0-053
Carcel lamp .
10 c.-p. pentane
10-8
9-47
9-0
I
0-982
0-474
lamp
VioUe's unit.
II-O
22-8
9-65
20-0
9-17
19-0
I -02
2-II
1
2-07
0-483
I
55°
Universal Developer
SSI
Uranium Intensifier
least five minutes before use ; there should be
a well formed cup of melted wax, and the flame
should be well shielded from draughts.
The French standard is the Carcel lamp, burn-
i*ig 43 g. of colza oil per hour in a circular
hollow wick lamp.
The German standard is the Hefner-Kerze,
that is, the Ught emitted by the Hefner- Alteneck
amyl-acetate lamp.
The German standard candle has a flame
height of 50 mm.
The Vemon-Harcourt 10 c.-p. pentane lamp
and the Harcourt-Simmance i c.-p. pentane lamp
are also used, especially the former. These lamps
biim a mixture of air and pentane vapour.
Violle's unit is the light emitted by the sq. cm.
of glowing platinum, and is extremely difficult
to reproduce.
The bougie decimale of the Geneva Congress
(1896) is the Hefner lamp reduced to the one-
twentieth of Violle's unit.
Other standards of less general use have been
suggested by Werner-Siemens and l,ummer-
Kurlbanm. The table at the foot of page 550
shows the relation between the above units.
UNIVERSAL DEVELOPER
Any developer which wiU serve alike for dry
plates, bromide and gaslight papers and lantern
plates. The metol-hydroquinone developer is a
popular universal developer, but the name
' universal " was probably first used by the
Hford Company for a developer in 1891 : —
A. Hydroquinone . 80 grs. 18 g.
Potass, bromide . 15 „ 3'5 „
Sodium sulphite . i oz. no „
Water to . 10 „ 1,000 ccs.
B. Sodium hydrate . 50 grs. 11 -5 g.
Water . . 10 oz. 1,000 ccs.
For negatives use equal parts of A and B ; for
bromide papers, one part A, one part B, and one
part water ; for lantern plates equal parts of
AandB.
UNIVERSAL LENS
A symmetrical anastigmat lens, highly cor-
rected, and suitable for almost any kind of work.
UNOFOCAL LENS
A lens, invented by Rudolph Steinheil, of
Munich, working at a large aperture. Astig-
matism and other kinds of aberration are
eliminated by employing unusually thin and
I J'i If J
Unofocal Lens
transparent glasses of very slight curvature.
The four elements {see illustration) are of the
same refractive index and focal length, there
being slight distances between them so as to
prevent one combination neutralising the other.
The lens has great rapidity, gives good definition,
and has excellent covering power.
URANIC SALTS (Fr., Sels uraniques ; Ger.,
Uranylsahen)
Uranium forms two classes of salts, the
uranous and uranic. The latter are readily
reduced to the uranous state by the action of
light in the presence of organic matter, and this
forms the basis of several printing processes.
URANIN {See "Eosine.")
URANIUM ACETATE (Fr., Acetate d'urane ;
Ger., Uranylacetat)
Synonym, uranyl acetate. U02(CjH,Oj)2 2H2O.
Molecular weight, 426. Solubilities, very easily
soluble in water and alcohol. It is poisonous,
the antidote being cobalt nitrate and emetics.
It is in the form of small yellow crystals or
crystalline powder, obtained by dissolving uranic
oxide in acetic acid. It generally contains a
little basic salt ; therefore a perfectly clear solu-
tion cannot be obtained without the addition of
acetic add. It has been suggested in place of
the uranyl nitrate.
URANIUM CHLORIDE (Fr., Chlorure d'urane;
Ger., Uranylchlorid)
Synonyms, uranyl chloride or oxychloride.
COjOaHaO. Molecular weight, 361. Solubili-
ties, soluble in water and alcohol. It is poisonous
{see "Uranium Acetate"). It occurs as flat
deliquescent greenish yellow plates, obtained by
dissolving uranic oxide in hydrochloric acid. It
can be used as a sensitive salt for printing out,
and also confers hardness or increase of contrast
when added to a chloride emulsion.
URANIUM COLLODION PROCESS {See
"Wothly's Process.")
URANIUM FLUORIDE SCREENS
Fluorescent screens {which see) coated with
uranium fluoride.
URANIUM INTENSIFIER
An intensifier which gives great additional
printing power to thin negatives, the effect not
being permanent. A simple formula is : —
Uranium nitrate . 40 grs. 9 g.
Potass, ferricyanide . 40 ,, 9 „
Acetic acid . . 27 mins. 6 ccs.
Water . . .10 oz. 1,000 „
A well-washed negative assumes in this a reddish-
brown colour. It is next briefly washed in water
slightly acidified with acetic acid, and finally
in plain water until the stain has gone. Any
" hypo " left in the film will produce red stains,
while any iron in the water, say rust from the
waterpipes, will produce blue ones. The inten-
sification may easily be removed by placing the
negative in a weak solution of sodium carbonate
or in ammonia, or by prolonged washing. The
negative may be treated loc^y by intensifying
the whole in the usual way and working over
any parts that are too dense with a camel-hair
brush dipped into a weak solution of ammonia
and soda. Many other formulse have been
recommended. Dr. Liippo Cramer's (used as
above) being noteworthy. The originator claims
that his formula, given on the next page, keeps
well in the dark and gives a clear image.
Uranium Nitrate
552
Uranium Toning
• 2 I
)art
• 5
»»
• 5
tt
. I
)»
. lO
)i
Potass, femcyanide (lo % sol.)
Uranium nitrate (lo % sol.)
Potassium oxalate (lo % sol.)
Hydrochloric acid (lo % sol.)
Water ....
Washing is complete when the stain has dis-
appeared from the shadow (clear) portions of the
negative. When this stain is obstinate and
there is a danger of the whole of the intensifica-
tion being removed by prolonged washing, it is
best to apply a 2 per cent, solution of ammonium
sulphocyanide. This bath should not be used
when the negative is to be worked upon locally
with ammonia. Negatives intensified with
uranium keep better if varnished, failing which
store them, in a dry place, not exposed to a
strong light.
URANIUM NITRATE (Pr., Azotate d'urane ;
Ger., Uranylsalpetersdure)
Synonyms, uranyl nitrate, uranium oxynitrate.
U02<N0j)ii 6H2O. Molecular weight, 504. Solu-
bilities, very soluble in water, alcohol and ether.
It is poisonous {see "Uranium Acetate"). It
is in the form of yellow efflorescent crystals
with a greenish lustre by reflected light, obtained
by dissolving uranic oxide in nitric acid. It is
used for printing out, and in conjunction with
potassium ferricyanide to tone bromide prints
and intensify negatives, brown or reddish-brown
uranyl ferrocyanide being formed on the image,
which is partially soluble in water.
URANIUM PRINTING
The first uranium printing processes were
worked out by J. C. Burnett (1857-8) and
Niepce de Saint Victor, who took out an BngUsh
patent in 1858. Paper was floated upon a i in 30
solution of uranium nitrate, dried in the dark,
exposed under a negative to dayUght until a
faint image printed out, developed by floating on
a bath of silver nitrate (40 grs. to the ounce) or
upon a solution of gold chloride (9 grs. to the
ounce), then washed and dried, la 1864 a pro-
cess in which the uranium and silver were mixed
with collodion and applied to paper was patented
by Wothly. (See " Wothly's Process.")
One uranium process has points of similarity
with platinotype. Paper is coated with ferrous
oxalate in the proportion of i gr. to each square
inch of paper, each ounce of the solution contain-
ing also I gr. of mercuric chloride. When dry
the paper is exposed in contact with a negative
and developed on the following bath : —
Gold chloride .
3 grs.
•7 g-
Uranium nitrate
• 45 „
10-5 „
Water
. 3 oz.
300 ccs
It is washed, fixed in a weak solution of hydro-
chloric add, washed again and dried. Other
formulse have been published.
Uranium for Gaslight Printing. — In Dr. J.
Bartlett's process (1906), the paper is sized with
gelatine containing potash alum and oxalic acid,
and sensitised with —
Silver nitrate .
. 275 grs.
63 g-
Uranium nitrate
4i oz-
495 .,
Distilled water .
. 8 „
800 ccs
On account of the radiations from uranium it
is necessary to prepare and use the sensitive
solution in the dark-room. Exposure is made
under a negative in the usual way ; with an
average negative, from twenty to sixty seconds
will be enough at 6 in. or 8 in. from a gas
mantle ; one to five seconds to sunlight, and
thirty seconds to dull daylight. The print is
then developed in the following : —
Ferrous sulphate
I oz.
no g.
Tartaric acid .
i „
55 „
Sulphuric add .
60 mins.
12-5 ccs
Glycerine .
60 „
12-5 „
Water to .
10 oz.
1,000 „
Float the paper on this bath for three minutes,
dry in the dark, and keep free from moisture.
The image develops rapidly and varies from
brown to a. warm black. Should the whites
not be pure, due to over-exposure, add tartaric
add to the developer ; the tendency to discolour
the whites is entirely prevented by adding a
trace of nickel nitrate to the original coating
solution, but this renders the paper less sensitive.
A rinse in weak add or plain water completes
the process.
URANIUM TONING
Uranium toning is really a modified form of
intensification, and is not therefore suitable for
dense prints. It is not considered to yield
lasting results. It resembles the process de-
scribed imder the heading " Uranium In tensifier."
J. Weir Brown's one-solution formula is : —
Gladal acetic add . i drm. 12-5 ccs.
Potass, ferricyanide . 3 grs. 7 g.
Uranium nitrate . 3 „ '7 >,
Water ... 6 oz. 600 ccs.
This acts slowly and less water may be used in
order to make it work more quickly. Many
modifications have been made in the formula,
and the solutions which appear to find the most
favour are : —
A. Uranium nitrate . 45 grs. 10-5 g.
Distilled water . 10 oz. 1,000 ccs.
B. Potass, ferricyanide 45 grs. iO'5 g.
Gladal acetic add 2 drms. 25 ccs.
Distilled water . 10 oz. 1,000 „
Uranium persulphate is said to act in predsely
the same way as the nitrate above mentioned.
The two solutions keep indefinitely as long as
they are not mixed. For use, mix equal parts
of A and B, and if this works too rapidly dilute
with water. The prints should not have been
developed with ferrous oxalate, as iron causes
greenish spots to appear. Metol-hydroquinone
developed prints tone excellently, espedally if
the toning is to be carried no farther than the
sepias. Amidol developed prints tone to a full
red. Prints if dried after washing should be
immersed in water previous to toning so that the
toner may work evenly. Toning begins as soon
as the prints are immersed in the toner ; starting
with a warm black the tones progress through
the various shades of brown to red, and the
image increases in density at the same time A
little before the desired tone has been reached
the prints are transferred to a bath of weak
acetic add (about 100 drops to 10 oz. of water) ;
after two or three minutes, they are washed by
soaking in still water until the yellow stain has
Uranium Toning
disappeared. If washed in mnning water colour
will be washed away, leaving a patchy result.
Dilute citric acid (lo grs. to the ounce), and
oxahc acid (5 grs. to the ounce), are said to give ■
clearer tones than when acetic acid is used.
Permanent yellow stains are caused by in-
sufficiency of acid in the toner, the acid keeping
the gelatine soft and f acUitating the washing out
of the stains. The last mentioned may be re-
moved by dabbing them with cotton-wool soaked
m a very weak solution of ammonium sulpho-
cyanide. The toned image can be restored to
its original state by soaking in a weak solution of
ammonia or sodium carbonate and washing well.
Uranium may also be used for platiniun
prints : —
SS3
Vandyke Process
Uranium nitrate
Potass, ferricyanide .
Glacial acetic acid .
Ammonium sulpho-
cyanide.
"Water
5 grs.
S „
5 mins.
25 grs.
10 oz.
I g-
1 cc.
5 g.
1,000 CCS.
Toning is carried out in the maimer described
for bromide prints above.
Uranium is also used in combination with gold
for ordinary P.O.P. (gelatino-chloride) prints.
The bath is —
Sodium bicarbonate
Sodium chloride
Sodium acetate
Water
10 grs.
30 „
60 „
15 oz.
I g-
3 „
6„
750 ccs.
Dissolve and add—
Uranium nitrate
Gold chloride .
Water
S grs.
4 „
20 oz.
•2S g.
■2 „
1,000 ccs.
The toner gives brownish black or pure black
tones according to the quality of the negative
used for printing from. The bath must not be
acid. After toning, the prmts are fixed in an
alkaline fixing bath and washed as usual.
URANIUM. RECOVERING
Uranium is recovered by adding to the old
baths aqua regia, which destroys the ferricyanide,
and then adding Uquor ammonise in excess.
Collect the precipitate, wash with hot water, and
boil with slight excess of acetic add ; then, on
evaporating to dryness, uranium acetate will be
left.
URANOTYPE
Prints made by the uranium mercuro-urano-
type, and the platino-uranotype processes are
known as uranotypes.
URANYL NITRATE
Nitrate.")
{See
" Uranium
UVIOL
A term appUed by Schott and Genossen, of
Jena, to a variety of glass which is transparent to
the ultra-violet rays. The name is derived from
the words ultra-violet
VACUUM TUBES {See " Crookes' Tube"
and "X-ray Photography.")
VANADIUM CHLORIDE (Pr., Chlorure de
vanade ; Ger., Chlorvanadium)
Synonyms, hypovanadic hydrochloride,
divanadyl tetrachloride. 2VO3 4HCI 3H,0.
Molecular weight, 366. Solubilities, very soluble
in water and alcohol. It is a dark green syrupy
deliquescent liquid obtained by dissolving van-
adic anhydride in hydrochloric acid. It is used
for toning bromide prints green, and also in
the Donisthorpe process.
VANADIUM PRINTING
The brothers Lumi^e produced a vanadium
printing paper in 1894. Paper with a gelatine
coating is sensitised with a solution of vanadium
chloride in alcohol and water, dried, and printed
under a positive transparency. The joint posi-
tive image so produced needs to be treated with
a solution of paramidophenol, washed, and any
yellowness in the high lights removed in a
weak bath of hydrochloric add, afterwards
washing free of add.
M.M. I<umi&e found potassium vanadium
tartrate the best salt to use, and they prepared
it by dissolving vanadium pentoxide in potassium
bitartrate.
VANADIUM TONING
Vanadium chloride was first used for toning
bromide prints by Somerville in 1903. A
formula is : —
Ferric chloride .
10 grs.
2-3 g.
Oxahc add (sat. sol.) .
I J oz.
12s ccs.
Vanadium chloride .
20 grs.
4-6 g.
Nitric acid
50 mins.
ID ccs.
Water to .
S oz.
soo „
Then add, stirring the while, 10 grs. of potas-
sium ferricyanide dissolved in 5 oz. water.
Tone for one to two minutes, the longer the
immersion the lighter being the green. Wash
for ten minutes, and fix in a solution of 2 oz.
of "hypo" and 200 grs. of boric add in 10 oz.
of water ; finally wash for ten minutes.
VANDYCK GRAVURE
An American imitation of Rembrandt photo-
gravure.
VANDYKE PROCESS
A photo-Uthographic process invented by
P. Vandyke, of the Survey of India Office, Cal-
cutta, and used largely for map printing in British
and Colonial Government printing offices. Thin
zinc plates are grained with sand, and coated
with a fish-glue enamel printing solution, the
Vansant's Intensifier
554
Varnishes
following being a suitable formula : — ^Fish-glue,
I oz. ; ammonium bichromate (20 per cent, solu-
tion), 2 oz. ; water, 6 oz. ; chromic acid (10 per
cent, solution), 5 mins. The copy, drawn or
printed in black on white paper or a transparency
on glass or celluloid, is placed in contact with
the film side of the plate, and exposure made
either to daylight or to an arc lamp. The plate
is developed in plain water until the glue is
removed from the Hues, and it is then dyed with
aniline dye, producing a negative image on the
zinc. The following ink is next rolled over it : —
Powdered bitumen, 4 oz. ; lithographic chalk
printing ink, : oz. ; lithographic writing ink,
I oz. ; Burgundy pitch, i oz. These ingredients
are mixed together, with the aid of gentle heat,
and sufficient turpentine added to dissolve the
mass. After the plate has been inked it may be
developed in water containing about 48 mins.
of hydiochloric acid per pint of water, rubbing
gently with cotton-wool. The result is that the
image is reversed, yielding black lines on the
plain ground. The plate is then treated in the
usual way for lithographic printing.
VANSANT'S INTENSIFIER
A modification of the mercuric chloride in-
tensifier. The bleached negative is washed and
immersed in a freshly prepared bath of water
4 oz., gallic or tannic acid 60 grs., caustic
potash 2 grs. ; it is then washed and dried.
VAPOGRAPHY
A S3monym for atmography.
VARNISH, REMOVAL OF
Varnishes may be removed by soaking the
negative, etc., in the solvent used for making
the varnish ; generally, this solvent is alcohol
(methylated spirit). In the case of celluloid
varnish, acetone, amyl acetate, etc., must be
used. The negative is immersed in a bath of
the solvent, allowed to remain for several
minutes, with occasional rocking, and then while
in the bath rubbed well with cotton-wool. Another
solvent is a mixture of 10 parts of alcohol, 10
parts of water, and i part of caustic potash, after
treatment with which wash the negative in water.
VARNISHES (Pr., Vernises ; Ger., Firnisse,
Lacke)
Spirit varnishes are the most widely used for
negatives upon glass, but for film negatives water
varnishes are used, because of the action of the
spirit upon the celluloid. Cold varnishes are
more easily applied than warm ones, but take
longer to dry. Some approved formulae are : —
For Hot Varnishing —
(i) Bleached shellac . i oz. no g.
Alcohol . . 10 „ 1,000 CCS.
Keep in a corked bottle in a warm place, and
shake up at intervals until dissolved. Set aside
to settle, and then decant the clear part for use.
(2) Orange shellac . ij oz. 69 g.
Turpentine • i „ i4 „
Mastic . ' i „ 14 „
Castor oil . .1 drm. 6-25 ccs.
Sandarach . . ij^ oz. 69 g.
Methylated spirit 20 „ 1,000 ccs.
Place all except the castor oil in the spirit, and
shake at intervals till dissolved. Filter or allow
to stand, pour off the clear portion, and add
the castor oil, which gives elasticity to the film.
(3) Orange shellac . i^ oz. 138 g.
Methylated spirit 10 „ 1,000 ccs.
Mix as above, and when clear add 20 mins.
or 4 ccs. of castor oil, or i oz. or 25 ccs. of spike
oil or turpentine. The addition of a teaspoonful
of chalk or whiting assists to clear the varnish.
For Coi,d Varnishing —
(i) Gold size
Benzole
I oz.
I „
no g.
100 ccs.
This was largely used in the early days. It
dries rather slowly.
(2) Celluloid Varnish {see "Celluloid").
Monckhoven's Water Varnish
(3) Shellac . . i oz. no g.
Sodium carbonate
(saturated sol.) 8 „ 800 ccs.
Allow to stand for twenty-four hours, pour off
the liquid and replace with clean water; boil
till the shellac is dissolved, allow to stand,
decant, and filter.
Borax Varnish
(4) Borax. . . i oz. 55 g.
SheUac . . 5 ., 275 ,.
Water. . . 20 „ 1,000 ccs.
Dissolve the borax in boiling water, add the
shellac slowly, and keep hot till dissolved. When
cool, pour off the clear part for use.
PUM Varnishes —
Either a shellac or a celluloid varnish given
above, as is suitable, and the films may be
varnished wet or dry. For wet films use —
(i) Borax. . . 120 grs. 28 g.
Sodium carbonate 30 „ 7 „
Hot water . si ., 55° ccs.
When dissolved, add i oz. or no g. of broken
gum lac, and when this has dissolved add 20
mins. or 4 ccs. of glycerine, and more water to
make 10 oz., or 1,000 ccs. in all. Allow to stand,
or filter, and use the clear part. The film is
immersed bodily for a minute or two and then
pinned up to dry. For dry films use —
(2) Dammar . . i oz. no g.
Benzole . . 10 „ 1,000 ccs.
The dried and slightly warmed film is immersed
bodily and hung up to dry ; or it is pinned by
its four corners to a board, varnish poured in a
pool in the centre, and spread with a brush.
For Wex Cohodion Negatives —
(i) Gum arabic . i oz. no g.
Water . . 10 „ 1,000 ccs.
(2) White of one egg
Water . . 20 oz. 568 ccs.
Print Varnishes —
Prints are sometimes varnished in order to
remedy the dead or sunken-in effects so common
with matt surface papers. Valenta's formula is
Benzole . . . 4 oz. 400 ccs.
Sandarach . • i „ no g.
Acetone . . • 4 ,1 400 ccs.
Absolute alcohol . 2 „ 200 „
Varnishing Negatives, etc.
555
View Finder
BifACK Varnish —
Bleached shellac . 3 oz.
Methylated spirit . 10 „
Aniline black (sol. in
spirit) . . .60 grs.
330 g-
1,000 CCS.
14 g-
VARNISHING NEGATIVES, ETC.
The object of varnishing is to protect the gela-
tine film from scratches, damp, etc., and to pre-
vent silver staining due to the absorption of
damp by both papers and negatives.
Hot Process. — ^The negative is warmed to drive
out all moisture, and then allowed to cool. The
negative need not be hot when the varnish is
applied ; it is much more important that the
negative is dry. Hot negatives may crack when
cold varnish touches them, and the varnish may
dry with marks and streaks, while a damp film
will cause the varnish to dry milky, fish-scale
markings possibly appearing later. The negative
is held film side upwards in the left hand, the
bottle of varnish in the right, and a pool poured
into the centre of the plate and allowed to
spread almost to the edges ; then the negative
is tilted slightly until the varnish flows to the
top right-hand comer, next to the left, then to
the bottom left-hand comer, and finally to the
bottom right-hand comer, from which comer
the superfluous vamish is poured back into the
bottle, holding the comer of the negative in the
mouth of the bottle, and " see-sawing " the nega-
tive to prevent streaks. The negative is next
heated before a fire or over a gas-burner until the
coating is hard and dry, it being kept on the
move to obviate the formation of streaks.
Cold Process. — In applying cold varnishes the
chief consideration is absolute dryness. The
vamish is applied in the manner described for
the hot process, although with care it may be
brushed on sparingly with a soft brush. The
negatives are set aside to dry in a place where
dust cannot form on them. Films may be im-
mersed bodily in some varnishes.
Varnish Sttbstitutes. — ^Various substitutes for
varnishing are known. One method is to place
a very thin celluloid film between the negative
and the printing paper, but this is a protection
only during printing. Another method is to
harden the film with tannic acid and alum.
VELVET SURFACES
The semi-glossy surfaces of some bromide and
gaslight papers ; practically identical with
" carbon surface," " semi-matt," etc.
VENEER, PHOTOGRAPHIC
A photographic veneer is a print fixed to
transparent celluloid and applied to cabinetwork.
VENICE TURPENTINE {See " Turpentine.")
VERANT (Pr. and Ger., Verant)
An optical instrument invented by Dr. Moritz
von Rohr, in 1903, and used for viewing single
photographs. It adopts a principle originally
suggested by Prof. A. Gullstrand. It consists of
an open holder for the print, and a viewing lens
of such a focal length as to be practically equal
to that of the objective with which the photo-
graph was taken. The eye thus sees the print
in the same manner as the camera lens viewed
the original landscape or object. The result, with
a properly lit, well-modelled photograph, is
almost equivalent to stereoscopic effect. The
single-lens Verant is for use with one eye only,
but a double pattern for viewing two similar
photographs is also made.
VERASCOPE
A two-lens camera taking twelve stereoscopic
or twenty-four single pictures. It may be used as a
viewing apparatus for the pictures taken with it.
VERDIGRIS
Impure copper acetate.
VERRE SOUPLE
An early name for celluloid or other flexible
material used instead of glass for negative
making.
VERTICAL CAMERA {See "Camera, Ver-
tical" and "Copying Stand.")
{See " Buttonhole, or Vest,
VEST CAMERA
Camera.")
VICE, PLATE
A wooden clamp laid on the bench for holding
plates whilst being cleaned.
VICTORIA
A commercial size of portrait mount measur-
ing about 5 in. by 3^^ in. ; the Victoria midget
measmres 2I in. by i J in. These sizes are subject
to slight variation.
VIEW ANGLES, TABLE OF
The following table gives the degree of angle
subtended by any lens on the longer sides of
various sizes of plates : —
Lens
Fo-
Size of Plate in
Inches.
cus.
4iX3i
5X4
61X4i
8iX6i
9X7
10 X 8
12 X 10
Ins.
3
74
79
97
4
58
64
78
5
48
53
62
81
84
6
41
45
53
70
73
79
7
36
39
50
62
65
r
81
8
31
35
44
56
59
64
74
9
28
31
40
51
53
58
67
10
24
28
38
46
49
53
62
ZI
22
26
33
42
44
49
57
12
20
24
30
39
*i
45
53
13
19
22
28
36
38
42
50
1+
20
26
34
36
39
46
15
19
24
32
33
37
44
16
22
3?
31
35
41
17
20
28
30
33
39
18
19
26
28
31
37
19
18
25
27
29
35
20
24
25
28
33
VIEW FINDER (Pr., Viseur ; Ger., Bild-
sucher, Sucher)
An accessory showing the amount of subject
included by tiie lens of a camera. The com-
monest form A resembles a miniature camera
obscura. A small convex lens r, throws upon a
mirror M the rays proceeding from objects in
front of the camera, m is inclined at an angle
of 45°, and reflects an image upon a horizontal
View Finder
556
View Points
gtovmd-glass screen s. Usually a hood shields
the ground glass from extraneous light. The
frame, or mask, surroimding the ground glass
should be of such a size that the image contains
the same amount of subject as is shown by the
camera lens on the focusing screen or plate. A
new finder should be tested, and if it includes
too much, pencil lines should be drawn round
the margins of the ground glass to exclude the
surplus subject, the outer space being then
blocked out with black paint. If it shows too
little, a mental allowance will have to be made
when exposing. With this type of finder the
image is dull, due to loss of light caused by the
ground glass.
In the brilliant finder B the ground glass is re-
placed by a second convex lens, which receives
the rays from the mirror, forming a very bright
image. The first finder of this kind was con-
structed by A. I/. Adams and H. Hill in 1894,
and there have been many modifications. Some
View Finders
patterns have a reflecting prism instead of a
mirror, with one side ground to a curve to form
a lens. An unfortunate peculiarity of the bril-
liant finder in its simplest form is that the
amount of image included varies slightly accord-
ing to the position of the observer's eye. This
defect was overcome, in 1898, by Beck, who
placed a rectangular opening or mask m between
the two lenses at the focal distance of the first
lens. (See diagram C.)
There is a growing tendency to use a finder in
which the object is directly viewed. This may
consist either of a small concave lens or an open
wire frame with a sight. {See " Direct Finder.")
A few cameras for special purposes are fitted with
field-glass or telescopic finders.
Among more recent improvements in finders
must be mentioned the Adams Identoscope
(1905), Ulustrated at D, the front lens of which
is made to move in unison with the camera lens,
so that the exact effect of using the rising or
falling front is immediately shown.
The reflex and twin-lens cameras have full-
size finders of the camera obscura type, the
camera lens itself, in the case of the reflex, serv-
ing also as the finder lens.
VIEW METER (Fr., Cherckeur, Iconomitre,-
Ger., Bildmesser)
A device for showing the amount of subject
which would be included on the plate if the
camera were set up in a given position, thus
enabling the operator to judge the best point of
view without experimentally erecting the appara-
tus. One pattern is like a small telescope with
View Meter
a suitable mask or opening inserted to limit the
view to the required proportions. Another form
consists of a small rectangular frame sliding on
a graduated rod, at the other end of which is a
sight. (See the illustration.) The opening should
be proportional to the size of plate to be used,
while the distance from the sight to the opening
should bear the same proportion to the focal
length of the lens. Thus, for a quarter-plate
camera with a lens of 6-in. focal length, the open-
ing might be 2^ in. by 1} in. and the distance of
the sight 3 in. On applying the eye to the sight,
the view seen through the opening is then exactly
identical with that which would be included if
the camera were set up with its lens in the posi-
tion of the sight and pointing in the same
direction. Such a view meter is readily made
to fold up when not in use, and may be carried
in the pocket.
By marking different distances on the rod, the
finder may be made to show the view included
by lenses of various focal lengths. Thus, in the
foregoing example, if the frame is slid along the
rod until it is 2 in. from the opening, it gives the
same amount of view as a 4-in. focus lens, and
so on. The open frame gives the clearest view ;
but, if preferred, a piece of blue glass may be
fixed in or against the opening, when the subject
is seen in monochrome and its photographic
value is more easily judged.
VIEW POINTS
On the selection of the point of view depends
the composition of the subject. A slight change
in the point of view frequently results in a great
change in the lines and arrangement of the sub-
ject. When the lighting is strong a still further
alteration is made in ^e residt by varying the
position and direction. It should form a part
of every photographer's practice to select a
subject and carefully study the variations pro-
duced by examining it from every possible point
of view ; these should include tiie variations
resulting from a different standpoint and those
obtained by placing the camera above or below
normal eye level. A striking example of wide dif-
ferences in form is given by the appearance of a
sailing vessel as seen broadside on, bows on,
stern on, or " three-quarters." But differences
almost as striking may be noted by studying
Viewing Devices
the- different aspects of a cottage, or even of a
landscape. In figure work, also, the many
variations are obvious.
VIEWING DEVICES (See " Alethoscope,"
" Graphoscope," " Lantemoscope," " Neo-
monoscope," " Pantoscope," " Stereo-
scope," ^' Verant," etc.)
VIGNETTERS AND VIGNETTING
A vignetted picture softens off gradually until
whiteness is met with at the edges. Vignetting is
believed to have been introduced in photography
by Latimer Oark in 1853, and while it is
invariably condemned by artistic workers, it is
still popularly considered a pleasing style of finish-
Si7
Vignetters and Vignetting
D,
E| ^ Paper D
Principle of Vignetting
ing for portrait heads. It is produced by allow-
ing the centre part to print out while the edges
are shielded in such a way that the light gradu-
ally decreases in actinic power as it reaches the
edges. From the diagram it is seen that a vig-
netted contact print is produced by the diffusion
of the light rays as they fall upon the negative
with the sensitive paper beneath. Assuming
the light rays to proceed from a source L,
their full force acts upon the negative between
D and Dj. The diffused rays from M, however,
act upon the area EEj, and consequently the
part between d and Ej is more strongly lighted
than the other parts. Also, as the light rays
become more obhque, an increased am^ount of
light is lost by means of reflection. The greater
the separation, up to a certain point, between
the vignetter and the negative, the more gradual
will be the merging of the print into a white
border. If, for example, the vignetter were
lowered or the negative raised to the dotted lines
shown the result in the latter case would be that
the /parts between Hj and H would be printed
strongly and the image would not soften off to
S as it would do with a greater separation. In
practice, it is found that f in. to i in. is enough
for a carte de visite portrait, and from i in. to
li in. for a cabinet.
Clark, in the published account of his methods
(1853), states that he used a hole cut in an
opaque substance placed i in. above the negative ;
the whole arrangement was caused to revolve by
means of a bottle-jack to assist the diffusion of
the light at the edges.
In 1857, Forrest, of Liverpool, introduced the
stained glass vignetter, which is a piece of
flashed ruby or orange glass with a colourless
centre ; it is usually of the same size as the
negative, and is often placed in the frame with
it, but it gives softer and better results if laid
on the frame in such a way as to increase the
space between it and the negative ; being of
the same size as the negative, the separation
possible is not great. The extent of the clear
glass portion is fixed, and in order to do good
work the photographer must have a supply of
such glasses with different shapes and sizes of
openings.
The iris vignetter consists of a piece of vul-
canised fibre or thin wood large enough to cover
the printing frame, and having a central aper-
ture, round the edge of which is a series of
riveted plates, one slightly overlapping the
other. The shape and size of the opening are
altered by moving the plates.
An easily made vignetter utilises a piece
of card or the Ud or bottom of a plate box ; it
must be large enough to cover the whole frame,
and a hole is cut in the centre. This card is laid
over the frame during printing, the separation
between card and negative being such as to
diffuse the light at the edges. To assist in obtain-
ing a soft edge to the image, the edge of the
card may be serrated, and small holes made
around the large hole, or one, two, three, or
more thicknesses of issue paper may be pasted
around the edge of the hole. Of the many other
kinds of vignetter only the sand vignetter need
be mentioned. A lid of a plate box large enough
to cover the frame is taken and the bottom of
the lid cut away, leaving a narrow ledge, about
i in. wide, all round. A piece of plain glass is
then dropped into the lid and rests upon the
ledges, thus forming a glass-bottomed tray. This
is laid on the printing-frame, and fine dry sand
is poured into the shallow tray in such a way as
to leave a clear glass centre.
Portrait heads make the most effective vig-
nettes. Dark backgrounds should not be vig-
netted, neither should Rembrandt and other
strongly Ughted portraits. When printing
vignettes, it is necessary to use diffused light
and to select a spot where the light reaches the
frame equally from all parts ; the more slowly
a vignette is printed the better and softer will
be tie grading, and any attempt to use strong
light or direct sunlight would cause the outlines
of the vignetter to show in the form of a well-
defined line on the print. Should the light
spread too much under the vignetting device,
place loose cotton-wool between the negative
and the vignetter ; but this must be done with
great skill, or the wool will form an outline on
the print. The above remarks apply to the vig-
netting of prints made upon printing-out paper
in difhised daylight.
The methods of vignetting given above do
not give the best effects with bromide and gas-
light paper, although some commercial vignettes
allow of printing to be performed by artificial
light almost as easily as by diffused daylight.
For vignetting bromide prints or enlargements
the vignetter must be moved while the exposure
is being made, cut-out cards being used. A card
is cut of the desired shape and size, the latter
being sufficient to prevent the light creeping
roimd the sides and causing fog in the case of
enlargements. The card is held between the
sensitive paper and the lens, and moved back-
wards and forwards in order to spread the light.
Villain's Dye Process
558
Vulcanite
The nearer the lens the greater the difEusion, and
the more of the image upon the paper. Contact
bromide and gaslight prints are vignetted in the
same way, except, of course, that the bromide
paper is placed in a frame with the negative in the
usual way and the vignetter held between the
frame and the source of light. The hole in the
card must be small in comparison with the size
of the vignette desired, as the light spreads
considerably ; it is also advisable to arrange the
light so that the print or enlargement takes
some little time to expose, in order to give
more time for effective vignetting.
In process work, half-tones are vignetted by
special means. Holt's vignetter is a triangular
frame supporting at its apex a clockwork move-
ment which gives an eccentric motion to a
serrated white cardboard frame, placed some
distance in front of the copy and illuminated by
arc lamps on the side towards the lens. The
frame is set in motion during the exposure,
and the effect is a darkening of the negative
towards the margins. Mole's vignetter acts by
chamfering the edges of the half-tone plates from
undemeati. A revolving cutter projects slightly
through a slot in the table, and the back of the
plate is pressed over it at the parts where the
cutting down has to be done. 'The edges of the
plate are then beaten down with a fibre mallet,
so that they are lower than the central part ; thus
when the plate is mounted the edges are below
the type height and print lighter.
VILLAIN'S DYE PROCESS (See "Photo-
tincture.")
VIOLET TONES
These are invariably difficult to obtain. For
toning black-and-white bromide prints to n.
violet colour, use : —
A. Copper chloride . 25 grs. 575 g.
Water . . 5 oz. 500 ccs.
B. Ferric oxalate . 2J grs. -575 g.
Potass, ferricyanide 2^ „ '575 „
Water . . .10 oz. 1,000 ccs.
To each solution add a saturated solution of
ammonium carbonate until the first precipitate
formed is dissolved. The bromide print is placed
in B until it is a strong blue, and then in A until
it appears a good violet ; finally it is washed.
VIRTUAL FOCUS
An imaginary focus, or focal length, as, for
example, that of a concave lens, which does not
form an image.
VIRTUAL IMAGE (Fr., Image virtuelle ; Ger.,
Virtuelles Bild)
An image formed in the air by negative lenses
and used in contradistinction to the real image
projected by a positive lens.
VISCOUS DEVELOPER
A developer made thick with glycerine or
treacle ; said by some to give greater softness,
finer grain, and prevent halation to a very large
extent. Treacle is the most widely recom-
mended, a solution of equal parts of treacle and
water being used instead of plain water when
preparing any developer for use.
VISION, PERSISTENCE OF (See " Kine-
matography.")
VISUAL FOCUS
The focus of those rays most visible to the
eyes ; that is, the green-yellow rays, as opposed
to the focus of the blue-violet or chemical rays.
VISUAL RAYS
The luminous rays of the spectrum, by which
an image is focused in the camera, as opposed
to the less visible actinic or chemical rays.
VITRIOL (See " Sulphuric Acid.")
VITROTYPE
A process of producing burnt-in photographs
on glass or ceramic ware and patented in 1857
by McCraw, of Bdinburgh.
VOICE PHOTOGRAPHY (Pr., La photo-
graphie de la voix ; Ger., Stimmenphoto-
graphie)
The photography of sound vibrations due to
the voice. Various workers have experimented
in this direction, among them being Czermak
(1862), Blake (1878), and Hermann. The first-
named secured photographs of the vocal chords
in action. Prof. Blake, of Brown University,
U.S., used a small mirror caused to move by the
vibration of a telephone diaphragm. A beam of
Ught was thrown on the mirror, and the move-
ments of the latter which resulted from the use
of the telephone were recorded on a photographic
plate kept in regular motion by clockwork.
Prof. Hermann, at an International Congress of
Physiology, at Li^ge, demonstrated the possi-
bility of using a microphone in connection with
a phonograph to record vowel sounds. The
vowels were spoken or sung into a phonograph,
and the cylinder containing the reproduction
was afterwards revolved very slowly before a
microphone furnished with a small mirror. A
beam of electric light was thrown on the mirror,
which vibrated in accordance with the sound
given out by the phonograph, and reflected the
beam through a slit upon a revolving cylinder
covered with sensitised paper.
VOLATILE ALKALI
A synonym for ammonium carbonate.
VON BENTIVEGNIS COLOUR PROCESS
A kind of crystoleum process. The glass,
with the motmted and dried print attached,
is soaked in a warm mixture of castor-oU, vase-
line, etc., then in castor-oil alone, and is then
rubbed dry and coloured.
VULCANITE (Fr., Vulcanite; Ger., Ebonit)
India-rubber treated (" vulcanised ") with sul-
phur in a closed furnace and obtainable in many
different colours. Black vulcanite is commonly
known as ebonite.
w
WARNERKE. LEON
Bom in Hiingary, 1837 ; died at Geneva,
1900. He settled in England about 1870, and
was a civil engineer, but took to photographic
experimenting, and contributed largely to photo-
graphic knowledge. He was well known to the
photographic societies of many countries. In
1877 he was awarded a prize in Belgium for the
best dry-plate process, and in i88i the British
R.P.S. Progress medal. His sensitometer num-
bers were used by plate makers for indicating
speeds, his actinometer being introduced in
1880. As early as 1869 he experimented with
other supports than glass for the sensitive film,
and used Steinbach paper sized with starch,
coated with collodio-bromide emulsion. At one
time he used the sheets of sensitive material
interleaved with orange paper in the form of a
block resembling an artist's sketching block, and
employed it in this form in the camera. The
difficulties of using these early types of films led
him, in 1875, to invent a roller dark-slide, in
order that the film in a band could be wound
from one roUer at one end to a roller at the other.
In 1885 he introduced and patented a negative
paper coated on both of its sides. In 1 881 he
found that an exposed gelatine film developed
with pyro-ammonia becomes insoluble in hot
water in the parts affected by light, and that if
soaked in warm water and attached to a glass
plate, the paper can be stripped ofi and the
soluble gelatine washed away, leaving a reversed
negative attached to the glass.
WARNERKE'S SENSITOMETER
A sheet of glass bearing a series of numbered
squares, ranging from i to 25, with varying quan-
tities of Gpaque pigment, used for testing the
sensitiveness of plates. With it was issued a
plate of phosphorescent calcium sulphide or
Balmain's luminous paint, which was excited
with I in. of burning magnesium ribbon, and
after the lapse of a given time (30 seconds) the
plate to be tested was exposed to the luminous
rays emitted by the tablet ; after development
the last nimiber legible when the negative was
laid against white paper was taken as the speed
of the plate. It is now practically obsolete.
WARNERKE'S TISSUE
A gelatino-silver emulsion tissue used in an
obsolete process of photo-engraving.
WARNER.POWRIE PROCESS
A method of producing screen-plates for colour
photography based on the insolubilisation of
bichromated fish-glue by the action of light, and
subsequent mordanting and staining of the in
soluble gelatine. The chief feature of the pro-
cess is the extreme simplicity of its working, and
the absence of overlap of or interspaces between
the lines. Briefly, the details of the process are
as follows : A sheet of glass is coated with bi-
chromated fish-glue and exposed under a black-
and-white line screen in which the black lines
are twice the width of the transparent spaces.
After exposure the plate is developed in warm
water, which removes the gelatine not rendered
insoluble by the action of light. The insolu-
bilised gelatine lines are then mordanted with
an acid aniline dye and stained with a basic dye,
the result being an insoluble, transparent pre-
cipitate of dye. The coloured lines thus pro-
duced are hardened with tannin or other agent,
and the whole plate coated with bichromated
fish-glue again. After drying, the original black-
and-white matrix is now arranged in contact
with the screen plate so as to cover all the
coloured lines thereon and a second exposure
made. The result is a second series of lines of
insoluble coUoid which may or may not be in
contact with the first series. This second series
is now mordanted, stained, and hardened pre-
cisely as at first. Again the plate is coated with
bichromated fish-glue, and, after drying, exposed
without the intervention of any screen through
the back of the plate. The previously coloured
lines, which should be the red and green, act
as the protection for those portions of the third
coating of bichromated colloid immediately
over tiiem, whereas in the interspaces, where
there is no protecting colour, the bichromated
colloid is rendered insoluble, and again mor-
danted, stained and hardened.
A more recent modification of the process is
the placing of the second set of lines at right
angles to the first and the subsequent filling up
of the third interspace by a similar process as
above outlined. This gives a screen with one
set of lines and the interspaces divided up into
rectangles of the two other colours.
WASHERS (Fr., Panier-laveur ; Ger., Positiv-
wdsserung, Papierwdsserung)
Vessels or appliances for washing photographic
prints, usually consisting of an enamelled metal
Two Forms of Washer
tank with or without a syphon outlet. They are
frequently made of a circular form, or with
curved sides, the water being introduced in
SS9
Washing
560
Washing Tank
such a way that a rotary motiou is given to the
prints. The motion should not be overdone by
using too violent a stream of water, or the prints
may be damaged. Commonly a perforated plate
is fitted near the bottom of the washer, to pre-
vent the prints being carried away through the
outlet, and to allow a more efficient separation
of the " hypo." The illustrations show two
typical patterns .of print washer. Por work on
a large scale, flat dishes or tanks are usually
preferred.
WASHING (Fr., Lavage; Ger., Waschen,
Negatives and prints that have been fixed in
"hypo" must be freed of this substance by wash-
ing with water before they can be safely dried ;
otherwise the permanency of the result is im-
paired. " Hypo " being of greater specific
gravity than water, it follows that as part of the
washing water removes " hypo " from the gela-
tine and paper it becomes a solution which is
denser than plain water, and therefore tends to
sink to the bottom of the washing vessel. Agita-
tion is necessary to cause the plain water and
the " hypo " solution to mix thoroughly, although
slight admixture must, of course, occur. It
Negative Holder for use in Washing
follows, then, that the worst method of wash-
ing is to place a negative or print film side up-
wards in stiU water, and that the quickest and
best way is to support the film in such a way
that the " hypo " may, as it were, fall out of the
film to the bottom of the vessel. For washing a
single negative quickly, it may be held in the
hand, face downwards in a pail of water, where
it will be freed from " hypo " much more quickly
than if laid in a dish and water allowed to run
upon it. A convenient accessory for holding a
negative film side downwards is shown. To a
piece of wood the same size as the negative are
nailed strips of tin-plate, as shown, these being
bent under so as to hold the negative. The last
named is slid into place, film side outwards, and
the whole floated in a vessel of water ; in this
way the suspending of a negative film side down-
wards in water becomes a very simple matter.
Another method is to use a dish with sloping
sides, which support the negative when this is
placed horizontally. Most of the commercial
washers hold the negatives in a vertical position,
in which position they wash quickly and well if
space is left below the negatives. When a
negative is held vertically, the " hypo " solution
flows to the lower edge and congregates in a dense
mass at the bottom of the vessel ; this demon-
strates the necessity of having a space below
the negative if still water is used. The prop-
ping up of a negative on a brick placed in a pail
of still water is a simple method of washing
when running water is not available, as by
frequent changes the " hypo " may be quickly
got rid of.
The time taken to wash a negative or print
depends upon the method employed and upon
other considerations. Several experimenters,
after exhaustive trials, have stated that
a washing of twenty minutes is enough
for negatives under favourable conditions.
Complete removal of " hypo " from negatives
occupies about twice the time the plates take
to fix, in favourable circumstances. Negatives
do not hold " hypo " as prints do, as in the latter
there is the porous paper to consider. Lumiere
and Seyewetz concluded that the use of running
water for washing was both wasteful and in-
efficient, and that the best way to wash negatives
is to immerse each negative, vertically or upside
down, in five successive baths for five minutes
each (twenty-five minutes in all), allowing 17 oz.
of water to each half -plate. Gaedicke discovered
a number of useful facts, the most important of
which is that when the water is changed every
five minutes, three times as much " hypo " is
extracted as when the water is changed every
half-hour.
As regards the washing of prints, practically
all the above remarks apply. Prints and celluloid
films should be kept on the move and the water
frequently changed or carried away from the
bottom of the tank. If they are soaked in still
water, this must be frequently changed, or the
prints should be transferred from one dish to
another. From data published by Messrs.
IiUmiSre, it seems that eight changes, using 3J oz.
of water for each 7-in. by 5-in. print, are suffi-
cient ; 90 per cent, of the " hypo " is soaked
out by the first two baths. In the case of a
print placed for twenty minutes under a tap
passing about 14 pints per minute, and then
allowing it to soak for five minutes in 3J oz. of
water, the latter was found to contain about the
same quantity of " hypo " as the water after
one-fiftii the washing in the manner above
described. The experimenters state, however,
that these methods do not remove the last minute
traces of " hypo," and that even twenty-four
hours in running water will not do it. Haddon
and Grundy stated in 1 894 that they had proved
that gelatino-chloride prints, washed for ten
minutes in running water and under proper con-
ditions, had lost tiie whole of the soluble salts,
and that there was no necessity whatever to
wash longer ; further, they also found that six
changes of water after five minutes' soaking were
equally effective. Thus it is obvious that the
amount of washing necessary for both negatives
and prints depends entirely upon the conditions
under which they are washed, no two experi-
menters agreeing.
Por methods of testing washing water for
" hypo," see " Sodium Hyposulphite, Testing
for."
WASHING EMULSION (See "Emulsion.")
WASHING SODA [See " Sodium Carbonate.")
WASHING TANK (Fr., Cuve d lavage, Cuve d
rainures ; Ger., Wdsserungskasten)
Tanks for washing negatives are generally of
metal or porcelain, with grooves at the sides.
Washings
S6i
Wave-lengths
They should be furnished with syphons to empty
off all the water from the bottom when it reaches
a certain height ; otherwise the current from the
tap will merely run over the top of the full tank,
and the water in the latter will not get changed.
A shows a porcelain washing trough of practical
A. Porcelain Trough B. Metal Tank
design. Metal tanks are frequently fitted with
a removable rack, as shown at B, which serves
for drying the negatives after they are washed.
(For print washers, see " Washers.")
WASHINGS {See " Residues.")
WASH-OUT GELATINE PROCESS
A modification of the swelled-gelatine process
for the production of photo reliefs. The un-
exposed parts of the image were washed away,
instead of being swelled up, and a plaster cast
was taken from the relief, intimately, either a
stereotype or electrotype was made from the cast.
WASTES (See "Residues.")
WATCH CAMERA (Pr., Chambre montre ;
Ger., Uhrkamera)
Various cameras have been made in the form
of a watch. In one, a series of telescopic metal
tubes forming the body sprang out into posi-
tion on pressing a spring. A more recent form
of watch camera, the " Ticka " introduced in
1906, takes roll-films, twenty-five negatives
the size of a postage stamp being obtained.
Owing to its short focus, the depth of definition
is great, and the small negatives will stand en-
larging to 3J in. by aj in., or even larger.
WATCH-DIAL PHOTOGRAPHS
A miniature of the portrait is taken by the
collodion emulsion process, transferred to the
dial, and varnished over. Similar results have
been obtained by the carbon process. If the
collodion film is toned with platmum, the image
may be fired and burnt into the enamel.
WATER (Pr., Eau ; Ger., Wasser)
Ordinary tap-water usually contains chlorides,
sulphates and earthy salts, which, by causing
precipitates, may give rise to trouble, particu-
larly ia the case of developers. AU tap-water
contains carbonic add and oxygen, which tend
to discolour the developing agent. Distilled
water can be obtained very cheaply. In any
case, ordinary water shoijd be well boiled,
allowed to cool, and filtered before use. For
all solutions of the noble metals, platinum, gold
and silver, distilled water is an absolute necessity.
(See also " Distilled Water.")
36
WATER LENSES (Sea " Fluid Lens.")
WATER. DEVELOPED PLATES {See
" Self-developing Plates.")
WATERFALLS, PHOTOGRAPHING
The strong contrast between the bright water
and the dark foliage or rocks surrounding it
make the photographing of waterfalls somewhat
diflacult. If the quality, the sparkle, and the
movement of the water are to be retained, a
very short exposure is necessary ; and such an
exposure cannot be expected to secure detail
and gradation in the surroundings at the same
time. On the other hsmd, if an exposure is given
to render the setting properly the water will
lose its texture and become woolly or streaky.
Sometimes, with a very fast plate and a large
lens aperture a compromise may be arrived at,
and the whole subject be properly rendered on
one plate. The effect may be further improved
by shielding the dark portions (light portions of
the negative) with paper or matt varnish, and so
allowing the denser water to print out more fully.
When this is not feasible, it is well to make
two exposures, timing one for the moving water
and the other for the surroundings. Each nega-
tive is then masked so that one prints only Sie
water, the other the setting.
WATER-GLASS {See "Potassium Silicate"
and "Sodium Silicate.")
WATERHOUSE STOPS {See "Diaphragms.")
WATERPROOF PAPER
Waterproof paper is used for mounting and
wrapping up chemicals and sensitive material.
A serviceable waterproof paper may be made by
brushing a strong solution of Castile soap over
some paper, and when nearly dry brushing over
with a strong solution of chrome alum. This
method of waterproofing answers well for fabrics
generally.
WAVE-LENGTHS (Pr., Longueurs des ondes;
Ger., Wellenldngen)
Light is considered to be an undulatory or
wave-like motion in the ether, and the conven-
tional figures used to illustrate this are the fol-
lowing : —
d'"
Red Light \JlJ^' K^^" '' ^
all gin
Lf >B fc \D /e ^f Q
b b b
Wave-lengths
Assume that the light is travelling from left
to right in each of the above figures. A, B, and
C; tiie ether particles vibrate to and fro, and
Wax
562
Weights and Measures
each excites its neighbour till the motion reaches
the maximnm of the crest of the wave at A, and
then it vibrates in the contrary direction till it
reaches the maximum of the farough at B, each
ether particle merely moving to and fro between
the planes bounding A and B. Now, a wave
lengtii is the distance from any two points in
the same phase of movement, such as A and C,
c and E, B and d, and d and F. These points
have been taken on the axis of the direction of
the propagation of light, but any two other
points could be measured from, such as a' and
a" or a' and o", or ;8 and /3", or 6' and 6". If
the distance A C is a wave length, A B or B C is
exactly half a wave length, and so on ; further,
the length of the wave A to c in A red light is
double that of C, the violet A to c, whilst in B
green light, the length is midway between them.
The wave length of any pure spectrum is always
constant, no matter what the source of light ;
and it could be used as a definite standard of
colour ; and it is by no means uncommon to see
the expression that a colour is that of D f B ;
that is to say, a colour can be matched by the
spectrum ray, which lies exactly midway be-
tween the solar Fraunhofer lines B and B.
There are several units of measurement or
methods of writing the wave-length, which is
usually abbreviated to A. The unit most gener-
ally adopted is the tenth-metre = i x lo^"
metre or the ten-miUionth of a millimetre, which
was the unit adopted by the great Swedish phy-
sicist Angstrom, one of the first to give a reliable
map of the solar spectrum, and this is then
abbreviated to A.U. (Angstrom's Unit) or t.m.
It may also be expressed in miUionths of a milli-
metre, called a milli-microne, an^ written fi ju, or
in thousandths of a millimetre, called a micron,
and written jx; or it is also written as a ten-
thousandth of a centimetre or 10' cm. So that
we might describe the Di line as —
K 5-89616 X 10' cm. = -0000589616 cm.
or A 0-589616 !>.
or A. 589-616 ii-ii.,
or A 5896-16 A.U. or t.m.
For all methods for measuring wave-lengths,
except rough visual work, that of photographic
coincidence is usually adopted.
WAX (See " Beeswax " and " ParaJBBn.")
WAX ENGRAVING
Synonym, cerography. A brass plate is
cleaned, then blackened by flowing with a solu-
tion of silver nitrate 10 g., water 250 g., and
nitric acid 2 drops. It is rinsed, dried, warmed,
and covered with a mixture of paraffin-wax and
white pigment such as zinc white. When cool,
an outiine tracing is set-off on to the surface
with red chalk, and the lines of the design are
scratched through the film. For map work,
the names are pressed into the wax with heated
metal type. Finally, the large whites are built
up with wax run off a hot tool, and the surface is
made conductive with blacklead. Then the plate
is used as a mould for electro-deposition.
WAX PROCESS
A general term for reproduction processes in
which wax is used ; in particular, wax engraving.
WAXED-PAPER PROCESS
A modification of the calotype process intro-
duced, in 1855, by Le Gray. The wax was
used in order to prevent the grain showing, and
also to stop up the pores of the paper. The
original process was, briefly, as follows: A
suitable paper was placed on a heated silvered
copper plate, and pure white wax rubbed well
into it ; it was ironed between sheets of blotting-
paper. For preparing the iodising solution,
rice was soaked in distilled water. To a little
less than a quart of the rice water 620 grs. of
sugar of milk, 225 grs. of potassium iodide, 12
grs. of potassium cyanide, and 7 grs. of potassium
fluoride were added, and the waxed paper was
soaked therein for about an hour and dried.
The paper was then sensitised by floating for
four or five minutes on a bath made by dissolv-
ing 78 grs. of silver nitrate in 2,325 grs. of dis-
tilled water, and then adding 186 grs. of crystal-
lised acetic acid ; for portrait work, however,
I,e Gray advised 155 grs. of silver nitrate. The
paper was then dried in the dark and exposed
in the camera, the exposure being from twenty
seconds to fifteen minutes. It was developed
by immersing in a solution of gallic acid (1^ grs.
to the I oz.).
WAXING
Wax is applied to paper negatives in order
to make them more translucent, and to facili-
tate printing.
WEATHER PICTURES {See "Barometer,
Photographic")
WEDGWOOD, THOMAS
Bom 1 771, died 1805. Third son of Josiah
Wedgwood, the potter. He studied the action
of light upon certain compounds of silver, and
in 1795 obtained "sun pictures" by placing
more or less opaque objects upon paper and
white leather coated with a. weak solution of
silver nitrate.
WEIGHTS AND MEASURES
Recognised abbreviations are : Pounds, lb. ;
ounces, oz. or 5 1 drams, drs., drms., or 5 ;
scruples, sc. or 9 ; grains, grs. ; pints, pt. ;
minims, mins. ; pennyweights, dwt. The only
metric abbre-nations of interest are : gramme,
g. ; cubic centimetres, ccs. ; millimetres, mm. ;
centimetre, cm.
The grain has the same value in apothecaries',
avoirdupois, and troy weight.
Apothecaries' Weight
(Fonnulas are made up by this weight.)
lb. oz. drms.
sc. gis.
fMETRTC.)
grammes.
I 12 96
2B8 5,760
373-276
I 8
24 480
31-106
X
3 60
3-887
X 20
i-2g5
I
0-0648
Fluid Measure
(Metric.)
Pt. oz.
drms. mins
CCS.
r (American) 16
128 7,680
454-4
I (English) 20
160 g,6oo
568
z
8 480
28-4
I 6d
3-5
I
0-058
The fluid pound = la oz.
. = 5,?6o mins. =
340-8 CCS.
The fluid ounce of water weighs 437! grs. =
28-4 g.
Weights and Measures
563
Weights and Measures
Avoirdupois Weight
(Most chemicals are sold by this weight.)
_ (Metric.)
"'• 02. dims. gis. grammes.
I i6 256 7,000 453-59
' 16 437i 28-4
I 27ii 17-7
Troy Weight
(Gold, silver, etc., are sold by this weight.)
,. (Metric.)
1°. 02. dwt. grs. graimnes.
I 12 240 5,760 373-2
I 20 480 3I-I
I 24 1-55
r 0-6
Cubic Centimetres {ccs.) to Minims
Grains to Grammes
Odd numbers
may be found by simple addition.
gis. g.
grs.
g.
I equals 0-065
12 equals o-775
55 equals 3-564
» 0-13
15
, 0-972
60 „ 3-888
3
. 0-194
18
. 1-166
65 „ 4-212
4
■ 0-259
20
, 1-296
70 „ 4-536
5
. 0-324
25
, 1-620
75 „ 4-860
, 0-389
30
. 1-944
80 „ 5-184
7
. 0-454
35
, 2-268
85 ■> 5-508
. 0-518
40
. 2-592
90 „ 5-832
9
. 0-584
45
, 2-916
95 >, 6-156
10 , 0-648
50
. 3-240
100 „ 6-480
Ounces {Apothecaries') to Grammes
i equals
g-
7-776
15-553
23-329
31-106
oz. g.
2 equals 62-212
3 .. 93-318
4 „ 124-424
5 ,. 155-530
oz. g.
6 equals 186-636
7 „ 217-742
8 „ 248-848
9 .. 279-954
311-06
10
Fluid Measure to ccs.
TniTK!.
ccs.
dims
ccs.
oz.
ccs.
5 equals
0-3
I equals 3-55
1
equals
28-41
10
0-6
2
7-10
2
56-8
15 „
0-9
3
, 10-65
3
85-2
20
1-2
4
14-20
5
142-0
25 ■>
'■■*.
5
, 17-75
10
284-0
30 „
1-78
6
, 21-30
16
454-5
60 „
3-55
7
, 24-86
17
483-0
8
28-40
20
568-0
Inches to Millimetres
in.
tntn
in.
mm.
m.
TnTTl.
I equals
25-4
*
equals
15-9
A equals 7-1
a ,.
23-8
A
14-3
i
., 6-4
A ,.
23
*
12-7
A
„ 5-6
* „
22-2
tV
ii-i
A
„ 4-8 -
20-16
i
9-5
i
» 3-2
i »»
19.1
H
8-7
» 2-4
H ..
17-5
A
f*
7-9
t
„ 1-6
„ 0-8
Grammes to Grains
g. grs.
g. grs.
g. grs.
I equals 15-4
11 equals 169-4
20 equals 308
2 „ 30.8
12 „ 184-8
30 „ 462
3
, 46-4
13
, 200-2
40 „ 616
4
6i-6
14
, 215-6
50 „ 770
S
77
15
, 231
60 „ 924
6
92-4
16
, 246-4
70 „ 1,078
7
, 107-8
'2
, 261-8
80 „ 1,232
a
, 123-2
18
, 277-2
90 „ 1,386
9
, 138-6
19
, 292-6
100 „ 1,540
10
, 154
ccs.
mins.
ccs.
mins.
ccs.
mins.
1 equals
17
8 equals 136
50
equals 850
2 „
34
9
. 153
bo
„ 1,020
3 „
51
10
. 170
70
„ 1.190
4 >,
68
20
. 340
80
„ 1,360
S »
85
30
. 510
90
» 1,530
6 ..
102
40
, 680
100
„ 1,700
7 ..
119
Millimetres to Inches
mm.
in.
mm
in.
mm.
in.
1 equals
0-04
10
equals
0-39
19 e
quals
0-75
2 ,.
0-08
11
„
0-43
20
„
0-79
3 »
0-12
12
o-t7
21
0-83
4 ,.
0-16
13
0-51
22
0-87
? "
O-20
14
0-55
23
„
0-90
0-24
15
0-59
24
„
0-94
7 „
0-28
16
0-63
25
„
0.98
8 „
0-31
17
0-67
25-4
l-o
9 „
0-36
18
0-71
approx.,
approx.,
Rules for Conversions
Inches to centimetres : multiply by 2-54 ;
approx., multiply by 5 and divide by 2.
Centimetres to inches : divide by 2-54 ;
approx., multiply by 2 and divide by 5.
Inches to millimetres : multiply by 25-4 ;
approx., multiply by 100 and divide by 4.
Millimetres to inches ; di-vide by 25-4 ;
approx., multiply by 4 and divide by 100.
Ounces (fluid) to cubic centimetres : multiply
by 28-3.
Cubic centimetres to ounces (fluid) : divide
by 28-3.
Litres to pints: multiply by 1-76;
multiply by 7 and divide by 4.
Pints to litres: di-vide by 1-76;
multiply by 4 and di-yide by 7.
Grains to grammes: di-vide by 15-43.
Grammes to grains : multiply by 15-43.
Ounces (avoir.) to grammes: multiply by 28-4.
Grammes to ounces (avoir.) : divide by 28-4.
Ounces (apoth. ) to grammes : multiply by 3 1 • i .
Grammes to ounces (apoth.) : di-vide by 31 -i.
The standard method of presenting formulae
in the metric system is to make the quantity of
water equal 1,000 ccs., as in the majority of
cases throughout this work. The following
(merely approximate) table makes such conver-
sions easy. For example, " hypo," i oz. ; water
9 oz. becomes "hypo" 122 g.; water, 1,000 ccs.
By a simple proportion sum this table can be
used for converting metric formulse to British : —
If 1 oz. (fl.) becomes 1,000 ccs., 1 oz. (apoth.) becomes 1,100 g.
!■ 2 „ „ „ 1 „ „ 550 „
» 3 .> » .. I .. » 367,,
» 4 » » » I i> » 275 „
» 5 » u „ I » ., 220,,
„ 6 „ „ „ 1 „ „ 183,,
» 7 ., .. .. 1 .. >. 137,.
» 8 I „ „ 138,,
.. 9 » » >• 1 ., » 122 „
» ^O t M »> 1 » fl 110 ,,
„1S >. .. >. 1 .. ., 73..
., 20 „ „ „ I ,. „ 55 ..
Metric System
Proportion
LmgOi
Capacity
Weight
Unit
lAi part
A I.
Metre
Millimetre
Centimetre
Decimetre
39-37 in.
0-039 ..
0-394 ..
3-94 ..
Litre
Millilitre or cubic
centimetre
Centilitre
DeciUtre
35 oz. 94 mins.
17 ,,
170 „
3 oz. 250 „
Gramme
Milligramme
Centigramme
Decigramme
15-43 grs.
o-or543 gis.
0-1543 gis.
1-543 gis.
"Deka" = lo (dekametre = lo m., etc.) ; '
(kilogramme = i,ooo g., etc.) ; and
hecto " = 100 (hectolitre = loo 1., etc.) ; " kilo '* :
'* mjrria " = 10,000 (myriametre = zo,ooo m., etc.)
Wellington's Silver Intenslfier 564
Wilde's Restrainer
WELLINGTON'S SILVER INTENSIFIER
Wellington's original formula (1889) is given
under the heading " Silver Intensifier." In July,
191 1, Wellington published particulars of an
improved process which does not stain or dis-
solve the film of some plates, as the original is
said to do. The film is first hardened with
formaline (i part to 10 of water for five min-
utes), rinsed and immersed for one minute in
the following : a solution of potassium bi-
chromate, i gr. ; potassium bromide, lo grs. ;
hydrochloric acid, 30 mins. ; and water, 10 oz.
Too long an immersion causes the image to
bleach, and must be avoided. The intensifier is
in the form of two stock solutions, both of
which win keep good for years : —
A. Silver nitrate . . 400 grs. 92 g.
Water (distilled) to . 10 oz. 1,000 ccs.
B. Potass, sulphocyanide 700 grs. 161 g.
"Hypo" . . . 700 ,, 161 ,,
Water to . . . 10 oz. 1 ,000 ccs.
Take i oz. of B, and add i oz. of A, stirring
vigorously with a glass rod ; the result should
be a clear solution. Add 60 mins. of a. 10 per
cent, solution of pyro preserved with sulphite,
and izo mins. of a 10 per cent, solution of
ammonia.
The solution given above is poured over the
negative. The deposition of silver begins to
take place in a minute or two, and the image
gains in strength. When dense enough, the
negative is placed in an acid fixing bath until
the slight pyro stain is removed, and is then
well washed. The image can be reduced with
the ferricyanide-" hypo " reducer.
WET NEGATIVES, PRINTING FROM (See
" Quick Prints from Wet Negatives.")
WET COLLODION PROCESS {See "Col-
lodion Process (Wet), or Wet-plate Pro-
cess.")
WHEATSTONE, CHARLES
Bom 1802, died 1875. Professor of experi
mental philosophy at King's College, I/ondon.
He invented the stereoscope in 1838, his paper
on binocular vision being read at the Royal
Society on Jime 21, when the instrument was
first exhibited.
WHEY PROCESS (Pr., Proadi d petit-lait :
Ger., Molhen Prozess)
An early iodo-bromide enlarging process, used
with the solar camera. Paper was floated on : —
Potassium iodide . 88 grs. 20 g.
Potassium bromide . 44 „ 10 „
MUk whey (filtered) . 10 oz. 1,000 ccs.
for from two to three minites and himg up to
dry. It was then sensitised with silver nitrate,
exposed for from ten to sixty seconds and devel-
oped with pyro.
WHIRLER (Fr., Tournette ; Ger., Schleuder-
apparat)
An appliance for rapidly drying glass or metal
plates to which a sensitive coating has been
applied, and for securing an evenly distributed
film. It is principally used in photo-mechanical
processes. The pneumatic whirler A has a rubber
bulb, which is simply pressed against the plate
to be coated, holding it firmly by suction. The
whirler is then turned upward, and the sensitis-
ing mixture, as, for example, the fish-glue solu-
tion used in the enamel process of h^-tone, is
poured in the centre of the plate until the pool
covers about three-fourths of the surface. The
whirler is now reversed, so that the plate is face
downward, and revolved at a moderate speed by
turning the handle at the side, holding it mean-
while over a sink until the surplus solution ceases
to be thrown off. The whirler is finally held over
a gas burner, still face down, and the revolution
continued tUl the plate is dry.
Another type of whirler, invented by Max Levy
and employed in process work, is shown at B.
This is supported by a bracket, which may be
fastened to a wall. The adjustable jaws which
hold the plate can be turned upward for coat-
ing ; then, when ready, a lever is pressed and the
plate holder is turned down for whirling, a
stove being placed beneath and a metal casing
built round to receive the splashings. Or, S
Two Types of WTiirler
preferred, the whirler may be fixed over a. tub
and then swung from the latter over a gas burner
for drying. For lithographic stones and thick
heavy plates a fixed whirler with a circular turn-
table is used.
WHITE LAC (See " Gums and Resins.")
WHITE, PERMANENT (See "Barium Sul-
phate.")
WHITE WAX (See "Beeswax.")
WHITENED CAMERA
An old French idea for whitening the interior
of the camera with the object of reflecting some
Ught on to the plate to reduce harsh contrasts.
It has somewhat the same effect as giving a pre-
liminary exposure to white paper.
WHOLE-PLATE
A commercial size of camera, plate, paper, etc.,
measuring 8f by 6J in. ; sometimes written " i/i ."
(See also "Sizes of Plates and Papers.")
WIDE-ANGLE LENS
A lens of short focal length, including, even at
close quarters, a wide angle of field or of view,
and therefore frequently of great advantage in
general photography. (See also " Angle of
Field or of View.")
WILDE'S RESTRAINER
A solution of 19 grs. of iodine in 200 mins.
of alcohol, afterwards adding 200 mins. of water.
WUlis's Proces*
56s
Woodbury type
From a to 4 drops is added to i oz. of fetrous
oxalate developer,
WILLIS'S PROCESS {See "Aniline Process.")
WINDOW, BLOCKING UP
The best way of blocking up a window when
the room is to be used for developing or similar
work, is to make a light wooden frame to fit in-
side the beading of the window-frame, and over
this to paste or glue two thicknesses of ruby-
fabric or paper. If artificial light is to be used for
working, as is preferable owing to its unitormity,
two thicknesses of stout brown paper will serve
the purpose. The advantage of the wooden frame
is that it can be instantly removed ; otherwise
the fabric is secured round the window itself.
WINDOW TRANSPARENCIES
In the production of transparencies upon glass
or paper for window decoration, specially pre-
pared plates are generally used, these being made
and used exactly like lantern slides. If made
upon glass in which the high lights are repre-
sented as clear glass, it is advisable to bind the
transparency up in contact with a piece of finely
groimd glass or thin opal glass in order that the
view outside the window may not be seen through
the dear glass parts of the transparency. Coat-
ing the plain glass side with a matt varnish,
tinted if requdred, has the same effect, and allows
of obtaining good results in one or more colours.
Certain plates ("matt ground" or "M.G.")
have a matt surface and obviate the use of
additional ground glass, but the film side
should be protected with plain glass.
Window transparencies may be made from
any paper prints, but the blue - prints and
platinotype prints are considered the best. The
print is made darker than usual, finished
and finally made translucent by oiling or waxing.
Platinotype prints on thin paper answer admir-
ably without waxing, as do also blue -prints on
tracing paper sensitised on one side only. Paper
prints should be bound up between glass, with
strips of paper or linen round the edges.
WINE, SPIRIT OF {See "Alcohol.")
WOLLASTON AND FRAUNHOFER LINES
{See "Praunhofer Lines.")
WOOD, PHOTOGRAPHS ON
Photography on wood as a guide to the en-
graver was extensively practised when wood
engraving was at its height of popularity. One
of the simplest methods is to prepare the surface
at the boxwood with a mixture of gum and zinc-
white, then to coat it with albumen mixed with
ammonium chloride ; and after drying and
waterproofing the sides of the block with wax
to dip the surface into a silver nitrate bath. The
surface is then dried and exposed under a nega-
tive until an image is obtained like the ordinary
albumen silver print. Fixing with "hyj)o,"
rinsing, and drying complete the operation.
Care has to be taken not to get the body of the
wood block wet. An improvement on this is to
coat the albumenised surface with iodised collo-
dion, thinned down considerably ; then to sen-
sitise in a silver bath and print as before. After
developing and fixing, the block is dried o£E and
is ready for engraving.
Various processes of toning with gold, etc., have
been used for strengthening the image.
WOOD NAPHTHA, OR WOOD SPIRIT
{See "Alcohol.")
WOODBURY, WALTER BENTLEY
Bom at Manchester, 1834 ; died at Margate,
1885. Inventor of the Woodburytype process,
which he first demonstrated in London in 1865,
and patented the following year. He went to the
Australian gold fields in 1849, and four years
later became a professional photographer there.
In 1859 he went to Java, where he did much
photographic work, returning to England and
settling in Birmingham in 1863. Between 1864
and 1884 he took out twenty patents for im-
provements in photographic apparatus and for
photo-mechanical processes.
WOODBURYTYPE
A photo-mechanical process invented by Mr.
W. B. Woodbiiry in 1865, and patented by him
on July 24, 1866. A relief image is obtained
on bichromated gelatine, covered with lead, and
the two forced together in a hydraulic press,
which produces a reverse or mould in the lead.
The mould is then ink^d with pigmented gela-
tine and printed from under pressure. A modi-
fication of the process was afterwards published
under the name of " Stannotype," in which no
hydraulic process was necessary. Woodbury-
type is quite unlike any other process in its
working details, which, based on the inventor's
own words, are as follow : The production of
pictures, either on white paper, upon glass as
transparencies, opal, etc., by this method of
printing is based on the principle that layers of
any semi-transparent material seen against a
light ground produce different degrees of light
and shade, according to their thickness, as the
carbon process, for example. Therefore, by
having a mould in intagho produced by the
action of light upon bichromated gelatine, and
filling the intaglio so produced with a semi-
transparent material, there is obtained a mould
in which the parts that are the thickest give a
dark colour ; while the thinner the layer becomes
it gradually merges into white. By pouring a
mixture of coloured gelatine on to the intaglio
mould, and placing a piece of white paper
thereon, and squeezing the whole between two
perfectly true planes, the superfluous colour is
squeezed out, and the gelatine, having set, ad-
heres to the paper and leaves the mould quite
clean. When the picture leaves the mould it is
in slight relief, but during drying the gelatine
contracts and leaves hardly any perceptible
relief. 'To make the gelatine relief, wet several
pieces of talc, and affix them to a large sheet of
glass ; squeeze out the superfluous moisture, and
polish the whole of the pieces. Next prepare
the bichromatised gelatine as follows : — Soak
4 oz. of opaque gelatine in 28 oz. of water ;
dissolve by heat, darify with white of egg, and
filter. To 4 oz. of this solution add 60 grs. of
ammonium bichromate dissolved in i oz. of
warm water and a small quantity of Prussian
blue ; the latter serves to give the finished relief
36*
Woodbiuytype
566
Wood's Grating Process
a colour by which to judge of its printing quali-
ties, and does not interfere with the action of
the light in penetrating the gelatine. When
well mixed, the solution is filtered through mus-
lin, and is then ready for coating upon the talc-
covered glass, placed upon a levelling stand, and
dried. When set, each piece of talc is cut round
the edges with a sharp knife and stripped from
the glass. Lay the sensitised talc upon blotting
paper and clean the talc side ; then place in
contact with the negative, and having placed
a piece of glass behind, fasten all together with
rubber bands, and place in the light of a con-
denser of 6 in. to 9 in. in diameter, at a distance
of about 2 ft. ; after exposing for i or 2 hours
lay in a dish, and pour hot water over it until
no soluble gelatine is left ; then allow to dry
by gentle heat. Having obtained the relief, it
is ready for taking the mould.
The above is Woodbury's original process.
A later method of making the relief plate is to
clean sheets of plate glass with French chalk
and coat with collodion. When dry, the sensi-
tive mixture, made as follows, is poured on, and
laid on a level place to set : — Sheet gelatine,
if oz. ; glycerine, 50 drops ; sugar, J oz. ;
Indian ink, i gr. ; carbolic acid, i drop ;
ammonium bichromate, 150 grs. ; hquor am-
moniae, -J- drm. ; water, 6 oz. The gelatine is
soaked in three-fourths gf the water, melted by
heat, and the glycerine, sugar, carbolic acid, and
ammonia added. The Indian ink is dissolved
in the remaining water, and added gradually,
and the bichromate, well powdered, stirred in.
Exposure and development are the same as
for carbon printing, hot water at a temperature
of 1 10° P. (43° C.) being used to begin with,
afterwards raising it to 160° P. (71 ° C). Develop-
ment— that is, the dissolving away of the unacted-
upon bichromated gelatine — may take two hours
or longer, but the process must not be hurried.
When the image is developed, it is immersed in
a 4 per cent, solution of chrome alum for a few
minutes, washed, soaked in methylated spirit
for an hour, and then dried.
Several other formulae for making the necessary
relief from the negative have been recommended,
but all except one are based on the above. The
exception is the use of a modem dry plate. The
plate should be 6i the thickly coated variety ;
it is printed from in contact with the original
negative, a full exposure being given, and
developed with the following solutions : — No. i :
Pjrrogallic acid, 30 grs. ; water, 5 oz. No. 2 ;
Sodium sulphite, J oz. ; potass, hydrate, i oz. ;
water, 2 oz. No. 3 : Potassium bromide, 60 grs. ;
water, i oz. For use, take i^ oz. of No. i and
4 oz. of No. 2 ; develop the plate until all
details are out, then add about 20 drops of No. 3
and continue development until dense enough.
Place in a 10 per cent, solution of chrome alum
warmed to 95° F. (35° C), and brush the surface
while under the solution with a camel-hair
brush, allow to remain until in good relief, then
wash well, fix in " hypo," and again wash well.
It is absolutely essential that the dry plate is
very thickly coated, and should there be any
tendency to frUl, this may be avoided by coat-
ing the edges with india-rubber solution. The
dry plate process is the least satisfactory.
The metal mould has now to be madt from
the relief. Woodbviry in his early experiments
used the electrotype process to obtain an intaglio
from the gelatine relief, but found that for prac-
tical purposes it was impossible to obtain uniform
results. Soft metal (a mixture of lead and type
metal) was found by him to be better. A sheet
of the soft metal is placed in contact with the
gelatine relief, then both in between two per-
fectly true plates of steel ; a pressure of 50 to
200 tons is applied, according to size, 4 tons
to the sq. in. being about the pressure necessary.
The gelatine film is not damaged as might be
supposed, and the result is a perfectly sharp
intaglio in about one minute, and the same relief
wiU serve for several moulds. Before taking the
mould, however, the film or talc containing the
relief image must be stripped from the plate and
used with the metal, as the enormous pressure
would break the glass support, and for this
reason the talc support, as advocated originally,
will be found the most convenient, even iit more
difiicult to prepare. The mould is placed in a
press, and oiled sUghtly with a mixture of equal
parts of oUve and paraffin oils, and the mixture
of gelatine and ink poured on. A suitable ink
is made by dissolving 4 oz. of gelatine in about
25 oz. to 30 oz. of water, and then adding
Indian ink, etc., the whole being kept at about
126° F. (52° C). When the mould is covered
with the ink, the paper to receive the picture
is placed upon it, then a sheet of plate glass and
pressure applied. The superfluous ink is forced
out at the sides by the pressure, while that in the
mould adheres to the paper and forms the image.
After the gelatine has set, the glass plate and
the paper are lifted off, and the image thereon
placed in a weak solution of alum to harden.
The modified process needing no great pressure
consists in making the gelatine relief in any of
the ways named above ; it is then, without
stripping from the glass, covered with tinfoil
and passed between rubber rollers. This presses
the tinfoil into the interstices of the rehef, pro-
ducing a perfect counterpart. Copper is tiien
electrically deposited on the tinfoil for the
purpose of strengthening it.
WOOD'S DIFFRACTION GRATING PRO-
CESS
This is practically a modification of the three-
colour process in which diffraction gratings ruled
with a varying number of lines to the inch are
used instead of the three stained filters, and
the principle of the process can be easily grasped
from the following explanation. In the diagram
Centrat
Image
D Green
Blue
Red
.Sp
Use of Diffraction Grating
S is an intense source of light ; between it and
a lens i,, is a. diffraction grating G. There will
be obtained not only the central white image,
as indicated, but also on both sides a spectrtmi,
and for the moment only consider the one spec-
trum, s^. Now, if we make an aperture in a
Wool, Cotton-
567
Wortley's Process
card at the point where red falls, and place the
eye there, we shall see red only. If we replace
the grating by one with finer rulings, then we
shall find the green fall in the place of the red,
and if we use a finer grating still, we should find
there the blue. Now, if we put the two first
gratings in front of the lens and overlapping one
another, the red and green would faU on the
aperture in the screen, and this would give us
the sensation of yellow. If the third grating
be added, then we should have red, green and
blue light reaching the eye, and the result would
be white.
The gratings used should have 2,000, 2,400
and 2,700 lines to the inch respectively for red,
green and blue light to fall in the same spot.
To produce a picture in colours, three negatives
are taken in the usual manner through red,
green and blue-violet screens as in ordinary
three-colour work, and from these positives are
made. A sheet of thin patent plate should be
flowed over with the following : —
Gelatine . . 384 grs. 40 g.
Potassium bichromate
(sat. sol.) . . 1 54-226 mins. 16-24 ccs.
Distilled water to . . 20 oz. 1,000 „
Filter whilst warm and allow the glass to drain
for about 10 seconds, and then set on a level
slab to dry. The sensitised glass is placed in
contact with one of the three positives. The
two plates should be held up in front of a lamp
and register marks made on the glass surface
of the sensitised plate, using minute ink dots
and some prominent object that appears in all
three pictures. Corresponding ink dots should
now be made on the fUm side of the sensitised
plate and the others rubbed ofi.
Then the grating with the coarsest ruling,
which furnishes the red light, should be placed
on the sensitised plate and on this the positive
of the red light sensation. The lines of the
grating should be vertical and the ink dots
made to carefully register with the object in
the positive. Expose the plates to sunlight for
about 30 seconds, gripping them tightly in the
fingers and holding them perpendicularly to the
sun's rays. It is advisable to do this in a
darkened room, using only a narrow beam of sun-
light. The exposure wiU be about 30 seconds.
Now remove the positive and grating, and sub-
stitute those for the green picture and repeat
the operation, and finally, repeat the operation
for the blue picture. Or preferably wash the
plate in warm water after exposure through the
red and green positives. The blue picture can
then be made on a separate plate, placing the
positive film out so as to reverse it, and after
exposure, washing the plate, and then super-
imposing and building up.
The apparatus for viewing these pictures is
a lens cut square like a reading glass mounted
on a light frame, provided with a black screen
perforated with an eyehole.
WOOL. COTTON- (See "Cotton-wool.")
WOOLLINESS
A loss of correct texture, and a substitution
of a vague irregularity of definition and tone
suggestive of masses of wool. It may appear^
for example, in renderings of trees and water
when the focusing has been faulty or there has
been movement during exposure. It sometimes
results from misguided efforts at control by
working on the back of the negative.
WORKING UP NEGATIVES
Methods of treating the glass side of negatives
with thin tracing paper or with matt varnish
are described under the heading " Control in
Printing." In addition, pencil work may be
applied to the tracing paper to give increased
emphasis to small portions or details. {See
also " Retouching.")
WORKING UP PRINTS
A term usually applied to working up photo-
graphs by means of crayon or water colour.
The air-brush may be employed effectively for
soft, shaded or clouded backgrounds, or for any
mass of shading that is required to be evenly
or delicately graded or perfectly flat.
The prints most suited for treatment are
those on matt-surfaced bromide or gaslight
papers ; the colour dries with a matt or smooth
surface and becomes disagreeably evident on
any paper with a semi-glossy surface, and still
more prominent on a glossy print. The materials
required are water colours and brushes of good
quality, small saucers or china palettes for mixing
ttie colours, and prepared ox-gall. A Uttle of
the last-named is mixed with the colour if the
surface of the print is so repellent that the
colour will not take readily. For black prints,
the best pigments are lamp black, blue-black,
ivory black, and zinc white or Chinese white.
Ivory black is required only for warm black
prints. For all excepting the deepest tones
a little white should be mixed with the black
to destroy its transparency and give body or
soUdity. All the pigments should be purchased
in the moist form in tubes. For brown and
purple-toned prints other pigments will be
necessary, the most suitable being either Van-
dyke brown or burnt umber, which may be
combined with ivory black for various shades
of brown ; and neutral tint and either scarlet
madder or alizarin crimson for mixing different
shades of purple. Crimson lake and carmine
should be avoided, as they are very fugitive.
The aim should be to strengthen or modify
in depth, and to follow the character of existing
work as closely as possible. The added work
should improve the photograph as a photograph.
For this reason, the outlining of details should
not be attempted.
In working up photographs for process repro-
duction, the colours employed must be such
that their photographic value is the same as their
visual effect. For working in black, process
white, blanc d'argent, and process black should
be employed. Blanc d'argent is not permanent,
but it possesses great body and mixes with black
for producing greys. Chinese white reproduces
as a distinct grey.
WORTLEY'S PROCESS
A dry collodion process introduced by Col.
Stuart Wortley, in which a solution containing
saUcin, tannin, gallic add, alcohol, sugar, and
water was used as a preservative.
Wothly't Process
$68
X-ray Photography
Col. Wortley, in 1873, discovered that a
strongly alkaline developer had a more powerful
action than the weaker one previously employed.
Much shorter exposures were thus rendered
possible. In 1879, he found that a gelatine
emulsion might be ripened — that is, increased in
sensitiveness — equally well by keeping it for
a few hours at a fairly high temperature as
by maintaining it for days at a lower one.
WOTHLY'S PROCESS, OR WOTHLVTYPE
A process of printing-out, patented by Wothly
in 1864, in which the sensitive salts were a
mixture of the nitrates of uranium and silver
dissolved in collodion. The prints were washed
after insolation with acetic or hydrochloric acid,
and then toned with gold chloride. This process
was practically the immediate predecessor of
collodio-chloride printing-out papers.
WRINKLING OF FILM
When a film wrinkles at the edges it is known
as frilling {which see). When the whole of the
film is wrinkled in wavy lines the defect is
known as reticulation {which see).
WRITING INK. PRINTS IN {See "Ink
Process.")
WYNNE'S EXPOSURE METER {See
" Exposure Meter.")
WYNNE'S PLATE SPEEDS {See "Sensito-
metry.")
X
XANTHO-COLLODION
An iodised collodion to which is added a
tincture of powdered turmeric giving to it a
rich yellow colour. Positives are made with it
on black glass, giving an effect like a gilded
daguerreotype.
X-RAYS (Fr., Rayons X; Ger., X-Strahlen,
Rontgen-Strahlen)
Prof. Rontgen, in 1895, discovered certain
rays, to which he gave the name of X-rays,
and he investigated their action on the sensitive
emulsion of the dry plate. X-rays are pro-
duced by the discharge of a high-potential
current through a special form of vacuum tube,
known as a Crookes' tube {which see). The
positive terminal of an induction coil or Wims-
hurst machine is connected to the anode and
the negative to the cathode of the tube. The
anticathode is connected to the anode and is
also positive. The vacuum of a tube is not
perfect, and the current is conveyed through
the tube by the infinitesimal quantity of air
contained therein.
The " cathodal rays " which pass from the
cathode to the anticathode consist of infinite-
simal particles travelling at a high rate of
speed ; when the progress of these minute
bodies is arrested, X-rays are produced. The
green fluorescence on the sides of the tube
opposite the anticathode, though not caused
by the X-rays, demonstrate their presence.
The X-rays are ethereal vibrations liavelling
with much the same velocity as light. They
travel in a straight line in all directions from
the point of origin, and are almost incapable
of reflection or refraction.
X-rays are invisible to the eye, but have the
property of rendering fluorescent certain sub-
stances— ^for example, calcium tungstate and
barium platino-cyanide. When a screen coated
with these substances is placed near the X-ray
tube in a darkened room, the tungstate or barium
surface emits a fairly bright fluorescence. If
an object such as the hand or a lead pencil
is placed between the screen and the tube.
the denser parts (the bones or the graphite)
appear as black shadows in a grey background.
X-rays penetrate all substances to a greater
or less degree, although heavy metals, such as
lead and mercury, are, for photographic or
visual purposes, practically opaque to the rays.
The greater part of X-ray examination is
conducted by photographic methods, as the
image given by the rays on a dry plate or film
show far more detail than can be seen by visual
examination with the fluorescent screen.
X-RAY DERMATITIS
A painful and incurable disease, of a cancerous
nature, to which radiographers are liable,
caused by frequent and prolonged exposure
to X-rays. Many of the pioneers of radio-
graphy have fallen victims to this complaint,
but greater precautions are now taken to protect
the operators from the X-rays. There is little
danger of contracting this disease in X-ray
photography, as the exposures are short and
the operator need not stand directly in front
of the tube. The chief risk is entailed by
visual examination with the fluorescent screen.
The disease first makes its appearance in the
hands and gradually spreads to the arms and
body. The skin at first appears as if it had
been burned, hence the term X-ray burning."
X-RAY PHOTOGRAPHY, OR RADIO-
GRAPHY (Pr., Radiographic : Ger.,
Rontgenphotographie)
There being no method of bringing X-rays
to a focus, the images produced on the photo-
graphic emulsion are merely shadows of the
objects. The illustration shows the outfit for
radiography, A being a metal-lined box con-
taining the X-ray tube ; b, couch for patient ;
C, plumb for centring tiie tube ; D, induction
coil ; E, switchboard ; and F, amp^e meter.
X-ray photographs are produced by means
of a mgh-voltage electrical apparatus and
a Crookes' tube. The high pressure current
necessary to produce fluorescence in the vacuum
tube is obtained from a Wimshurst machine or
X-ray Photography
569
Xylo-autography
an induction coil. The Wimshurst machine is
self-contained, the current being generated by
revolving glass or vulcanite plates in opposite
directions, but these machines have serious
drawbacks, and the induction coil is now almost
invariably used. The positive pole of the
wires is connected to the anode, and the negative
is connected to the cathode end of the tube.
If the current flows in a reverse direction, the
tube is quickly ruined. The half of the tube
opposite the anticathode gives out a bright
green fluorescence when the current is flowing
from anode to cathode ; but if the current is
passing the reverse way, a flickering bluish-
green fluorescence appears all over the tube.
A coil giving a 4-in. spark is sufSciently
powerful for experimental radiography, but an
8-in. or lo-in. spark is the lowest that can be
used for practical work.
The X-rays are not visible to the eye, and for
the visual examination of objects a fluorescent
screen of barium platino-cyanide must be used
in a darkened room. Radiography, however,
need not be conducted in a dark-room. The
Equipment for X-ray Photography
dry plates, packed in light-tight envelopes, are
placed behind the object to be photographed,
the film facing the tube. If only a 4-in. coil is
used, the object must be as close as possible
to the tube, but with a powerfiil coil the distance
should be increased to about 30 in. to ensure
a sharp image with but little distortion. In
medical X-ray work, the patient is placed upon
a couch consisting of a wooden frame covered
with canvas. A box containing the tube moves
on wheels and rails beneath the couch ; it is
lined with metal to shield the operator from the
X-rays. The time of exposure depends upon
the strength of current used, the power of the
coil, and the condition of the tube. A " hard "
tube — ^that is, a tube with an extremely high
vacuum — ^requires less exposure than a " soft "
or low-vacuum tube. The condition of the
tube is ascertained by finding its "equivalent
spark gap." While the coil and tube are
working, the terminal points of the induction
coU are slowly brought together. If a spark
passes between the points while they are 6 in.
or more apart, the vacuum is too high. If no
sparking takes place between the terminals
till they are within 3 in. of each other, the
tube is low. A good working spark gap distance
is 4^ in. A soft, or low-vacuum, tube gives
better definition than a hard, or high-vacuum,
tube, as the rays pass less easily through dense
substances and show greater differentiation of
tissue. A very high-vacuum tube may show
but little difference between the bones and
flesh, while a soft tube should give the minute
structure of the bones. Tubes are now fitted
with regulators for lowering the vacuum.
With a current of 5 amperes at 100 volts
passing through the primary winding of a lo-in.
coil, the exposure for a hand or foot would be
from 3 to 15 seconds. The exposure for the
thicker portions of the body would be from
20 seconds to 2 minutes. If an electrolytic
break is used, about half the exposure would
be required. Dry plates with extra thick
sensitive films are specially prepared for radio-
graphy, the development and fixation being
the same as in ordinary photography. The
image is sometimes barely visible on the surface
of Qie plate during development, but when
fixed the negative may give good density and
definition owing to the penetration into the
film of the X-rays.
Several forms of " intensifying screens " have
been introduced for the purpose of shortening
exposure. The screens are coated with a sub-
stance giving a white or violet fluorescence. The
coated side is placed in contact with the sensitive
film of the dry plate which is exposed with the
glass side facing the tube. Intensifying screens
greatly reduce the exposure, but the quality
of the negative is somewhat inferior owing to
the grain of the screen being reproduced.
An energetic developer, such as metol-hydro-
quinone, is most suitable for radiography, and
development should not be hurried.
The comparative resistance to X-rays of the
following list of substances wiU give some idea
of the penetrating power of the rays. The
figures are only approximate, as the results
vary with the hardness of the tube, etc. : —
The imit is a sheet of cardboard, and the other
substances are supposed to be of equal thick-
nesses. Cardboard, i ; wood, i ; linen, 2 ;
rubber, f ; iron, 1,000; glass, 40; lead, 3,000.
Dry plates must not be stored in an X-ray
room except in metal chests, as the paper boxes
and envelopes give no protection to the sensitive
fihn.
In X-ray work the operator often has to find
the position and depth of some foreign object,
such as a needle in the human body. This can be
ascertained by visual examination with the
fluorescent screen from both vertical and lateral
points of view. The best method for finding
the depth of a foreign body is to take two
radiographs on the same plate, moving the
tube to one side before the second exposure is
given. Two images will appear on the plate,
and the position of the foreign body is cal-
culated from the separation of the two images
and the distance of the tube from the plate.
J. I. P.
XYLO-AUTOGRAPHY
A half-tone block worked on by a wood-en-
graver to imitate the effects of wood engraving.
Xylographs
S;o
Zander's Colour Process
XYLOGRAPHS
Positive pictures by the wet collodion process,
toned and transferred to a paper support, and
thence to a wood block as a guide for the wood
engraver.
{See " Wood,
XYLOGRAPHY, PHOTO
Photographs on.")
XYLOIDIN
A substance analogous to pyroxyline and pro-
duced by acting on starch with a mixture of
pyroxyline and acids. It dries from its solu-
tions as a matt opaque film, which is very
inflammable and explosive.
XYLONITE
A synonym for celluloid.
XYLO-PHOTOGRAPHS
Photographs made upon wood for engraving
purposes.
YELLOW GLASS
This is used in the production of the yellow
light referred to in the next article.
YELLOW LIGHT
Used for dark-room illumination in the early
days of photography, and before the introduc-
tion of fast dry plates. It may be used at the
present time for bromide paper, lantern plates,
and very slow dry plates, but not for dry plates
of even the " ordinary " speed. Although a
patent was taken out for a ruby light in 1844,
yellow light was more widely used during the
collodion period, say 1851 to 1880, as it was
quite safe for the plates then in use.
YELLOW NEGATIVES
Yellowness in a negative must be regarded
as a defect. The time required for printing is
very long, and the result of intensifying or
reducing must always be uncertain. The usual
causes of yellowness are absence or insufficiency
of sulphite in the developer, prolonged develop-
ment with excess of alkdi, and fixing in a stale
or discoloured " hypo " solution. A good acid
fixing bath, if not overworked, will largely
correct the tendency to staining from the first
two causes. Thiocarbamide is the most satis-
factory reagent for removing the yellow stain.
When negatives gradually become yellow after
finishing, or when they develop a yellow staining
during the process of mercurial intensification,
the cause is, almost invariably, imperfect fixing,
that is, either too short an immersion in the
fixing bath or the use of an exhausted fixing
solution ; there is no remedy for such stains.
YELLOW PRINTS
Bromide prints may show a yellow discolora-
tion from the same causes as those given for
yellow negatives. If a print is allowed to float
on the top of the fixing solution, face upwards,
it is almost certain to become yellow stained.
Prints should be fixed face downwards. A weak
bath of thiocarbamide is the most effective
method of removing yellow staining.
YELLOW PRUSSIATE OF POTASH
" Potassium Perrocyanide.")
{See
YELLOW SCREENS {See " Isochromatic
Screens.")
YELLOW STAINS
Yellow stains, in isolated patches, on nega-
tives may arise from several causes. If too small
a quantity of fixing solution is used, and parts
of the negative become uncovered and exposed
to the air during fixing, those parts wiU show
a yellow discoloration. This cause can easily
be identified, as the yellow stains are visible as
soon as the plate is taken from the fixing bath.
They are very difficult to remove, thiocarbamide
being the most successful reagent.
Yellow stains that develop gradually after the
plate is fixed, or those that arise in mercurial in-
tensification, are due entirely to imperfect fixing.
There is no method of removing them. {See also
"Yellow Negatives" and "Yellow Prints.")
ZANDER'S COMPLEMENTARY COLOUR
PROCESS
A colour reproduction process invented and
patented in 1905 by C. G. Zander, who called
it the " Complementary Colour Process." The
inventor assumed that it was necessary to use
not three, but four, fundamental colours, namely,
red, yellow, green and blue, by mixture of which.
in suitable proportions, any colours in Nature
could be matched. The hues of these four funda-
mental (or monochromatic) colours may, in
popular terms, be described as magenta red,
lemon yellow, emerald green, and ultramarine
blue. The four colours were grouped into two
pairs of complementary colours, namely, red
and green and yellow and blue, so that when
Zapon Varnish, or Zaponlac S7i
Zinc, Transferring to
the elements of either pair were mechanically
mixed as pigments, by printing or staining, they
produced black. The inventor claimed that
practically the whole range of the spectrum
colours could be produced by this process,
besides extra spectral purples, dense pure black
and homogeneous greys. Zander asserted that
no pure black can be reproduced at all in three-
colour printing, whilst by his process either of
the two pairs would produce black or grey.
ZAPON VARNISH. OR ZAPONLAC
A varnish consisting of celluloid dissolved in
amyl acetate. It gives a brilliant surface, im-
pervious to heat or moisture, and may be used
for negatives and positives, or as a lacquer for
trays. " Zapon " is a proprietary and registered
name.
ZENKER, DR. WILHELM
Bom 1829; died 1899. A distinguished
astronomer and physicist, of Berlin. He pub-
lished, in 1868, Lehrbuch der Photochromie,
treating of all the then known methods of
colour photography, or approximations thereto.
In it he suggested the theory of standing or
stationary waves, on which I/ippmann's process
of interference heliochromy essentially depends.
ZENOTYPE
A process of toning introduced by E. J.
Browne in 1894. A powder was supplied com-
mercially which, when dissolved in water, was
used as a developer to produce coloured prints.
ZINC, BLACKENING (See "Blackening
Apparatus.")
ZINC BROMIDE (^t., Bromure de zinc ; Gst.,
Zinkbromid)
ZnBr^. Molecular weight, 225. Solubilities,
I in "3 water ; very soluble in alcohol and ether.
It is a white hygroscopic crystaUine powder,
obtained by dissolving zinc carbonate in hydro-
bromic acid. It is occasionally used in collodion
emulsion making.
ZINC CHLORIDE (Pr., Chlorure de zinc: Ger.,
Zinhchlorid)
ZnClj. Molecular weight, 136. Solubilities,
I in "3 water ; soluble in alcohol and ether.
It is poisonous, the antidotes being alkaline
carbonates preceding water or milk, albumen,
etc. It is a white powder which is very deliques-
cent, and is obtained by dissolving zinc or zinc
carbonate in hydrochloric acid. It is used in
collodion emulsion making.
ZINC ETCHING (Pr., Zincographie : Ger.,
Zinhhochdtzung)
The process of reproducing line originals by
transferring the image to zinc and etdbing into
relief. Strictly speaking, the term appUes to
GiUot's original process, in which the image
was put down on zinc by means of a Utho-
grapmc transfer or by drawing on the zinc
with lithographic ink or crayon as a preliminary
to etching into relief with add, but the term is
also now appHed to the " photo-zinco process."
Zinc etchings are all kinds of etched zinc plates
from line originals, or the equivalent of line
originals, such as coarse crayon grain, stipple,
transfers from type or engraved copper and
steel plates and woodcuts — anything, in fact,
which has not to be reproduced by the half-
tone screen.
ZINC HYPOCHLORITE C^., Hypochlorite de
zinc; Ger., Zinkhypochlorit)
ZnOClj. Molecular weight, 152. It is a
somewhat indefinite compound, obtained by
mixing solutions of zinc sulphate and bleaching
powder and filtering out the calcium sulphate.
Formerly it was used to eUminate the last traces
of " hypo," but it has now scarcely any practical
application.
ZINC IODIDE (Pr., lodure de zinc; Ger.
Zinhiodid) '
Znlj. Molecular weight, 319. SolubiUties,
I in -3 water, soluble in alcohol and ether. It
is a white deliquescent powder, obtained by
dissolving zinc oxide in iodic acid or direct
union of zinc and bromine, and it is used for
making collodion emulsion.
ZINC OXIDE (See "Zinc White.")
ZINC PLATES
The zinc plates used in process work are of
two kinds — thin, with grained surface for
photo-lithography, and thick with polished
surface for etching. A very piure zinc is re-
quisite for process work, and the plates must
be perfectly rolled, and free from surface
blemishes. The thin zinc for lithography is
chemically treated to free it from grease, and
then grained in a trough filled with marbles and
sand, which is then given a jogging motion. A
fine matt is given to the surface. The thicker
zinc, usually 16 B.W.G., or -065 in. thick,
is scraped and poUshed by bufiSng with abrading
and polishing powders mixed with oil, until a
high finish is obtained. Before use, the greasi-
ness is removed by rubbing with pumice powder
and water, and by passing through a bath of
weak add and alum.
ZINC SULPHATE (Pr., Sulfate de zinc ; Ger.,
Zinksulfat)
Synon3rms, white vitriol, zinc vitriol.
ZnSO, 7H2O. Molecular weight, 287. Solu-
bilities, I in -62 water, insoluble in alcohol.
It is in the form of colourless acicular crystals
that effloresce in dry air. It is obtained by
the direct action of sulphuric add on zinc, and
is used to form zinc hypochlorite.
ZINC, TRANSFERRING TO
Transfers may be put down on zinc in the
same way as upon lithographic stones. The
transfer, in lithographic ink on suitable transfer
paper, is damped from the back, and laid down
on a perfectly dean matted zinc plate ; then
the plate bearing the transfer is run through a
hthographic press several times with increasing
pressure. The back of the transfer paper is
then damped and peeled off, leaving the ink
image on the zinc. This is then treated with
a solution of gum and nutgalls and rolled up
with ink. The plate may then be printed
from lithographically or etched into reUef.
Zinc White
572
Zoopraxiscope
ZINC WHITE
Zinc osdde, ZnO.l It enters into the com-
position of some of the white pigments used for
retouching photographs for reproduction, and
it has the advantage that it does not discolour
so readily as the whites formed from lead
pigments. It photographs darker than paper.
{See also "Chinese White.")
ZINCOGRAPHY (Fr., Zincographie : Ger.,
Zinkographie)
The process of lithography from zinc plates,
first brought into regular use by Col. Sir Henry
James, in 1859, at tiie Ordnance Survey Office,
Southampton, for map printing. Originally
the image was put down on the zinc by litho-
graphic transfer, but this has been superseded
by photo-zincography, which at first involved
the making of a print on photo-lithographic
transfer paper. This, in turn, has given way
to methods of printing direct from the negative,
or through the drawing, as in the Vandyke
process.
ZIRCONIUM (Fr., Zirconium ; Ger., Zirkon)
One of the rarer metals from which is obtained
zirconium oxide, which has been suggested as
a substitute for the lime in the oxyhydrogen
light, and is also used in making incandescent
gas mantles.
ZOETROPE, OR "WHEEL OF LIFE"
An open cylinder with vertical slits round
its sides, and below them a series of motion
pictures which were viewed through the slits as
the cylinder revolved on its stand, the result
being a kinematograph effect. It embodies in
cylindrical form the principle of an earlier disc
device — the phenakistoscope (which see), and
was invented by Desvignes in i860. In 1867,
a patent for the same device was granted in the
United States of America to William E. Lincoln,
of Providence, who was the first to call it the
A. Zoetrope B. Stereoscopic Zoetrope
zoetrope. But this type of slotted machine had
its origin at a date far anterior to those quoted
above ; in fact, only a little more than a twelve-
month elapsed between the invention of the
phenakistoscope (1833) and the publication by
W. G. Homer in The Philosophical Magazine of
a description of a device strongly resembling
the zoetrope. The apparatus in its modern form
is shown at A. A band of pictures having been
placed inside the cylinder, the whole is rotated,
when the figures are seen in motion.
A great variety of zoetropic instruments hare
been devised, one of the most interesting being
the stereoscopic zoetrope shown at B. Anschiitz
used this form to produce the appearance of
motion from a series of animal movements photo-
graphically recorded. The series of phases was
taken in stereoscopic sets, and, as is shown, the
cylinder was turned on its side, and the slits
were long enough to permit of both eyes
gaining a view of their respective series ; the
blending of the two series was brought about
by suitable prisms or other optical device.
ZOLLNER'S PROCESS
An iodide of starch printing process, invented
in 1863 by Dr. P. Zollner, of Berlin, and used
for reproducing plans, drawings, etc. Thin,
smooth paper is sized with starch, and sensitised
by floating for from thirty to sixty seconds on a
solution of ferric chloride and ferric oxalate. The
exposure varies from two or three minutes in the
sun to fifteen or thirty minutes in diffused light,
the image being at first invisible. The exposed
prints should not be left longer than twelve
hours before developing. The image appears of
an intense blue colour on brushing on a solution
of potassium iodide in dilute albumen. The
developer should be washed off the print before
it has time to dry, and the washed prints dried
in the open air. To prepare the developing solu-
tion, the whites of two eggs of average size
are well beaten and left for several hours, after
which the liquid albumen is decanted from
the bottom of the vessel and diluted with
one-third its quantity of distilled water, 78 grs.
of potassium iodide being then added and
dissolved.
ZOOLOGICAL PHOTOGRAPHY
This includes not only the photography of
animals and birds, but also of nests and eggs,
insects, and their larvae and pupse, reptiles, fish,
etc. Under separate headings will be found
much information on these subjects, and in this
place only general remarks will be given. The
chief aim of all naturalistic photography is
reahsm. Texture of aU kinds should therefore
be most truthfully indicated, and no pains
be spared to secure the highest technical excel-
lence ; not only should knowledge of the par-
ticular branch of natural history dealt with be
acquired, but careful consideration should be
devoted to accurate colour rendering, exposure,
development, and printing methods. Within
limits, some form of colour plate is of great
value to the natural history photographer,
especially for use as lantern slides ; and this
value will increase with the inevitable advance
in the speed and quality of the plates available.
{See also " Animals, Photography of," " Birds,
Photography of," " Pish, Photographing,"
" Insects, Photographing," " Reptiles, Photo-
graphy of.")
ZOOPRAXISCOPE
An instrument used to exhibit studies of
animals in motion ; a forerunner of the kine-
matograph.
PRINTED BY CASSELL AND COMPANY, LIMITED, LA BELLE SAUVAGE, LONDON, E.C.
'iif i y,''-.
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